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TPS23523: TPS23523 datasheet spec might need correction

Wenhao Wu
Genius 9046 points
Part Number: TPS23523
Other Parts Discussed in Thread: CSD19532Q5B

Hi team,

Description:

(1) When testing GATE2, I found the really sourcing current is 5mArather than 50uA, please kindly comment on this.

(2) Please refer to datasheet Figure. 12. As datasheet noted, when load current increases, BGATE has to rise to lower Rdson to mimic 25mV drop on Oring MOSFET. However, I found that when the current increases, BGATE will drop conversely from Figure. 12. When current grows, Rdson*I_IN will increase, resulting in Neg48 decreasing. In this occasion, AMP will bring its output down, so that BGATE will tend to act to push MOSFET close, which is apparently contradictory with what has been noted in datesheet.

Therefore,

(1) Please kindly point out the real sourcing current of GATE2;

(2) Please kindly check if AMP's input polarity has been rightly drawn. Thank you very much!

-Wenhao

  • 0 in reply to Wenhao Wu
    TI__Guru** 105361 points
    Hi Wenhao,

    I will look into it and get back to you.

    Best Regards,
    Rakesh
  • 0 in reply to Rakesh
    TI__Genius 9046 points
    Hi Rakesh,

    Could you please give an answer before this Friday? Sorry by pushing you, but this is really important to my customer. Thank you for your great help!

    -Wenhao
  • 0 in reply to Wenhao Wu
    TI__Guru** 105361 points
    Hi Wenhao,

    (1) Please kindly point out the real sourcing current of GATE2
    How you measured the GATE2 sourcing current?

    (2) Please kindly check if AMP's input polarity has been rightly drawn.
    your interpretation is correct. when load current increases, BGATE has to rise to lower Rdson to mimic 25mV drop on Oring MOSFET. We will look into polarity and take action in the next datsheet revison

    Best Regards,
    Rakesh
  • 0 in reply to Rakesh
    TI__Genius 9046 points

    Hi Rakesh,

    I did not directly test sourcing current. Instead, I calculated it, please see waveform below. When test 23523's EVM, in terms of GATE2, it takes ~11us for csd19532q5b Vgs to reach 15V. In addition, csd19532q5b's Ciss is 3.7nF. Calculate current using C*dv/dt, approximately sourcing value is 5mA rather than 50uA.

    Further more, could you please clarify the purpose of the comparator circled in red? Does it mean that when load current rises too fast and Oring MOSFET is substantially preventing current to increase, BGATE will be triggered to be high with 1.5mA sourcing current(15V/10kOhm)?

    Thank you for your great help!

    -Wenhao

  • 0 in reply to Wenhao Wu
    TI__Guru** 105361 points
    Hi Wenhao,

    The effective capacitance at GATE2 will be lower than 3.7nF as the main FET is already ON and VDS=0V. Ideal way to measure is place a 10nF at GATE2 and capture the waveform.

    The comparator marked in the picture is the FWD-FAST (forward-fast) comparator for BGATE. During startup the body diode of the OR-ing FET provides the path for the fast rising load current, the forward drop across the OR-ing FET will be high. So, the controller quickly turns ON the OR-ing FET with 1.5mA sourcing current(15V/10kOhm) to reduce stress on the body diode of the OR-ing FET.

    Best Regards,
    Rakesh