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TL1963A-Q1: TL1963A-Q1 output voltage in shutdown mode is not zero.

user5113602
Prodigy 160 points
Part Number: TL1963A-Q1
Other Parts Discussed in Thread: TL1963A

Dears,

   I use TL1963A-Q1 to convert 13.5V input voltage to 12V output voltage, with the ShutDown pin of TL1963A-Q1 being controlled by external controller. Please see the schematics below.

When the ShutDown pin is pulled low and the IN pin is 13.5V, I get 1.59V at the OUT pin which is expected to be zero or a very low voltage. Could you please explain why there is a relatively high voltage at the OUT pin while I pulled down the ShutDown pin?

  When I put a parallel resistor of 1k ohms to the OUTpin, I get a voltage of about 0.2V.  So I think it might be the leakage current that makes the non-zero output voltage. But it does not make sense since the leakage current is only several amperes when in shutdown mode by the datasheet.

Thank you very much.

Regards,

Tang Yaosheng

  • 0 in reply to user5113602
    TI__Genius 10200 points
    Hi Tang Yaosheng,

    The output voltage remaining high is likely due to the TL1963A-Q1 or a downstream component providing a fixed amount of current. Adding a load resistor draws some of this current away from the output capacitors, resulting in a lower output voltage. If TL1963A-Q1 is not quite in shutdown mode, the pass device can still allow some current through to charge the output capacitors. This possibility can be confirmed or eliminated by measuring the shutdown pin voltage. If the voltage is less than the low-level threshold of 0.25 V, the device is in shutdown mode, and a downstream component is likely providing the current that is holding up the output voltage. If possible, disconnect all loads from the output of the TL1963A-Q1, ensure that the shutdown pin is low, and measure the output voltage. If it is still relatively high, the TL1963A-Q1 is the root cause. If not, a downstream component was responsible for holding up the output.

    Thanks,
    Gerard
  • 0 in reply to Gerard Copeland
    Prodigy 160 points

    Hi Gerard,

        Thank you very much for the replying.

    I disconnect the downstream components and repeat the tests again. When input 13.6V and pull down the ShutDown pin(0.13V measured), the output becomes 1.99V, and it is still 1.99V even when the ShutDown pin is short to ground.

    Regards,

    Tang Yaosheng

  • 0 in reply to user5113602
    TI__Genius 10200 points

    Hi Tang Yaosheng,

    Your initial thought was correct - the output voltage is the result of leakage current through the pass device. The TL1963A and TL1963A-Q1 can show leakage currents of up to 100 uA for high input voltages. As such, the output voltage during shutdown can be reduced by decreasing the size of the feedback resistors. Please see the following thread for more information:

    https://e2e.ti.com/support/power-management/f/196/p/680165/2505213

    Thanks,

    Gerard