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BQ25100: Using the BQ25100 without a battery?

Boyer Jeff
Prodigy 70 points
Part Number: BQ25100

I'm using the BQ25100 as a lithium battery changer and also as to provide power to the design. There are times when a lithium cell will not be needed. So how do I make sure the BQ25100 voltage out remains with in range with or without a lithium cell? 

  • 0
    TI__Guru 65846 points
    Hello
    The BQ25100 has a mode call Termination and Timer Disable Mode (TTDM). In this mode the device acts similar to a power supply and is intended for conditions where the battery is removed.
    To enter this mode TS pin needs to be pulled high or float.
    For more info see section 8.4.5 of data sheet.
  • 0 in reply to Bill Johns
    Prodigy 70 points

    Bill, I find your answer much clearer then section 8.4.5 of the spec. If I let TS float to support no battery operation, does that mean I must give up the function of the thermister? Below I show the charger circuit which can use a 10K or a thermister. Right now the 10K is populated.

    Thx for your help.

     

     

  • 0 in reply to Boyer Jeff
    TI__Guru 65846 points
    Hello
    On the TTDM mode also take a look at FAQ:
    e2e.ti.com/.../762756

    The TS pin and TTDM, plan was to removed battery pack with NTC this would float TS and enter TTDM.
    But if NTC is on PCB and battery can be removed independent of the NTC ALSO want TTDM and Temp monitor -- You could pull TS high, above 1.6V to trigger TTDM. Would need some way to tell the battery has been removed to pull the pin high. When battery is installed this drive circuit would float and let the TS current source drive NTC.
  • 0 in reply to Bill Johns
    Prodigy 70 points

    Bill, 

    I finally got around to testing what you recommended for my battery removal problem by removing the 10K to GND from TS (B1) and letting TS float. But that didn't work. With 5V on VIN (A2) and no battery connected, I get 1.76V on VOUT (A1). This voltage is to low to run the board. With a battery connected VOUT is 4.24V and the BQ25100 does seems to be working. I have tested several charge/discharge cycles and both charge current and voltage on the battery seem to be correct.

    Also the TS pin is definitely floating with the voltage on this pin at 1.98V. The resistance of this floating pin to ground with my VOM is infinite with the positive terminal on the TS and about 5.8M with the negative terminal on TS.

    When I start the board up without the battery, the board does run for a few seconds, but VOUT quickly fad to 1.76V. At that point I can connect the battery and everything then seems to function properly.

    So what am I doing wrong? Do I need to pull TS high via a resistor? If so what rail do I connect this pin too? The output of the BQ25100 or the input of BQ25100 (5V)?

    Jeff

      

  • 0 in reply to Boyer Jeff
    TI__Guru 65846 points
    Jeff
    What you could be seeing is a battery Pre-Charge condition where the output current is limited. Below 2.5V the current is limited to about 20% of fast charge current. If a system load is applied at start up the device may not make it out of pre-charge.
  • 0 in reply to Bill Johns
    TI__Guru 65846 points
    Hi Jeff
    Any update on this one?
  • 0 in reply to Bill Johns
    Prodigy 70 points

    This issues is resolved... Thx