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bq24070 "OUT" start up problem

Rhino
Prodigy 190 points
Other Parts Discussed in Thread: BQ24070

Dear All,

One of my customer is facing a start up problem with bq24070.

For the experiments, they use 10-ohm resisteor instead of system load.

If a battery pack is connected to the BAT pin, OUT pin goes up to 4.4 V with 10-ohm load just after AC adaptor is connected to IN pin.

But if BAT pin is open, OUT pin does not start up from 0 V.

The datasheet describes that "run with an absent or defective battery pack".

Please let me know the reason why OUT pin does not start up without battery connection.

Best Regards,

Rhono

 

 

 

  • 0
    Prodigy 190 points

    Dear All,

     

    I received three kinds of oscilloscope plots from the customer.

     

    4075.bq24070 Start Up_20110308.doc

    I think this will help you to understand the phenomenon.

     

    Best Regards,

    Rhino

  • 0 in reply to Rhino
    TI__Mastermind 32350 points

    Hi Rhino,

     

    In your case, the system load is powered directly from the AC adapter through the internal transistor Q1 (See Figure 5 in the data sheet). The output should be regulated at 4.4 V (bq24070).

     

    On the first application of power to the bq24070/1, this feature enables the 100-mA USB charge rate for a period of approximately 150 ms, (t (BOOT-UP), ignoring the ISET2 and CE inputs setting. At the end of this period, the bq24070/1 implements CE and ISET2 input settings. (See “boot-up” section in page 12th )

     

    For 10 ohm output load, the output voltage is around 1V. If the output voltage drops below ~1 V, an input short-circuit condition is declared and the input FET, Q1 is turned off. But, if there is a battery, the output voltage drops down to the battery's voltage. And If battery’s voltage is much higher than 1V, the charger is not in short-circuit mode.

     

     

    Best Regards,

    Tahar Allag