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TPS61085: How can I isolate load from input during shutdown?

Stoian Tzenkov
Prodigy 70 points
Part Number: TPS61085
Other Parts Discussed in Thread: TLV61046A, TLV61046, TPS61093

Hi. I am planning to use TPS61085 Boost converter in an battery (2.2~3.6)Volt energized device, and I need to have for a short time 18Volts output to supply 2 current output (4~20)mA sensors. To save energy of battery it is mandatory to isolate output load of converter from battery voltage, which is at the input of converter, during shutdown time. Can you recommend where to place PMOS FET - at the input of boost or at the output?

  • 0
    TI__Mastermind 34201 points

    Hi Stoian,

    It's ok to put the PMOS FET at both input and output. If you put it at input, the PMOS voltage rating is small, a 10V/0.5A rating is enough. Put the PMOSFET at output needs a higher rating device.

    Another solution is using TLV61046A, which has isolation inside.

  • 0 in reply to Zack Liu
    Prodigy 70 points

    Hi Zack. Thx for fast reply. If I put PMOS in front of boost, do I have to control Enable pin simultaneously to use the option of lowering inrush current?

    And in second solution - if I put PMOS at the output, there will be some current thru feedback resistors, which is more than I need.

    I started discussion in this forum about TLV61046A, but there is another problem with startup with full load of 50mAmps. So, I must assess which approach fits my design better.

    Maybe I missed another solution.

  • 0 in reply to Stoian Tzenkov
    TI__Mastermind 34201 points

    Hi Stoian,

    Yes. TLV61046A has a precharge current limit of 50mA maximum. If you want to startup with full load, TLV61046 is not suitable.

    If you put PMOS in front of TPS61085, Enable pin could connect to Vin pin after the PMOS. So you don't have to control Enable pin simultaneously.

  • 0 in reply to Zack Liu
    Prodigy 70 points

    Hi Zack,

    I will try to switch to TPS61093, thank you.

    BR,

    Stoian