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BQ51010B: Undervoltage Lockout

Part Number: BQ51010B
Other Parts Discussed in Thread: BQ51050B


I am experiencing strange behavior with this part. I have I_BULK set at 147mA, and K_TERM is set at 10%, so I_TERM will will ~14.7mA.

However, I am seeing our batteries stuck in an UVLO condition, at 2.40V. V_RECT is fine ~5.10V. No matter how long it stays on the charger it won't give any charge to the battery, just stays stuck at 2.40V.

I have seen this response on another forum, from Application Engineer Mr. Bill Johns, and wonder if it applies to thus UVLO condition I'm seeing:

The problem has to do with the behavior of KILIM at low current, it will lose accuracy and has a wide deviation from unit to unit. Result is early termination or no termination. The no termination condition can trip the 10 hour safety timer resulting in a fault shutdown. 
We recommend to set termination at about 50mA to avoid the above problem.

Any help will be appreciated.

Thank You,


  • Hi Billy
    I think your question is on the bq51050B, part number on the post is bq51010B.
    With the battery at 2.4V ( less than 3.0V) it will be in Precharge condition and current will be limited to 20% of charge current about 30mA. This condition has a 30min timer on it.
    I recommended checking the current going to the battery during precharge and rate the voltage in increasing.