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TPS2378: The APD function of TPS2378

chentsu chung
Mastermind 6180 points
Part Number: TPS2378

Hi,

For the external adapter application as the picture below

1. If TPS2378 get power source only from external 12V adapter, then TPS2378 get 12V at VDD and about 1.5V at APD, is those voltage could make TPS2378 turns off internal hot swap MOS?

2. If yes, then what is the minimum VDD and APD voltage could make internal hot swap MOSFET tures off?

(what is the minimum voltage for external adapter )

3. What is the exactly condition for APD function? Only APD voltage above 1.5V? Or need VDD for internal logic usage?

Thank you,

C.T.

  • 0
    TI__Genius 9230 points

    Hi Chentsu,

    1. Yes. As long as the APD rising threshold of 1.5V is met, then the internal hotswap FET will turn off.

    2 & 3. Let me get back to you on this.

    Regards,
    Tom Amlee
    PoE PD Apps Engineer

  • 0 in reply to Thomas Amlee
    TI__Genius 9230 points
    Hi CT,

    At any Vdd-Vss operational voltage above the rising UVLO (when the hotswap FET turns on), APD turns off the hotswap FET regardless of the voltage at Vdd-RTN.

    When Vdd-Vss is below its falling UVLO, the hotswap FET would not be conducting, so APD does not apply here.

    Regards,
    Tom Amlee
    PoE PD Apps Engineer
  • 0 in reply to Thomas Amlee
    Mastermind 6180 points

    Hi Tom,

    According to datasheet, the rising UVLO is 38.1V, so only the 12V adapter plug-in won't makes hotswap FET turn off?

    Here's a scenario:

    a) Using 12V adapter without PSE source: TPS2378 doesn't get enough VDD(38.1), so TPS2378 no functioned, so hotswap FET equal to off, and PWM portion work well due to the adapter power.

    b) Then PSE source plug-in: TPS2378's VDD get powered and turns hotswap off due to APD voltage, so it's still Adapter Preference, PWM portion works well.

    am I right?

    Thank you,

    C.T.

  • 0 in reply to chentsu chung
    TI__Genius 9230 points
    Hi CT,

    The rising UVLO is referring to the VDD-VSS (PoE input), only. Not Vdd-RTN, where you would attach your primary side 12V adapter.

    a) Correct

    b) Correct

    Thanks,
    Tom Amlee
    PoE PD Apps Engineer