4

IR2171/IR2172

www.irf.com

Application Hint:

Temperature drift of the output carrier frequency can be cancelled by measuring both a PWM period and the on-time

of PWM (Duty) at the same time. Since both periods vary in the same direction, computing the ratio between these

values at each PWM period gives consistent measurement of the current feedback over the temperature drift.

Vin+= -260mV

Vin- = 0V

Vin+= +260mV

Vin- = 0V

Duty=93%

Duty=7%

Carrier Frequency =

40kHz

PO

PO

Timing Waveforms

Figure 1 Output waveform

Figure 2. OC Waveform (2172 only)

+260mV

-260mV

Vin

OC

t

woc

t

doc