IR3094M International Rectifier Corp., IR3094M Datasheet - Page 13

• Manufacturer Part Number: IR3094M
• Description: 3 Phase Pwm Controller For Point Of Load
• Manufacturer: International Rectifier Corp.

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
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.
Page 13 of 29
PWM
Ramp1
CLK1
PULSE
GATEH1
GATEL1
0.6V
EAOUT
Figure 5 – Inductor Current Sensing and Current Sense Amplifier
STEADY-STATE
OPERATION
Figure 4 – PWM Operating Waveforms
CO
CSA
DUTY CYCLE INCREASE
DUE TO LOAD
INCREASE
i
L
L
R
s
0.575V
v
L
R
C
v
c
L
s
DUTY CYCLE DECREASE DUE TO LOAD
DECREASE (BODY BRAKING) OR FAULT
V
o
C
o
IR3094PBF
STEADY-STATE
OPERATION
09/26/05