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TPS65721: TPS65721 enable DCDC1 & LDO

Part Number: TPS65721

Hello,

Is it mandatory to use the PB1 push press first and then activate HOLD_DCDC1/LDO lines (in this order) to keep powered on the buck and LDO in TPS65721 ?

I would like simply use a permanent switch ON-OFF connected between HOLD_DCDC1 and SYS power to enable the buck/DCDC1 without to use the PB1 push button. Idem for LDO.

Figure 17. PB_IN Timing pg. 30 in DS suggest YES, that should be possible, but I am not sure because it shows the PB press action (required ?) first also.

Also, in this case :

- should I connect pull-down resistor on HOLD_LDO1/DCDC (at switch ON-OFF entry) ? DS says that should be terminated.

- additionally, will any press on PB1 be detected on INT line ?

Thank you

Lucian

  • Sorry, PB1 above I reffer to PB_IN on pin 15
  • Lucian,

        You can pull the HOLD_DCDC1 and HOLD_LDO line to SYS and leave them connected. You do not need pull up or down resistors on these lines. They should be terminated means that you should not leave them floating.

      PB will not be detected on the INT line. The INT line is from tied directly to the state machine and is not affected by pressing PB.

      Finely, yes you need PB_IN pulled low (does need a pull up resistor to SYS) in order to start this PMIC. This is a safety feature that prevents damage to the battery when the battery voltage goes below the minimum threshold. It takes a user to initiate a restart of the system after checking on the battery.

      There is a power-hold pin for DCDC1 (HOLD_DCDC1) and one for LDO1 (HOLD_LDO1). When HOLD_DCDC1 is pulled HIGH, DCDC1 is kept enabled after PB_IN was released HIGH. HOLD_LDO1 serves the same function and keeps LDO1 enabled after PB_IN was released HIGH. After first power-up by pulling PB_IN = LOW or applying voltage at AC, the HOLD pins HOLD_DCDC1 and HOLD_LDO1 can also be used as enable pins, such that they turn on LDO1 or DCDC1, respectively when they are pulled HIGH. This function is available as long as there is a voltage at the battery. After the battery was removed or was discharged, first power-on needs to be done by pulling PB_IN = LOW.

       This is a potential work around TPS65721 PB work around.pdf You need to test and verify this circuit as this is only a suggestion.

    The link to the document looks ok, let me know if you have a problem linking to it.

    Sincerely,

     

  • Thank you, again, Gordon!
    Lucian