IR3094PBF

Page 13 of 29

09/26/05

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 0.575V, this

comparator turns off the low side gate driver.

Figure 4 depicts PWM operating waveforms under various conditions

Figure 4 – PWM Operating Waveforms

Current Sense Amplifier

A high speed differential current sense amplifier is shown in Figure 5. Its gain decreases with increasing

temperature and is nominally 24 at 25ºC and 20.9 at 125ºC (-1400 ppm/ºC). This reduction of gain tends to

compensate the 3850 ppm/ºC increase in inductor DCR. Since in most designs the IR3094 IC junction is hotter than

the inductors these two effects tend to cancel such that no additional temperature compensation of the load line is

required.

The current sense amplifier can accept positive differential input up to 75mV and negative up to -25mV before

clipping. The output of the current sense amplifier is summed with the VREF voltage which is used for over current

protection, voltage positioning and current sharing.

Figure 5 – Inductor Current Sensing and Current Sense Amplifier

CLK1

PULSE

EAOUT

0.6V

PWM

Ramp1

GATEH1

GATEL1

STEADY-STATE

OPERATION

DUTY CYCLE INCREASE

DUE TO LOAD

INCREASE

DUTY CYCLE DECREASE DUE TO LOAD

DECREASE (BODY BRAKING) OR FAULT

STEADY-STATE

OPERATION

0.575V

L

CSA

CO