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BQ25713: No change in BATDRV when I2C register values are changed

John Nowocin
Prodigy 30 points
Part Number: BQ25713

A new circuit design using the BQ25713 was done. Unfortunately there were some mistakes that are now corrected and we are trying to test. 

I am now able to communicate reliably to the BQ25713 via I2C (thank you tech support from previous case). The issue now faced is that on the circuit board the BattDrv does not change when sending any I2C command. The python script that is being used works as expected on the eval board and is being used it to test the circuit design.

Things to Note from the Schematic:

BMS Schematic.pdf

  • PGnd did not get tied to GND (fixed now)
  • CELL_BATT Presz = 1.5V to be 1S (Voltage Divider of two 10kohm resistors
  • Ilim has been left floating (when tied to a voltage it has a large ringing on the output and battery)
  • disabled via 0x32[7] -ILim is 1.835V on the EVAL Board and 0.167V on mine (left floating and disabled via 0x32[7])
  • Chrg_Ok is good
  • Vsys to BATDRV is a static (-3.2V or -1.6V) and does not move
  • EN_OTG is true (3.3V to the IC Pin)
  • The BatFET (ie. Q10) was originally a N channel mosfet (though it needed to be a P Channel) and the board has been powered several times before this error was realized. It is now corrected to a P channel.

Notes:

  • When Ilim is not floating (ie tied to 3.3V) the Vsys and Vbattery have a noisy decaying sinusoidal signal.
  • When disabled via 0x32[7] then the output of BattDrv is static.

What is the best way to troubleshoot the BattDrv not changing at all?

Could the chip be bad since many incorrect hardware configurations were powered up? If so what is the best way determine it is bad.

Should I configure a new board that has not been powered?

  • 0
    TI__Mastermind 25800 points
    Hey John,

    Some comments:
    1) I don't see any output or input capacitance on your board. Are these capacitors off-page?
    2) You mentioned you corrected the BATFET on the board to a P.Ch but did you also swap the source and drain connections. The drain needs to be tied to SRP and the source needs to be tied to VSYS.
    3) Because ILIM is 0.167V on your board, the charger is in HIZ mode. This automatically enables the BATFET. You will need to program the BATFET_OFF_HIZ bit in the ChargeOption3 register, 34h[1] = 0b1
    4) The REGN capacitance is way too low. It should be at least 2.2uF. Same for VDDA, which should be at least 1uF.
    5) COMP1 and COMP2 networks are backwards. Your current COMP1 network should be on COMP2, and vice-versa for COMP2's current network.


    Regards,
    Joel H
  • 0 in reply to Joel Hernandez II
    Prodigy 30 points
    Thank you a bunch.

    1. Yes, they are off page. The capacitance on the input side is larger than the reference design's 50uF and comes from a more than needed heavy duty regulated supply. The capacitance on the output side will be modified based on the applications final load characteristics and is currently a bit smaller than the reference designs 136uF mainly because the Vsys load is not going to be large.
    2. Yes; P channel source is tied to Vsys, P channel drain is tied to SRP, and P channel gate is tied to BATdrv
    3. Ok, will try that. Just curious, does setting EN_EXTILIM 0x32[7] to 0 disable this HIZ Mode functionality so it does not matter about the ILIM voltage? Is the 0x35[7] a status register to check if it is in HIZ mode or a control register to force it into that operation?
    4 Ok, will find the appropriate larger capacitors and add them.
    5. Oh wow. Thank for this catch.

    I will work on this over the weekend and get back to you on the outcome.
  • 0 in reply to John Nowocin
    TI__Mastermind 25800 points
    Hey John,

    To 3) The ILIM_HIZ pin serves two purposes. One is to set an initial current limit separate from the register setting, such that the charger selects from the lower of either the external pin setting or the register setting. The second is to externally force the converter to shut off and go into a high impedance state (HIZ).

    The EN_EXTILIM bit (0x32[7]) only operates on the first purpose, which is to make the charger only rely on the register set input current limit. However, this does not disable the HIZ functionality which functions when the pin falls below 0.4V.


    Regards,
    Joel H