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TPS25221: questions about how to use the device

Noriyuki Takahashi
Genius 11020 points
Part Number: TPS25221

Tool/software:

Hi team

There are several questions. Could you help these?

1. Based on the datasheet, it seems TPS25221 has the inrush current protection. However I can't see any ways to adjust the amount. Could you tell the calculation of this?

2. The values of R_FAULT in the several figures in the datasheet are different. Could you tell how to decide the recommended R_FAULT?

3. It seems /FAULT pin needs to be connected to EN-pin like figure 27 and 28 in order to make the device Auto-retry mode. Is this connecting /FAULT pin and EN-pin required to  to make the device Auto-retry mode? Are there any ways to get the mode without the connection?

Regards,

Noriyuki Takahashi

  • 0
    TI__Genius 11285 points

    Hi Takahashi san,

    You can set RILIM to set the current limit of TPS25221.  This current is the output from the IC/input to the USB sink device.  The formulas to calculate this are on the bottom of page 13 of the datasheet.  There is a corresponding graph on page 14.

    /FAULT is an open drain output.  The exact value is not important.  Anything from 10k-200k is fine.

    Shorting /FAULT to EN is the easiest method.  If you are using an MCU to monitor /FAULT and control EN, you can simply program the MCU to toggle the EN pin when FAULT is present.  If you fix EN as high and an overcurrent event occurs, I expect the device will enter constant current operation according to RILM until reaching thermal shutdown.  After the die detects <145C, it will retry without intervention (refer to datasheet section 9.3.5).

    Regards,
    Eric

  • 0 in reply to Eric Hartigan
    TI__Genius 11020 points

    Eric,

    Eric Hartigan said:
    You can set RILIM to set the current limit of TPS25221.  This current is the output from the IC/input to the USB sink device.  The formulas to calculate this are on the bottom of page 13 of the datasheet.  There is a corresponding graph on page 14.

    Does this mean that the inrush current protection of this device is the current limit function and is not same with efuse devices? I mean efuse devices have adjustable slew rate (dVdt) for inrush current control, but does this device have the adjustable slew rate function?

    Regards,

    Noriyuki Takahashi

  • 0 in reply to Noriyuki Takahashi
    TI__Genius 11285 points

    Hi Takahashi san,

    TPS25221 limits current going out of the downstream facing USB port.

    I'm not an eFuse expert, but my understanding is that it is traditionally used to limit the current in from the upstream facing USB port.

    Here is an application report on the different switch topologies.  It will help determine the best type of switch for your application.  https://www.ti.com/seclit/eb/slyy168/slyy168.pdf

    Regards,
    Eric