ir3092 International Rectifier Corp., ir3092 Datasheet - Page 12

• Manufacturer Part Number: ir3092
• Description: 2 Phase Opteron, Athlon, Or Vr10.x Control Ic
• Manufacturer: International Rectifier Corp.

Body Braking
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
body diode occurs. This increases the voltage across the inductor from Vout to Vout + V
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
Page 12 of 37
TM
0.7V
EAOUT
CLK1
CLK2
50% INTERNAL OSCILLATOR RAMP
DUTY CYCLE
FIXED RAMP1
RAMP1 SLOPE = 57mV / % DC
Figure 3 – 2 Phase Oscillator and PWM Waveforms
T
SLEW
= [L x (I
T
SLEW
RAMP2
= [L x (I
MAX
- I
MIN
MAX
)] / (Vout + V
- I
MIN
RAMP2 MIN 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.
)] / Vout
BODY DIODE
)
RAMP2 MAX DUTY
CYCLE ADJUST
BODY DIODE
06/25/04
. The minimum time
IR3092