Datasheet TS2940 (Taiwan Semiconductor) - 5

TS2940
Taiwan Semiconductor 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) * 1A + 3.3V * 11mA = 800mW + 36mW = 836mW 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°C 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: RӨJA = TR(max) / PD IMPORTANT: if the maximum allowable value for is found to be ≥60°C /W for the TO-220 package, ≥80oC/W for the TO-263 package, ≥150°C/W for the TO-252 package, or ≥170°C /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 RӨJA falls below these limits, a heatsink is required. Document Number: DS_P0000211 5 Version: D15