SC1486ITSTRT datasheet(14/17 Pages) SEMTECH

14 / 17 page

 2002 Semtech Corp.

www.semtech.com

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.

Thermal Considerations

The junction temperature of the device may be calculated

as follows:

•

Application Information (Cont.)

Where:

A = ambient temperature (°C)

D = power dissipation in (W)

JA = thermal impedance junction to ambient from

absolute maximum ratings (°C/W)

The power dissipation may be calculated as follows:

() W

VCCA

•

Where:

VCCA = chip supply voltage (V)

VCCA = operating current (A)

g = gate drive voltage, typically 5V (V)

g = FET gate charge, from the FET datasheet (C)

f = switching frequency (kHz)

Inserting the following values as an example:

A = 85°C

JA = 37°C/W

VCCA = 5V

VCCA = 1100µA (data sheet maximum)

g = 5V

g = 60nC

f = 300kHz (enter the higher of the two set frequencies

here)

gives us:

()

300

1100

•

−

As can be seen, the heating effects due to internal power

dissipation are practically negligible, thus requiring no

special consideration thermally during layout.

SC1486ITSTRT bảng dữ liệu(PDF) 14 Page - Semtech Corporation

SC1486ITSTRT bảng dữ liệu(HTML) 14 Page - Semtech Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

bảng dữ liệu tải về

Link URL