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BQ29700EVM-610: BQ29700

Jeffrey Adams
Prodigy 10 points
Part Number: BQ29700EVM-610

I am having trouble with the BQ29700EVM-610 eval board.  I have three of the eval boards.

I have attached a NCR18650GA Li-ion battery connected to each BQ29700EVM-610 board with a battery holder.  The wires from the battery holder are short and are 18AWG.

https://www.imrbatteries.com/sanyo-ncr18650ga-3500mah-10a-flat-top-battery/

I have not been able to make the TI eval boards play nicely. 

I have placed a 8000 ohm resistor across PACK+ and PACK-   to simulate a small current draw    (approx 4VDC / 8000ohm ==  0.5mA)  I am able to measure the cell voltage across this small load.

Then I VERY briefly attach a 2 ohm non-inductive resistor across this this same load   (approx 2 Amp draw)   to simulate a short RF transmission.   The voltage between PACK+ and PACK-  goes to zero on each eval board.  Removing the 2 ohm load does NOT make the voltage reappear between PACK+ and PACK-  and the eval board does not recover.

The measured cell voltage is 3.88VDC  (CELL+   CELL-)        The output (PACK+  PACK-) does NOT return to 3.88VDC after removal of the load.

Briefly placing a charge on the output (PACK+  PACK-)  returns the output to the cell voltage.

I have also removed the battery holder from one board and soldered 2” of 18AWG red and black wire directly to the cell, thinking it might be contact resistance of the battery holder.  This also did not solve the problem of the voltage disappearing when a 2 ohm load is briefly attached.  The eval datasheet says I shoulld be able to operate up to 5A of current draw.

What am I doing wrong?

Thanks, Jeff        jadams@mcqinc.com

  • 0
    TI__Guru 54715 points
    Hi Jeff,
    The EVM terminals are rated above 5A and the FETs are rated at 5A, but the circuit may trip at a lower current based on the RDSON of the FETs at the applied voltage.
    You may try applying a higher resistance/lower current to see if that current allows continued operation. If you have access to an electronic load try to apply current to the cell to see where the part trips. If you have pulse measurement capability you might apply your load and see what current is applied and where the IC trips to know if it is an over current protection or short circuit.
    Since recovery depends on the pack voltage returning near normal (see the data sheet), it may require connection of a charger to restore voltage after the fault since the 8k load is present. The charger must power the 8k load to restore voltage to the PACK terminals.