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TLV9064: Thermal pad connected to GND?

Shawn_Wang
Expert 3811 points
Part Number: TLV9064

Hi Team

For the TLV9064 RTE package, D/S shows the thermal pad is needed to be connected to V-. 

Due to some reason, my customer connected its thermal pad to GND and the customer wants to know the possible risk or problem under the following application, could you help check it and give your comments? 

  1. V+=3.3V, V- = -3.3V , thermal pad = GND
  2. V+=3.3V, V- = GND , thermal pad = GND. This should be the correct connection. 
  3. V+=GND, V- = -3.3V , thermal pad = GND

  • 0
    Guru 140200 points

    Hi Shwan,

    it's mandatory to connect the thermal pad to the negative supply voltage pin (V-) of OPAmp and not to any other potential. The reason is that the die is glued onto the thermal pad with a somewhat electrically conductive glue. And as the bottom of silicon die sits on the V- potential the thermal pad must also sit on the V- potential. Otherwise an insane current can flow through the die.

    But keep in mind that the glue is not conductive enough to allow the customer to omit the connection between the V- pin and the circuit.

    Kai

  • 0 in reply to kai klaas69
    TI__Guru*** 140106 points

    Shawn,

    The current Kai mentioned might be small or large, it could even change over the lifetime of the device (which could be very short).

    For 1, the supply voltage is 6.6V which is greater than the absolute maximum voltage. The thermal pad connection is unsafe.

    For 2, That is correct.

    For 3, The thermal pad connection is unsafe.

    I highly recommend fixing the board layout. 

  • 0 in reply to kai klaas69
    TI__Expert 3811 points

    Hi Kai

    Thanks for your information. Is it acceptable to leave the thermal pad float with the output current less than 10mA? The D/S in the customer's hand does not say the thermal pad is needed to be connected to V- and this requirement is added in the latest version. 

  • 0 in reply to Ron Michallick
    TI__Expert 3811 points

    Hi Ron

    Sorry for the typo and for 1 the V- is -1.8V.

  • 0 in reply to Shawn_Wang
    TI__Guru*** 140106 points

    Shawn,

    There are two valid connections for pad. Unconnected to anything else, connected to V- pin. 

    Prior to revision J, there was no direction, so connection would be assumed same as precedence for other thermal pad devices. "Do not connect unless it is stated as safe to do so".  

  • 0 in reply to Ron Michallick
    TI__Expert 3811 points

    Hi Ron

    Because there are many pcs of PCBA already and could you help give your insights on how to solve this problem?

    For V+=GND, V- = -3V , thermal pad = GND

    1. The test result shows that the power consumption would increase and V- changes to -2.2V.
    2. The customer tried to add insulation rubber between GND and TLV9064 thermal pad and found the circuit seems working well. Could you help check if leaving the thermal pad floating is acceptable? 
  • 0 in reply to Shawn_Wang
    TI__Guru*** 140106 points

    Shawn,

    Floating is acceptable.