Control circuit and method for reducing output ripple in constant on-time switching regulator
AssigneeRichtek Technology Corporation, R.O.C.
InventorYu-Nung Tsai
Life of this patent
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Abstract
The present invention discloses a control circuit for reducing output ripple in a constant on-time switching regulator and a method thereof, for controlling a power stage. The control circuit determines whether a zero current period wherein an output current is zero is longer than a threshold period, and switches the on-time period to a shorter period if it is longer, whereby the power stage operates according to the shorter period while still in the discontinuous conduction mode (DCM).
Claims14
A control circuit for reducing output ripple in a constant on-time switching regulator, the control circuit controlling a power stage to convert an input voltage to an output voltage and to provide an output current to a load, the control circuit comprising:
- a zero current detector (ZCD) detecting a zero current period wherein the output current is about zero, and generating a zero current period signal representing the zero current period;
- an on-time (TON) adjustment circuit receiving the zero current period signal to determine whether the zero current period is longer than a first threshold period, and generating a TON control signal accordingly;
- and
- a constant on-time (COT) generation circuit determining a TON of a square wave signal according to the TON control signal, the power stage being controlled according to the TON of the square wave signal,
- wherein when the zero current period is shorter than the first threshold period, the COT generation circuit generates the square wave signal with a longer TON, and when the zero current period is longer than the first threshold period, the COT generation circuit generates the square wave signal with a shorter TON whereby the power stage operates in a discontinuous conduction mode (DCM) according to the shorter TON.
A method for reducing output ripple in a constant on-time switching regulator, the switching regulator including a power stage for converting an input voltage to an output voltage and providing an output current to a load, the method comprising:
- detecting a zero current period wherein the output current is about zero, and generating a zero current period signal representing the zero current period;
- determining whether the zero current period is longer than a first threshold period, and generating a TON control signal accordingly;
- generating a square wave signal with a longer on-time (TON) when the zero current period is shorter than the first threshold period, and generating a square wave signal with a first shorter TON when the zero current period is longer than the first threshold period;
- and
- controlling the power stage according to the TON of the square wave signal,
- wherein the power stage operates in a discontinuous conduction mode (DCM) according to the first shorter TON.
Dependencies are inferred from the claim text.