IR3092

Page 12 of 37

06/25/04

Figure 3 – 2 Phase Oscillator and PWM Waveforms

In a conventional synchronous buck converter, the minimum time required to reduce the current in the inductor in

response to a load step decrease is;

The slew rate of the inductor current can be significantly increased by turning off the synchronous rectifier in response

to a load step decrease. The switch node voltage is then forced to decrease until conduction of the synchronous rectifier’s

required to reduce the current in the inductor in response to a load transient decrease is now;

Since the voltage drop in the body diode is often higher than output voltage, the inductor current slew rate can be

increased by 2X or more. This patent pending technique is referred to as “body braking” and is accomplished through the

“0% Duty Cycle Comparator”. If the Error Amplifier’s output voltage drops below 0.55V, this comparator turns off the low

side gate driver.

Figure 4 depicts PWM operating waveforms under various conditions

CLK1

CLK2

50% INTERNAL OSCILLATOR RAMP

DUTY CYCLE

RAMP1 SLOPE = 57mV / % DC

0.7V

FIXED RAMP1

EAOUT

RAMP2

RAMP2 MIN DUTY

CYCLE ADJUST

RAMP2 MAX DUTY

CYCLE ADJUST

THE SHARE ADJUST ERROR AMPLIFIER

CAN CHANGE THE PULSE WIDTH OF

RAMP2 FROM 0.5x RAMP1 TO 2.0x

RAMP1 TO FORCE CURRENT SHARING.