参数资料
型号: IR3081
厂商: International Rectifier
英文描述: XPHASE VR 10.0 CONTROL IC
中文描述: XPHASE村10.0控制IC
文件页数: 9/20页
文件大小: 396K
代理商: IR3081
IR3081
Page 9 of 20
9/1/03
This control method is designed to provide “single cycle transient response” where the inductor current changes in
response to load transients within a single switching cycle maximizing the effectiveness of the power train and
minimizing the output capacitor requirements.
An additional advantage is that differences in ground or input voltage
at the phases have no effect on operation since the PWM ramps are referenced to VDAC.
Body Braking
TM
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;
T
SLEW
= [L x (I
MAX
- I
MIN
)] / Vout
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
BODY DIODE
. The
minimum time required to reduce the current in the inductor in response to a load transient decrease is now;
T
SLEW
= [L x (I
MAX
- I
MIN
)] / (Vout + V
BODY DIODE
)
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” located in the Phase IC. If the Error Amp’s output voltage drops below
91% of the VDAC voltage this comparator turns off the low side gate driver.
Figure 4 depicts PWM operating waveforms under various conditions
PHASE IC
PULSE
EAIN
VDAC
PWMRMP
GATEH
GATEL
STEADY-STATE
DUTY CYCLE INCREASE
DUE TO LOAD
DUTY CYCLE DECREASE
DUE TO VIN INCREASE
DUTY CYCLE DECREASE DUE TO LOAD
DECREASE (BODY BRAKING) OR FAULT
STEADY-STATE
91% VDAC
Figure 4 – PWM Operating Waveforms
Lossless Average Inductor Current Sensing
Inductor current can be sensed by connecting a series resistor and a capacitor network in parallel with the inductor
and measuring the voltage across the capacitor. The equation of the sensing network is,
1
)
(
)
(
S
S
L
L
S
S
L
C
C
sR
sL
R
+
s
i
C
sR
s
v
s
v
+
=
+
=
1
)
(
1
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