IR3502MTRPBF International Rectifier, IR3502MTRPBF Datasheet - Page 11

• Manufacturer Part Number: IR3502MTRPBF
• Description: IC XPHASE3 CONTROLLER 32-MLPQ
• Manufacturer: International Rectifier
• Series: XPhase3™r

Specifications of IR3502MTRPBF

• Applications: Processor
• Current - Supply: 8mA
• Voltage - Supply: 8 V ~ 16 V
• Operating Temperature: 0°C ~ 100°C
• Mounting Type: Surface Mount
• Package / Case: 32-MLPQ
• Package: 32-Lead MLPQ
• Circuit: X-Phase Control IC
• Switch Freq (khz): 250kHz to 1.5MHz
• Pbf: PbF Option Available
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: IR3502MTRPBFTR

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
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, enabling the
bottom FET body diode to take over. There is 100mV upslope and 200mV down slope hysteresis for the body
braking comparator.
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 6. The equation of the sensing network is,
Usually the resistor Rcs and capacitor Ccs are chosen, such that, the time constant of Rcs and Ccs equals the time
constant of the inductor, which is the inductance L over the inductor DCR R
voltage across Ccs is proportional to the current through L, and the sense circuit can be treated as if only a sense
BODYDIODE
PHASE IC
CLOCK
PULSE
PWMRMP
GATEH
GATEL
Page 11 of 39
EAIN
VDAC
. The minimum time required to reduce the current in the inductor in response to a load transient
TM
STEADY-STATE
OPERATION
DUTY CYCLE INCREASE
DUE TO LOAD
INCREASE
v
C
Figure 5 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
DUTY CYCLE DECREASE DUE TO LOAD
DECREASE (BODY BRAKING) OR FAULT
(VCCLUV, OCP, VID=11111X)
+
CS
sL
C
CS
L
. If the two time constants match, the
July 28, 2009
IR3502
STEADY-STATE
OPERATION