Pre-charge management for power-managed voltage references

Patent metadata

Field	Value
Publication number	US-2022011797-A1
Application number	US-202016922654-A
Country	US
Kind code	A1
Filing date	Jul 7, 2020
Priority date	Jul 7, 2020
Publication date	Jan 13, 2022
Grant date	—

Abstract

A power managed voltage reference quickly provides accurate operation when enabled and also avoids back-charging power supply rails when disabled. When disabled, the voltage reference filter capacitor is decoupled from the voltage reference buffer and coupled to a pre-charge source having a voltage magnitude greater than the reference voltage. When the voltage reference is enabled, the capacitor is coupled to a discharge path and the voltage across the capacitor is detected to determine when to decouple the capacitor from the discharge path and couple the capacitor to the voltage reference buffer. The capacitor voltage is also detected while disabling the voltage reference. Back-charging the pre-charge supply is prevented by coupling the capacitor to the discharge path until the magnitude of the capacitor voltage is less than the lowest voltage specified for the pre-charge supply, then coupling the capacitor to the pre-charge supply to prepare for enabling the voltage reference.

First claim

What is claimed is:

1 . A method of initializing a voltage reference having a voltage reference filter capacitor, the method comprising:
maintaining the voltage reference in a low power state, wherein an output of the voltage reference is disabled; while the voltage reference is in the low power state, maintaining a voltage across the voltage reference filter capacitor in a pre-charged state from a pre-charge source selectively coupled to a first terminal of the voltage reference filter capacitor, wherein the voltage maintained is approximately equal to a target reference voltage of the voltage reference, and wherein a second terminal of the voltage reference filter capacitor is coupled to a return current path; responsive to an indication to transition the voltage reference to a normal power state, decoupling the pre-charge source from the voltage reference filter capacitor, enabling the voltage reference and coupling the first terminal of the voltage reference filter capacitor to a discharge path; comparing a voltage across the voltage reference filter capacitor to a threshold voltage to determine whether or not a magnitude of the voltage across the voltage reference filter capacitor is less than the threshold voltage; and responsive to the comparing determining that the magnitude of the voltage across the voltage reference filter capacitor is less than the threshold voltage, coupling the voltage reference to the first terminal of the voltage reference filter capacitor.

2 . The method of claim 1 , wherein the coupling the voltage reference buffer to the first terminal of the voltage reference filter capacitor comprises coupling the output of the voltage reference buffer to the first terminal of the voltage reference filter capacitor, and wherein the maintaining the voltage across the voltage reference filter capacitor in a pre-charged state from a pre-charge source further comprises de-coupling the first terminal of the voltage reference filter capacitor from the output of the voltage reference buffer.

3 . The method of claim 1 , wherein the voltage reference comprises a voltage reference source having an input coupled to an input of a voltage reference buffer, wherein an output of the voltage reference buffer provides the output of the voltage reference, and wherein the coupling the voltage reference buffer to the first terminal of the voltage reference filter capacitor comprises coupling the output of the voltage reference source and the input of the voltage reference buffer to the first terminal of the voltage reference filter capacitor.

4 . The method of claim 1 , wherein the pre-charge source is a power supply, and wherein the maintaining the voltage across the voltage reference filter capacitor in the pre-charged state is performed by coupling the power supply to the first terminal of the voltage reference filter capacitor to pre-charge the voltage reference filter capacitor to a voltage of the power supply.

5 . The method of claim 1 , further comprising:
responsive to an indication to transition the voltage reference to a low power state, disabling the voltage reference and coupling the first terminal of the voltage reference filter capacitor to a discharge path; comparing a voltage across the voltage reference filter capacitor to a predetermined threshold having a magnitude less than a minimum magnitude of the voltage of the power supply to determine whether or not a magnitude of the voltage across the voltage reference filter capacitor is less than the predetermined threshold; and responsive to the comparing determining that the voltage across the voltage reference filter capacitor is less than the predetermined threshold, decoupling the first terminal of the voltage reference filter capacitor from the discharge path, and coupling the first terminal of the voltage reference filter capacitor to the power supply to pre-charge the voltage reference filter capacitor to a voltage of the power supply.

6 . The method of claim 1 , wherein the voltage reference output is provided by a class A reference buffer.

7 . The method of claim 1 , wherein the threshold voltage is a predetermined threshold voltage having a magnitude less than or equal to a minimum magnitude of a voltage of the output of the voltage reference when the voltage reference is in the normal power state.

8 . The method of claim 1 , wherein the threshold voltage is the target reference voltage of the voltage reference.

9 . A method of power managing a voltage reference having a voltage reference filter capacitor, the method comprising:
responsive to an indication to transition the voltage reference to a low power state, disabling the voltage reference and coupling a first terminal of the voltage reference filter capacitor to a discharge path, wherein a second terminal of the voltage reference filter capacitor is coupled to a return current path; comparing a voltage across the voltage reference filter capacitor to a predetermined threshold having a magnitude less than a minimum magnitude of the voltage of the power supply to determine whether or not the voltage across the voltage reference filter capacitor is greater than the predetermined threshold; and responsive to the comparing determining that the voltage across the voltage reference filter capacitor is less than the predetermined threshold, decoupling the first terminal of the voltage reference filter capacitor from the discharge path, and coupling the first terminal of the voltage reference filter capacitor to the power supply to pre-charge the voltage reference filter capacitor to a voltage of the power supply.

10 . The method of claim 9 , wherein the voltage reference output is provided by a class A reference buffer.

11 . The method of claim 9 , wherein the threshold voltage is a predetermined threshold voltage having a magnitude less than or equal to a minimum magnitude of the voltage of the power supply.

12 . The method of claim 9 , wherein the threshold voltage is the voltage of the power supply.

13 . A voltage reference circuit, comprising:
a voltage reference source; a voltage reference filter capacitor; a voltage reference buffer having an input coupled to an output of the voltage reference source, wherein the voltage reference buffer operates in a normal power state and has a selectable low power state responsive to a control signal that selects between the normal power state and the low power state; a comparator for comparing a voltage across the voltage reference filter capacitor to a threshold voltage; and a switching circuit responsive to the output of the comparator and to the control signal, wherein the switching circuit selectively couples a first terminal of the voltage reference filter capacitor to the voltage reference buffer when the normal power state is selected, wherein a second terminal of the voltage reference filter capacitor is coupled to a return current path wherein the switching circuit, when the low power state is selected, selectively couples the first terminal of the voltage reference filter capacitor to a pre-charge source having a voltage approximately equal to a target reference voltage of the voltage reference, wherein the switching circuit, responsive to the control signal transitioning from the low power state to the normal power state, decouples the pre-charge source from the first terminal of the voltage reference filter capacitor and couples the first terminal of the voltage reference filter capacitor to a discharge path, and wherein the switching circuit, responsive to the output of the comparator indicating that a magnitude of the voltage across the voltage referen

Assignees

• Cirrus Logic Int Semiconductor Ltd

Inventors

• Prakash Chandra
• Drakshapalli Prashanth

Classifications

• H02J7/345

  using capacitors as storage or buffering devices · CPC title

• H02J2207/50

  Charging of capacitors, supercapacitors, ultra-capacitors or double layer capacitors · CPC title

• G05F1/468 Primary

  characterised by reference voltage circuitry, e.g. soft start, remote shutdown · CPC title