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BQ25713: BQ25713 I2C Programming is failing when it is only connected to battery

Part Number: BQ25713
Other Parts Discussed in Thread: EV2400, BQSTUDIO


We are using  BQ25713 as part of main charge control IC in our battery back up based design.

Battery used is 2-terminal 3SP1 with 10.7V as max voltage. 

We are using following register setting

ChargeCurrent() [Reg 0x03/02] - 1A

ChargeVoltage() [Reg 0x04/05] - 10.7V

InputVoltage() [Reg 0X0B/0A] - 2V

IIN_HOST() [Reg 0x0F/0E] - 3.3A

MinSystemVoltage() [Reg0x0D/0C] - 10.7V

When we do I2C programming of BQ25713 using Main power supply(12V) , I2C communication will happen and we are able to read the register, however when we disconnect Main power supply and connect only battery, I2C programming of BQ25713 is failing(all the I2C voltage levels are as expected), and we will not able to read any register.

We are observing this issue in not all the boards but almost on 20% of the boards.

OTG/VAP signal is set high ie 3.3V

When only Main is connected,

ILIM_HIZ - 1.21V



CHRG_OK - 3.3V

When only battery is connected,





Board -2 OTG EN =1  OTG EN =0
  Only Main Only Battery Only Main Only Battery
OTG/VAP 3.3V 3.3V 0V 0V
CHRG_OK 3.3V 0V 3.3V 0V
ILIM_HIZ 1.21V 0V 1.21V 0V
REGN 6.4V 0V 6.4V 0V
VBUS 12V 1.5V 12V 1.5V
VSYS 10.7V 9.5V(Battery v- 10.2V) 10.7V 9.5V(Battery v- 10.2V)

Could you please help us to solve this issue or give us a direction .

Best Regards,

Sudha Nayak

  • Hi,

    I kindly request your suggestions, to solve this issue.

    Best Regards,

    Sudha Nayak

  • Hi, Sudha,

    Could this be related to the 3.3V rail? I2C is an open-drain communication protocol, which needs a separate 3.3V pull-up when it is powered by an adapter or a battery. A schematic is needed to look further. 

  • Dear Tiger, 

    Thank you for your input. Please find the attached schematic for your reference. 

    We do have 3.3V Pull up attached to each of the I2C - SCL and SDA lines. 

    Also, the I2C is driven by processor as master which gets power supply from the same buck converter that generates 3.3v and so power supply should have come first. 

    Is there any internal control which will prevent I2C communication? 

    Thanks and warm regards

    DharinBAT_V1 (1).pdf

  • Could you isolate the I2C traces to the charger and use EV2400 to monitor the I2C communication?

  • Dear Tiger, 

    Noted. We will try to isolate I2C bus and directly connect BQ25713 to EV2400 and check it out with just battery.

    We shall keep you posted on the outcome of the same. 



  • Hi Tiger,

    We have isolate I2C bus and directly connect BQ25713 to EV2400. We tried to read the BQ25713 registers using BQStudio, however we are receiving Acknowledgement error . Please find the attached image for the same.

    BQ25713 is powered by Battery only mode.

    All voltage levels are as expected.

    Please guide us on how to solve this issue.

    Best Regards,

    Sudha Nayak

  • Hi, Sudha,

    I noticed you have D4 and R49, a few other jumpers. Your schematic is different from our EVM configuration. Please get an EVM or match our EVM and try again. The BQ25713 should power from battery as low as 2.55V. Also check SRN voltage, which should be the same as VBAT. 

  • Dear Tiger,

    The schematic has a good amount of bypass mechanism in order to get the system working with adapter supply in case battery back up system fails to work.

    D4 is a diode assembly and R49 is 0 ohm resistor just to ensure that when we do not want battery back up system, we have direct supply available at Vsys. 

    We are bypassing this by removing R49 when we are working with battery back up system. 

    Same way, jumper J1, J2 and J3 are bypass mechanism in order to get system working with main in case battery is dead or battery back system response is not as expected.

    While we are working on realizing battery back up system, these jumpers and D4+R49 combination helps us get other part of the board and system working and we can continue shipping product without battery back up system. 

    If we do not populate R49 and jumper J3, the system is exactly same as EVM design. 

    We have ensured that part of design to make sure it matches with EVM solution. 

    Thanks and warm regards


  • Since this happens intermittently, please change to a new part to see if this goes away. 

  • Dear Tiger,

    Noted. We are seeing this behaviour in 2 out of 8 parts that is very high number. 

    So we would like to understand if there is any specific design issue that we need to address in our realization. 

    Do we need to add any protection mechanism or remove any bypass designs that we have in order to ensure this does not happen in future?

    Thanks and warm regards


  • Hi, Dharin,

    I would suggest you monitoring the SDA/SCL signals and make sure it conforms to the I2C timing requirements as described in datasheet session 8.6. Also follow the layout guidelines in session 12.1.

  • Hi Tiger,

    We did monitor the I2C signals and signa looks fine. 

    We also tried to run the I2C with 100KHz in place of 400KHz and still we run into the same issue.

    The entire system works fine with we have adapter supply in available. Our processing system is able to communicate with BQ25713 over I2C. 

    Same system fails to communicate with BQ25713 over I2C when adapter is absent and battery is supplying the power. 

    Battery does turn on our processing system as in absence of adapter, entire system works from battery and the same one tries to establish communication over I2C with BQ25713. 

    But in this case, we get no response from BQ25713 to I2C communication from processing system. We also observed I2C signals - SDA and SCL on Oscilloscope and they look to be ok. 

    Is there any signal or supply on BQ25713 which can cause IC not to respond to I2C?

    Thanks and warm regards


  • In battery only mode, I2C starts communication when VBAT is above UVLO threshold 2.55V, and stops communication when VBAT is below UVLO threshold 2.4V. 

    Similar thresholds for adapter mode.