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BQ24092: Using TTDM mode without NTC or uC

eric Tremblay
Prodigy 20 points
Part Number: BQ24092
Other Parts Discussed in Thread: BQ24074, , TPS22914

Hi,

In my application the battery does not have a thermistor, so i put a 10K resistor between TS and VSS to disable that feature.

However, i would like to be able to put the chip in TTDM mode in a standalone way. I dont want it to depend from my uC.

Is there a way to accomplish that by maybe using the CHG pin ?

Thanks for your help

  • 0
    TI__Guru 68686 points
    With no connection to TS unit will be in TTDM mode. But you do not want TTDM all the time, only a battery absent mode?
    CHG is not a good indicator of battery absent, will indicate first charge but not recharge.
    Another device to consider is BQ24074, this is a power path device that will charge battery and service load at the same time.
  • 0 in reply to Bill Johns
    Prodigy 20 points
    Maybe my understanding of the TTDM mode is not accurate.

    What are the limitation if i'm always using the TTDM mode ?

    if by letting TS floating i can disable the temperature sensing, charge my battery when it is present and power my system when it is not. It seems the perfect case for my application.

    Otherwise i may be look for the BQ24074 it is however a little bit more expensive.

    Thanks for your help
  • 0 in reply to eric Tremblay
    TI__Guru 68686 points
    Hello
    When in TTDM the BQ24092 will act a lot like a power supply. Output voltage will be 4.2V and current is battery charge current, set by ISET or ISET2.
    Unit will go thru normal charge if battery is present but not turn off after termination, voltage remains on battery. May want to confirm that this is acceptable for cell manufacture.
    Things to watch out for is the start up current needs to be low, pre-charge and short current is limited. Once output voltage is above 2.5V full current is available. A switch can be used to isolate load at start up, TPS22914.