• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 62 subscribers
  • Views 122 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS7A02: How much reverse current?

ArTzy
Genius 13959 points
Part Number: TPS7A02

Hi Experts,

Seeking your assistance to this query:

I am designing a product which is powered from a battery (+BATT) via the TPS7A0222 regulator. A Programmer may be connected to the MCU directly to program the device at 3.3V, powered via PROG_PWR which is on the regulator's output. The circuit diagram is attached below.

While the battery is diode protected via D1, if the battery is dead, C1 will be 0 volts. In this case, if the programmer is connected, reverse current will flow from the output to the input to charge C1 (10uF).

The datasheet is not specific how much reverse current will damage the device, only specifying: This reverse current flow can cause damage to the device. Limit reverse current to no more than 5% of the device rated current for a short period of time.

Thank you.

Regards,
Archie A.

  • 0
    TI__Mastermind 37945 points

    Hi Archie,

    The 5% figure was determined in a study done some years ago. It was determined that the pass device could reliably sink ~5% of its rated current without damage, and going beyond the 5% figure starts to introduce risk of damage. So for TPS7A02, the reverse current needs to be limited to 10mA. If PROG_PWR can be brought up at a controlled rate, the magnitude of reverse current can be controlled and this issue can be mitigated. If not, the input cap may need to be made smaller. 

    Regards,

    Nick

  • 0 in reply to Nick Butts
    TI__Genius 13959 points

    Hello Nick,

    Thanks for your response.

    That makes sense and customer will ensure to adhere to the pass device current limit you've specified. One possible solution they're considering it to put D1 in front of C1 as in the diagram attached:


    Is this a better solution?

    Thank you,
    Archie A.

  • 0 in reply to ArTzy
    TI__Mastermind 37945 points

    Hi Archie,

    TPS7A02 does not require an input capacitor for stability, so as far as I can tell this shouldn't cause stability issues. However, this (I think) would make transients worse since the actual input voltage of the LDO isn't held up by the input cap anymore. Maybe it wouldn't make much of a difference, but it would need to be verified on the bench. 

    Regards,

    Nick