SC1480A Просмотр технического описания (PDF) - Semtech Corporation

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SC1480A

DDR and DDR Memory VTT power Supply Controller

Semtech Corporation 

POWER MANAGEMENT

Applications Information (Cont.)

TA = ambient temperature (°C)

PD = power dissipation in (W)

θJA = thermal impedance junction to ambient from

absolute maximum ratings (°C/W)

The power dissipation may be calculated as follows:

PD = VCCA • IVCCA + Vg • Qg • f W

Where:

VCCA = chip supply voltage (V)

IVCCA = operating current (A)

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

Qg = .ET gate charge, from the .ET datasheet (C)

f = switching frequency (kHz)

Inserting the following values as an example:

TA = 85°C

θJA = 100°C/W

VCCA = 5V

IVCCA = 1100µA (data sheet maximum)

Vg = 5V

Qg = 60nC

f = 342kHz

gives us:

PD = 5 • 1100 • 10−6 + 5 • 60 •10−9 • 342 • 103 = 0.108 W

and

TJ = 85 + 0.108 • 100 = 95.8 °C

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

dissipation are practically negligible, thus requiring no

special consideration thermally during layout.

SC1480A

 2003 Semtech Corp.

13

www.semtech.com

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