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BQ25892: Variation of Charging Current with respect to temperature

Aditya kumar singh
Intellectual 270 points
Part Number: BQ25892
Other Parts Discussed in Thread: BQ27220

Hi E2E Team,

We are using BQ25892 battery charger IC in our project for charging of 18000mAh battery. We have set our fast charging current to 2.8A but when we start charging our battery fast charging current decreases rapidly (attaching the logs for the same taken by BQ27220 fuel gauge). 

1) Is it because of rapid change in temperature? 

2) Is this behaviour of BQ25892 is expected?

2) How current will change with respect to temperature?Charging_logs.xlsxow charging current will change with respect to temperature?

  • 0
    TI__Guru**** 153006 points
    Hi Aditya,

    The charger does have a thermal regulation loop that will reduce current if the IC itself gets too hot. Is your IC attached to a ground plane for heat sinking? If so, what is your input current limit setting? Is the ILIM pin enabled and potentially reducing the input current limit of the charger? How is the TS configured? What is the voltage at the charger's BAT pin? If the resistance is high between the BAT pin and gauge, then the voltage drop across that resistance may be causing the charger to enter CV mode prematurely.
  • 0 in reply to Jeff F
    Intellectual 270 points

    Hi Jeff,

    Please find my comments inline-

    1) Is your IC attached to a ground plane for heat sinking?

    Yes IC is connected to the ground plane for heat dissipation.

    2) What is your input current limit setting?

    Input current limit is set for 3A@5V.

    3) Is the ILIM pin enabled and potentially reducing the input current limit of the charger?

    Yes ILIM pin is enabled but it is not limiting the input current because we have connected 120-ohm resistance between ILIM pin and ground to current limit to 3A.

    3) How is the TS configured?

    TS pin is configured for 0°C to 60°C for charging.

    4)  What is the voltage at the charger's BAT pin?

    We are getting same voltage as the battery (measured by the multimeter).

    5) Is charger is entering in CV mode prematurely?

    No charger is not entering in CV mode prematurely because the resistance between is BAT pin and the battery is very low.

    Previously attached log file shows that it starts charging at 2.72A but rapidly decrease the charging current. Is this because of the rapid increase in temperature of battery? If so, then how charging current will change with respect to temperature?

  • 0 in reply to Aditya kumar singh
    TI__Guru**** 153006 points
    HI Aditya,

    The battery temperature increase causes charging to stop. IC die temp increase can cause the IC to scale back charge current. Can you monitor IC die temp while charging?
  • 0 in reply to Jeff F
    Intellectual 270 points
    Hi Jeff,

    Yes, battery temperature increase causes charging to stop but in my case charging is not stopping. You can see from previously attached logs that charging current is decreasing very rapidly, but battery temperature is within required range for charging. Why is this so?

    Temperature of charger IC is not going above 48°C during whole charging process.
  • 0 in reply to Aditya kumar singh
    TI__Guru**** 153006 points

    Can you post your schematic along with your inductor part number? 

  • 0 in reply to Jeff F
    Intellectual 270 points

    Hi Jeff,

    Please find the attached schematics and inductor part number is XFL3010-102ME (Coilcraft).

  • 0 in reply to Aditya kumar singh
    Intellectual 270 points
    And maximum system current is 1.1A.
  • 0 in reply to Aditya kumar singh
    TI__Guru**** 153006 points

    I think your inductor is saturating.  It's ISAT at 30% drop is only 2.7A.  If you measure the inductor current, is it nice triangles or triangles with narrow peaks?  ISAT should be about 30% higher than maximum IBAT+ISYS.