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BQ76940: Reading value unstable

chentsu chung
Mastermind 6180 points
Part Number: BQ76940

Hi,

To read the voltage value of V5 and V10, we see the voltage are unstable, and we think that should be the voltage drop on the resistor R18/R30 due to power sink from V5 and V10.

And the voltage become stable after modify resister to 100Ohm.

Please check the link below for schematic detail, thank you.

drive.google.com/.../view

Thank you.

C.T.

  • 0
    TI__Guru 54715 points
    Hi C.T.
    I think you are missing power supply resistors at VC5X, VC10X and BAT. I don't recognize them in the schematic.
    At V5/C5 there should be 3 connections for the bq76940: a Rc resistor to VC5, your R30; a Rc resistor to VC5B, your R28; and a Rf resistor to VC5X. All 3 resistors are typically 1k. Without the Rf resistor supply currents will flow from R30 through D16, as these vary with operation VC5 will be loaded and show the unstable voltage you report. When you reduce the resistor the voltage will move less, but the effect will still be present. Please add the resistors for proper operation.
    The same condition exists at V10/C10.
    At the top cell there would be the Rc to VC15 which is your R3, a Rf resistor which may be your R9, and there should be a diode from VC15 to BAT which may be your D6, but R9 and D6 do not look connected properly. Please check your planned connections.