TPS7A47-Q1: Will TPS7A47 has additional thermal protection against 36V->1.4V/Short scenario?

Albert Sun

Part Number: TPS7A47-Q1
Other Parts Discussed in Thread: TPS7A47

Hi,

When TPS7A47's output is short when VIN=36V, VOUT=1.4V and IOUT is short. Therefore the power dissipation on pass FET will be about 36*1.26=45W. Will thermal shutdown protects the device in time? I know some LDO, when pass FET's power dissipation is too large, it will damage because internal FETs's highest temperature could have temperature accumulation when TSD is in and out, At the end, the FET can enter thermal avalanche breakdown. Will TPS7A47 has something called foldback current limit?

Below green line is FET's highest temp. Black line is thermal sensing temperature. Thank you for the help.

-A

11 months ago

0 John Schneider 11 months ago

TI__Genius 12511 points

Hi Albert,

Thank you for your patience, We are aware of the question and our assigned engineer will get back to you as soon as they are able to get a concrete answer from the designers, thank you again

0 Juliette 11 months ago in reply to John Schneider

TI__Genius 16606 points

Hello Albert,

This part has a brickwall current limit protection, explained here:

https://e2e.ti.com/blogs_/b/powerhouse/posts/ldo-current-limit

Why is this device being shorted?

Thermal shutdown will protect the device if the power dissipation across the FET is too large. An instantaneous short may damage the device and so can prolonged use in thermal shutdown.

Page 9 of this app note explains that the device may oscillate on and off to protect itself: https://www.ti.com/lit/eb/slyy151a/slyy151a.pdf

This app note explains how to calculate thermal performance and how to increase the package size to accommodate for large power dissipations: https://www.ti.com/lit/an/slva118a/slva118a.pdf

Updated thermal metrics: https://www.ti.com/lit/an/spra953c/spra953c.pdf

Best,

Juliette

0 Albert Sun 11 months ago in reply to Juliette

Intellectual 310 points

Hi Juliette,

Thanks for reply. I am interested in how TPS7A47 is protecting itself in high vin/short scenarios. Could you please explain more?

-A

0 Juliette 11 months ago in reply to Albert Sun

TI__Genius 16606 points

Hello Albert,

In high Vin scenarios, once the power dissipation across the device is too high, the LDO will turn off the output to cool the device down. once the device cools down, the LDO will turn on and begin regulating again. However, if the VIN is never dropped the output will continue to oscillate through thermal shutdown - long term usage in this stage will damage the device.

In a short scenario, the result is more unpredictable. The device may have the opportunity to shut itself off before damage is caused to the device but, depending on the extent to which abs max is violated, the device may be permanently damaged.

Best,

Juliette

Power management

Power management forum

TPS7A47-Q1: Will TPS7A47 has additional thermal protection against 36V->1.4V/Short scenario?