TS4274 datasheet(4/6 Pages) TSC

4 / 6 page

TS4274

5V/400mA Fixed Voltage

Ultra Low Dropout Voltage Regulator

4/6

Version: B13

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:

JA = TR(max) / PD

IMPORTANT: if the maximum allowable value for is found to be ≥60

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

JA falls below these limits, a heatsink is required.

DPAK Thermal Resistance and Maximum Power Dissipation vs. P.C.B Copper Length

TS4274 Datasheet(PDF) 4 Page - Taiwan Semiconductor Company, Ltd