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TPS929240-Q1: VBAT and SUPPLY power connections

Giacomo Barbero
Prodigy 20 points
Part Number: TPS929240-Q1

To whom I may concern,

I am design an automotive application where quiescent current is critical. 

Since leakage current from VBAT pin is quite high (2mA, page 6 of datasheet), I connected such pin to a dedicated net which is turned off when MCU is entering sleep mode.
Meanwhile, on SUPPLY pins quiscent current is acceptable (5uA, page 6 of datasheet) therefore I left such pins connected to permanent battery voltage.

My question are the followings:

  1. are there any risks in having SUPPLY pins powered ON while VBAT is powered OFF?
  2. May this configuration damage the chip internally?
  3. Is it prefereable to have VBAT and SUPPLY pins tied together and connected to a switchable power source?

Regards

  • 0
    TI__Genius 15430 points

    1&2, no risk. While device will run into POR status. 

    3. You may tie them together or separate them flexibly. Generally, DC DC before SUPPLY Pins provides regulated voltage and helps to improve efficiency. Battery voltage varies always and increases overall power loss at high voltage, or can't provide regulated current at low voltage. 

    What is frequency of switchable power source? And the purpose? Please note that there is initial time for VLDO set up and internal state machine.   

    You may also consider TPS929160, which can run into sleep mode and reduces quiescent current with NSTB/EN control pins. 

  • 0 in reply to Xiaoguang1
    Prodigy 20 points

    Hello Xiaoguang1,

    thanks for your reply, very clear. When I wrote "swtichable power source" I didn't mean a DCDC. Basically we have car battery which is pemanently   connected to SUPPLY pins while VBAT pin is connected to the same car battery by mean of a P-mos in order to switch it on or off indipendently.


    Hope it is more clear. Let me know if after my clarification you still do not see any issue in the design, so that I can mark my question as "resolved".


    Regards

  • +1 in reply to Giacomo Barbero
    TI__Genius 15430 points

    It is OK to use in this way.