Voltage regulator wake-up

Abstract

A system includes a voltage regulator having an output voltage and a power management system, coupled to the voltage regulator. The power management system operable to determine whether the output voltage is within an active range, set the active range to a first range during a first time, or during a first mode, and set the active range to a second range for a second time, or during a second mode.

Description

BACKGROUND

Many electronic systems include a voltage regulator. For example, battery powered devices often include a DC-DC voltage regulator to provide power at a different voltage than provided by the battery. In general, voltage regulators may be switching or linear. Advantages of linear regulators include low noise (no switching noise) and small size (no large inductors or transformers). One particular linear voltage regulator design is the Low-Drop-Out (LDO) regulator. One advantage of LDO regulators is that the minimum input/output differential voltage at which the regulator can no longer regulate (drop out voltage) is low, hence the name Low-Drop-Out. Another advantage of LDO regulators is a rapid response to a load change.

Many systems, particularly battery powered systems, are switched to a very-low-power sleep mode during periods of inactivity. When the system “wakes up” (comes out of sleep mode), the power supply sees an instantaneous change in load current from essentially zero load current to a large load current. Even though LDO regulators have a relatively fast response to a load change compared to other regulator designs, there is still a finite response time (called wake-up time) during which the output voltage and current may ring around their steady-state values over a finite settling time. In some LDO regulators, additional current (boost current) is supplied by a separate parallel path during wake-up time to reduce the response time. Switching in the boost current can cause voltage glitches and can increase the peak magnitude of output voltage ringing.

Some systems monitor power supply voltages and reset the system when a power supply voltage exceeds a certain range. Voltage ringing during wake-up and voltage glitches from boost current can cause a spurious system reset. A system reset can be catastrophic, for example, in a mission-critical computer system. Accordingly, to avoid spurious system resets, in some systems the voltage reset range is permanently fixed at a wide range such that expected worst case transients do not cause a reset. Alternatively, in some systems voltage monitoring is completely suspended during the entire wake-up period.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram schematic of an example embodiment of a system.

FIG. 2 is a timing diagram illustrating voltage output from a voltage regulator in the system of FIG. 1.

FIG. 3 is a flow chart for a method of managing power to a system.

DETAILED DESCRIPTION

In the following discussion, a system is described having continuous monitoring of voltage regulator output but with variable power management thresholds for system reset. Relaxed thresholds are used during low power and wake-up when there may be glitches and ringing, and more stringent thresholds are used during normal operation.

FIG. 1 shows part of a system 100 including an example voltage regulator 102. The example is simplified to facilitate discussion and illustration. In the example of FIG. 1, the voltage regulator 102 is a linear LDO regulator. The voltage regulator 102 includes a series transistor 104 (a power FET in the example of FIG. 1) driven by a feedback amplifier 106. The feedback amplifier 106 regulates the output voltage V_OUT to equal a reference voltage V_REF. In addition (optionally), a transistor 108 is enabled by a BOOST signal to provide additional current (boost current) at the output of the voltage regulator 102 when there is a need to rapidly transition from a low load current to a high load current during wake-up.

The system 100 also shows a power management system 110. The power management system 110 generates a RESET signal to reset the system 100 when the output voltage V_OUT is outside a specified range (above a high threshold or below a low threshold). The power management system 110 may also generate the BOOST signal.

FIG. 2 is an example timing diagram for the system 100. At time to, the system 100 and the voltage regulator 102 are in a low-power sleep mode, the boost current transistor 108 is off, and the range between the LOW THRESHOLD and the HIGH THRESHOLD is set by the power management system 110 to set to be relatively high. At time t₁, the system 100 wakes up, and the voltage regulator 102 switches to a high power mode. If there is a boost current transistor 108, then at time t₁ the boost current transistor 108 is turned ON. During low power mode (before t₀), and during wake-up, the range between LOW THRESHOLD and HIGH THRESHOLD is set to be sufficiently high so that worst case ringing of V_OUT will not trigger a system reset. At time t₂, the transient ringing of the output voltage V_OUT has settled substantially and the range between the LOW THRESHOLD and HIGH THRESHOLD is set by the power management system 110 to be relatively low. If there is a boost current transistor 108 then the boost current transistor 108 is turned OFF at time t₂. The time period between t₁ and t₂ may be a predetermined fixed time based on expected worst case settling times.

In some prior art systems, the LOW THRESHOLD and HIGH THRESHOLD are fixed at levels to accommodate worst case V_OUT transients and ringing, such as the levels shown between t₁ and t₂ in FIG. 2. Fixed thresholds reduce protection during normal operation after wake-up. In some prior art systems, power management is turned off during wake-up, which results in no protection during wake-up against harmful V_OUT transients. In addition, if there is a period of no protection, there is an opportunity for possible system tampering or attack. The system illustrated in FIGS. 1 and 2 is more robust, providing continuous power management (to protect against harmful transients during wake-up and to protect against tampering or attack), with relaxed thresholds during low power and wake-up (to avoid spurious resets), and more stringent thresholds during normal operation (to provide improved protection during normal operation).

FIG. 3 is a flow chart for a method 300 of managing power to a system. At step 302, a power management system continuously monitors an output voltage of a voltage regulator. At step 304, the power management system determines whether the output voltage is outside a range. At step 306, the power management system generates a reset signal when the output voltage is outside the range. At step 308, the power management system sets the range to a relatively low range during normal operation of the system. At step 310, the power management system sets the range to a relatively high range during a low power mode and during a wake-up from a low power mode.

Claims

1. A system comprising: a voltage regulator operable to provide an output voltage at an output of the voltage regulator;a current supply coupled to the voltage regulator and operable to provide an additional current to the output of the voltage regulator; anda power management system, coupled to the voltage regulator, operable to: set a voltage range that is associated with resetting the voltage regulator to a first range during a period in which the voltage regulator switches from a low power mode to a high power mode, wherein the first range extends from a first low threshold to a first high threshold; andset the voltage range to a second range after the voltage regulator switches to the high power mode, wherein the second range extends from a second low threshold to a second high threshold, and wherein the second range is narrower than the first range.

2. The system of claim 1, in which the voltage regulator is a linear voltage regulator.

3. The system of claim 1, wherein the second low threshold is larger than the first low threshold, the second high threshold is less than the first high threshold, or a combination thereof.

4. The system of claim 1, wherein the low power mode corresponds to a sleep mode of the voltage regulator.

5. The system of claim 1, wherein the high power mode corresponds to normal operation of the voltage regulator.

6. The system of claim 1, wherein the voltage regulator comprises: an input;a transistor having a control terminal, a first current terminal coupled to the input, and a second current terminal coupled to the output;an amplifier having a first input, a second input configured to be coupled to a reference voltage, and an output coupled to the control terminal of the transistor;a first resistor having a first terminal coupled to the second current terminal of the transistor and to the output and a second terminal coupled to the first input of the amplifier; anda second resistor having a first terminal coupled to the first input of the amplifier and to the second terminal of the first resistor and a second terminal coupled to ground.

7. The system of claim 6, wherein the current supply comprises: a second transistor having a first terminal, and a second terminal coupled to ground; anda third transistor having a first terminal coupled to the input, a second terminal coupled to the output, and a control terminal coupled to the first terminal of the second transistor.

8. The system of claim 1, wherein the power management system is operable to enable the current supply to provide the additional current during the period in which the voltage regulator switches from the low power mode to the high power mode.

9. A system, comprising: a voltage regulator configured to generate an output voltage; anda power management system coupled to the voltage regulator and configured to: based on a determination that the voltage regulator operates in a period to switch from a low power mode to a high power mode, determine a monitoring range to be a first range extending from a first low threshold to a first high threshold;based on a determination that the voltage regulator operates in the high power mode, determine the monitoring range to be a second range extending from a second low threshold to a second high threshold, wherein the second range is narrower than the first range;determine whether the output voltage is within the monitoring range; andgenerate a signal to reset the voltage regulator based on a determination that the output voltage is outside the monitoring range.

10. The system of claim 9, wherein the low power mode corresponds to a sleep mode of the voltage regulator.

11. A system comprising: a voltage regulator operable to provide an output voltage at an output of the voltage regulator;a current supply coupled to the voltage regulator and operable to provide an additional current to the output of the voltage regulator; anda power management system coupled to the voltage regulator and operable to: set a voltage range that is associated with resetting the voltage regulator to a first range during a period in which the voltage regulator switches from a low power mode to a high power mode, wherein the first range extends from a first low threshold to a first high threshold; andset the voltage range to a second range after the voltage regulator switches to the high power mode, wherein the second range extends from a second low threshold to a second high threshold, and wherein the second range is narrower than the first range.

12. The system of claim 9, wherein the high power mode corresponds to normal operation of the voltage regulator.

13. The system of claim 11, wherein the second low threshold is larger than the first low threshold, the second high threshold is less than the first high threshold, or a combination thereof.

14. The system of claim 11, wherein the low power mode corresponds to a sleep mode of the voltage regulator.

15. The system of claim 14, wherein the high power mode corresponds to normal operation of the voltage regulator.

16. The system of claim 9, wherein the voltage regulator is a linear voltage regulator.

17. The system of claim 11, in which the voltage regulator is a linear voltage regulator.

18. The system of claim 11, wherein the power management system is operable to enable the current supply to provide the additional current during the period in which the voltage regulator switches from the low power mode to the high power mode.

19. The system of claim 11, wherein the voltage regulator comprises: an input;a transistor having a control terminal, a first current terminal coupled to the input, and a second current terminal coupled to the output;an amplifier having a first input, a second input configured to be coupled to a reference voltage, and an output coupled to the control terminal of the transistor;a first resistor having a first terminal coupled to the second current terminal of the transistor and to the output and a second terminal coupled to the first input of the amplifier; anda second resistor having a first terminal coupled to the first input of the amplifier and to the second terminal of the first resistor and a second terminal coupled to ground.

20. The system of claim 19, wherein the current supply comprises: a second transistor having a first terminal, and a second terminal coupled to ground; anda third transistor having a first terminal coupled to the input, a second terminal coupled to the output, and a control terminal coupled to the first terminal of the second transistor.