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bq24040 TS operation

Argail
Expert 2080 points
Other Parts Discussed in Thread: BQ24040, BQ24041

Hi everyone,

I'm having some interogation about the the bq24040 battery charger.

What I want to do is:

- TS "controlled" by a NTC during normal operation

- TS pulled low by a MSP430 uC if software safety timer exceeded

- MSP430 completely OFF during cut-off -> interfacing with bq24040

I was thinking to put the I/O of the MSP430 as input  for normal operation and as output low only for disabling the bq24040 (I/O resets as input when wall charger removed; !PG status pin). But, during the cut-off protection, the MSP430 could be completely OFF, how will act the TS pin if the MSP430 is powered down, I don't want to stuck the battery charger in disable mode while the cut-off protection...

The !BAT_EN pin of bq24041 should work as I want, this pin is active low, so the charger is enabled when the MSP430 is OFF.

Moreover, whath happen with the !PG pin while the uC is shutted down? It is an active low output, so output a "1" while there is no input voltage, this "1" will go on a disabled uC, will this create any problem? 

!PG pin could be in Pull-Up by the voltage applied to the MSP430, but is there a "start up" problem in this case? In fact I'm asking me if it is a "good" solution to pull-up the two bq24040 status pin by "software" through an output pin of the MSP430....

  • 0
    TI__Mastermind 31120 points

    I not totally clear on what you want so I will through out some ideas and see if it helps.

    First, it the charger's timer expires and goes into fault mode, the charger will most likely stay in this mode.  Is the purpose of pulling the TS pin low, after a timer fault, to reset the timer and continue to charge?  If so....

    If the MSP430 is connect to the TS pin as an "open drain", the processor can drive the TS pin low and then high to start a new charger.  If the processor gets cut-ff, then the connection to the TS pin should be an open drain so the charger can power up when an input source is available.

    The OR gate is a way to enable a system with the ASO signal once a power source is available.  This could be used to sequence an event after the charger power is applied.

    Maybe a block diagram and a flow chart would be helpful in understanding your requirements.

  • 0 in reply to Charles Mauney
    Expert 2080 points

    Thank you for the reply and sorry not to be clear enough, The answer at your first question is no.

    The battery planned to be used is specified with a maximum charging time of 3 hours, so the 10 hours safety timer integrated in the bq24040 should be too long. What I want to do, is to make a software timer with the MSP430 wich will disable the charger while the 3 hours timers has expired.

    This will be something like that:

     "if (!CHG==0)> 3 hours then

               y.PxDIR=1, y.PxOUT=0 (x.y is connected on TS, force disabling the charger)

              display "Error" (show the user that an error happens)

     until (!PG==1) (resume charger operation if wall charger retired -> in use condition TBD)

              y.PxDIR=0 (x.y as input, for nominal operation -> let the NTC control the charger)"

     The circuit will looks like something below:

    CVCC will power the !PG and !CHG pull-up only while uC is ON and in a known state after reset. TS will force the pin down to disable the charge, and is set as input for normal operation.

    Here is the question: what happens if the uC is powered off due to cut-off protection and the pin previously set to "input"? Will the TS pin always be down and the charger OFF or should I add an interface to works as I want?

    Hopping to be clear enough this time:)

    Best regards

  • 0 in reply to Argail
    TI__Mastermind 31120 points

    If the TS pin has been pulled low the charger is disabled but as long as there is a valid input voltage the TS current source will be on delivering ~30uA, when low, so if the pull down on the TS pin goes away, the IC will turn on and start a charge routine if needed.