IR3508ZMPBF International Rectifier, IR3508ZMPBF Datasheet - Page 9

• Manufacturer Part Number: IR3508ZMPBF
• Description: The IR3508ZM Phase IC combined with any IR XPhase3 Control IC provides a full featured and flexible way to implement a power solution for the latest high performance CPUs and ASICs.
• Manufacturer: International Rectifier

Specifications of IR3508ZMPBF

• Package: 20-Lead MLPQ
• Circuit: X-Phase Phase IC
• Pbf: PbF Option Available

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
minimum time 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 comparable to the output voltage, the inductor current slew rate can be
increased significantly. This patented technique is referred to as “body braking” and is accomplished through the “body
braking comparator” located in the phase IC. If the error amplifier’s output voltage drops below the output voltage of the
share adjust amplifier in the phase IC, this comparator turns off the low side gate driver.
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, as shown in Figure 4. The equation of the sensing network is,
PHASE IC
CLOCK
PULSE
PWMRMP
GATEH
GATEL
Page 9 of 19
EAIN
VDAC
TM
STEADY-STATE
OPERATION
DUTY CYCLE INCREASE
DUE TO LOAD
INCREASE
v
C
(
Figure 3: PWM Operating Waveforms
s
)
=
v
L
T
T
(
SLEW
SLEW
s
)
1
+
=
=
sR
L
L
V
1
CS
DUTY CYCLE DECREASE
DUE TO VIN INCREASE
(FEED-FORWARD)
O
( *
( *
C
+
I
I
CS
V
MAX
MAX
BODYDIODE
V
=
O
−
−
i
L
I
I
(
s
MIN
MIN
)
1
)
)
+
R
sR
L
+
CS
DUTY CYCLE DECREASE DUE TO LOAD
DECREASE (BODY BRAKING) OR FAULT
(VCCLUV, OCP, VID=11111X)
sL
C
CS
Jan 09, 2009
IR3508Z
STEADY-STATE
OPERATION
BODYDIODE
. The