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 2004 Semtech Corp.

www.semtech.com

SC801

POWER MANAGEMENT

Applications Information (Cont.)

Layout Guidelines

Try to keep the traces from the adaptor input to the VCC

pins as wide as possible, to eliminate any voltage drop

across the device input traces. You want to make sure

the input-to-output voltage differential of the device does

not approach the dropout voltage. A curve of the drop-

out voltage vs. output current is shown on page 15. Any

voltage dropped over the input traces from the adaptor

will reduce the dropout voltage margin.

Make the high current output trace from the VOUT pins

as wide as possible. The BSEN line should be used prop-

erly to compensate for any voltage drops from the out-

put trace to the battery. Make a Kelvin connection with

the BSEN trace to where VOUT connects the battery ter-

minals. This is done by taking the BSEN trace and tying it

to the VOUT trace as close to the battery terminals as

possible. This way, any voltage drop across the trace re-

sistance to the battery will be compensated for because

BSEN will regulate the device output voltage (VOUT) at

the point it connects to the VOUT trace. If you tie the

BSEN line to the VOUT pin at the device you will eliminate

the benefit of its purpose and the trace resistance drop

will not be compensated. Therefore, it is best to have

the BSEN trace follow in parallel the VOUT trace and tie

them together at the contact point of the battery termi-

nal for the best result.

The bottom of the SC801 package has a heat slug and

this slug should be tied to a ground plane of the PCB

through one large via or a series of smaller vias. If there

is no ground plane, an area should be dedicated on the

bottom of the PCB to act as a heat sink. The evaluation

board has 1 square inch of copper and allows an output

current of greater that 1A. The more copper tied to this

slug the greater the output current available before ther-

mal limitations dominate. The two pins that are labeled

NC are not connected to the die. Therefore, tying these

pins to the ground plane offers no aide in heat removal

and has no electrical benefit.