IR3521 datasheet(33/45 Pages) IRF

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IR3521

Page 33

V3.03

IR3508 EXTERNAL COMPONENTS

Inductor Current Sensing Capacitor CCS and Resistor RCS

The DC resistance of the inductor is utilized to sense the inductor current. Usually the resistor RCS and capacitor

CCS in parallel with the inductor are chosen to match the time constant of the inductor, and therefore the voltage

across the capacitor CCS represents the inductor current. If the two time constants are not the same, the AC

component of 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 affect the current signal ISHARE as well

as the output voltage during the load current transient if adaptive voltage positioning is adopted.

Measure the inductance L and the inductor DC resistance RL. Pre-select the capacitor CCS and calculate RCS as

follows.



(19)

Bootstrap Capacitor CBST

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

0.1uF-1uF decoupling capacitors are required at VCC and VCCL pins of phase ICs.

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