• State TI Thinks Resolved
  • Locked Locked
  • Replies 1 reply
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 686 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ24450: The battery charger works but I am unable to get the Status lines to show the correct state.

Robert Cohen
Prodigy 80 points
Part Number: BQ24450

I have design a circuit on a PCB and it works well.

The datasheet states that the Stat1 and Stat2 are open-collector outputs. Therefore I assumed they needed to be pull-up. I have tried several times to pull-up the signal with a 100 k ohm resistor but I still do not see any state changes.  I know I am changing states because I can monitor the current draw via R14.

Another observation is that in the datasheet it shows Stat1 connected to the VFB pin.   I would assume that if I add a pull-up on this signal I might distort the VFB signal.  My testing confirmed this and I have removed both pull-up resistors from the status lines.   Stat2 is connected directly to an Atmel D20 processor and I want to connect Stat1 so I can monitor the charging status.  What do suggest I do to allow me to monitor these status lines without effecting the battery charger chip.  

As a side note we have seen current as high as 409mA  and we have 0mA when the battery is fully charged. The applied voltage has been as high as 14.5 volts.  The  14.5 is coming from a Buck regulator.

Thank you,

Rob

  • 0
    TI__Guru* 75656 points
    Hi Rob
    One approach to the STAT1 and STAT2 lines would be to feed them directly into the processor then have the processor drive an external mosfet for the signal lines. This would give you a clean digital signal from BQ24450 and the external mosfet would give a good analog signal for the circuit.
    As you pointed out STAT1 is connected to VFB, could cause control issues. An alternate signal to look at is ISNS pin it will transition at the same time as STAT1 and is less sensitive. But current source on the signal is low, direct connection difficult.
    Does the processor have an ADC, would it be possible to monitor signals?
    One possible cause of the detection problem you are seeing above is the low and high signal levels provided by the BQ24450, looking at the V-SAT for STAT1 and STAT2 the voltage on the pin is on the high side for relatively low currents.