THS4541IRUNR.B datasheet(32/66 Pages) TI2

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7.8 Thermal Analysis

The relatively low internal quiescent power dissipation for the THS4541, combined with the excellent thermal

impedance of the 16-pin VQFN (RGT) package, limits the possibility of excessively-high, internal-junction

temperatures. The 10-pin WQFN (RUN) package has a much higher junction-to-ambient thermal impedance

(θJA = 146°C/W); therefore, a more detailed analysis can be warranted.

To estimate the internal junction temperature (TJ), an estimate of the maximum internal power dissipation (PD)

is first required. There are two pieces to the internal power dissipation: quiescent current power and the power

used in the output stage to deliver load current. To simplify the latter, the worst-case, output-stage power is

driving a dc differential voltage across a load using half the total supply voltage. As an example:

1. Assume a worst-case, 5% high 5-V supply. This 5.25-V supply with a maximum ICC of 11 mA gives a

quiescent power term = 58 mW.

2. Assume a 100-Ω differential load with a static 2.5-V differential voltage established across the load. This 25

mA of dc load current generates a maximum output stage power of (5.25 V – 2.5 V) × 25 mA = 69 mW.

3. From this total worst-case internal PD = 127 mW, multiply times the 146°C/W thermal impedance for the

very-small, 10-pin WQFN package to get a 19°C rise from ambient.

Even for this extreme condition and the maximum rated ambient temperature of 125°C, the junction temperature

is a maximum 144°C (less than the rated absolute maximum of 150°C). Follow this same calculation sequence

for the exact application and package selected to predict the maximum TJ.

THS4541

SLOS375B – AUGUST 2014 – REVISED FEBRUARY 2024

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THS4541IRUNR.B Datasheet(PDF) 32 Page - Texas Instruments