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ISO35T: Multiple parts on same board - drawing excess current

solarmax2
Prodigy 15 points
Part Number: ISO35T

I have 7 ISO35T's on one board.  My design is very very close to the reference design. The differences in my design are:

  • I have DE tied high, and /RE tied to ground
  • I have all of the isolated grounds tied to each other (these will be tied to an earth ground)  The isolated grounds are not connected to the A side ground (or anything else).

I just recieved my prototype boards back, and when I try to power it up, the on-board regulator goes into current limit.  Thinking there may be an issue with the regulator, I bypassed it with a bench supply, and it also goes into current limit, and the voltage drops to around a volt.  The ISO35T's are all getting warm to very warm (depending on the current that I allow them to draw). I have not allowed them to get hot.   Nothing else on the board is warming up except for the ISO32T chips.

I lifted pins 1 & 2 that drive the transformer on each of the devices, with no difference. I lifted the +3V3 pin on the center of the transformer on the non-isolated side, with no difference.  Evidently the chip itself is drawing  the current since the driver for the transformer is disconnected.

Does anyone have any idea what is going on?  Is it OK to tie all of the isolated grounds together?

  • 0
    TI__Genius 17100 points
    Hi Solarmax,

    I'm sorry to hear about these issues with the ISO35T. There may be a short somewhere in the system. To help solve this mystery, can you provide the following information?

    1. A schematic of your design with notes on where bench supplies are connected. I requested your friendship so you may send it to me directly or you may post it on this forum
    2. Which reference design is your system based on? (w/ hyperlink preferred)
    3. Relevant part numbers for parts connected directly to the ISO35T


    Thank you for trusting this to the E2E forums!

    Regards,
    Manuel Chavez
  • 0 in reply to Manuel Chavez
    TI__Genius 17100 points
    Hi Solarmax,

    This reply is being posted for completeness to everyone following this thread:

    Upon following up offline and testing on both Solarmax's end and TI's end, it was determined that the ISO35T devices used in this system were defective out of the box. This was confirmed by taking power measurements and waveforms of devices in this system and comparing with known good units.

    The appropriate method for exchanging the devices is being handled by Solarmax. Since this thread is no longer active, I will close it out. If new questions or concerns arise please feel free to ask a related question or post a new question using the yellow and red buttons above.


    Thank you for choosing TI parts,
    Manuel Chavez