SC418 datasheet(27/30 Pages) SEMTECH

27 / 30 page

SC418

Applications Information (continued)

All components connected to the FB pin must

be located near the pin. The FB traces should be

kept small and not routed near any noisy switch-

ing connections or power components.

Place the R

ILIM resistor near the IC. For an accu-

rate I

LIM current sense connection, route the RILIM

trace directly to the drain of the low-side MOSFET

(LX). Use an inner routing layer if needed.

Place the R

TON resistor near the TON pin. Route

TON to the TON pin and to AGND using short

traces and avoid all switching signals.

For the LDO components

The FBL resistors should be placed near

the FBL pin. The area of the FBL traces

should be minimized, avoiding all switch-

ing connections.

The top FBL resistor must route directly

to the LDO output capacitor. The LDO

load current should not flow through this

trace.

Bypass Capacitors

The device requires bypass capacitors for the following

pins.

VDDA pin with respect to AGND. This 0.1μF

minimum capacitor must be placed and routed

close to the IC pins, on the same layer as the IC.

VDDP with respect to PGND. This 1μF minimum

capacitor must be placed and routed close to

the IC pins and on the same layer as the IC.

BST pin with respect to LX. This 0.1μF minimum

capacitor must be placed near the IC, on either

side of the PCB. Use short traces for the routing

between the capacitor and the IC.

VLDO pin with respect to AGND.

This is the LDO output capacitor.

The placement of this capacitor is not

critical, however for routing it is important

that the top FBL resistor connects directly

to this capacitor, and that the LDO load

current does not flow through this trace.

If VLDO is not used to power the device

then a minimum 1μF capacitor referenced

to AGND is required.

If VLDO is used to power the device then

•



•



the VDDA and VDDP capacitors also

function as the LDO output capacitor.

For VDDA, a minimum 0.1μF capacitor ref-

erenced to AGND is required. For VDDP,

a minimum 1μF capacitor referenced to

PGND is required.

VIN pin with respect to AGND. This 0.1μF

minimum capacitor must be placed and routed

close to the IC pins. This capacitor provides

noise filtering for the input to the internal LDO.

•

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