SC1486 datasheet(14/17 Pages) SEMTECH

14 / 17 page

 2002 Semtech Corp.

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SC1486

POWER MANAGEMENT

DDR Supply Selection

The SC1486 can be configured so that VTT and VDQ are

generated directly from the battery. Alternatively, the VTT

supply can be generated from the VDDQ supply. Since

the battery configuration generally yields better efficiency

and performance, the eval board is configured to

generate both supplies from the battery.

DDR Reference Buffer

The reference buffer is capable of driving 3ma and sinking

25ua. Since the output is class A, if additional sinking i s

required an external pulldown resistor can be added.

Make sure that the ground side of this pulldown is tied

to the VTT AGND plane near the AGND2 pin of the

SC1486.

As with most opamps, a small resistor is required when

driving a capacitive load. To ensure stability use either a

10 ohm resistor in series with a 1uf capacitor or a 100

ohm resistor in series with a 0.1uF capacitor from

REFOUT to AGND2.

REFIN should also be filtered so that VDDQ ripple does

not appear at the REFIN pin. If a resistor divider is used

to create REFIN from VDDQ, then a 0.1uF capacitor from

REFIN to AGND2 will provide adequate filtering.

Application Information (Cont.)

SC1486 Datasheet(PDF) 14 Page - Semtech Corporation