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BQ2970: Battery protection design not working

Mike Rankin
Prodigy 35 points
Part Number: BQ2970

Can someone please tell me what I did wrong on my battery protection design? The 18650 battery charges normally measuring around 4v or so but VBAT always measures around 1.4v. It is possible the dual mosfets are the wrong type but they have a Vgs of 1v.

Parts used are:

TI BQ29700DSER: www.digikey.com/.../5973209

Vishay SI1922EDH-T1-GE3: www.digikey.com/.../3679992

  • 0
    TI__Guru 54715 points

    Hi Mike,

    I don't recognize a problem.  TI recommends the Rgs resistors  but the part works without them.

    Check that the layout put the pins where you expect for all the chips.

    When charging be sure COUT goes high, check that the charger takes GND below VSS of U3.  Shorting across the FETs should also put the part in normal operation mode. Watch what happens to COUT and DOUT when the charger is disconnected.  A transient could but the BQ2970 in fault mode, but it would seem unlikely.

    If it is a new build try another board, if it is one of a kind, try different parts to see if it might be a damaged part in handling or assembly. 

    Monitoring the circuit is interesting as the BQ2970 has voltages defined from VSS, most of the system sees voltages with respect to GND.