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Original question:

TPS2121: ST Pin

TPS2121: Which source is used and the State of ST PIN

Jomon
Intellectual 660 points
Part Number: TPS2121

Voltage on PR1: 1.99V
Voltage on CP2: 1.64V

Which source will be used and what will be the state of ST pin when each of this drops to 0V ?

Thanks in advance

  • 0
    Intellectual 660 points

    Found my own reply

    When those are the voltages observed, IN1 is given priority until the input drops.

    ST pin is low when IN2 is used.

    I observed the issue due to soldering problems on CP2 pin, as the pin was not soldered properly to TPS2121.

    Regards,

    John

  • 0
    TI__Mastermind 32650 points

    Hi John,

    The ST pin works in a way that indicates which input voltage is passed through the output. If IN1 is passed to the output the the ST pin is high. If IN2 is passed to the output then ST is low. This is irrespective of the voltages on PR1 and CP2.

    When both PR1 and CP2 are 0V, the comparator within the device makes the decision on which source to pass by directly comparing IN1 and IN2. The output will be the higher of the two voltages.

    More information on the behavior of the TPS2121 can be found in Table 3 on the datasheet.