TPS746-Q1: RθJA，RθJB，RθJC(top)

Hi Xiaoxiang,

To calculate the internal junction temperature of TPS746-Q1, or any LDO, you must first calculate how much power you are dissipating. Power dissipation in an LDO can be calculated by the following equation:  You can use the value obtained from this equation to calculate junction temperature: .  T_J is junction temperature, T_A is ambient temperature and R_ΘJA is the device thermal resistance. Refer to section 8.1.6. in the datasheet or Semiconductor and IC Package Thermal Metrics for more detailed information.

R_ΘJA is the measure of thermal performance of an IC mounted on a PCB. It is one of the only R_ΘJ parameters that assumes heat leaves through all sides of the package, thus is one of the easiest of the R_ΘJ parameters to use to estimate device temperature without board temperature. 

R_ΘJB is the junction to board thermal resistance, measured 1mm from a device. 

R_ΘJC is the top of case thermal resistance. It is defined as the thermal resistance from the operating portion of a semiconductor to the outside surface of the package. R_ΘJC assumes that heat leaves only from the top of the package.

I hope this is helpful,

Erin

Hi Xiaoxiang,

R_ΘJA should improve 15-30% on the EVM. 

R_ΘJB is harder to predict, and we cannot say how this will change.

R_ΘJC should not change depending on the board it is on as it is the thermal resistance on the top of the package. 

I hope this is helpful,

Erin