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Original question:

TPS92612-Q1: Heat Sharing resistor Rp

TPS92612-Q1: TPS92612-Q1 output - Short to VBAT Protection

Shubham Jagtap
Prodigy 90 points
Part Number: TPS92612-Q1

Hello Concern,

We are using TPS92612-Q1 in our Application - as we have a requirement of Short to Battery protection.

But when we are shorting the OUT pin to VBAT --> LED Driver got damaged (After Reset Showing the 0.4V @ OUT Pin).

Rp is populated in our case - please check the attached Snap.

VBAT - 13V and Iload - 32mA.

What will be the cause that device got damaged as Device is short to VBAT protected.

  • 0
    TI__Genius 17855 points

    Dear Shubham,

    There will be a delay in the response to the post as the responsible engineer is not in the office.

    -fhoude

  • 0 in reply to fhoude
    Prodigy 90 points

    Hello fhoude,

    Noted. as it is critical for us. Can you please expedite in other way. 

  • 0 in reply to Shubham Jagtap
    TI__Genius 17855 points

    He will answer tomorrow.  

    Did they capture any waveforms of the event?  There are number of ways a part can get damaged when doing a short to batt on the output.  You probably violated an abs max of the part's current or voltage requirements.  Maybe they forward biased a device in the part and it got damaged.  If the part isn't designed to withstand that fault you may have to put external devices to protect it.  You may want to get the part FA'd, but I would try and reproduce the event with a new part and try to capture as many things as I can using a scope.  Voltages at the pins, current through the short?  stuff like that.  I would also like to know the test setup and method.  Do you have pictures?  Descriptions of what exactly was done?

    Maybe Pedro might be aware of a better answer for you.  

    -Francis Houde

  • 0 in reply to fhoude
    Prodigy 90 points

    Hello fhoude,

    We are using TPS92612-Q1- 
    So we are not violating the abs max of part's current (32mA) and voltage (13V). 



    Please check the above snap - We are failing to survive the LED Driver during the Short to VBAT test.
    What do you mean by "Forward bias of Device and get damaged"?

    Looking Forward for positive response.

  • 0 in reply to Shubham Jagtap
    TI__Expert 4955 points

    Hello Shubham, 

    In order to be able to analyze this problem properly. I need you to send me the waveforms of the different pins during the test. We need to determine where the current is going and the only way to do it is by obtaining voltage and current waveforms of the output pin, the supply pin, and the load. Without waveforms I can only guess what is going on inside. 

    Additionally, I would recommend performing this test with a battery and not a power supply, as the power supply is going to have a much higher impedance than the battery would. Also, I would short Output to to battery with a wire, not using two separate power supplies to recreate the interaction as close as possible. 

    For your question of what does "Forward bias of device and get damage". Internally the FET that controls the current has a body diode that can conduct current in the opposite direction of normal operation. If enough voltage is seen from anode to cathode then the internal body diode will begin to conduct and damage the part, this is why we need to know the difference in voltage between out and supply as well as the current flowing into the pin. 

    Additionally, implementing a diode in series with the load will not help in this case at all, as it will just operate during normal operation, instead you need a Schottky diode with a lower forward voltage than the body diode of the device such that the current is conducted through it. This diode should be placed between the output pin and the supply pin with the anode in the out pin and the cathode in the supply pin. This way it will conduct in the fail scenario. 

    With these in mind I would recommend the following:

    • Set up the board to take waveforms of the voltage at OUT, supply, and current flowing into out.
    • Use a single battery, or if not at least a single power supply to recreate the use situation more accurately and short it with a wire. If you are concerned with current then place a resistor to limit it. 
    • Add the Schottky diode as described above. 
    • If these does not clarify the situation then doing an FA is the best route as it will determine if it is a voltage or current failure. 

    Best,

    Pedro Arango Ramirez.