IR3093

Page 13 of 39

07/15/04

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 0.47V, 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 23.5 at 25ºC and 20.4 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 IR3093 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 DAC 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

0.47V

L

CSA

CO