10.2.2.3 Thermal Considerations
The maximum IC junction temperature must be restricted to 125°C under normal operating conditions. To calculate the maximum allowable dissipation, PD(max) for a given output current and ambient temperature, use Equation 6.
- PD(max) is the maximum allowable power dissipation
- TJ(max) is the maximum allowable junction temperature (125°C for the TPS22968)
- TA is the ambient temperature of the device
- RθJA is the junction to air thermal impedance. See theThermal Information table. This parameter is highly dependent upon board layout.
Equation 7 to Equation 10 and Equation 11 to Equation 13 show two examples to determine how to use this information correctly:
For VBIAS = 5 V, VIN = 5 V, the maximum ambient temperature with a 4-A load through each channel can be determined by using Equation 7 to Equation 10:
Equation 7. PD = I2 × R × 2 (multiplied by 2 because there are two channels)
Equation 9. TA = TJ(MAX) – RθJA × 2 × I2 × R
Equation 10. TA = 125°C – 62.5°C/W × 2 × (4 A)2 × 27 mΩ = 71°C
For VBIAS = 5 V, VIN = 5 V, the maximum continuous current for an ambient temperature of 85°C with the same current flowing through each channel can be determined by using Equation 11 to Equation 13: