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BQ24715: PWM Converter Startup Issue

Carl Gallenson
Prodigy 210 points
Part Number: BQ24715
Other Parts Discussed in Thread: BQ24707

Hello,

I am using bq24715 for a battery charger for a 3S Li-ion battery.  It is charger only with no system power output.

Vin and Vcc are 19V.  I am not using CMSRC and ACDRV with input FETs, ACOK and ACDET are just pulled up to 3.3V.  

This is similar to the circuit I used successfully in the past with bq24707 but in the new circuit I do not see any PWM switching activity.

Charging voltage is set to 12.6V, charging current is set to 1024mA.  Cell is pulled up to 3.3V.

I am able to read back from the Charge Option and Minimum System Voltage Registers, so SMBus Comms appear to be OK

The following voltages were observed:

Vin: 19.09V

Vcc: 19.08V

ACDET: 3.29V

REGN: 6.03V

HIDRV: 9.29V

LODRV: 0V

ACOK: 3.3V

BTST: 9.04V

ACN: 19.08V

ACP: 19.08V

SRN: 9.29V

SRP: 9.29V

PHASE: 9.29V

Circuit Schematic

Can you see a reason why the PWM converter would not start up switching?

Thank you,

Carl G.

  • 0
    TI__Mastermind 25800 points

    Hey Carl,

    Can you try adding between 100kOhm and 500kOhm between ACDRV and CMSRC?

    Its possible the charger is trying to enable the ACFET/RBFET, but since they are not present and the pins are floating, ACDRV does not rise >0.2V above CMSRC and does not enable the converter. 

    Regards,

    Joel H

  • 0 in reply to Joel Hernandez II
    Prodigy 210 points

    Hi Joel,

    Thank you for your reply.  We found that CMSRC needed to be pulled up with a resistor to the input voltage in order to enable the converter.  No connection appears to be needed at ACDRV since we are not implementing the FETs.  But it was a mistake to leave CMSRC floating as you suspected.

    The bq24715 is now charging and we are proceeding with our firmware debug.

    Regards,

    Carl G.