SBVA105 April   2025 TPS74801

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Simulation and Measurement Results
    1. 2.1 Measurements
  6. 3Summary
  7. 4References

2.1 Measurements

Measurements were taken using the TPS74801EVM-177 at an ambient temperature, TA , of 25°C. Measurements were conducted comparing the legacy TPS748 design and the new TPS748 design, using test methodologies described in Measuring the Thermal Impedance of LDOs in Situ.

Table 2-1 Legacy Die vs. New Die Thermal Performance: VIN and VBIAS = 3V
Conditions Legacy Die New Die
VOUT 1.2V 1.2V
IOUT 1A 1A
Power Dissipated (PD) 1.8W 1.8W
Ambient Temperature (TA )' 132.8°C 122.6°C
Table 2-2 Legacy Die vs. New Die Thermal Performance: VIN and VBIAS = 4V
Conditions Legacy Die New Die
VOUT 1.2V 1.2V
IOUT 1A 1A
Power Dissipated (PD) 2.8W 2.8W
Ambient Temperature (TA )'' 115.3°C 101.9°C

Using the following junction to ambient thermal resistance equation stated in the Measuring the Thermal Impedance of LDOs in Situ, paper:

Legacy die:

Equation 2. R θ J A = T A ' - T A " P D " - P D ' = 132.8 ° C - 115.3 ° C 4 V - 1.2 V × 1 A - 3 V - 1.2 V × 1 A = 17.5 ° C W

New die:

Equation 3. R θ J A = T A ' - T A " P D " - P D ' = 122.6 ° C - 101.9 ° C 4 V - 1.2 V × 1 A - 3 V - 1.2 V × 1 A = 20.7 ° C W

Finally, thermal camera imaging was used to measure the case temperature for both the legacy and new devices. Both devices with the VSON package were placed on the EVM. The test conditions were Vout = 1.2V, Vin = 2.2V, Vbias = 2.7V, and Iout =1.5A (for example, Power Dissipation =1.5W), and after maintaining this for 30 minutes, thermal camera imaging was done as shown in Figure 2-3 and Figure 2-4. Maximum case temperatures were measured as 71°C and 69°C for the legacy and new device respectively.

Thermal Camera Shot LegacyTPS748 DeviceFigure 2-3 Thermal Camera Shot Legacy
TPS748 Device
Thermal Camera Shot RedesignedTPS748 DeviceFigure 2-4 Thermal Camera Shot Redesigned
TPS748 Device

Now using equation 8 stated in the Semiconductor and IC Package Thermal Metrics paper, TJ = TC + (ψJT x Power), and ψJT values mentioned in the data sheet, TJ can be calculated as 72.05°C for the legacy die and 75.3°C for the new die.