Enhanced on-time generator
AssigneeFairchild Semiconductor Corporation
InventorsJuha-Matti Kujala, Jouni Mika Kalervo Vuorinen
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Abstract
This document discusses, among other things, voltage converters and computed on-time voltage converters. In an example, an on-time generator for a voltage converter can include a timing capacitor configured to provide a timing voltage, a comparator configured to receive the timing voltage and a threshold voltage and to provide the timing signal using a comparison of the timing voltage and the threshold voltage, a current source configured to discharge the timing voltage of the timing capacitor after a start-up delay, and first and second compensation capacitors configured to bias the timing voltage of the timing capacitor to compensate for the start-up delay.
Claims18
An on-time generator configured to provide a timing signal to terminate an on-time interval of a voltage converter, wherein the on-time interval is associated with a low-impedance mode of a transistor of the voltage converter, the on-time generator comprising:
- a timing capacitor configured to provide a timing voltage;
- a comparator configured to compare the timing voltage to a threshold voltage and to provide the timing signal using a comparison of the timing voltage and the threshold voltage, the comparator configured to be disabled outside of the on-time interval and having a start-up delay prior to comparing the timing voltage and the threshold voltage;
- a current source configured to discharge the timing voltage of the timing capacitor after the start-up delay;
- first and second compensation capacitors configured to bias the timing voltage of the timing capacitor to compensate for the start-up delay, wherein the size of the first compensation capacitor is different than the size of the second compensation capacitor;
- a first switch configured to couple a second node of the first compensation capacitor with an input voltage of the voltage converter during the start-up delay;
- and
- wherein a first node of the first compensation capacitor, a first node of the second compensation capacitor, and a first node of the timing capacitor are coupled together with a first input of the comparator.
A method of generating a signal indicative of an end of an on-time interval of a voltage converter, wherein the on-time interval is associated with a low-impedance mode of a transistor of the voltage converter, the method comprising;
- initiating a start-up delay of a comparator at a beginning of the on-time interval;
- receiving a timing voltage from a timing capacitor coupled to a first input of the comparator;
- receiving a threshold voltage at a second input of the comparator;
- pre-charging the timing capacitor and first and second compensation capacitors during the start-up delay;
- biasing the timing capacitor after the start-up delay to compensate for the start-up delay using the first and second compensation capacitors;
- discharging the timing capacitor after the start-up delay;
- comparing the timing voltage and the threshold voltage;
- and
- generating a transition of the signal as the timing voltage becomes less than the threshold to indicate an end of the on-time interval;
- wherein the biasing the timing capacitor includes coupling the second node of the second compensation capacitor to an output voltage of the voltage converter using a second switch.
A voltage converter comprising;
- a first transistor configured to increase current through an inductor during an on-time interval of the first transistor;
- an on-time generator configured to provide a timing signal to terminate the on-time interval, the on-time generator comprising:
- a timing capacitor configured to provide a timing voltage;
- a comparator configured to be disabled outside of the on-time interval to save power, to receive the timing voltage and a threshold voltage, and to provide the timing signal when the voltage of the timing capacitor becomes less than the threshold, the comparator having a start-up delay prior to providing an output indicative of a comparison of the timing voltage and the threshold;
- a current source configured to discharge the timing voltage of the timing capacitor after the startup delay;
- first and second compensation capacitors configured to bias the timing voltage of the timing capacitor to compensate for the start-up delay, wherein the size of the first compensation capacitor is different than the size of the second compensation capacitor, wherein a first node of the first compensation capacitor, a first node of the second compensation capacitor, and a first node of the timing capacitor are coupled together with a first input of the comparator;
- a first switch configured to couple a second node of the first compensation capacitor with an input voltage of the voltage converter during the start-up delay;
- a second switch configured to couple a second node of the second compensation capacitor to ground during the start-up delay;
- a third switch configured to isolate the current source from the first node of the comparator during the start-up delay;
- a fourth switch configured to couple a second node of the first compensation capacitor with ground after the start-up delay;
- a fifth switch configured to couple a second node of the second compensation capacitor to an output voltage of the voltage controller after the start-up delay;
- and
- a sixth switch configured to couple the current source to the first node of the comparator after the start-up delay.
Dependencies are inferred from the claim text.