Switching regulator including PFM detector
A switching regulator has an error amplifier supplying an error current, a phase compensation portion generating an error voltage, a clamper clamping the error voltage, a PFM detector supplying a comparison result signal of a first level or a comparison result signal of a second level based on the error current, an oscillator supplying a clock signal in response to the comparison result signal at the second level and fixing the clock signal in response to the comparison result signal at the first level, and a PWM converter turning on/off a switching element with a desired pulse width based on the error voltage and the output from the oscillator.
1. A switching regulator generating a predetermined output voltage at an output terminal from a power supply voltage supplied to a first power supply terminal, the switching regulator comprising:
an inductor having one end connected to the output terminal;
a switching element connected between the first power supply terminal and another end of the inductor;
an error amplifier configured to amplify a difference between a voltage based on the predetermined output voltage and a reference voltage and supply an error current;
a phase compensation portion configured to receive the error current and generate an error voltage;
a clamper configured to clamp the error voltage in such a manner that the error voltage is more than a predetermined voltage;
a PFM detector configured to:
determine whether the error current has a predetermined polarity;
output a comparison result signal having a first level in response to determining that the error current has the predetermined polarity and in response to receiving a clamp detection signal indicating the clamper is presently clamping the error voltage, wherein the clamp detection signal is a different signal from the error voltage and the error current; and
output the comparison result signal having a second level in response to at least one of determining that the error current does not have the predetermined polarity or not receiving the clamp detection signal indicating the clamper is presently clamping the error voltage;
an oscillator configured to:
receive the comparison result signal from the PFM detector;
output an oscillating clock signal of a predetermined frequency in direct response to the comparison result signal received by the oscillator being at the second level; and
stop outputting the oscillating clock signal in direct response to the comparison result signal received by the oscillator being at the first level; and
a PWM converter configured to turn on/off the switching element with a desired pulse width based on the error voltage and an output from the oscillator.
2. The switching regulator according to claim 1 , further comprising:
a resistor between an output from the error amplifier and the phase compensation portion, wherein
the PFM detector detects a polarity of the error current by a voltage between both ends of the resistor.
3. The switching regulator according to claim 1 , further comprising:
a clamp detector configured to detect a clamp operation of the clamper and output the clamp detection signal to the PFM detector, wherein
the PFM detector determines the clamp operation of the clamper with the clamp detection signal.
4. The switching regulator according to claim 3 , further comprising:
a resistor between an output from the error amplifier and the phase compensation portion, wherein
the PFM detector detects a polarity of the error current by a voltage between both ends of the resistor.