Control for Voltage Regulators
A mixed signal approach is applied to detect an output voltage condition as applied to a load. A current mode monitoring approach can be adopted and applied in discrete time using a mixed analog and digital approach. For application to various low drop-out voltage regulator situations, a sensing transistor can be connected in parallel with a feedback loop transistor of the low drop-out voltage regulator circuit to create a sensing current that is proportional to the current passing through the feedback loop transistor and thus the output current provided to the load. This sensing approach can be adapted to sense both overload and light load conditions to allow dynamic power control of the device.
1 . An apparatus for detecting load on an input power, the apparatus comprising:
a low dropout voltage regulator circuit configured to provide an output voltage to a load;
a current mode comparator circuit connected to the low dropout voltage regulator circuit to monitor a low dropout voltage regulator circuit current driven by the output voltage of the low dropout voltage regulator circuit;
wherein the current mode comparator circuit is configured to monitor the low dropout voltage regulator circuit current in a discrete time mixed analog/digital approach.
2 . The apparatus of claim 1 wherein the low dropout voltage regulator circuit comprises a feedback loop transistor connected to pass the low dropout voltage regulator circuit current driven by the output voltage; and
wherein the current mode comparator circuit comprises:
a sensing transistor connected in parallel with the feedback loop transistor and configured to output a sensing current proportional to the low dropout voltage regulator circuit current;
a reference current source configured to provide a reference current;
a comparator circuit configured to perform a comparison between the sensing current and the reference current and to output a comparison signal based on the comparison.
3 . The apparatus of claim 2 wherein the comparator circuit comprises a Schmitt-Trigger circuit configured to output a digital flag signal in response to the sensing current dropping below the reference current.
4 . The apparatus of claim 1 wherein the low dropout voltage regulator circuit comprises a feedback loop transistor connected to pass the low dropout voltage regulator circuit current driven by the output voltage; and
wherein the current mode comparator circuit comprises:
a sensing transistor connected in parallel with the feedback loop transistor and configured to output a sensing current proportional to the low dropout voltage regulator circuit current;
a resistive element connected to have the sensing current pass through the resistive element to provide a sensing voltage proportional to the sensing current;
an n-bit analog to digital comparator circuit connected to convert the sensing voltage to a digital output.
5 . A method of detecting load on a microcontroller, the method comprising:
a low dropout voltage regulator circuit providing an output voltage to a load;
monitoring a low dropout voltage regulator circuit current driven by the output voltage of the low dropout voltage regulator circuit in a discrete time mixed analog/digital approach with a current mode comparator circuit.
6 . The method of claim 5 further comprising:
passing the low dropout voltage regulator circuit current driven by the output voltage through a feedback loop transistor of the low dropout voltage regulator circuit; and
outputting a sensing current proportional to the low dropout voltage regulator circuit current from a sensing transistor of the current mode comparator circuit, the sensing transistor connected in parallel with the feedback loop transistor;
a comparator circuit comparing the sensing current and a reference current;
the comparator circuit outputting a comparison signal based on the comparison of the sensing current and the reference current.
7 . The method of claim 6 further comprising a Schmitt-Trigger circuit of the comparator circuit outputting a digital flag signal in response to the sensing current dropping below the reference current.
8 . The method of claim 5 further comprising:
passing the low dropout voltage regulator circuit current driven by the output voltage through a feedback loop transistor; and
outputting a sensing current proportional to the low dropout voltage regulator circuit current from a sensing transistor connected in parallel with the feedback loop transistor; an n-bit analog to digital comparator circuit converting a sensing voltage derived from the sensing current to a digital output.