IR3513Z International Rectifier Corp., IR3513Z Datasheet - Page 14

• Manufacturer Part Number: IR3513Z
• Description: Xphase3tm Pol 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
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 higher than the 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 “body braking comparator”. If the error amplifier’s output voltage drops below the VREF voltage or a programmable
voltage, 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 6. The equation of the sensing network is,
Usually the resistor Rcs and capacitor Ccs are chosen so 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
resistor with the value of R
DC current, but affects the AC component of the inductor current.
Page 14
TM
L
was used. The mismatch of the time constants does not affect the measurement of inductor
v
C
Figure 5 - PWM Operating Waveforms
(
s
)
=
v
L
T
T
(
SLEW
SLEW
s
)
1
+
=
=
sR
L
L
V
1
CS
O
( *
( *
C
+
I
I
CS
V
MAX
MAX
BODYDIODE
V
=
O
−
−
i
L
I
I
(
s
MIN
MIN
)
1
)
)
+
R
sR
L
+
CS
sL
C
CS
L
). If the two time constants match, the
May 11, 2009
IR3513Z
BODYDIODE
. The