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TPS51206: Pin short - VDD to VTT

JosefMieslinger
Intellectual 2170 points
Part Number: TPS51206

Dear TI Team,

we are doing some tests where device pins are shorted and check the application behaviour.
On the TPS51206 we did a test and shorted Pin10 (VDD) to Pin3 (VTT). In this test the device gets very hot >>150°C and we see a risk of fire hazard.

- VDD = 5V
- VLDOIN/VDQSNS = 1.5V
- VTT = 0.75V

1) Are VTT pin or VDDQSNS pin diode clamped to VLDOIN?
2) In case yes, what is the maximum clamp current?

We consider to limit the current on VDD to avoid the themal runaway issue.
Other recommendations to overcome this issue in a pin short event are welcome.

Thanks and best regards,
Joe

 

  

  • 0
    TI__Mastermind 24075 points
    Hi Joe,

    TPS51206 is a linear regulation. When VTT pin is shorted to a high voltage (3.3V or 5V) power supply, the part will sink current to try to regulate VTT voltage. Due to the limited sink current capability, the VTT voltage will be pulled to a high voltage level.
    The potential power loss on the part is: VTT*Isink, here Isink is 2-3A, actual VTT voltage should be measured during test.
    With large power loss, the part will be heated up until OT protection is triggered.

    Limiting VDD current is a good idea to limit power loss on the part.
    As VTT pin and VDD pin are not next to each other, will pin3 and pin10 short happen in real situation?

    Thanks
    Qian
  • 0 in reply to Qian Chen
    TI__Intellectual 2170 points

    Hi Qian,

    thanks for the quick feedback.
    Agree to your point, but this means the OT protection is kicking in at 150°C and the device should stop to heat up further.
    As we see the device getting significantly hotter that the 150°C of the OT protection we think there must be some additional mechanism that still draws current while OT protection already switched on. We suspect some clamping diodes, or similar...

    The short test between Pins is a test needed for our product safety to ensure there is no risk of fire on cause of a malfunction. Therefore this is very critical for this product.

    Can you please check regarding the clamping diodes?

    Thanks!
    Joe 

  • 0 in reply to JosefMieslinger
    TI__Mastermind 24075 points
    Hi Joe,

    First, please check if the part works fine after short condition is removed. If the part is damaged during test, anything could happen.

    In short condition, if VTT voltage is higher than VLDOIN, the current will flow from VTT pin to VLDOIN pin through internal high-side bode diode, even the part is in OT protection. In that case, there is power loss on the part and the temperature will keep rising.

    Thanks
    Qian