LM5067: Hotswap Controller gets damaged during normal operation

Hi Jaison,

Thanks for reaching out!

Under which test condition, you are observing the failures ? Can you share test waveforms to understand the issue

Why back to back FETs are used in 45A design. I don't think Q1 gets enough drive in steady state. Can you check its GATE voltage. 

Are you seeing damages of LM5067 or FETs as well ?

Best Regards,

Rakesh

Hi Rakesh,

Thanks for following up on this.

Failure is observed in normal test condition with 48V applied to input. Will capture and share the waveforms after replacing the damaged device.

Back to back FETs are used for reverse polarity protection (Diode in series is used for the low power design).

Gate voltage was observed around 12 to 13V with reference to the source,

Regards,

Jaison

Hi Jaison,

Thanks for the details. we will wait for the test result. Also check, Are you seeing damages on LM5067 or FETs  ?

Best Regards,

Rakesh

Hi Rakesh,

FETs are not getting damaged. Only LM5067 is getting damaged (Short or very low impedance between SENSE & OUT pins).

Pls provide your feedback on design as further test results will take some more time as we are waiting for new stock of LM5067 to replace the damaged devices.

Thanks,

Jaison

Hi Jaison,

Please fill out the design calculator and share with us for reviewing the design. 

https://www.ti.com/tool/LM5067QUICK-CALC 

Hi,

Pls find the design calculator sheet.

LM5067_Design_Calculator_REV_E_48V_40A_IXTH240N15X4_300uF_60vMax.xlsx

Thanks

Hi Jaison,

We need to know the RthjA, which is summation of Rthjc, Rthcs, and Rthsa. The values of Rthjc and Rthcs are mentioned in the MOSFET datasheet. Please find out the value of Rthsa from the heat-sink datasheet. The vale of RthJA should be entered in the F59 cell of the LM5067 design calculator to get the Maximum FET Junction Temperature.

Do you know the exact test conditions where the device got damaged? 

Hi,

Pls note that the FET i snot getting damaged and only LM5067 is getting damaged.

PFB the thermal performance of he heatsink used for FETs. Air velocity in the system will be around 600 feet/min.

Hi Jaison,

SENSE to OUT is equivalent to MOSFET SOURCE to DRAIN. Is the board working after replacing the controller? Do you know the exact test conditions where the device got damaged? As Rakesh suggested, please share the experiment waveforms when the device got damaged.

Hi Avishek,

The devices are removed from the board and checked for damage/short. FETs are found ok and LM5067 is found shorted.

Request you to review the design till we can reproduce the issue with the dammed devices replaced.

Hi Jaison,

I am not sure about the maximum steady-state MOSFET junction temperature while carrying the full load current. Otherwise, the design looks good. 

Hi,

Here are some more observations after replacing the damaged LM5067.

- Two MOSFETs connected back to back are definitely causing some issues though this scenario was confirmed by one of our designer in this forum during design time (https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1201886/lm5067-reverse-polarity-protection?keyMatch=LM5067). LM5067 gets damaged the moment  input 48V is applied to the circuit. It's not the Gate pin that is getting damaged, but the Sense and & Out pin are getting shorted and FET stays fine.

- Replaced LM5067, Removed one FET  & the extra cap provided at Gate pin. This case is working fine (it became stable only after removing extra capacitor present on Gate pin).

We couldn't capture any waveforms for the failure case it happened quickly.

Regards.

+note captures taken in the working condition (also note that diodes D24, D25 are removed & R115 is replaced with 0 ohm in the working condition) ,

We will analyze and get back to you by tomorrow. 

Pls update on this.