Often linear voltage regulators are utilized to maintain a steady voltage of a circuit. However, the loading circuit can introduce high frequency noise into the circuit. In order to reduce the noise as well as further steady the voltage of the circuit, a large bypass capacitor is often connected to an output of a linear regulator. When the linear voltage regulator is initially powered on, there is often a large current drawn from a power supply to charge the large bypass capacitor. This large rush of current may cause the voltage output of the power supply to dip severely due to the resistance of a power switch of the power supply. However for many applications, the dip in voltage may lead to a failure of circuit components that are sensitive to voltage fluctuations. Therefore, there exists a need for a better way to handle powering of a linear voltage regulator.
Various embodiments of the invention are disclosed in the following detailed description and the accompanying drawings.
The invention can be implemented in numerous ways, including as a process; an apparatus; a system; a composition of matter; a computer program product embodied on a computer readable storage medium; and/or a processor, such as a processor configured to execute instructions stored on and/or provided by a memory coupled to the processor. In this specification, these implementations, or any other form that the invention may take, may be referred to as techniques. In general, the order of the steps of disclosed processes may be altered within the scope of the invention. Unless stated otherwise, a component such as a processor or a memory described as being configured to perform a task may be implemented as a general component that is temporarily configured to perform the task at a given time or a specific component that is manufactured to perform the task. As used herein, the term ‘processor’ refers to one or more devices, circuits, and/or processing cores configured to process data, such as computer program instructions.
A detailed description of one or more embodiments of the invention is provided below along with accompanying figures that illustrate the principles of the invention. The invention is described in connection with such embodiments, but the invention is not limited to any embodiment. The scope of the invention is limited only by the claims and the invention encompasses numerous alternatives, modifications and equivalents. Numerous specific details are set forth in the following description in order to provide a thorough understanding of the invention. These details are provided for the purpose of example and the invention may be practiced according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the invention has not been described in detail so that the invention is not unnecessarily obscured.
A linear voltage regulator is disclosed. For example, a low-dropout regulator is disclosed. The linear voltage regulator includes an amplifier. For example, a differential electronic amplifier connected to a reference voltage of the linear voltage regulator is included. The linear voltage regulator further includes a plurality of power devices, wherein at least one of the power devices is electrically connected to the amplifier. For example, the linear voltage regulator includes a plurality of different power transistors that are sized differently. A switch is configured to control at least one of the power devices, and a delay component is configured to trigger the switch.
For example, initially when the linear voltage regulator is powered on, a small sized power device with a comparatively larger resistance is utilized by the linear voltage regulator to provide limited current to a bypass capacitor. Although this current limited by larger resistance power device effectively limits the current to reduce the voltage dip of the power supply, this power device may not be ideal to be utilized by the linear voltage regulator in its normal operation that may require larger power and current or when the bypass capacitor needs to be charged faster (e.g., after the bypass capacitor is charged to a certain point, more current may be allowed without a severe voltage dip because the capacitor has built up voltage). After a delay time of the delay component, the delay component triggers the switch to allow the linear voltage regulator to utilize another larger sized power transistor with a comparatively smaller resistance to enable larger current to be provided by the linear voltage regulator.
Graph 202 shows the voltage of an output voltage of a linear voltage regulator (e.g., voltage output of the linear regulator of
Graph 204 shows the corresponding output current of the linear voltage regulator of graph 202 after being switched on. The output current of the linear voltage regulator spikes to a large negative current to charge the bypass capacitor and returns to zero once the bypass capacitor is charged. This large spike in current will often cause a power supply voltage to dip severely.
Graph 206 shows the output voltage of a power supply (e.g., power supply 110 of
The linear voltage regulator is utilized to provide a steady voltage to loading circuit 306. Examples of loading circuit 306 include an analog to digital converter, a gating signal generator, a timing signal generator, a phase-locked loop, a clock, an oscillator, a memory controller, a memory component, a storage controller, a storage component, a controller of embedded Multi-Media Controller (i.e., eMMC), a NAND flash memory controller, and any circuit desired to be voltage regulated by the linear voltage regulator. Bypass capacitor 308 is connected to the output of the linear voltage regulator and functions to reduce the noise as well as further steady the voltage provided to loading circuit 306. For example, the bypass capacitor is sized on the microfarad level and may conform to a specification/standard such as a standard for eMMC devices. Power supply 310 provides power to the circuit shown in
The linear voltage regulator and loading circuit 306 of
In some embodiments, as capacitor 308 becomes charged (e.g., capacitor builds up voltage), less current will be drawn by capacitor 308 and an additional power device is added to increase the charging of the current within an acceptable level and/or allow the linear voltage regulator to be able to handle voltage fluctuations more effectively with the additional power device. After a first amount of delay time (e.g., amount of time required to charge capacitor 308 to a desired level using power device 304), delay component 320 activates and turns on switch 316 and effectively turns off switch device 313 to turn on power device 312. Power device 312 may be sized larger than power device 304 and power device 312 is able to provide additional/more current to charge capacitor 308 and/or maintain desired voltage output of the voltage regulator. For example, the resistance of power device 312 is smaller than the resistance of power device 304 and by turning on power device 312, the effective resistance of the combination of power device 312 and power device 304 becomes smaller (e.g., resistances combined in parallel), allowing larger current to flow. The size of power device 312 may be selected such that the effective combined resistances of power device 304 and power device 312 will allow a desired amount of current to be provided by the linear voltage regulator. In some embodiments, rather than allowing both power device 304 and power device 312 to be utilized at the same time after the first delay time, power device 304 is turned off/disabled when power device 312 is turned on/enabled. In various embodiments, power device 312 may be sized larger, equal or smaller than power device 304.
After an additional second amount of delay time has passed (e.g., amount of time required to charge capacitor 308 to a second desired level (e.g., fully charged) using power device 304 and power device 312), delay component 322 activates and turns on switch 318 and effectively turns off switch device 315 to turn on power device 314. Power device 314 may be sized larger than power device 304 and power device 312, and power device 314 is able to provide additional/more current to charge capacitor 308 and/or maintain desired voltage output of the voltage regulator. For example, the resistance of power device 314 is smaller than the resistance of power device 312 and by turning on power device 314, the effective resistance of the combination of power device 314, power device 312 and power device 304 becomes smaller (e.g., resistances combined in parallel), allowing larger current to flow. The size of power device 314 may be selected such that the effective combined resistances of power device 304, power device 312 and power device 314 will allow a desired amount of current to be provided by the linear voltage regulator. In some embodiments, rather than allowing multiple power devices to be utilized at the same time, power device 312 is turned off/disabled when power device 314 is turned on/enabled. In various embodiments, power device 314 may be sized larger, equal or smaller than power device 312.
In various embodiments, the delay time of delay components and the sizes of power devices of the linear voltage regulator are determined based at least in part on one or more of the following: a size of a bypass capacitor, an amount of time required for the bypass capacitor to be charged, an amount of time required for the voltage regulator to provide a stable voltage, a resistance of a power supply, an amount of power supply voltage fluctuation tolerance, and a desired maximum current output of the voltage regulator.
For example, a specification requires a voltage output of the linear voltage regulator to be stable within less than 100 us after power on and based on this time value, 40 us is selected as the first delay time to activate switch 316 and 20 us is selected as the second delay time to activate switch 318 (e.g., taking into account +/−25% clock frequency various utilized by delay component 320 and delay component 322).
In another example, a specification requires a voltage drop of a power supply to be no more than 150 mV when the linear voltage regulator is powered on. In this example, the power supply has a resistance of 0.8 ohms and provides 1.8V, which requires the current to be less than 187.5 mA at any time and to drop no more than 150 mV. For example, initially the voltage on capacitor 308 is 0. Because Voltage=Current*Resistance (1.8V−0=187.5 mA(0.8 ohms+power device resistance)), resistance of power device(s) to be utilized upon voltage regulator power on initially should be greater or equal to 8.8 ohms. After the first delay time, the voltage on capacitor 308 will be charged up (0.7V for example). Base on the formula above (1.8V−0.7V=187.5mA*(0.8 ohm+power device resistance)), resistance of power devices can be reduce to 5 ohm. So another power device may be enabled and the resistance of the second power device is added in parallel with resistance of the initial power device to charge the bypass capacitor. A final third large power device may be enabled after the bypass capacitor is charged to enable the voltage regulator to maintain a desired output voltage using the large power device (e.g., by not enabling the large power device until the bypass capacitor is charged, the large power device does not spike output current during the initial power on to charge the capacitor).
Graph 402 shows the voltage of an output voltage of a linear voltage regulator (e.g., voltage output of the linear regulator of
Graph 404 shows the corresponding output current of the linear voltage regulator of graph 402 after being switched on. The output current of the linear voltage regulator spikes to a maximum negative current of 150 mA to charge the bypass capacitor using a first power device, then spikes to the maximum negative current again when a second power device is enabled after the delay time.
Graph 406 shows the output voltage of a power supply (e.g., power supply 310 of
Examples of amplifier 502 include a differential amplifier, an operational amplifier, and any other type of amplifier. Examples of power devices 511-515 include a transistor, a power transistor, a field-effect transistor, junction gate field-effect transistor, a bipolar transistor, and any other type of transistor. Examples of switches 516-519 include a transistor switch, an electrical mechanical switch, a solid-state switch, and any other type of switch. Examples of delay components 521-524 include a counter component, a signal control logic, and any other component that provides a delayed signal. Examples of oscillator 520 include a ring oscillator and any other type of oscillator. For example, delay components 521-524 determine time using a signal provided by oscillator 520. Dashed area 500 in
Although the foregoing embodiments have been described in some detail for purposes of clarity of understanding, the invention is not limited to the details provided. There are many alternative ways of implementing the invention. The disclosed embodiments are illustrative and not restrictive.
This application claims priority to U.S. Provisional Patent Application No. 61/840,715 (Attorney Docket No. LINKP139+) entitled NEW LOW DROPOUT REGULATOR SOFT START filed Jun. 28, 2013 which is incorporated herein by reference for all purposes.
Number | Date | Country | |
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61840715 | Jun 2013 | US |