• State
  • Locked Locked
  • Replies 3 replies
  • Subscribers 63 subscribers
  • Views 151 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ25171-Q1: The charge current setting by the Iset resistor won't change the charging current.

Nan Liu
Prodigy 110 points
Part Number: BQ25171-Q1

Tool/software:

Hello support team,

I have made the BQ25171-Q1 charger followed exactly the sample schematic on datasheet, it will charge  single cell LiFePO4 battery with 400mA current. 
The Vset resistor then is 82K (3.6V according to the table on datasheet), the Iset resistor  is 750ohms according to the equation on datasheet.

The input voltage is 12V, but the charge current measured is only 150mA. I changed the Iset resister to some other value, but it will not change the charge current at all.

what will be the problem?

Thanks in advance.

  • 0
    TI__Guru* 75606 points

    Hi Nan

    Nan Liu said:
    The input voltage is 12V, but the charge current measured is only 150mA. I changed the Iset resister to some other value, but it will not change the charge current at all.
    Nan Liu said:
    what will be the problem?

    The BQ25171-Q1 has a thermal protection feature and will reduce output current when the die temp reached 125C.  The device is probably reaching this point due to power dissipation.  Check ISET pin it should be 1V when in regulation but during thermal regulation it will decrease.

  • 0 in reply to Bill Johns
    Prodigy 110 points

    Thank you Bill. I do tried to lower the input voltage down to 9V, 6V and 5V, it won't change the charge current. The charge current stay 147mA to 159mA whatever the input voltage and Iset resister value, two boards behavior the same. In addition, the batteries I tried were with different no-load voltage (different capacity) . but whatever I change the initial conditions, the charge current stays low.

  • 0 in reply to Nan Liu
    TI__Guru* 75606 points

    Hi Nan

    How are you measuring output current?

    Current meters in the output have caused problems in other test set-ups, resistance in the meter shunt is the issue.