CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Patent Application No. 63/175,239 filed on April 15, 2021. The entire contents of this application are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0002] The present invention relates to high-speed switching devices. More specifically, the present invention relates to an optimized layout of a gate driver circuit for high-speed switching devices.

2. Description of the Related Art

[0003] Gallium nitride high-electron-mobility transistors (GaN HEMTs) are widely used for high-power applications, including, for example, server and telecommunications applications. GaN HEMTs achieve high-frequency, high-efficiency, and high-density power conversion. However, GaN HEMTs typically require drivers that are supplied with power from auxiliary power supplies, which connects the GaN HEMTs, the drivers, and the auxiliary power supplies together. In addition, special care is required to drive GaN HEMTs because GaN HEMTs have a low gate-source threshold voltage that can cause the GaN HEMTs to unexpectedly turn-on, i.e., self-turn-on, when exposed to a small amount of electromagnetic interference (EMI) or noise. Unexpected turn-on of the GaN HEMTs causes limitations and problems in the physical layout of the circuit with the GaN HEMTs, including the gate driver circuit of the GaN HEMTs. GaN HEMTs typically have very fast switching, thereby causing large voltage spikes, i.e., large voltage changes over time (dv/dt), in connected circuitry, which can increase noise.

[0004] Due to the sensitivity of GaN HEMTs, it is desirable that the lines connected to the gates of the GaN HEMTs be as short as possible. The lines connected to the gates of the GaN HEMTs can be patterns or traces on a printed circuit board (PCB) or other substrate. Typically, in circuit layouts, an auxiliary power supply is located far from a gate driver circuit (e.g., the auxiliary power supply and the gate driver may be located on different PCBs), such that the lines between the gate driver circuit and the auxiliary power supply can be susceptible to EMI or noise. Also, a gate-line current loop defined by the line between the isolated driver and the gate of the GaN HEMT and the line between the source of the GaN HEMT and the ground of the isolated driver of the gate driver circuit tends to be long (e.g., greater than about two times a width of the GaN HEMT), increasing parasitic inductances, which causes self-turn-on of the GaN HEMTs. Additionally, the complexity of the gate signal pattern layout can significantly increase in topologies where multiple GaN HEMTs are used.

[0005] Fig. 1 is a block diagram of a known circuit including switches Qi and C , which can be GaN HEMTs, and associated driver circuitry, including isolated drivers ICi and IC2. The switches Qi and Q2 are connected in series, with the switch Qi being a high-side GaN HEMT and the switch Q2 being a low-side GaN HEMT. A controller 100 provides signals that turn on and off the switches Qi and Q2 via the isolated drivers ICi and IC2. The isolated driver ICi is a high-side isolated driver and is connected to the high-side switch Qi, and the isolated driver IC2 is a low- side isolated driver and is connected to the low-side switch Q2. An auxiliary power supply 101, which, for example, can be a DC power supply that rectifies pulse voltages received from auxiliary windings of an LLC converter, provides a high-side voltage V _CC H to the isolated driver ICi and a low-side voltage V _CC L to the isolated driver IC2. The auxiliary power supply 101 is also connected to a low-side ground terminal GNDH of the isolated driver ICi and a low-side ground terminal GNDL of the isolated driver IC2. The low-side ground terminal GNDH of the isolated driver ICi is connected to a source terminal Si of the switch Qi, and the low-side ground terminal GNDL of the isolated driver IC2 is connected to a source terminal S2 of the switch Q2.

An input voltage V _m is provided across a drain terminal Di of the switch Qi and the source terminal S2 of the switch Q2. Gate terminals Gi and G2 of the switches Qi and Q2 are respectively driven by voltages output from the isolated drivers ICi and IC2 according to control signals provided to the isolated drivers ICi and IC2 by the controller 100.

[0006] As shown in Fig. 1, the lines connecting the isolated drivers ICi and IC2 and respective gates Gi and G2 of the switches Qi and Q2 are as short as possible to provide reliable operation by reducing the influence of EMI or noise. Although the components of the circuit shown in Fig. 1 may be concentrated in a small area to provide reliable operation, this solution may not be possible in certain applications due to the size of the circuit, components, packaging, etc. For example, an auxiliary power supply may be located far from the gate driver circuit, e.g., the auxiliary power supply and the gate driver may be located on different PCBs, which results in gate-line current loop being a long current loop that is susceptible to EMI or noise.

SUMMARY OF THE INVENTION

[0007] To overcome the problems described above, preferred embodiments of the present invention provide printed circuit board (PCB) layouts of high-speed switching devices that each simplify PCB layout design even if an application requires high power density packaging in which the PCB layout is constrained.

[0008] Preferred embodiments of the present invention with layouts of gate driver circuity for high-speed switching devices can include one or more of the following features:

1) A transformer located between an auxiliary power supply and gate driver circuitry to simplify the circuit layout design so that the gate lines can be made shorter as compared to if a transformer is not included in the gate driver circuitry. For example, the gate line can be made as short as the width of one of the high-speed switching devices.

2) To decrease parasitic inductance, the gate-line current loop can be made shorter compared to conventional layouts of gate driver circuitry, even if a line between the auxiliary power supply and the gate driver circuity is long. For example, the gate-line current loop can be made as short as the width of one of the high-speed switching devices, even if the auxiliary power supply and the gate driver circuitry are located on different PCBs.

3) By locating the transformer between the auxiliary power supply and the gate driver circuitry, an increase in noise caused by large voltage spikes, i.e., large voltage changes over time (dv/dt), can be significantly reduced or prevented due to the decoupling of the gate currents and the current of the auxiliary power supply.

4) By using the inherent properties of a structure of a transformer, the complexity of the design of gate driver circuity can be significantly reduced.

[0009] According to a preferred embodiment of the present invention, a switching circuit includes a first switch; a second switch connected in series with the first switch; a first isolated driver connected to a gate terminal of the first switch; a second isolated driver connected to a gate terminal of the second switch; and a transformer including a primary winding connected to an auxiliary power supply, a first secondary winding to supply a first voltage to the first isolated driver, and a second secondary winding to supply a second voltage to the second isolated driver.

[0010] The switching circuit can further include a first rectifier connected between the first secondary winding and the first isolated driver and a second rectifier connected between the second secondary winding and the second isolated driver. Each of the first switch and the second switch can be a GaN transistor. A source terminal of the first switch can be connected to a drain terminal of the second switch. The switching circuit can further include a control circuit connected to each of the first isolated driver and the second isolated driver. An output of the transformer to the first isolated driver can be located on a different side of the transformer from an output of the transformer to the second isolated driver. A size of the transformer can be smaller than a size of either of the first isolated driver or the second isolated driver. Each of the first switch, the second switch, the first isolated driver, the second isolated driver, and the transformer can be provided on a single circuit board or a single substrate. A length of at least one of a first gate line connected between the first isolated driver and the gate terminal of the first switch and a second gate line connected between the second isolated driver and the gate terminal of the second switch can be equal to or shorter than a width of at least one of the first switch and the second switch. A first gate-line current loop of the first switch can be defined by a path from the first isolated driver to the gate terminal of the first switch and to a ground terminal of the first isolated driver; a second gate-line current loop of the second switch can be defined by a path from the second isolated driver to the gate terminal of the second switch and to a ground terminal of the second isolated driver; and a length of at least one of the first gate line current loop and the second gate-line current loop can be equal to or shorter than a width of at least one of the first switch and the second switch.

[0011] According to a preferred embodiment of the present invention, a gate driver device includes a substrate including terminals to receive an auxiliary voltage from an auxiliary power supply that is not located on the substrate; a first switch and a second switch that are located on the substrate and that are connected in series; a first isolated driver that is located on the substrate, that is connected to the first switch, and that includes first input circuitry and first output circuitry that are isolated from each other; a second isolated driver that is located on the substrate, that is connected to the second switch, and that includes second input circuitry and second output circuitry that are isolated from each other; a transformer that is located on the substrate and that includes a primary winding to receive the auxiliary voltage, a first secondary winding to supply a first voltage to the first output circuitry, and a second secondary winding to supply a second voltage to the second output circuitry.

[0012] The gate driver device can further include a first rectifier connected between the first secondary winding and the first isolated driver and a second rectifier connected between the second secondary winding and the second isolated driver. Each of the first switch and the second switch can be a GaN transistor. A source terminal of the first switch can be connected to a drain terminal of the second switch. A first line connecting the transformer to the first isolated driver can be located on a different side of the transformer from a second line connecting the transformer to the second isolated driver. A size of the transformer can be smaller than a size of either of the first isolated driver or the second isolated driver. The first isolated driver and the second isolated driver can be located on a first side of the substrate; and the first switch, the second switch, and the transformer can be located on a second side of the substrate opposite to the first side. A length of at least one of a first gate line connected between the first isolated driver and a gate terminal of the first switch and a second gate line connected between the second isolated driver and a gate terminal of the second switch can be equal to or shorter than a width of at least one of the first switch and the second switch. A first gate-line current loop of the first switch can be defined by a path from the first isolated drivers to a gate terminal of the first switch and to a ground terminal of the first isolated driver; a second gate-line current loop of the second switch can be defined by a path from the second isolated driver to the gate terminal of the second switch and to a ground terminal of the second isolated driver; and a length of at least one of the first gate-line current loop and the second gate-line current loop can be equal to or shorter than a width of at least one of the first switch and the second switch. [0013] According to a preferred embodiment of the present invention, a gate driver system includes the gate driver device of one of the various preferred embodiments of the present invention and the auxiliary power supply that is not located on the substrate.

[0014] The gate driver system can further include a control circuit connected to each of the first isolated driver and the second isolated driver. The auxiliary power supply can be a pulse voltage power supply.

[0015] The above and other features, elements, characteristics, steps, and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS [0016] Fig. 1 is a block diagram of a known gate driver circuit.

[0017] Fig. 2 is a block diagram of a gate driver circuit with a transformer located between isolated drivers and an auxiliary power supply.

[0018] Fig. 3 shows a top view of a component layout of a substrate with a gate driver circuit.

[0019] Fig. 4 is a schematic view showing components on the top and the bottom surfaces of the substrate of Fig. 3.

[0020] Fig. 5 shows a bottom view of a component layout of the substrate of Fig. 3.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS [0021] Fig. 2 shows that gate driver circuitry with a transformer Ti provided between the gate driver circuitry and the auxiliary power supply AUX, where the gate driver circuity and an auxiliary power supply AUX can be placed far apart, e.g., the gate driver and the auxiliary power supply AUX and may be located on different PCBs. The gate driver circuitry includes a controller 10, isolated drivers ICi and IC2 that receive signals from the controller 10, and switches Qi and Q2 connected in series and including gates terminals G1 and G2 connected to the isolated drivers ICi and IC2. The gate driver circuitry can include a gate resistor RgH connected between the controller 10 and to the gate terminal G1 of switch Qi and a gate resistor RgL connected between the controller 10 and to the gate terminal G2 of switch Q2. Switches Qi and Q2 can be high-power and/or fast-switching transistors such as GaN HEMTs. Terminals of an input voltage Vin can be provided across a drain terminal Di of the switch Qi and the source terminal S2 of the switch Q2. The gate driver circuitry includes the transformer Ti respectively connected to the isolated drivers ICi and IC2 via rectifiers RECi and REC2. The transformer Ti is also connected to the auxiliary power supply AUX. The controller 10 can be any suitable controller, including, for example, a digital signal processor (DSP) or a microcontroller. The controller 10 can include a single controller or can include multiple controllers. Transformer^ can be any suitable transformer. Rectifiers RECi and REC2 can be any suitable rectifiers, including, for example, small signal Schottky diodes. The isolated drivers ICi and IC2 can be any suitable isolated drivers that provide enough source/sink current and high-speed switching to turn on/off the switches Qi and Q2. The auxiliary power supply AUX may be a pulse-voltage power supply.

[0022] Isolated drivers such as isolated drivers ICi and IC2 can be used in applications in which a controller, such as controller 10, is located on a different side of an isolation barrier as the devices to be driven, such as switches Qi and Q2. For example, in a converter with a transformer that provides isolation between a primary side and a secondary side of the transformer, if the controller is located on the primary side of the transformer, then an isolated driver can be used to drive devices on the secondary side of the transformer, while maintaining the isolation barrier between the primary and secondary sides of the transformer. Conversely, if the controller is located on the secondary side of the transformer, then an isolated driver can be used to drive devices on the primary side of the transformer, while maintaining the isolation barrier between the primary and secondary sides of the transformer.

[0023] Because of the isolation between the inputs and the outputs of the isolated driver, each of the input circuitry and the output circuitry of the isolated driver must be independently supplied with power. The output circuitry of the isolated drivers can be powered by an auxiliary power supply that is separate from the power supply circuitry that powers the input circuitry of the isolated drivers. The input circuitry of the isolated drivers can be powered by the same power supply circuitry as the controller (not shown). For example, the power supply that supplies voltage to the controller 10 can also supply power and ground of the isolated drivers ICi and IC2. The isolation in the isolated drivers can be provided by any suitable device, including, for example, a transformer, an opto-isolator, etc.

[0024] In the gate driver circuit of Fig. 2, the transformer Ti can be relatively small in size, while still being able to supply power to the gate driver circuitry, and the transformer Ti can be smaller in size than each of the switches Qi and Q2· However, the transformer Ti decouples the signals between the auxiliary power supply AUX and the switches Qi and Q2, in particular, at the gates Gi and G2 of the switches Qi and Q2. Accordingly, the switches Qi and Q2 can be cleanly switched by significantly reducing or preventing any effect of noise from the auxiliary power supply AUX.

[0025] The controller 10 can be any suitable controller. The controller 10 can be an 1C chip or suitable device that provides control signals to turn on and off switching devices, such as GaN HEMTs. For example, the controller 10 can provide pulse-width modulation (PWM) signals to control the switches Qi and Q2 based on the output of a converter in which the switches Qi and Q2 are included.

[0026] As shown in Fig. 2, the auxiliary power supply AUX includes two terminals that supply voltages VP and VPR to a primary winding of the transformer Ti. The transformer Ti includes first and second secondary windings that are respectively connected to rectifiers RECi and REC2. The first secondary windings can supply a first voltage to the high-side isolated driver I Ci, and the second secondary winding can supply a second voltage to the low-side isolated driver IC2. The first and the second voltages can be different, depending on the turns ratio of the first and the second secondary windings. That is, the outputs of the transformer Ti separately power the isolated drivers ICi and IC2 via the corresponding rectifiers RECi and REC2. [0027] Rectifier RECi is a high-side rectifier that provides a high-side voltage V _CC H to the isolated driver ICi, and rectifier REC2 is a low-side rectifier that provides a low-side voltage V _CC L to the isolated driver IC2. Rectifier RECi is also connected to a low-side ground terminal GN DH of the isolated driver ICi, and rectifier REC2 is also connected to a low-side ground terminal GNDi_ of the isolated driver IC2. The low-side ground terminal GN DH of the isolated driver ICi is connected to a source terminal Si of the switch Qi, and the low-side ground terminal GNDL of the isolated driver IC2 is connected to a source terminal S2 of the switch Q2. Fig. 2 shows optional signal ground pins SGi and SG ₂ that can be used in switches with four pins (i.e., drain, source, gate, and signal ground) to ensure proper gate-source voltage V _gs . An input voltage V _m is provided across a drain terminal Di of the switch Qi and the source terminal S ₂ of the switch Q ₂ . Gate terminals Gi and G ₂ of the switches Qi and Q ₂ are respectively driven by voltages VGI and V _G2 output from the isolated drivers ICi and IC ₂ according to control signals provided to the isolated drivers ICi and IC ₂ by a control device. The switches Qi and Q ₂ are connected in series, with the source terminal Si of the switches Qi connected to the drain terminal D ₂ of the switch Q ₂ . The switches Qi and Q ₂ are preferably transistors, for example.

[0028] A gate-line current loop (Gate loop H/Gate loop L) of each of the switches Qi and Q ₂ is defined by a path from the isolated drivers ICi and IC ₂ to the corresponding gate terminal Gi and G ₂ and to ground GNDH and GNDL of the isolated drivers ICi and IC ₂ . A power-supply current loop (Supply loop H/Supply loop L) of the power supplied to each of the isolated drivers ICi and IC ₂ is defined by a path from the low-side voltages -V _CC H and -V _CC L of the isolated drivers ICi and IC ₂ , through the rectifiers REC1 and REC2 and secondary windings of the transformer Ti, and to the high-side voltages +V _CC H and +V _CC L of the isolated drivers ICi and IC ₂ . Accordingly, by including the transformer Ti between the auxiliary power supply AUX and the isolated drivers ICi and IC ₂ , a length of the gate-line current loop (Gate loop H/Gate loop L) of each of the switches Qi and Q ₂ and a length of the power-supply current loop (Supply loop H/Supply loop L) to each of the isolated drivers ICi and IC ₂ can be significantly reduced. Therefore, clean switching can be provided due to the power-supply current loops (Supply loop H/Supply loop L) being less susceptible to EMI and noise caused by large voltage spikes, which provides more ideal switching waveforms with significantly reduced voltage spikes and dips.

[0029] Figs. 3 and 5 show top and bottom sides of a substrate with an example of a component layout of a gate driver circuit, and Fig. 4 is a schematic view showing components on the top and the bottom surfaces of the substrate. Any suitable substrate can be used, including, for example, a PCB. As shown in Figs. 3-5, the transformer Ti, rectifiers RECi and REC ₂ , switches Qi and Q ₂ can be located on the top side of the substrate, and the isolated drivers ICi and IC ₂ and the gate resistors RgH and RgL can be located on the bottom side of the substrate. By locating the transformer Ti and the switches Qi and Q ₂ on different sides of the substrate, the component placement and layout design of the rectifiers RECi and REC2 can be simplified, and an area circumscribed by a current loop from the power supply (e.g., auxiliary power supply AUX) can be significantly reduced. In addition, by locating the isolated drivers ICi and IC2 on the bottom side of the substrate, the gate-line current loop (Gate loop H/Gate loop L) of each of the switches Qi and Q2 can be made relatively short, i.e., an area circumscribed by the gate-line current loop (Gate loop H/Gate loop L) of each of the switches Qi and Q2 can be significantly reduced. For example, the gate-line current loop (Gate loop H/Gate loop L) of the switches Qi and Q2 can be made as short as the width of one of the switches Qi and Q2.

[0030] However, component arrangements other than those described above and shown in Figs. 3-5 are also possible.

[0031] The auxiliary power supply AUX is not shown in Figs. 3-5. The auxiliary power supply AUX is not located on the substrate and can be connected to the terminals corresponding to V _p and V p shown in Fig. 3. The controller 10, which is not shown in Figs. 3-5, can be located on a different substrate. The power supply of the controller 10, which is not shown in Figs. 3-5, can also be located on a different substrate and can provide power to the input circuitry of the isolated drivers ICi and IC2.

[0032] As shown in Figs. 3-5, each of the switches Qi and Q2, the isolated drivers ICi and IC2, the rectifiers RECi and REC2, and the transformer Ti can all be provided on a single substrate. [0033] A line from the transformer Ti to the rectifier RECi can be on a different side of the transformer Ti than a line from the transformer Ti to the rectifier REC2, for example. By providing the lines from the transformer Ti to the rectifiers RECi and REC2 on different sides of the transformer Ti, the component placement and layout design of the gate driver circuitry and GaN HEMTs connected to the transformer can be simplified. This implementation is particularly advantageous if only the components provided for GaN HEMTs are mounted on a sub-board, and the sub-board is then connected to a main board.

[0034] It should be understood that the foregoing description is only illustrative of the present invention. Various alternatives and modifications can be devised by those skilled in the art without departing from the present invention. Accordingly, the present invention is intended to embrace all such alternatives, modifications, and variances that fall within the scope of the appended claims.