IR3092

Page 13 of 37

06/25/04

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 24.5 at 25ºC and 20 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 IR3092 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 -20mV 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

VCC Under Voltage Lockout (UVLO)

The VCC UVLO function monitors the IR3092’s VCC supply pin and ensures enough voltage is available to power the

internal circuitry. During power-up the fault latch is reset when VCC exceeds 7.8V and all other faults are cleared. The

fault latch is set when VCC drops below 7.3V, resulting in 500mV of nominal VCC hysteresis for powering up into a load.

5VUVL Under Voltage Lockout (5VUVL)

The 5VUVL function is provided for converters using a separate voltage supply other than VCC for gate driver bias. The

5VUVL comparator prevents operation by discharging SS/DEL and forcing EAOUT low. The 5VUVL comparator has an

OK threshold of 4.3V ensuring adequate gate drive voltage is present and a fault threshold of 4.125V.

CLK1

PULSE

EAOUT

0.7V

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

0.6V

L

CSA

CO