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UCC5870-Q1: VEE2 bypass capacitors

Ross Parlour
Intellectual 1875 points
Part Number: UCC5870-Q1


Hi,

Regarding the UCC5870 VEE2 bypass capacitors; there are two VEE2 pins specifically pins 19 and 30 (~ far ends of the device). 

The application example shown in section 8.2 (and a previous customer layout) have decouplers only at one pin.

Reading 8.2.2.1, I take it that there ought to be capacitors local to each pin i.e. each VEE2 pin has its own local decoupling. Do you know what the intention was here please?

In addition, what behaviour might be expected if one of the VEE2 pins were to go open circuit?

Cheers,

Ross

  • 0
    TI__Genius 13760 points

    Hi Ross,

    We recommend to add the VEE-GND2 capacitance close to pin30(VEE) and pin28(GND2) of the gate driver. Pin19(VEE) should still be connected to the VEE net on the board and should not be left floating. Due to the gate driver pin out it is recommended to add the VEE to VREG2 capacitance between pin19(VEE) and pin20(VREG2).

    We do not perform tests with VEE pins floating and do not recommend either of them be left floating. These pins need to be connected to the VEE net on the board to prevent potential un-characterized behavior of the gate driver.

    Best regards,

    Andy Robles

  • 0
    TI__Intellectual 1875 points

    Sorry Andy for the delayed response, I have been OoO.  Regarding the first part of my question – sorry that really was a bit of an obvious one. 

    Regarding one of the VEE2 pins going open (perhaps due to a solder joint failure) agreed – we certainly wouldn’t plan to have an open circuit but we really do need to better understand the behaviour.

    There is an internal monitoring circuit that will report out of range for VEE2 voltage. However there remains the possibility (I hope this has been considered) that the two VEE2 pins are not internally connected and that only one is monitored… leading to undesirable behaviour without triggering the relevant status bit?

    Would it be possible please to determine

    1. Are the two VEE2 pins internally connected together
    2. If no to 1 - does the VEE2 monitor look at both pins independently

    Cheers,
    Ross

  • 0 in reply to Ross Parlour
    TI__Genius 13760 points

    Hi Ross,

    I see the concern. Both VEE pins are internally connected, and we have ran full UCC5870-Q1 tests with VEE pin 19 disconnected and have observed no abnormal behavior of the driver.

    We have no evidence from our test information that leads us to believe that any issue would happen by having VEE pin 19 disconnected. Nevertheless we still recommend that VEE pin 19 be connected to the VEE net on the board. Reason is that although both pins are internally connected the internal connection will have a higher impedance from VEE pin 19 to the board VEE net than if the VEE pin 19 was directly connected to the VEE net on the board.

    Best regards,

    Andy Robles