LM7171AMJQML datasheet(21/31 Pages) NSC

21 / 31 page

LM7171QML, LM7171QML-SP

www.ti.com

SNOSAR5C – FEBRUARY 2009 – REVISED APRIL 2013

Figure 61. The LM7171 Driving a 150 pF Load

with a 50

Ω Isolation Resistor

Power Dissipation

The maximum power allowed to dissipate in a device is defined as:

PD = (TJ(max) − TA)/θJA

(2)

Where

PD is the power dissipation in a device

TJ(max) is the maximum junction temperature

TA is the ambient temperature

θJA is the thermal resistance of a particular package

For example, for the LM7171 in a CFP package, the maximum power dissipation at 25°C ambient temperature is

680 mW.

Thermal resistance,

θJA, depends on parameters such as die size, package size and package material. The

smaller the die size and package, the higher

θJA becomes. The 8-pin CDIP package has a lower thermal

resistance (106°C/W) than that of the CFP (182°C/W). Therefore, for higher dissipation capability, use an 8-pin

CDIP package.

The total power dissipated in a device can be calculated as:

PD = PQ + PL

(3)

PQ is the quiescent power dissipated in a device with no load connected at the output. PL is the power dissipated

in the device with a load connected at the output; it is not the power dissipated by the load.

Furthermore,

PQ: = supply current × total supply voltage with no load

PL: = output current × (voltage difference between supply voltage and output voltage of the same side of

supply voltage)

For example, the total power dissipated by the LM7171 with VS = ±15V and output voltage of 10V into 1 kΩ is

PD = PQ + PL

= (6.5 mA) × (30V) + (10 mA) × (15V

− 10V)

= 195 mW + 50 mW

= 245 mW

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LM7171AMJQML Datasheet(PDF) 21 Page - National Semiconductor (TI)