Littelfuse, Inc.
Synchronous sensing of inductor current in a buck converter control circuit

Abstract:

A sense resistor is placed in series with an output capacitor of a buck converter. The buck converter operates in a discontinuous mode such that there is a dead time in each switching cycle. A control circuit senses a voltage across the sense resistor and thereby generates a first signal I.sub.CS. The control circuit detects an offset voltage in I.sub.CS, where the offset voltage is the voltage of I.sub.CS during the dead time in a first switching cycle. The control circuit level shifts the entire I.sub.CS by the offset voltage, thereby generating a second signal I.sub.CLS. I.sub.CLS has the same waveform as the waveform of the inductor current. In a second cycle, I.sub.CLS is used to determine when to turn off the main switch and when the start of the dead time occurs. I.sub.CLS and the offset voltage are used together to determine when to turn the main switch on.