TLV755P: Help solving a thermal shut down problem

Hi Jeff,

Thermal shutdown has a specific signature on a scope. Please provide a multi-channel scopeshot showing Vin, Vout, and Iout. Iout is particularly important if testing with an electronic load.

For thermal calculations, the first step is to calculate the power being dissipated in order to use any of the thermal metrics. Please provide Vin, Vout, and Iout in order to calculate the power dissipation in the LDO. We also need to know which of the packages for TLV755P you are using.

The Theta metrics will vary with board layout. As such, they are not recommended when you have a board layout. If you are going to use the Theta metrics, perhaps the easiest method is to use Rtheta_ja to estimate the junction temperature because you only need to measure the ambient temperature (which you have already done).

Tj = Pd x Rtheta_ja + Ta
Tj = (Vin - Vout) x Iout x Rtheta_ja + Ta

Keep in mind that the Thermal Information table in the datasheet is modeled on a JEDEC Hi-k board. Your specific layout will impact the thermal performance in your application as discussed in the following application note.

www.ti.com/.../slvae85.pdf

In order to use the Psi thermal metrics, you will either need to measure the board temperature or the temperature of the top of the case. Often a thermal couple can be used to measure the top of the case. At this point you can calculate the junction temperature using:

Tj = Pd x Psi_jt + Ttop_of_case
Tj = (Vin - Vout) x Iout x Psi_jt + Ttop_of_case

Very Respectfully,
Ryan