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TPS709: Reverse current and output behavior

MarcB
Genius 11160 points
Part Number: TPS709

Can you please help to answer the following question that came up during the design phase?

1 . What is the maximum reverse current depending on the temperature?

Do you have a graphic or at least maximum values for this?

In the data sheet we found only the typical indication of 100nA:

2. How does the LDO behave when the input voltage is lower than the desired output voltage (3.3V), or when the minimum dropout voltage cannot be guaranteed? Is the max. output voltage simply delivered?

3. What does it look like if a higher voltage «pressed on" at the LDO output from another voltage source than the LDO itself controls?

Can the specified reverse current be expected or are there side effects (higher leakage currents)?

Thank you!

  • 0
    TI__Mastermind 37025 points

    Hi Marc,

    Please see my answers to your questions below.

    1. I spent some time reviewing the archives on this question but I was unable to locate any additional data.  I would suggest taking an EVM and making measurements at the customers specific Vin and Vout, and temperature, to obtain the values they will see in their application.

    2. When the Vin drops below Vout or the minimum dropout voltage cannot be guaranteed, the device is unable to maintain regulation on the output, and it is operating in dropout.  The output voltage will then droop as a function of load current until it settles at Vin - dropout, but it will still be operating in dropout.  Transient performance is very poor in dropout, as well as PSRR.

    3. From section 7.3.4 in the device datasheet:

    "The reverse current protection is always active regardless of the enable pin logic state or if the OUT pin voltage is greater than 1.8V.  Reverse current can flow if the output voltage is less than 1.8V and if input voltage is less than the output voltage.  If voltage is applied to the input pin, then the maximum voltage that can be applied to the OUT pin is the lower of three times the nominal output voltage or 6.5V.  For example, if the 1.2V output voltage version is used, then the maximum reverse bias voltage that can be applied to the OUT pin is 3.6V.  If the 5.0V output voltage version is used, then the maximum reverse bias voltage that can be applied to the OUT pin is 6.5V."

    Thanks,

    - Stephen

  • 0 in reply to Stephen Ziel
    Prodigy 40 points

    Hi Stephen

    Many thanks for your effort and your answer. These questions originally comes from me.

    1. It is a pity that there is no data on this, but then we have no choice but to measure it.

    2. That's ok for our application, because we require very less current (max. 3mA) so the dropout will stay also low.

    3. In this case this means the reverse current protection is running and as soon as the voltage at the output is back at the nominal output voltage the LDO will regulate the output as in normal operation.

    Thanks a lot for your support and kind regards,

    Ueli