Pre-charge management for power-managed voltage references

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.

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 reference filter capacitor is less than the threshold voltage, couples the voltage reference to the first terminal of the voltage reference filter capacitor.

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;
• a switching circuit responsive to an output of the comparator and to the control signal, wherein the switching circuit, responsive to the control signal transitioning from the low power state to the normal power state, decouples a first terminal of the voltage reference filter capacitor from the voltage reference buffer and couples the 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, and wherein the switching circuit, responsive to the output of the comparator indicating that a magnitude of the voltage across the voltage reference filter capacitor is less than the threshold voltage, decouples the first terminal of the voltage reference filter capacitor from the discharge path and couples 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.