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BQ78350-R1: Issues with my batterymanagmentsystem (BQ78350-R1 and BQ24617)

Paul K52
Intellectual 640 points
Part Number: BQ78350-R1
Other Parts Discussed in Thread: BQ76920, BQSTUDIO, BQ24617

BQ78350-R1

1. issue: My Batterymanagmentsystem can work with 4 cells. The BQ76920 can work with 5 cells. As described in the datasheet of the BQ76920 on page 46 I have to short pin VC4 and VC3, if I want to work with 4 cells.

But now in the AFE Cell Map Register, which I can see in BQStudio, there is only CELL_5, CELL_2 and CELL_1 in onstate. Normally I would expect that CELL_4 would also be in onstate.

So I tried to change the state of CELL_4 from 0 to 1. But than BQStudio is loosing connection with the BQ78350-R1 and I cant get connection anymore?

Was it correct to connect VC4 and VC3 together?

What can I do now? Must I replace the BQ78350-R1?

BQ24617

2. issue: When Im charging the battery I should see that the Pin STAT1 should be HIGH and STAT2 should be LOW?

In my case its the other way arround. In my case STAT1 is LOW and STAT2 is HIGH, while im charging?

What could be the problem here?

3. issue: The Batterymanagmentsystem is connected with BQstudio. Imt trying to calibrate the voltage and the current. It is said that I have to have at least 1 A flowing through the load.

What kind of load are you using to simulate these current? Obviously I cant use resistors because the maximum power dissipation of resistors is to low.

4. 

2. issue: I have a problem with the charge current. I decided to choose a RSR-Resistor with a value 0.05 Ohm. This should give me a charge current of 2 A.

Because: I_charge=Viset1/(20*RSR)  => 1/(I_charge*20)*Viset1=RSR => RSR=1/(2*20)*2=

But my system is only charging with 120 mA.

I measure the maximum voltage of 2 Volts at ISET1 and ISET2.

Which reasons could there be, that restrict the charge current.

  • 0
    TI__Guru 54715 points
    Hi Paul,
    For the bq78350-R1: Several questions, the answers may not be in your order.
    Because of the common mode capability of the bq769x0 inputs, the top cell of each group should be used when reducing cell count. See the bq76920 EVM user guide section 6.3. www.ti.com/.../slvu924c.pdf Of course if you are building your own board you may not have read it.
    If you set the AFE Cell Map to 0x001B with VC3 to VC4 shorted, the gauge will not see a voltage on cell 4 and shut down.
    Shorting VC3 to VC4 is the correct connection according to the bq76920 data sheet.
    The AFE cell map provides a mapping from physical connection to logical cells. Default is 0x0013. For 4 cells with the recommended connection select cell 3 also or 0x0017.
    To change the configuration, as noted the user guide, apply a simulated charge current before booting. The gauge will stay awake and allow you to correct the configuration. A few mV on SRP is sufficient.
    I will see if someone can help with your charger questions. In future posts response may be faster if you separate the monitor-gauge and charger questions.
  • 0 in reply to WM5295
    Intellectual 640 points

    I have connected it like this:

    If I have understood you correctly, the next step would be to configure the AFE Cell Map register to 0x0017. So Cell 5, Cell 3, Cell 2 and Cell 1 should be High.

    Correct?