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TPS7A49: [TPS7A4901] Questions about discharging operation

Kwonjoon Lee
Prodigy 110 points
Part Number: TPS7A49
Other Parts Discussed in Thread: TPS61288

Tool/software:

Hello.
This is Kwonjoon Lee from South Korea.

I would like to ask about a discharging operation of the TPS7A4901.

(Detailed Situation)

1. The VIN of my TPS7A4901 is connected to the output of TPS61288 (boost converter)
2. The EN of my TPS7A4901 is connected to the VIN.

(Questions)

1. In the case that a voltage of the VIN of my TPS7A4901 is rapidly decreased by
    the TPS61288's disabling (the EN pin of the TPS61288 = Low), and
    the VIN of the TPS7A4901 is lower than the VOUT of the TPS7A4901,
    what is a main discharge path of my TPS7A4901's output?

    I think that I have the following three candidates for discharging path:

   1) a power clamp diode (or a PN diode of the internal PMOS pass transistor) between the VOUT and the VIN of my TPS7A4901
      (what is the maximum allowable current?)
   2) the feedback resistances of my TPS7A4901 (a few tens of kohm)
   3) a load of my TPS7A4901's output (light load)

2. I would like to ask the discharging operation of the TPS7A4901 (and TPS61288) is modeled in the SPICE model for PSpice for TI?

Best regards,
Kwonjoon Lee

  • +1
    TI__Mastermind 47335 points

    Hi Kwonjoon,

    The possible discharge paths are the ones that you listed; the load is normally the main discharge path. If the LDO input collapses quickly and the condition VOUT > VIN occurs, current will conduct through the body diode of the pass device as you mentioned. We recommend limiting this current to 5% of the device rated current. In cases like this where the reverse current is not limited by a substantial amount of resistance, it's best advised to protect the device with a diode from OUT to IN to provide an alternative current path so that the channel does not conduct in the reverse direction. The PSPICE models likely will not show accurate transient details like this because they are behavioral models and are not directly modeled with transistors. 

    Regards,

    Nick