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BQ25155EVM: Excessive current drain while in battery undervoltage lockout mode.

Part Number: BQ25155EVM

I've removed J4 (extra 3.3V header) from the board and connected J7 (VBAT header) to a Keythley 2450 SourceMeter. The board preforms as expected with ~800nA being consumed from VBAT while PMID is also outputting the same voltage as on VBAT but when reaching the battery undervoltage lockout threshold (3V) the current consumed from VBAT jumps to ~3uA. In this mode when 5V is applied briefly to J6 (VIN header) the current drain from VBAT jumps to ~400uA !!! this drain is constant until the voltage on VBAT drops to 2.7V when the current drain again becomes ~3uA.

Is this behavior considered to be working as designed? What can I try to mitigate these issues? As described the behavior would kill the battery our product is using within hours. 

  • Hi Kalle,

    Is the VIN still present when the 400uA is measured? What is the status of the /LP pin? 

    Do you have a plot of when this occurs? When VIN is disconnected, device should either cut off the battery path due to BUVLO being reached or stay in low power mode. 

    Regards,

    Gautham

  • VIN is not present. LP pin is low. I don't have a plot yet - I can create one but roughly it's the following.

    I believe this a glitch where the IC enters an unknown state where current draw from VBAT is high when during a low battery disconnect state battery charging begins but does not bring the battery level to be high enough to exit the low battery state. 

  • Hi Kalle,

    I was able to match your setup and I can replicate the behavior. The device had issued a BUVLO (shutting off) and then VIN was applied for brief amount with charging disabled to get it to the 400uA state. In this state the I2C and ADC was running along with VDD active which caused the power consumption. When I issued a hardware reset (which forced the BUVLO check on powerup after the autowake timer) or setting BUVLO to lower value even before this test- such as 2.2V I did not see this mode. 

    What is the BUVLO setting you plan to use?

    Regards,

    Gautham

  • Unfortunately we were planning on powering our system from PMID (for battery discharge protection) and since all registers get reset when entering low power mode any fixes that require active intervention from the system aren't feasible.

    Can I get confirmation that this is unintended/unexpected behaviour? Is there any chance of a future revision of the IC where this is fixed?

  • Hi Kalle,

    This is unexpected behavior where in the VIN or BAT supply are not valid for the device. 

    What is the available capacity under 3V for your battery? Are you using an external protector IC- is setting BUVLO lower an option on boot up?

    We are working on a device with BAT startup by default and BUVLO default set to 2.2V and is pin2pin, BOM2BOM and software compatible with this device. I can check this device and get back if this will be a good fit for you. We plan to release in 2 months. 

    Regards,

    Gautham

  • Our battery is a very low capacity lipo type battery and as such capacity below 3V is virtually non existent. 

    Having to use an external protection IC instanty greatly reduces the appeal of the BQ2515x family as a single solution for battery management.

    Thank you for the answers but the relative immaturity of the product line means we'll have to consider other options for now. Which is a shame since if the IC could property handle the BUVLO condition it would be a perfect fit for us.

  • Hi Kalle, 

    Thanks for the feedback. We will look into this type of use case in our future products. 

    Regards,

    Gautham