• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 63 subscribers
  • Views 804 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.

BQ21040: BQ21040

Jeremy Sklute
Prodigy 135 points
Part Number: BQ21040

I am currently trying to build a single cell LIPO battery charger with your chip (BQ21040), however when I try to charge a 400mah 3.7V LIPO battery with it,The chip seems to discharge the battery not charge it. I have the Riset set to 270ma using Kiset @ 540Aohm and Riset's resistor is 2Kohm. I have attached a schematic of the battery charging section where Vin is the output to the battery, USB_in/5V is power from a USB and BATT_GND is the common ground between the battery and USB. I would appreciate any help you can give me in regards to trying to resolve my issue.

  • 0
    TI__Guru* 75656 points

    Hello

    The schematic did not make it could you re-send?

    Battery should not discharge, input is pretty well protected.  Any indication if the current is going to ground thru device?

  • 0 in reply to Bill Johns
    Prodigy 135 points

    Here is the schematic of the charging circuit, along with the PCB layout of it.

  • 0 in reply to Jeremy Sklute
    Prodigy 135 points

    The current is not going to ground through the device, I just checked the voltage coming out of the battery (after using it to power the overall device), and got a voltage of 3.659VDC.  I then turned off the overall device and plugged in the charger with no change in the voltage going to the battery. is it possible the 270mah charge rate is to low for the battery. the battery is rated at 400mah with a recommended charge rate of 0.5C.  I chose the lower rate to test the board design with components I already had on hand.  I also replaced the 10k ohm NTC thermistor with a 10k ohm resister, which caused no change with the behavior of the charger. I have checked for good connection(s) between all charger related components as well and found no problems.

    -Jeremy Sklute

  • 0 in reply to Jeremy Sklute
    Prodigy 135 points

    I found my problem, I was using to low of an Riset for the battery to charge properly.  I was charging it with 270mA (maximum CC charge for the battery is 400mA),

    I switched to using 1550ohms for my Riset (@ Iout of 348mA) and got the battery to charge correctly. Thanks for the help.

    -Jeremy Sklute