IR3508ZMPBF International Rectifier, IR3508ZMPBF Datasheet - Page 14

• 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

IR3508Z
DESIGN PROCEDURES - IR3508Z
Inductor Current Sensing Capacitor C
and Resistor R
CS
CS
The DC resistance of the inductor is utilized to sense the inductor current. Usually the resistor R
and capacitor C
CS
CS
in parallel with the inductor are chosen to match the time constant of the inductor, and therefore the voltage across
the capacitor C
represents the inductor current. If the two time constants are not the same, the AC component of
CS
the capacitor voltage is different from that of the real inductor current. The time constant mismatch does not affect the
average current sharing among the multiple phases, but does affect the current signal IOUT as well as the output
voltage during a load current transient if adaptive voltage positioning is being implemented.
Measure the inductance L and the inductor DC resistance R
. Pre-select the capacitor C
and calculate R
as
L
CS
CS
follows.
L
R
L
R
(1)
=
CS
C
CS
Bootstrap Capacitor C
BST
Depending on the duty cycle and gate drive current of the phase IC, a capacitor in the range of 0.1uF to 1uF is
needed for the bootstrap circuit.
Decoupling Capacitors for Phase IC
A 0.1uF-1uF decoupling capacitor is required at the VCCL pin.
CURRENT SHARE LOOP COMPENSATION
The internal compensation of current share loop ensures that crossover frequency of the current share loop is at least
one decade lower than that of the voltage loop so that the interaction between the two loops is eliminated. The
crossover frequency of current share loop
is approximately 8 kHz.
Page 14 of 19
Jan 09, 2009