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ISOW7841: Short term high current draw on ISOW output

franziskus
Expert 6706 points
Part Number: ISOW7841
Other Parts Discussed in Thread: TLV61046A

Team,

my customer uses ISOW7841 in a new application. Supply voltage is 3.3V.
On the output of ISOW7841, there is a TLV61046A boost converter, boosting to 12V / 1mA.


WEBENCH shows that the TLV61046A draws peak currents of 150mA for 8usec.
Do you think this will be a problem for the ISOW7841 or will this be compensated by the capacitors?

Thanks!

  • 0
    TI__Mastermind 49445 points
    Hi Franziskus,

    Thanks for sharing details related to customer application.

    Can you please confirm if you meant to say that VCC is 3.3V and VISO is set to 3.3V with respect to ISOW7841?
    Did you mean to say that 150mA for 8us is a one time transient or is this the periodic current requirement?

    From TLV61046A datasheet Figure 14 waveform, it looks to me that the boost converter is going to consume 150mA (with duty cycle) for about 8us every 20us. Is this the way you are observing 150mA in WEBENCH simulation as well?
    Can you please also share me what are the input and output decoupling caps that customer is going to use?


    Regards,
    Koteshwar Rao
  • 0 in reply to Koteshwar Rao
    TI__Mastermind 49445 points

    Hi Franziskus,

    Please do help us with the requested information in my previous post so that we can confirm if such an operation is fine or not, thanks.


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    TI__Expert 6706 points

    Hi Koteshwar,

    I have more background information:

    • Yes, both VCC and VISO are set to 3.3V on ISOW7841.
    • The observation in WEBENCH is as described in figure 14 in the TLV61046A datasheet.
    • The TLV input and output caps are 4.7uF each. They have tested several other values in range of 3-10uF, but there was no effect on the behavior (current draw).
    • The ISOW output caps are 100nF + 2x 10uF, rated at 10V.

    I have also sent a TLV EVM for practical tests.
    I hope this helps!

    BR, Franziskus

  • 0 in reply to franziskus
    TI__Mastermind 49445 points
    Hi Franziskus,

    Thank you for sharing the requested information.
    Please note that ISOW7841 with VCC and VISO at 3.3V will support an output current of >75mA.

    Since the load current at TLV61046A output is only 1mA @ 12V, I believe the output cap at VISO is going to support the 150mA requirement while VISO might not see this current directly. In that case, I think ISOW7841 should work fine for this application.

    Please do make sure the input cap at VCC of ISOW7841 is greater than its output cap at VISO. Thanks.


    Regards,
    Koteshwar Rao