TS4274_13 Datasheet, PDF (4/6 Pages) Taiwan Semiconductor Company, Ltd – 5V/400mA Fixed Voltage Ultra Low Dropout Voltage Regulator

TS4274
5V/400mA Fixed Voltage
Ultra Low Dropout Voltage Regulator
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, P_D
must be calculated.
The below formula shows the voltages and currents for calculating the P_D in the regulator:
IIN = IL / IG
P_D = (V_IN-V_OUT) * I_L + (V_IN) * I_G
Ex. P_D = (3.3V-2.5V) * 0.5A + 3.3V * 11mA
= 400mW + 36mW
= 436mW
Remark: I_L is output load current,
I_G is ground current.
V_IN is input voltage
V_OUT 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.
T_A(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, θ_JA, can now be found:
θ_JA = TR(max) / PD
IMPORTANT: if the maximum allowable value for is found to be ≥60^oC /W for the TO-220 package, ≥80^oC/W for
the TO-263 package, ≥150^oC/W for the TO-252 package, or ≥170^oC /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
θ_JA falls below these limits, a heatsink is required.
DPAK Thermal Resistance and Maximum Power Dissipation vs. P.C.B Copper Length
4/6
Version: B13