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BQ25618EVM: Charge Current higher than specified

Ved Soni1
Prodigy 20 points
Part Number: BQ25618EVM

Hello everyone!

I am using a BQ25618EVM charger IC for Li-ion battery charging. While testing the IC using an electronic load instead of a battery and setting the input current via the EV2400 I2C interface, I found that when I set the charging current to 60 mA using BQStudio, the measured current supplied to the electronic load is 80 mA. This trend existed even when I increased the current until 160 mA. However, upon increasing the current beyond 200 mA, the measured and set current values matched again. Also, when I set the current to 40 mA, the measured current was recorded as 40 mA.

I have multiple units of BQ25618EVM and I found this issue only with 2 out of 10 units. Also, I tried testing these ICs again using actual batteries and the same trend existed. Moreover, I checked the startup register settings of this IC, and it matched the default settings mentioned in the BQ25618 IC datasheet.

So why is the measured current different than the set current in some of the ICs? Please let me know how I can troubleshoot this issue.

  • 0
    TI__Expert 5590 points

    Hi Ved:

    I think this could be setup issue. Did you use electronic load alone to simulate battery? When you do that, do you have additional power supply in parallel? Need to understand more about your setup. When you use real battery, how did you measure charge current? What is the battery voltage? Adding resistance between the charger and battery may reduce charge current.

    Regards,

    Hong

  • 0 in reply to Hong Mao
    Prodigy 20 points

    Yes, I only used a constant voltage electronic load to simulate the battery. The voltage was set to 3.7 V which is the operating voltage of the battery. 

    The voltage range of the actual battery is 3 to 4.2 V. With the battery connected, I measured the charge current using a DMM and also using a current sensor. This same setup when tested with other units of BQ25618EVM in my possession do not show a higher measured charge current when I set the registers to 60 mA. 

  • 0 in reply to Ved Soni1
    TI__Expert 5590 points

    When you use real battery, I would recommend you have 100m Ohm current resistor in series with battery and measure the voltage across the resistor to calculate the actual charge current. DMM with cable may affect charge current accuracy. Check the charge current from 3V to 4V for the whole VBAT range.