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OPA462: OPA462 Heating

Danilo A.
Mastermind 26940 points
Part Number: OPA462

Hi Team,

A customer supplies 170-180V to OPA462 and the device turns hot. Whenever he reduced the supply voltage the device cools down. Upon checking the quiescent current of the device, it consumes 2mA which translate to 180V x 2mA = 0.36 watts of heat. He did not connect the thermal pad to ground so there will be no thermal path from the device to the board except for the V- of the device. 

Looking at the PCB layout at page 11 of the user's guide of OPA462EVM it seems that the thermal pad is not connected to ground as well. Can you please confirm? 

Regards,

Danilo

  • 0
    Guru 140200 points

    Hi Danilo,

    the pad has to be connected to V-, but not to the ground ground plane. A small, from ground isolated, local V- plane on the top layer could help a lot. The cooling can be furtherly enhanced with a 4-layer board design :-)

    Hhm, I'm a bit surprised that the EVM seems to have no such local V- plane, allthough there's place enough for this simple but very effective cooling measure.

    Kai

  • 0
    TI__Guru* 93105 points

    Hi Danilo,

    I was involved with the OPA462 EVM development and just checked the Altium files to see how we designed the PC board thermal system.

    The top layer metal shown below (orange image) shows a U1 top metal PowerPAD™ having 8 vias. These 8 vias connect downward to the V- layer which is an extensive copper plane (brown image). The PowerPAD™ requires connection to V-, not ground, unless the OPA462 is being powered by a single V+ supply in which case V- and ground would be connected together.

    The OPA462 pin functions table on Pg. 2 of the datasheet states "The PowerPAD is internally connected to V–. The PowerPAD must be soldered to a printed-circuit board (PCB) connected to V–, even with applications that have low power dissipation." If the PowerPAD™ is not soldered as required the OPA462 will become hot due to quiescent power dissipation alone.

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • 0 in reply to Thomas Kuehl
    Guru 140200 points

    Perfect! :-)

    Kai

  • 0 in reply to kai klaas69
    TI__Mastermind 26940 points

    Hi Thomas,

    Thank you for sharing the PCB layout of the evaluation board showing the connection of the thermal pad to the copper plane using 8 vias. The 8 vias are not shown in the PCB layout at page 11 of the OPA462EVM User's Guide. I have submitted a document feedback to update the PCB layout in the User's Guide.

    Thank you for your support.

    Regards,

    Danilo