INVENTOR:

Deepak Pancholi

Bhavin Odedara

Rohit Reddy

PRIORITY CLAIM

[0001] This application relates claims priority to New Ordinary Indian Patent Application No. 1109/CHE/2013 filed on March 14, 2013, entitled "CONTROLLED START-UP OF A LINEAR VOLTAGE REGULATOR", the entire disclosure of which is hereby incorporated by reference.

TECHNICAL FIELD

[0002] This application relates generally to a linear voltage regulator. More specifically, this application relates to improving a linear voltage regulator with a controlled start-up circuit mechanism that handles the input power supply when it is higher than a device's operational voltage.

BACKGROUND

[0003] As per Moore's law, advances in integrated circuit (IC) technologies have resulted in decreasing the size and operating voltages of devices used to fabricate circuitry. As process geometries are shrinking, the voltages required for support are also decreasing. For example, in CMOS 28nm process, standard voltage core devices support 0.9V input supply voltage while preferred thick oxide devices in this process support 1.8 V input supply. There is a trend of lower supply voltages for core and IO (thick oxide) devices. [0004] In battery operated devices, such as cellular phones, smartphones, tablets, and laptop computers, low-voltage integrated circuits allow the devices to operate proportionally longer than devices requiring higher voltage for operation. The lower supply voltages of the latest standards (e.g. USB3.0, SATA3.0, PCIe3 etc.) may not always be compatible with legacy host device interfaces but new interfaces are typically backwards compatible. For example, old standard hosts provide higher supply voltage than new standards. Many interface standards are still supporting higher voltages, including 5V, 3.3V or 2.5V along with lower voltages (from host devices) for analog design or for maintaining compatibility with older interface standards. Accordingly, regulators need to translate 3.3V to 1.8V or 3.3V to 0.9V or lower with devices whose typical operational voltage is 1.8V or lower. Maximum possible support for these 1.8V devices can be up to 2V but not necessarily up to 3.7V or so.

[0005] The latest computer peripheral devices may therefore be designed to accommodate connections from newer, lower voltage host supplies as well as older, higher voltage supplies. Devices constructed with newer technologies therefore must allow for the possibility that the host device in which they are used may supply a higher voltage with legacy products. In order to couple systems manufactured with newer interface standard technologies to legacy interface standard hosts that provide higher-supply voltages, voltage regulation from higher voltage to lower voltage with devices whose operating voltage is lower than the input supply voltage may be used to provide the correct voltage in steady state. However, the voltage regulation may not adequately handle this higher than operational voltage at start-up.

SUMMARY

[0006] It may be desirable to have a voltage regulation circuit that regulates voltage with a controlled start-up mechanism for handling voltages that are higher than the device operation voltage. The start-up mechanism handles a higher start-up voltage and limits the voltage seen at the device to be lower than the maximum allowed operation voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 is a controlled startup voltage regulator.

[0008] Figure 2 is a startup mechanism for controlling input voltage.

[0009] Figure 3 is a level shifter with high voltage protection.

[0010] Figure 4 is an exemplary implementation of resistor ladder switch using outputs of level shifter of Figure 3.

[0011] Figure 5 is an amplifier with level switching.

[0012] Figure 6 is a graphical illustration of the controlled intermediate input supply voltage.

[0013] Figure 7 is a block diagram of a host connected with a memory system having non-volatile memory.

[0014] Figure 8 is a block diagram of an exemplary flash memory system controller for use in the system of Figure 7.

BRIEF DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

[0015] By way of introduction, a circuit, according to the embodiments described below, utilizes a start-up mechanism for regulating voltage. The circuit may regulate voltage for operating a device coupled to a host when the host supply exceeds that necessary device operational voltage. The controlled start-up mechanism handles a sudden ramp up of supply voltage (voltage spike) and handles very high voltages relative to the device's operational voltage. The circuit may be implemented with transistors or other devices which are designed to operate at various voltage levels which may be independent of the host. The circuit should be able to handle higher supply voltage of the host even if device operational voltage limit is lower. The circuit should also make sure that the devices or the host is not damaged under any condition

[0016] The circuits described below may include a variety of different transistors including MOS transistors. Metal oxide semiconductor ("MOS") may refer to the physical structure of certain field effect transistors, having a metal gate electrode placed on top of an oxide insulator, which in turn is on top of a semiconductor material. Complementary metal oxide semiconductor ("CMOS") is a technology for constructing integrated circuits. CMOS may be used in a variety of digital logic circuits and may also be used in microprocessors, microcontrollers, static RAM, and memory devices, such as flash drives. CMOS technology may be used for analog circuitry, including image sensors, data converters, and/or transceivers for different types of

communication. CMOS circuits may utilize p-type and n-type metal oxide

semiconductor field-effect transistors ("MOSFETs") to implement logic gates and other digital circuits found in computing and signal processing equipment. Typical commercial CMOS products may be integrated circuits composed of millions of transistors of both types on silicon. These devices may be referred to as chips, die, or dies. CMOS circuits are used to implement logic gates with p-type and n-type

MOSFETs to create paths to the output from either the voltage source or ground.

When a path to the output is created from the voltage source, the circuit is said to be pulled up. The other circuit state occurs when a path to output is created from ground and the output pulled down to the ground potential. The devices or transistors used for the circuits below may include N-type metal oxide-semiconductor ("NMOS") or P-type metal oxide-semiconductor ("PMOS"). NMOS logic utilizes n-type metal oxide- semiconductor field effect transistors ("MOSFETs") to implement logic gates and other digital circuits. PMOS logic utilizes p-type MOSFETs to implement logic gates and other digital circuits.

[0017] In one example, the circuit may be suitable for use with a non- volatile memory system as illustrated in Figures 7-8. However, the circuit may also apply to a number of different environments and uses other than the memory system illustrated in Figures7-8. The system may be utilized with any number of types of host devices including cellular telephones, smartphones, digital cameras, personal digital assistants, mobile computing devices, tablets, laptops, netbooks, non-mobile computing devices, audio/mp3 players, video players, and other devices.

[0018] Figure 1 is a voltage regulator 100 with a controlled startup mechanism. PMOS PM1 generates an intermediate supply voltage (VINT SUP) so that PMOS PMl and PMOS PMO are not exposed to a voltage higher than the maximum allowable operational voltage for the devices (e.g. 2V). PMl may be a protection transistor and PMO may be a regulating power MOS. The input voltage (VIN) may be established during start up. Without startup mechanism 102, VIN may rise quickly upon start-up and the voltage of VINT SUP may not be controlled quickly enough which may expose pass MOS devices PMO and PMl to higher voltages than the operational voltages for those devices. When devices are subjected to voltages above the operational voltage that the device is designed for, it may burn or have a reduced life cycle. The startup mechanism 102 is included in the circuit to prevent the devices from being exposed to voltages above the operational voltage. The startup mechanism is illustrated in Figure 2 and described below. When the circuit received an input supply (e.g. a flash drive connected with a host), that supply may rise quickly from 0 volts to 5 volts (in the flash drive example), but all the devices in the circuit may not be designed for that high of a voltage, so the startup mechanism 102 controls the intermediate supply voltage (VINT SUP) which in turn slows down the initial spike or rising of the supply voltage to the main regulation circuit.

[0019] The amplifier REG AMP regulates the voltage within the circuit. The Resistors Rl and R2 are shown with REG AMP which receives a reference voltage Vref BG. As the Cload capacitor gets charged, the output voltage rises and voltage across transistors PMl and PMO remain below device operational voltage (e.g. 2V). The simulation results of circuit and node voltages of VINT SUP and VOUT are shown in Figure 6.

[0020] The cascode or protection device bias arm may include the devices PMDO, PMDl, and PMD2, which are step devices for generating the bias voltage for cascade or protection device PMl, and includes a mirror device N MIRR0. The devices PMDO, PMDl and PMD2 may be used to create bias voltage for PMl only after startup process is completed. In particular, the cascode or protection device bias arm creates a stable bias voltage for device PMl in steady state condition after the supply ramp is settled. Whereas the startup mechanism 102 creates the bias voltage of PMl as the supply is ramping up and before the supply ramp is settled. Accordingly, the devices which may have a lower operational voltage are not exposed to the higher voltage even during startup.

[0021] Figure 2 is the startup mechanism 102 for controlling intermediate supply voltage. The resistive ladder switches 202 can modify the reference voltage of the error amplifier CTRL AMP by switching on/off. As shown in Figure 2, one embodiment may include eight resistive ladder switches, but more or fewer switches may be utilized in other embodiments. The resistors arm may be referred to as a resistor divider. The resistance values for the resistor divider that correspond to each of the switches are shown in Figure 2 and are also exemplary. As shown switch S 1 has a lower arm resistance value of R/2 or one half, while switches S2-S8 each have a lower arm resistance value of R/ 16 or one sixteenth. The voltages for each switch VPROT1- VPROT8 may thus be fixed. Based on the resistance values, the voltage at switch SI may be the lowest.

[0022] The resistive ladder switches S1-S8 may create the reference voltage into the control amplifier CTRL AMP. The node VINT_SUP may be controlled by amplifier CTRL AMP. The CTRL AMP may ensure that at startup the VINT SUP is at 50% level of input power supply VIN. This results from the fact that one input of

CTRL AMP is at R/2 (when switch SI is closed) from resistor ladder. With the startup mechanism 102, if the maximum input supply (VIN) is 3.7V, then the voltage at node VINT SUP would be 1.85V. Assuming the device operation voltage is 2V, then the voltage at VINT SUP is lower than the operation voltage. Every regular interval of time (in this example lOuS) the switches are changed from SI to S 8 and this varies voltage at VINT SUP in fixed voltage step (in this example, of 200mV) as shown in Figure 6 such that every device in the circuit experiences voltage across it below its maximum allowed operational voltage.

[0023] Figure 3 is a level shifter with high voltage protection. Figure 3 illustrates one embodiment for implementing the control inputs for the resistive ladder switches S1-S8 shown in Figure 2. When the level shifter is active, any one of its arms (ARM A or ARM B) may consume constant DC current. Both ARM A and ARM B have voltages lower than maximum allowed operational voltage for the devices for each arm. ARM A or ARM B is a diode arm with a 3 diode structure near the top of ARM A or ARM B. The right side of ARM A or left side of ARM B may be referred to as the switch arm. There is an enable signal EN in ARM A and ENB in ARM B. The outputs ENHOUT and ENHOUTB are high level shifted signals of EN and ENB respectively.

[0024] Figure 4 is an exemplary implementation of resistor ladder switch using a pass transistor controlled by level shifter output signals. The pass MOS devices from Figure 2 are simplified with multiple outputs. The input IN and output OUT are shown along with the enabled outputs ENHOUT and ENHOUTB of level shifter.

[0025] Figure 5 is an amplifier with level switching. In this mechanism the differentional pair arms of the "CTRL AMP" amplifier are switched with switches "SMI" to "SM8" and "SM2_1" to "SM8_1". With this mechanism level shifters of Figure 3 are not required and stand-by current is reduced. Initially while Vin is ramping up, the VPROT1 signal goes to the amplifier as a reference voltage. The switching progressively continues through VPROT1-8. There is a mirror NMIR and switch SW or SM9 F, which shuts off the process when complete. The mirror and switches should not see a voltage higher than the operational voltage. The output node is VINT SUP, which is the intermediate supply voltage in Figure 1. Once start-up mechanism is complete, the amplifier "CTRL AMP" is "switched off with "SM9 F" and "cascode or protection device bias arm" remains active for controlling the protection cascode power device PM1 as in Figure 1.

[0026] Figure 6 is a graphical illustration of the controlled input voltage. The top graph illustrates the input voltage VIN over time. In particular, the voltage supply is ramped up initially to the value of 3.7 V. The top graph illustrates that the voltage ramps to 3.7V quickly. As a result of the controlled startup mechanism discussed above, the lower graph illustrates that the VINT SUP voltage value is ramped much more slowly over time in a well-controlled fashion. The value of VINT SUP may start around 1.85V and gradually step up to the value of VIN. In one particular example, every lOuS the switches are changed from SI to S 8 and this varies voltage at

VINT SUP in steps of approximately 200 millivolts (mV) as shown in Figure 6.

Gradually over time, the VINT SUP value is increased by 200 mV as the switches are opened/ closed. Even at different process and temperature corners, a fast input supply VIN will be ramped with slower VINT_SUP.

[0027] Non-volatile memory is one example of a device that may utilize voltage regulation as described above. For example, the controlled start-up voltage regulator in Figures 1-5 may be utilized in a flash memory card. A flash memory system which may utilize the controlled start-up voltage regulation is shown in Figures 7-8.

Examples of commercially available removable flash memory cards include the CompactFlash (CF), the MultiMediaCard (MMC), Secure Digital (SD), miniSD, Memory Stick, SmartMedia, TransFlash, and microSD cards. Although each of these cards may have a unique mechanical and/or electrical interface according to its standardized specifications, the flash memory system included in each may be similar. These cards are all available from SanDisk Corporation, assignee of the present application. SanDisk also provides a line of flash drives under its Cruzer trademark, which are hand held memory systems in small packages that have a Universal Serial Bus (USB) plug for connecting with a host by plugging into the host's USB receptacle. Each of these memory cards and flash drives includes controllers that interface with the host and control operation of the flash memory within them.

[0028] A host system 700 of Figure 7 stores data into and retrieves data from a flash memory 702. The flash memory may be embedded within the host, such as in the form of a solid state disk (SSD) drive installed in a personal computer. Alternatively, the memory 702 may be in the form of a flash memory card that is removably connected to the host through mating parts 704 and 706 of a mechanical and electrical connector as illustrated in Figure 7. A flash memory configured for use as an internal or embedded SSD drive may look similar to the schematic of Figure 7, with one difference being the location of the memory system 702 internal to the host. SSD drives may be in the form of discrete modules that are drop-in replacements for rotating magnetic disk drives.

[0029] Host systems that may use SSDs, memory cards and flash drives are many and varied. They include personal computers (PCs), such as desktop or laptop and other portable computers, tablet computers, cellular telephones, smartphones, personal digital assistants (PDAs), digital still cameras, digital movie cameras, and portable media players. For portable memory card applications, a host may include a built-in receptacle for one or more types of memory cards or flash drives, or a host may require adapters into which a memory card is plugged. The memory system may include its own memory controller and drivers but there may also be some memory-only systems that are instead controlled by software executed by the host to which the memory is connected. In some memory systems containing the controller, especially those embedded within a host, the memory, controller and drivers are often formed on a single integrated circuit chip.

[0030] The host system 700 of Figure 7 may be viewed as having two major parts, insofar as the memory 702 is concerned, made up of a combination of circuitry and software. They are an applications portion 708 and a driver portion 710 that interfaces with the memory 702. There may be a central processing unit (CPU) 712 implemented in circuitry and a host file system 714 implemented in hardware. In a PC, for example, the applications portion 708 may include a processor 712 running word processing, graphics, control or other popular application software. In a camera, cellular telephone or other host system 714 that is primarily dedicated to performing a single set of functions, the applications portion 708 includes the software that operates the camera to take and store pictures, the cellular telephone to make and receive calls, and the like.

[0031] The memory system 702 of Figure 7 may include non-volatile memory, such as flash memory 716, and a system controller 718 that both interfaces with the host 700 to which the memory system 702 is connected for passing data back and forth and controls the memory 716. The system controller 718 may convert between logical addresses of data used by the host 700 and physical addresses of the flash memory 716 during data programming and reading. Functionally, the system controller 718 may include a front end 722 that interfaces with the host system, controller logic 724 for coordinating operation of the memory 716, flash management logic 726 for internal memory management operations such as garbage collection, and one or more flash interface modules (FIMs) 728 to provide a communication interface between the controller with the flash memory 716.

[0032] Figure 8 illustrates a controller integrated circuit chip that is the system controller 718. In particular, the system controller 718 may be implemented on a single integrated circuit chip, such as an application specific integrated circuit (ASIC) such as shown in Figure 8. The processor 806 of the system controller 718 may be configured as a multi-thread processor capable of communicating via a memory interface 804 having I/O ports for each memory bank in the flash memory 716. The system controller 718 may include an internal clock 818. Alternatively, the host may transmit a clock signal through a host interface 816 to the system controller 718. The host interface 816 may transmit and/or receive data signals to/from the host. The processor 806 communicates with an error correction code (ECC) module 814, a RAM buffer 812, the host interface 816, and ROM 810 via an internal data bus 802. The ROM 810 may be used to initialize a memory system 702, such as a flash memory device. The memory system 702 that is initialized may be referred to as a card. The ROM 810 may be a region of read only memory whose purpose is to provide boot code to the RAM for processing a program, such as the initialization and booting of the memory system 702. The ROM may be present in the ASIC rather than the flash memory chip.

[0033] A "computer-readable medium," "machine readable medium," "propagated- signal" medium, and/or "signal-bearing medium" may comprise any device that includes, stores, communicates, propagates, or transports software for use by or in connection with an instruction executable system, apparatus, or device. The machine- readable medium may selectively be, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, device, or propagation medium. A non- exhaustive list of examples of a machine-readable medium would include: an electrical connection "electronic" having one or more wires, a portable magnetic or optical disk, a volatile memory such as a Random Access Memory "RAM", a Read-Only Memory "ROM", an Erasable Programmable Readonly Memory (EPROM or Flash memory), or an optical fiber. A machine-readable medium may also include a tangible medium upon which software is printed, as the software may be electronically stored as an image or in another format (e.g., through an optical scan), then compiled, and/or interpreted or otherwise processed. The processed medium may then be stored in a computer and/or machine memory.

[0034] In an alternative embodiment, dedicated hardware implementations, such as application specific integrated circuits, programmable logic arrays and other hardware devices, can be constructed to implement one or more of the methods described herein. Applications that may include the apparatus and systems of various embodiments can broadly include a variety of electronic and computer systems. One or more

embodiments described herein may implement functions using two or more specific interconnected hardware modules or devices with related control and data signals that can be communicated between and through the modules, or as portions of an application-specific integrated circuit. Accordingly, the present system encompasses software, firmware, and hardware implementations.

[0035] The illustrations of the embodiments described herein are intended to provide a general understanding of the structure of the various embodiments. The illustrations are not intended to serve as a complete description of all of the elements and features of apparatus and systems that utilize the structures or methods described herein. Many other embodiments may be apparent to those of skill in the art upon reviewing the disclosure. Other embodiments may be utilized and derived from the disclosure, such that structural and logical substitutions and changes may be made without departing from the scope of the disclosure. Additionally, the illustrations are merely representational and may not be drawn to scale. Certain proportions within the illustrations may be exaggerated, while other proportions may be minimized. Accordingly, the disclosure and the figures are to be regarded as illustrative rather than restrictive.