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BQ25150: BQ25150 not entering ship mode upon battery insertion

Part Number: BQ25150
Other Parts Discussed in Thread: BQ21061

Hi,

We have encountered a strange issue with the BQ25150 in our system. According to p. 33 of the data sheet, the device is supposed to enter ship mode upon battery insertion with no valid VIN present.

However, in our application, this does not seem to be the case. Upon battery insertion, we are still seeing a current consumption of around 230mA and can still measure 1.8V at the VDD pin (D1) with respect to ground. Both of these observations seem to indicate that the device is not currently in ship mode.

What could be possible reasons preventing the device from entering ship mode upon battery insertion and how could we debug this situation?

Thank you!

  • Hi David, 

    When there in no VIN present the device conducts a power up sequence upon battery insertion. The VDD rail will go high to allow the device to check the state of the /MR pin. If the /MR pin is high VDD will immediately be disabled and the device will enter ship mode. If the /MR pin is being held low the device starts the wake timer and powers up PMID.

    Please also insure the /LP (Low power enable) pin is pulled high. Driving this pin low enables low power mode where the battery powers the VDD output. Having either of these input pins low prevent the device from entering ship mode when no VIN is present. 

    Regards,

    Garrett

  • Hi Garrett,

    Thank you for your quick reply. Unfortunately, we left the /LP (Low power enable) pin floating in our design, and this pin seems to be pulled low internally. Is there any way for us to enter ship mode under these circumstances?

    Regards,
    David

  • Hi David, 

    I confirmed having a floating /LP pin should not affect the startup procedure of the device entering ship mode. In my testing with no VIN and the /LP pin floating the current consumption is in the nA range and the VDD output is off. Keeping the /MR pin high upon battery insertion should allow the device to enter ship mode. Is there anything in your design connected to the input other than the power source? 

    Also, would you be able to provide a schematic so we can verify your design and attempt to duplicate the behavior you are seeing?

    Regards,

    Garrett

  • Hi Garrett,

    Thanks for the update and please find the relevant part of our schematic below:



    The /MR pin is connected to our MCU, which is powered from PMID (VSYS) through an LDO.

    Also, we don't have anything else connected to the IN pin.

    Please let us know if you can come up with anything. Thanks!

    Regards,
    David

  • Hi David, 

    We have reviewed your schematic and everything looks good. Since your device has a voltage on VDD I suspect the device is in active battery or low power mode instead of ship mode. When you are getting the 230 mA current draw are you able to communicate through I2C? Also if possible can you please provide voltage waveforms for PMID, VDD, /MR, and BAT when the battery is inserted. Based off your schematic a potential root cause of the problem may be the state of /MR pin during startup.

    Regards,

    Garrett  

  • Hi Garrett,

    Thank you for the review of our schematic. I just checked the current draw again, we are consistently getting around 230 uA (not mA, that was a typo in my original post) following battery insertion. In ship mode, we would expect 2 to 3 uA maximum, coming from the BQ25150 and a fuel gauge IC which are both running off the battery voltage.

    I can't comment on I2C communication yet, we are still looking for a way to reliably test this.

    The voltage waveforms after a battery insertion look as follows:



    Please let us know if any of these look unusual to you. Thanks!

    Regards,
    David

  • Hi David, 

    Looking at the waveforms the /MR pin does not go high until there is voltage on the PMID pin. This appears to be due to your /MR pins connection to the MCU powered by PMID. The problem is if the /MR pin is held low for t_wake2 (1 or 2 seconds depending on setting of MR_WAKE2_TIMER) the device starts wake up and will not enter ship mode. The waveforms you provided appears to show /MR being held low for more than 1 second causing the device to enter active battery mode instead of ship mode.

    I recommend attempting to test entering ship mode with the /MR pin floating. This should allow the device to enter ship mode successfully. 

    Regards,

    Garrett  

  • Hi Garrett,

    Thank you for taking a look at our waveforms. With the /MR pin floating (not connected to the MCU) we are indeed able to enter ship mode upon battery insertion with a current consumption in the low uA range, as expected.

    After investigating the issue further, it seems that the /MR pin being pulled high to BAT by the BQ25150 upon insertion exceeds the maximum voltage on the GPIO pin of our MCU (which is VDD + 0.3V, with VDD initially being 0V as MCU power is supplied from PMID). Probably an ESD protection diode internal to the MCU GPIO pin clamps this overvoltage to some lower value, which will then be registered by the BQ25150 as a low voltage and cause the chip to wake up after t_wake2 expires.

    Does this sound reasonable to you? If this is indeed the root cause for the behavior of our circuit, do you have any suggestions on how we could fix this issue? Having the MCU running directly off the battery is unfortunately not an option due to power consumption concerns, so we need to rely on the BQ25150 to cut it off during ship mode. Thanks again for your help!

    Regards,
    David

  • Hi David, 

    Yes that sounds reasonable. I suggest considering the use of a n-type mosfet with gate voltage controlled by the MCU GPIO pin. This should allow the /MR pin to be pulled high upon BAT insertion without the MCU clamping the voltage. 

    Attached below is an application note for the BQ21061 device, which is a similar device with the same /MR pin functions as the BQ25150. Design B from the document provides a reference schematic (figure 6) for toggling /MR through NMOS. If the MCU shares a ground with the charger IC the R1 resistor can be removed. 

    BQ21061 Two Layer Small Form Factor Design For Cost Optimized PCB

    Regards,

    Garrett

  • Hi Garrett,

    Seems like adding the MOSFET has resolved the issue, thank you again for your help.

    Regards,
    David