CHARGER CONTROL CIRCUIT AND METHOD FOR CHARGER CONTROL The invention relates to a charger control circuit, in particular for controlling charging and power supply of a portable electronic device and to a corresponding method for charger control.

To extend battery life time, some portable electronic devices, such as cameras, mobile phones, portable computers or the like, offer a possibility to attach a secondary battery for example for providing additional power to the system. For example due to a limitation of available connectors, a universal serial bus input or charger input may commonly be used to connect the secondary battery. For the sake of compliance with currently available charger inputs, a battery output voltage, which may originally lie at about 2.5V to 4.4V, for example at -3.7V, may have to be boosted to a higher voltage, for example to a voltage of about ~5V, corresponding for example to a minimum output voltage of an external charger or a charger detection voltage. This may require additional components and therefore increase costs and further may lower an efficiency of the power delivery. Charging of the secondary battery may have to be performed with a dedicated battery charger, which may be an additional external device. For providing the boost function, the dedicated battery charger for example needs to be either a switched mode charger with an on-the-go function, or a separate booster may be needed. Furthermore, existing charger control solutions may reconnect the main battery to the system supply when the system supply voltage falls below the main battery voltage, preventing from discharging the secondary battery to below the main battery voltage

It is therefore an objective to provide an improved concept for charger control that allows for a more efficient power supply and to overcome above mentioned disadvantages.

This objective is achieved by the subject matter of the independent claims. Further implementations and embodiments are subject matter of the dependent claims. According to the improved concept, it is determined by means of detecting a presence and a value of a voltage applied at a first charger terminal, whether a secondary battery or an external charger is connected to the terminal. The first charger terminal is comprised by a charger control circuit of an electronic device. Then, power may be supplied accordingly either from the secondary battery or the external charger.

According to an embodiment of the improved concept, a charger control circuit for a portable electronic device comprises a first charger terminal and a system terminal. The charger control circuit is configured to assign a voltage applied at the first charger terminal to one of at least three voltage ranges by performing at least one voltage comparison. The charger control circuit is further configured to determine and distinguish, based on the assignment, whether an external charger or a secondary battery is connected to the first charger terminal. In particular, the charger control circuit is configured to determine, based on the assignment, whether the external charger or the secondary battery or neither of both is connected to the first charger terminal and, in case the external charger or the secondary battery is connected to the first charger terminal, distinguish, based on the assignment, which of the external charger and the secondary battery is connected to the first charger terminal.

Furthermore, the charger control circuit is configured to, depending on a predetermined operating state of the first charger terminal, supply power from the secondary battery to the portable electronic device via the system terminal when the secondary battery is connected to the first charger terminal, and supply power from the external charger to the portable electronic device via the system terminal when the external charger is connected to the first charger terminal.

In some implementations, the three voltage ranges correspond for example to a first voltage range for voltage values below a first threshold value, to a second voltage range for voltage values above the first threshold value and below a second threshold value, and to a third voltage range for voltage values above the second threshold value. Therein, the second threshold value is greater than the first threshold value. The first threshold value may for example correspond to a minimum battery detection voltage, while the second threshold value may for example correspond to a minimum charger detection voltage. In some implementations, the charger control circuit determines that neither the external charger nor the secondary battery is connected to the first charger terminal if the voltage applied at the first charger terminal lies within the first voltage range, for example if no voltage is applied to the first charger terminal at all. The charger control circuit determines that the secondary battery is connected to the first charger terminal if the voltage applied at the first charger terminal lies within the second voltage range and that the external charger is connected to the first charger terminal if the voltage applied at the first charger terminal lies within the third voltage range.

Such implementations may be of particular advantage if the voltage applied at the first charger terminal, for example by construction of the secondary battery and/or the external charger, cannot be greater than the second threshold value in case the secondary battery is connected to the first charger terminal and cannot be smaller than the second threshold value in case the external charger is connected to the first charger terminal. In such a case, the assignment of the voltage applied at the first charger terminal to one of the three voltage ranges allows to uniquely distinguish between the secondary battery and the external charger being connected to the first charger terminal.

In some implementations, the charger control circuit is further configured to identify a pin assignment of a connector connected to the first charger terminal. Alternatively or in addition to the above described implementations, the charger control circuit is configured to determine and distinguish, based on the assignment of the voltage applied at the first charger terminal to one of the at least three voltage ranges and/or based on the identified pin assignment, whether the external charger or the secondary battery is connected to the first charger terminal.

Such implementations may for example be of particular advantage, if the voltage applied at the first charger terminal can be greater than the second threshold value in case the secondary battery is connected to the first charger input. In some implementations, the portable electronic device is a photo camera, a video camera, a mobile phone, a tablet computer, a notebook computer, a portable media player or a portable loudspeaker.

In some implementations, the charger control circuit is implemented as an integrated circuit, IC, in particular as a single IC or as two, three or more ICs.

In some implementations, the charger control circuit comprises a first circuit block, for example a charger block, and a second circuit block, for example a power-path-and- current-limiter block. The first charger terminal and the system terminal are for example comprised by or connected to the first circuit block. Alternatively, the first charger terminal and/or the system terminal are comprised by or connected to the second circuit block.

In some implementations, the predetermined operating state of the first charger terminal corresponds to an enabling or disabling of the first charger terminal. The operating state of the first charger terminal may for example be controlled by a firmware or a software of the portable electronic device. Alternatively or in addition, the operating state of the first charger terminal may be controlled by the charger control circuit.

In some implementations, the charger control circuit is configured to supply power from the secondary battery to the portable electronic device when the secondary battery is connected to the first charger terminal and the operating state of the charger terminal corresponds to an enabling of the first charger terminal and/or of the secondary battery.

Analogously, the charger control circuit is configured to supply power from the external charger to the portable electronic device when the external charger is connected to the first charger terminal and the operating state of the first charger terminal corresponds to an enabling of the first charger terminal and/or of the external charger. If the operating state of the first charger terminal corresponds to a disabling of the first charger terminal, no power is supplied from the secondary battery or from the external charger, respectively, to the portable electronic device. The secondary battery may for example be integrated, in an exchangeable or a non- exchangeable manner, into the portable electronic device. Alternatively, the secondary battery may be external to the portable electronic device. In further implementations, the charger control circuit further comprises a main battery terminal adapted to connect a main battery. In such implementations, the supply of power from the secondary battery to the portable electronic device may be carried out when an output voltage of the secondary battery is larger than an output voltage of the main battery and when the output voltage of the secondary battery is smaller than the output voltage of the main battery.

In further implementations, the charger control circuit further comprises a first current control element connected between the first charger terminal and the system terminal. The charger control circuit is configured to control, by means of the first current control element, a current from and/or to the charger control circuit via the first charger terminal.

In some implementations, the first current control element comprises a transistor, for example a bipolar transistor, a field effect transistor, a metal oxide semiconductor, MOS, field effect transistor, a power transistor or a power field effect transistor.

A source terminal of the first current control element is connected to the system terminal and a drain terminal of the first current control element is connected to the first charger terminal or vice versa. A gate terminal of the first control element is controlled by the charger control circuit.

In further implementations, the control of the current from and/or to the charger control circuit via the first charger terminal is based on a comparison of a value of the current from and/or to the charger control circuit via the first charger terminal to a specified first minimum current value and to a specified first maximum current value and/or to a specified first current range.

In some implementations, the charger control circuit further comprises a second charger terminal and is further configured to determine whether a further external charger is connected to the second charger terminal by performing a further voltage comparison. When the further external charger is connected to the second charger terminal, the charger control circuit is configured to supply power from the further external charger to the portable electronic device via the system terminal if a predetermined priority of the second charger terminal is higher than a predetermined priority of the first charger terminal. The charger control circuit is further configured to supply power from the secondary battery or from the external charger to the portable electronic device via the system terminal if the priority of the first charger terminal is higher than the priority of the second charger terminal.

In particular, this corresponds to a case in which the further external charger is connected to the second charger terminal and either the external charger or the secondary battery is connected to the first charger terminal. When the further external charger is connected to the second charger terminal and neither the external charger nor the secondary battery is connected to the first charger terminal or the operating state of the first charger terminal corresponds to a disabling of the first charger terminal, the charger control circuit may be configured to supply power from the further external charger to the portable electronic device via the system terminal also in case that the priority of the first charger terminal is higher than the priority of the second charger terminal.

Furthermore, the supply of power from the further external charger to the portable electronic device may depend on a predetermined operating state of the second charger terminal. In particular, the charger control circuit may be configured to supply power from the further external charger to the portable electronic device only if the operating state of the second charger terminal corresponds to an enabling of the second charger terminal and not to supply power from the further external charger to the portable electronic device if the operating state of the second charger terminal corresponds to a disabling of the second charger terminal. The priorities of the first and the second charger terminal and/or the operating state of the second charger terminal may for example be predetermined by a software or a firmware of the portable electronic device or by the charger control circuit. In some implementations, the charger control circuit is configured to determine whether the further external charger is connected to the second charger terminal by comparing a voltage applied to the second charger terminal to a further threshold value. The charger control circuit may for example determine that the further external charger is connected to the second charger terminal if a value of the voltage applied to the second charger terminal is greater than the further threshold value and determine that the further external charger is not connected to the second charger terminal if the value of the voltage applied to the second charger terminal is smaller than the further threshold value. In some implementations, the second charger terminal is connected to or comprised by the first circuit block or the second circuit block.

In some implementations, the first and/or the second charger terminal are implemented as terminals for universal serial bus, USB, connectors, for stereo jack connectors, for phone connectors or other connectors.

In some implementations, the charger control circuit is further configured to supply a secondary charging current to the first charger terminal for charging the secondary battery from the further external charger, when the further external charger is connected to the second charger terminal, in particular when supplying power from the further external charger to the portable electronic device. In some implementations, the supply of the secondary charging current may depend on a charging being enabled by the software or firmware of the portable electronic device and/or by the charger control circuit. In further implementations, the charger control circuit further comprises a main battery terminal adapted to connect a main battery and is further configured to supply a main charging current to the main battery terminal, in particular to the main battery, from the external charger, when the external charger is connected to the first charger terminal, in particular when supplying power from the external charger to the portable electronic device. The main battery may for example be integrated into the portable electronic device. In particular, the main battery may be integrated into the portable electronic device in an exchangeable or a non-exchangeable manner. In further implementations, the charger control circuit further comprises a main battery terminal adapted to connect a main battery and is configured to supply a main charging current to the a main battery terminal, in particular to the main battery, from at least one of the external charger and the further external charger, when the further external charger is connected to the second charger terminal, in particular when supplying power from the further external charger to the portable electronic device.

According to some implementations, the charger control circuit is further configured to supply the main charging current to the main battery terminal from the secondary battery, when the secondary battery is connected to the first charger terminal, in particular when supplying power from the secondary battery to the portable electronic device.

In further implementations, the charger control circuit further comprises a second current control element connected between the main battery terminal and the system terminal. The charger control circuit is further configured to control a current from and/or to the charger control circuit via the main battery terminal, in particular by means of the second current control element.

In some implementations, the supply of the main charging current may depend on the charging being enabled by the software or firmware of the portable electronic device and/or by the charger control circuit.

In some implementations, the second current control element comprises a transistor, a field effect transistor, a MOS field effect transistor, a power transistor or a power field effect transistor.

A source terminal of the second current control element is connected to the system terminal and a drain terminal of the second current control element is connected to the main battery terminal or vice versa. A gate terminal of the second control element is controlled by the charger control circuit.

In further implementations, the control of the current from and/or to the charger control circuit via the main battery terminal is based on a comparison of a value of the current from and/or to the charger control circuit via the main battery terminal to a specified second minimum current value and to a specified second maximum current value and/or to a specified second current range. In further implementations, the charger control circuit further comprises a third current control element connected between the second charger terminal and the system terminal. The charger control circuit is further configured to control a current from and/or to the charger control circuit via the second charger terminal, in particular by means of the third current control element.

In some implementations, the third current control element comprises a transistor, a field effect transistor, a MOS, field effect transistor, a power transistor or a power field effect transistor. A source terminal of the third current control element is connected to the system terminal and a drain terminal of the third current control element is connected to the second charger terminal or vice versa. A gate terminal of the third control element is controlled by the charger control circuit. In further implementations, the control of the current from and/or to the charger control circuit via the second charger terminal is based on a comparison of a value of the current from and/or to the charger control circuit via the second charger terminal to a specified third minimum current value and to a specified third maximum current value and/or to a specified third current range.

In further implementations of the charger control circuit, the second current control element comprises a field effect transistor, in particular a MOS field effect transistor, in particular a power MOS field effect transistor, and a bulk switch circuitry. The bulk switch circuitry is configured to connect and disconnect a substrate terminal of the second current control element to and from, respectively, a source terminal of the second current control element and/or a drain terminal of the second current control element, depending on a ratio of a voltage applied to the main battery terminal, for example the output voltage of the main battery, and the voltage applied to the first charger terminal, for example the output voltage of the secondary battery or the external charger.

In such implementations, power may be supplied from the secondary battery or the external charger to the portable electronic device if an absolute value of the voltage applied to the main battery terminal is larger than an absolute value of the voltage applied to the first charger terminal. However, power may also be supplied from the secondary battery or the external charger to the portable electronic device if the absolute value of the voltage applied to the main battery terminal is smaller than the absolute value of the voltage applied to the first charger terminal.

In some implementations, the field effect transistor comprised by the second current control element is implemented as a p-channel MOS transistor. In such implementations, if the output voltage of the main battery is larger than the output voltage of the secondary battery, the bulk switch circuitry is configured to connect the substrate terminal to the one of the source terminal and the drain terminal of the second current control element being connected to the main battery terminal. If the output voltage of the main battery is smaller than the output voltage of the secondary battery, the bulk switch circuitry is configured to connect the substrate terminal to the one of the source terminal and the drain terminal of the second current control element being connected to the system terminal.

In other implementations, the field effect transistor comprised by the second current control element is implemented as an n-channel MOS transistor. In such implementations, if the output voltage of the main battery is smaller than the output voltage of the secondary battery, the bulk switch circuitry is configured to connect the substrate terminal to the one of the source terminal and the drain terminal of the second current control element being connected to the main battery terminal. If the output voltage of the main battery is larger than the output voltage of the secondary battery, the bulk switch circuitry is configured to connect the substrate terminal to the one of the source terminal and the drain terminal of the second current control element being connected to the system terminal.

According to the improved principle, also a method for charger control in a portable electronic device is provided. The method comprises assigning a voltage applied at a first charger terminal of a charger control circuit to one of at least three voltage ranges by performing at least one voltage comparison. The method further comprises determining and distinguishing, based on the assignment, whether an external charger or a secondary battery is connected to the first charger terminal. The method comprises, depending on a predetermined operating state of the first charger terminal, supplying power from the secondary battery to the portable electronic device via a system terminal of the charger control circuit when the secondary battery is connected to the first charger terminal and supplying power from the external charger to the portable electronic device via the system terminal when the external charger is connected to the first charger terminal.

Some implementations of the method further comprise controlling, by means of a first current control element of the charger control circuit connected between the first charger terminal and the system terminal, a current from and/or to the charger control circuit via the first charger terminal.

In further implementations of the method, the controlling is performed based on a comparison of a value of the current from and/or to the charger control circuit via the first charger terminal to a specified first minimum current value and to a specified first maximum current value. Alternatively or in addition, the controlling is performed based on a comparison of a value of the current from and/or to the charger control circuit via the first charger terminal to a specified first current range.

Further implementations of the method comprise determining whether a further external charger is connected to a second charger terminal of the charger control circuit by performing a further voltage comparison. When the further external charger is connected to the second charger terminal, the method further comprises supplying power from the further external charger to the portable electronic device via the system terminal if a predetermined priority of the second charger terminal is higher than a predetermined priority of the first charger terminal and supplying power from the secondary battery or from the external charger to the portable electronic device via the system terminal if the priority of the first charger terminal is higher than the priority of the second charger terminal.

According to further implementations, the method further comprises charging the secondary battery from the further external charger, when supplying power from the further external charger to electronic device.

Further implementations of the method are readily derived from the various

implementations and embodiments of the charger control circuit. In particular, each of the described implementations of the charger control circuit directly results in a corresponding implementation of the method according to the improved concept.

In the following, the invention is explained in detail with the aid of exemplary

implementations by reference to the drawings. Components that are functionally identical or have an identical effect may be denoted by identical references. Identical components and/or components with identical effects may be described only with respect to the figure where they occur first; their description is not necessarily repeated insubsequent figures.

In the drawings,

Figure 1 shows an exemplary implementation of a charger control circuit according to the improved concept;

Figure 2 shows a further exemplary implementation of a charger control circuit

according to the improved concept; and

Figure 3 shows a flow chart of an exemplary implementation of a method according to the improved concept.

In Figure 1 , an exemplary implementation of a charger control

circuit CC according to the improved concept is shown. The charger control circuit CC comprises a first circuit block CB, being for example a charger block, for example a charger block for Lithium ion batteries. The charger control circuit CC further comprises a system terminal ST connected to the first circuit block CB, a first charger terminal CTl connected to the first circuit block CB and a main battery terminal MBT connected to the first circuit block CB. The first circuit block CB comprises a first current control element Ql connected between the first charger terminal CTl and the system terminal ST and a second current control element Q2 connected between the main battery terminal MBT and the system terminal ST. The main battery terminal MBT may be connected to a main battery MBAT of a portable electronic device and the first charger terminal CTl may be connected to a secondary battery SB AT or to an external charger EXC1.

The charger control circuit CC is comprised by the portable electronic device, which may for example be a camera, a mobile telephone, a notebook computer or the like. The main battery MBAT and the secondary battery SBAT may for example also be comprised by the portable electronic device. In particular, the secondary battery SBAT may also be external to the portable electronic device.

In the shown implementation, the first and the second current control element Ql, Q2 comprise for example respective field effect transistors, in particular power p-channel MOS field effect transistors. A source terminal and a drain terminal of the first current control element Q 1 , in particular of the field effect transistor comprised by the first current control element Ql, are for example connected to the system terminal ST and the first charger terminal CTl, respectively. A source terminal and a drain terminal of the second current control element Q2, in particular of the field effect transistor comprised by the second current control element Q2, are for example connected to the system terminal ST and the main battery terminal MBT, respectively. Gate terminals of the first and the second current control element Ql, Q2, in particular of the field effect transistors comprised by the first and the second current control element Ql, Q2, respectively, may be controlled by the charger control circuit CC, in particular by the first circuit block CB or by an optional charger control state machine (not shown) of the charger control circuit CC. The first and the second current control elements Ql , Q2 may also comprise respective bulk switching circuitries as indicated by switches between the source terminals and substrate terminals as well as between the drain terminals and the substrate terminals of the first and the second current control elements Ql, Q2, respectively. In the shown example, the switches between the source terminals and the substrate terminals of the first and the second current control element Ql, Q2 are open, while the switches between the drain terminals and the substrate terminals of the first and the second current control element Ql, Q2 are closed. This means that in the shown example the bulk switch circuitries of the first and the second current control element Ql, Q2 have disconnected the substrate terminals of the first and the second current control element Ql, Q2 from the source terminals of the first and the second current control element Ql, Q2 and have connected the substrate terminals of the first and the second current control element Ql, Q2 to the drain terminals of the first and the second current control element Ql, Q2. The secondary battery SBAT may be connected to the first charger terminal CT1. Then, due to an output voltage of the secondary battery SBAT, a voltage is applied at the first charger terminal CT1. The charger control circuit CC for example performs a voltage comparison based on the voltage applied at the first charger terminal CT1. For example, the charger control circuit CC compares the voltage applied at the first charger terminal to a first threshold value, for example a minimum battery detection voltage. For example, the voltage applied at the first charger terminal CT1 may be greater than the minimum battery detection voltage. The voltage applied to the first charger terminal CT1 may further be compared to a second threshold value, for example a minimum charger detection voltage. For example, the voltage applied at the first charger terminal CT1 may be smaller than the minimum charger detection voltage. Consequently, the charger control circuit CC may assign the voltage applied at the first charger terminal CT1 to a second voltage range, corresponding to voltages between the first and the second threshold value. In this way, the charger control circuit CC may determine that the secondary battery SBAT is connected to the first charger terminal CT1.

Consequently, the charger control circuit CC may control the first and the second current control element Ql, Q2 in order to supply power from the secondary battery SBAT to the portable electronic device via the system terminal ST. In particular, the field effect transistor of the first current control element Ql may be closed or conducting, while the field effect transistor of the second current control element Q2 may be open.

Alternatively, the field effect transistor of the second current control element Q2 may be closed or conducting, while the field effect transistor of the first current control element Ql may be open in order to allow a power supply from the main battery MBAT to the portable electronic device via the system terminal ST.

Alternatively, the field effect transistors of the first and the second current control element Ql, Q2 may both be closed or conducting, such that a main charging current may be supplied to the main battery terminal MBT. Consequently, the main battery MBAT, if connected to the main battery terminal MBT, may be charged by the secondary battery SB AT via the main battery terminal MBT. In this case, the output voltage of the secondary battery SBAT may for example be larger than an output voltage of the main battery MBAT. Then, the bulk switch circuitry of the second current control element Q2 may have disconnected the substrate terminal of the second current control element Q2 from the drain terminal of the second current control element Q2 and have connected the substrate terminal of the second current control element Q2 to the source terminal of the second current control element Q2, contrary to the situation shown in Figure 1.

Alternatively, a secondary charging current may be supplied from the main battery MBAT to the first charger terminal CT1 for example in order to charge the secondary battery SBAT. In this case, the output voltage of the main battery MBAT may for example be larger than an output voltage of the secondary battery SBAT. Then, the bulk switch circuitry of the first current control element Ql may have disconnected the substrate terminal of the first current control element Ql from the drain terminal of the first current control element Ql and have connected the substrate terminal of the second current control element Ql to the source terminal of the first current control element Ql, contrary to the situation shown in Figure 1.

In other situations, not the secondary battery SBAT but the external charger EXC1 may be connected to the first charger terminal CT1. In such a case, due to an output voltage of the external charger EXC1, the voltage applied at the first charger terminal CT1 may be greater than the first threshold value and greater than the second threshold value.

Consequently, the charger control circuit CC may assign the voltage applied at the first charger terminal CTl to a third voltage range, corresponding to voltages above second threshold value. In this way, the charger control circuit CC may determine that the external charger EXC1 is connected to the first charger terminal CTl .

Consequently, the charger control circuit may control the first current control element Ql in order to supply power from the external charger EXC1 to the portable electronic device via the system terminal ST. Additionally, the charger control circuit may control the second current control element Q2 in order to supply the main charging current to the main battery terminal MBT for example for charging the main battery MBAT by the external charger EXC1, as explained above for the secondary battery SB AT being connected to the first charger terminal CTl . In further situations, neither the secondary battery SB AT nor the external charger EXC1 may be connected to the first charger terminal CTl . In this case, no voltage is applied to the first charger terminal CTl . Then, the charger control circuit CC may assign the voltage applied to the first charger terminal CTl to a first voltage range corresponding to voltages below the first threshold value.

By means of the bulk switch circuitries of the first and the second current control element Ql, Q2 operating as described above, it may for example be avoided that a current flows through a substrate diode of the first current control element Ql and/or through a substrate diode of the second current control element Q2. In particular, by disconnecting the source terminal of the second current control element Q2 from the substrate terminal of the second current control element Q2 as shown in Figure 1, a voltage being lower than the output voltage of the main battery MBAT may be supplied from the secondary battery SB AT to the electronic device via the system terminal ST without a current flowing from the main battery MBAT through the substrate diode of the second current control element Q2.

The charger control circuit CC, in particular the first circuit block CB may for example be implemented as an integrated circuit. Figure 2 shows a further exemplary implementation of a charger control circuit CC according to the improved concept based on the implementation shown in Figure 1.

In addition to the implementation shown in Figure 1 , in the implementation of Figure 2 the charger control circuit CC further comprises a second circuit block CL, for example a power-path-and-current-limiter block. The second circuit block CL may for example be implemented as an integrated circuit, in particular the first and the second circuit block CB, CL may be implemented on the same integrated circuit or on different integrated circuits. The charger control circuit CC further comprises a second charger terminal CT2 connected to the second circuit block CL.

The second circuit block CL comprises a third current control element Q3 connected between the second charger terminal CT2 and the system terminal ST. In the shown implementation, the third current control element Q3 comprises for example a field effect transistor, in particular a power p-channel MOS field effect transistor. A source terminal and a drain terminal of the third current control element Q3, in particular of the field effect transistor comprised by the third current control element Q3, are for example connected to the system terminal ST and the second charger terminal CT2, respectively. A gate terminal of the third current control element Q3, in particular of the field effect transistor comprised by the third current control element Q3, may be controlled by the charger control circuit CC, in particular by the second circuit block CL or by the optional charger control state machine (not shown).

The third current control element Q3 may also comprise a bulk switching circuitry as indicated by switches between the source terminal and a substrate terminal as well as between the drain terminal and the substrate terminal of the third current control elements Q3. In the shown example, the switches between the source terminals and the substrate terminals of the first and the second current control element Ql, Q2 are closed, while the switches between the drain terminals and the substrate terminals of the first and the second current control element Q 1 , Q2 are open.

In the shown example, the switch between the source terminal and the substrate terminal of the third current control element Q3 is open, while the switch between the drain terminal and the substrate terminal of the third current control element Q3 is closed. This means, in the shown example the bulk switch circuitries of the first and the second current control element Ql, Q2 have connected the substrate terminals of the first and the second current control element Ql, Q2 to the source terminals of the first and the second current control element Ql, Q2 and have disconnected the substrate terminals of the first and the second current control element Ql, Q2 from the drain terminals of the first and the second current control element Ql, Q2. Furthermore, the bulk switch circuitry of the third current control element Q3 has connected the substrate terminal of the third current control element Q3 to the drain terminal of the third current control element Q3 and disconnected the substrate terminal of the third current control element Q3 from the source terminal of the third current control element Q3.

In the shown example, a further external charger EXC2 may be connected to the second charger terminal CT2. Due to an output voltage of the further external charger EXC2, a voltage is applied to the second charger terminal CT2. The charger control circuit CC may for example determine that the further external charger EXC2 is connected to the second charger terminal CT2 by performing a further voltage comparison. In particular, the charger control circuit CC may compare the voltage applied at the second charger terminal CT2 to a third threshold value, for example being a further minimum charger detection voltage. Therein, the third threshold value may or may not be equal to the second threshold value.

Consequently, the charger control circuit CC may supply power from the further external charger EXC2 to the portable electronic device via the system terminal if a predetermined priority of the second charger terminal CT2 is higher than a predetermined priority of the first charger terminal CT1. In this case, the field effect transistor comprised by the third current control element Q3 may be closed or conducting. Furthermore, the charger control circuit CC may for example supply a secondary charging current to the first charger terminal CT1 for example for charging the secondary battery SB AT from the further external charger EXC2, for example while also supplying the power to the electronic device from the further external charger EXC2. To this end, the field effect transistor comprised by the first current control element Ql may for example be closed or conducting. At the same time, the field effect transistor comprised by the second current control element Q2 may for example be open such that no current flows from or to the main battery MB AT.

If, on the other hand, the priority of the first charger terminal CT1 is higher than the priority of the second charger terminal CT2, the charger control circuit CC may supply power from the secondary battery SBAT or from the main battery MB AT to the electronic device via the system terminal ST as described with respect to Figure 1.

Alternatively, the field effect transistors comprised by the first, the second and the third current control element Ql, Q2, Q3 may all be closed or conducting. Consequently, power may be supplied from the further external charger EXC2 to the portable electronic device via the system terminal ST. At the same time, the secondary charging current may be supplied to the first charger terminal CT1 for example for charging the secondary battery SBAT and the main charging current may be supplied to the main battery terminal MBT for example for charging the main battery MB AT.

Figure 3 shows a flow chart of an exemplary implementation of a method according to the improved concept. The flowchart starts with block 400, where the portable electronic device is powered off. In block 405 is determined whether the further external charger EXC2 is connected to the second charger terminal CT2 as described above, for example with respect to Figure 2. If it is found that the further external charger EXC2 is connected to the second charger terminal CT2, the charger control circuit may enter an operating mode of block 410 denoted as "active charger input 2". During the operating mode of block 410, power may be supplied from the further external charger EXC2 to the portable electronic device via the system terminal ST as described with respect to Figure 2. In this operating mode, the portable electronic device may for example be started up using power from the further external charger EXC2. Furthermore, in this operating mode, the main battery MBAT and the secondary battery SBAT, if connected to the first charger terminal CT1, are for example not charged. During the operating mode of block 410, it may for example repeatedly be determined whether charging is enabled according to block 415. If charging is not enabled, the operating mode remains the operating mode of block 410. Further, during the operating mode of block 410, it may for example repeatedly be determined in block 420 whether the further external charger EXC2 is connected to the second charger terminal CT2. If the further external charger EXC2 is connected to the second charger terminal CT2, the operating mode remains the operating mode of block 410.

If it is determined in block 415 that charging is enabled, the charger control circuit may enter an operating mode of block 425 denoted as "active charging". In case the operating mode of block 425 is entered from the operating mode of block 410, power may be supplied from the further external charger EXC2 to the portable electronic device via the system terminal ST as for the operating mode of block 410. However, also the main battery MB AT and/or the secondary battery SBAT, if connected to the first charger terminal CT1, may be charged in the operating mode of block 425.

During the operating mode of block 425, it may for example repeatedly be checked in block 430 if charging is disabled. If it is found that charging is not disabled, the operating mode may remain the operating mode of block 425.

On the other hand, if it is determined in block 430 that charging is disabled, it may be proceeded with block 435. In block 435 it is determined whether the further external charger EXC2 is connected to the second charger terminal CT2. If it is found that the further external charger EXC2 is not connected to the second charger terminal CT2, it may be proceeded with block 440. Furthermore, if it is determined in block 420 that the further external charger EXC2 is not connected to second charger terminal CT2, it may also be proceeded with block 440.

In block 440, it is determined whether one of the secondary battery SBAT and the external charger EXC1 is connected to the first charger terminal CT1 and whether the first charger terminal CT1 is enabled as an input for operation of the secondary battery SBAT. If it is found in block 435 that the further external charger EXC2 is connected to the second charger terminal CT2, the charger control circuit CC may for example enter the operating mode of block 410 and it may be proceeded as described above. If it is found in block 440 that one of the secondary battery SBAT and the external charger EXCl is connected to the first charger terminal CTl and that the first charger terminal CTl is enabled as an input for operation of the secondary battery SBAT, the charger control circuit CC may enter the operating mode of block 445 denoted as "active secondary battery". During the operating mode of block 445, power may be supplied from the secondary battery SBAT or the external charger EXCl to the portable electronic device via the system terminal ST. For example, the main battery MBAT may be not charged in this operating mode. During the operating mode of block 445, it may for example be repeatedly checked in block 450 whether the further external charger EXC2 is connected to the second charger terminal CT2 and whether the second charger terminal CT2 is enabled. If it is determined that the further external charger EXC2 is connected to the second charger terminal CT2 and the second charger terminal is enabled, the charger control circuit CC may enter the operating mode of block 410 and proceed as described before. If it is determined in block 450 that the further external charger EXC2 is not connected to the second charger terminal CT2 or that the second charger terminal CT2 is not enabled, it is proceeded with block 455.

In block 455 is determined whether the external charger EXCl is connected to the first charger terminal CTl and whether charging is enabled. If it is found that the external charger EXCl is connected to the first charger terminal CTl and that charging is enabled, the operating mode of block 425 may be entered. If the operating mode of block 425 is entered in this way, power may for example be supplied from the external charger EXCl to the portable electronic device via the system terminal. Furthermore, the main battery MBAT may be charged from the external charger EXC 1.

If it is found in block 455 that the external charger EXCl is not connected to the first charger terminal or that charging is not enabled, it is proceeded with block 460. In block 460, it is determined whether a supply voltage for example applied at the system terminal is smaller than a minimum operating voltage or whether the first charger terminal CTl is disabled for operation from a secondary battery SBAT. If it is found that the supply voltage is not smaller than the minimum operating voltage and that the first charger terminal CTl is not disabled, the operating state may remain the operating state of 445. If, on the other hand it is found that the supply voltage is smaller than the minimum operating voltage or that the first charger terminal CTl is disabled, the charger control circuit CC may enter the operating mode of block 465, denoted as "active main battery". During the operating mode of block 465, power may be supplied from the main battery

MB AT to the portable electronic device via the system terminal ST. The operating mode of block 465 may also be entered if it is found in block 440 that neither the secondary battery SBAT nor the external charger EXCl is connected to the first charger terminal CTl or that the first charger terminal CTl is not enabled.

During the operating mode of block 465, it may for example be repeatedly checked in block 435 whether the further external charger EXC2 is connected to the second charger terminal CT2. It is then proceeded as described above for block 435. Furthermore, during the operating mode of block 465 it may for example be repeatedly checked in block 470 whether the supply voltage is smaller than the operating voltage. If it is found that the supply voltage is smaller than the operating voltage, the portable electronic device may be powered off in block 400. If it is found in block 470 that the supply voltage is not smaller than the operating voltage, the operating mode may remain the operating mode of block 465.

If it is determined in block 405 that the further external charger EXC2 is not connected to the second charger terminal CT2, it is determined in block 480 whether one of the external charger EXCl or the secondary battery SBAT is connected to the first charger terminal CTl . If it is found that one of the external charger EXCl or the secondary battery SBAT is connected to the first charger terminal CTl, the portable electronic device may for example be started up using power from the external charger EXC 1 or the secondary battery SBAT and it may be proceeded with the operating mode of block 445 as described above.

If it is determined in block 480 that neither the external charger EXCl nor the secondary battery SBAT is connected to the first charger terminal CTl it may be determined in block

485 whether startup conditions for the main battery MBAT are fulfilled. If the startup conditions for the main battery MBAT are fulfilled, the portable electronic device may for example be started up using power from the main battery MBAT and it may be proceeded with the operating mode of block 465 as described above. If the startup conditions for the main battery MB AT are found to be not fulfilled in block 485, the portable electronic device may remain powered off in block 400. The method displayed by the flowchart of Figure 3 corresponds to an implementation according to the improved concept, wherein the priority of the second charger terminal CT2 is higher than the priority of the first charger terminal CT1. In alternative

implementations, the priority of the first charger terminal CT1 may be higher than the priority of the second charger terminal. The blocks of Figure 3 may then be rearranged accordingly.

The charger control circuit CC according to the improved concept may for example further comprise a charger control state machine. The charger control state machine may for example control the first, the second and/or the third current control element Ql, Q2, Q3. In particular, the charger control state machine may control the bulk switch circuitries and/or voltages at the gate terminals of the first, the second and/or the third current control element Ql, Q2, Q3. The charger control state machine may also perform further tasks, for example tasks described with respect to the method of Figure 4. By means of the improved concept, power may be supplied from the secondary battery SBAT to the portable electronic device without a boost of the output voltage of the secondary battery SBAT being necessary. Therefore, costs may be reduced and an efficiency of the power supply via the secondary battery SBAT may be improved. In several implementations, also additional connectors or connector pins for attaching the secondary battery SBAT may be not needed due to the improved concept.

Furthermore, the secondary battery SBAT may be charged by means of the further external charger EXC2 without the need of a dedicated battery charger. In particular, the secondary battery SBAT may be charged simultaneously with the main battery MB AT. In addition, supplying power from the secondary battery SBAT to the portable electronic device is possible also when the output voltage of the secondary battery falls below the output voltage of the main battery. Furthermore, a charging and/or discharging of the main battery MBAT and the secondary battery SBAT may be controlled by a single circuit block of an integrated circuit, for example by the first circuit block CB, which may be a charger block.

Reference numerals

CC charger control circuit

CB, CL circuit blocks

ST system terminal

CT1, CT2 charger terminals MBT main battery terminal MBAT main battery

SBAT secondary battery

EXC1 , EXC2 external chargers Q1, Q2, Q3 current control elements