TS2937_07 datasheet(4/10 Pages) TSC

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TS2937

500mA Ultra Low Dropout Voltage Regulator

4/10

Version: A07

Application Information (Continue)

Thermal Characteristics

A heatsink may be required depending on the maximum power dissipation and maximum ambient temperature of the

application. Under all possible operating conditions, the junction temperature must be within the range specified under

absolute maximum ratings. To determine if the heatsink is required, the power dissipated by the regulator, PD must be

calculated.

The below formula shows the voltages and currents for calculating the PD in the regulator:

IIN = IL / IG

PD = (VIN-VOUT) * IL + (VIN) * IG

Ex. PD = (3.3V-2.5V) * 0.5A + 3.3V * 11mA

= 400mW + 36mW

= 436mW

Remark: IL is output load current,

IG is ground current.

VIN is input voltage

VOUT is output voltage

The next parameter which must be calculated is the maximum allowable temperature rise.

TR(max) is calculated by the using to formula:

TR(max) = TJ(max) – TA(max)

Where: TJ(max) is the maximum allowable junction temperature, which is 125

oC for commercial grade parts. TA(max)

is the maximum ambient temperature which will be encountered in the application.

Using the calculated values for TR(max) and PD, the maximum allowable value for the junction to ambient thermal

resistance, θja, can now be found:

θja = TR(max) / PD

IMPORTANT: if the maximum allowable value for is found to be ≥6

oC /W for the TO-220 package, ≥80oC/W for the

TO-263 package, ≥150

oC/W for the TO-252 package, or ≥170oC /W for the SOT-223 package, no heatsink is needed

since the package alone will dissipate enough heat to satisfy these requirements. If the calculated value for θja falls

below these limits, a heatsink is required.

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