FP5101 datasheet(13/20 Pages) FEELING

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FP5101 / FP5101A

This datasheet contains new product information.

Feeling Technology reserves the rights to modify the product specification without notice.

No liability is assumed as a result of the use of this product. No rights under any patent accompany the sales of the product.

Website: http://www.feeling-tech.com.tw

Rev. 0.64

13/20

Application Information

Frequency Compensation

The FP5101 / A is a voltage-mode controller for a synchronous-rectified buck converter. Figure 1

highlights the voltage-mode control loop for a synchronous-rectified buck converter. The output voltage

(VOUT) is regulated to the reference voltage level. The error amplifier (ERROR AMP) output (VCOMP) is

compared with the oscillator (OSC) triangular wave to provide a pulse-width modulated (PWM) wave

with an amplitude of VIN at the SW node. The PWM wave is smoothed by the output LC filter (LOUT and

COUT).

The modulator transfer function is the small-signal transfer function of VOUT / VCOMP. This function

is dominated by a DC gain and the output filter (LOUT and COUT), with a double-pole break frequency at

FLC and a zero at FESR. The DC gain of the modulator is the input voltage (VIN) divided by the

peak-to-peak oscillator voltage (

ΔV

OSC).

The following equations define the modulator break

frequencies as a function of the output LC filter:

OUT







The ESR zero is contributed by the ESR associated with the output capacitance. Note that this

requires the output capacitor should have enough ESR to satisfy stability requirements. The ESR zero

of the output capacitor is expressed as following

ESR

OUT

ESR







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