ISL62381 datasheet(21/23 Pages) INTERSIL

21 / 23 page

FN6665.4

August 7, 2008

inductor pads for accurate measurement. Connect ROCSET

to the phase-node side pad of the inductor, and connect

CSEN to the output side pad of the inductor. The ISEN

resistor should also be connected to the output pad of the

inductor with a separate trace. Connect the OCSET pin to

the common node of node of ROCSET and CSEN.

For resistive current sensing, connect ROCSET from the

OCSET pin to the inductor side of the resistor pad. The ISEN

resistor should be connected to the VOUT side of the resistor

pad.

In both current-sense configurations, the resistor and

capacitor sensing elements, with the exclusion of the current

sense power resistor, should be placed near the

corresponding IC pin. The trace connections to the inductor

or sensing resistor should be treated as Kelvin connections.

FB (Pins 9 and 32), and VOUT (Pins 10 and 31)

The VOUT pin is used to generate the R3 synthetic ramp

voltage and for soft-discharge of the output voltage during

shutdown events. This signal should be routed as close to

the regulation point as possible. The input impedance of the

FB pin is high, so place the voltage programming and loop

compensation components close to the VOUT, FB, and GND

pins keeping the high impedance trace short.

FSET (Pins 2 and 7)

These pins require a quiet environment. The resistor RFSET

and capacitor CFSET should be placed directly adjacent to

these pins. Keep fast moving nodes away from these pins.

LGATE (Pins 17 and 24)

The signal going through these traces are both high dv/dt

and high di/dt, with high peak charging and discharging

current. Route these traces in parallel with the trace from the

PGND pin. These two traces should be short, wide, and

away from other traces. There should be no other weak

signal traces in proximity with these traces on any layer.

BOOT (Pins 16 and 25), UGATE (Pins 15 and 26), and

PHASE (Pins 14 and 27)

The signals going through these traces are both high dv/dt

and high di/dt, with high peak charging and discharging

current. Route the UGATE and PHASE pins in parallel with

short and wide traces. There should be no other weak signal

traces in proximity with these traces on any layer.

Copper Size for the Phase Node

The parasitic capacitance and parasitic inductance of the

phase node should be kept very low to minimize ringing. It is

best to limit the size of the PHASE node copper in strict

accordance with the current and thermal management of the

application. An MLCC should be connected directly across

the drain of the upper MOSFET and the source of the lower

MOSFET to suppress the turn-off voltage spike.

ISL62381, ISL62382, ISL62383

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