BQ21040: BQ21040

shaffi ulla

Part Number: BQ21040

Hi to all,

I am using BQ21040 IC to charge lithium ion batteries,so my question is that when the battery voltage gets charged up to 4.2V the Red LED isn't turning off.

Can anyone,please help me out in solving the problem.Below attached is the schematic of battery charger.

Thanks in advance.

Regards,

Shafi.

over 7 years ago

0 Bill Johns over 7 years ago

TI__Guru* 75656 points

Hi Shafi
What is the value of R1 (ISET) and R3 (TS)?

/CHG will go from low (led on) to high Z (led off) when battery is at 4.2V and current is 10% of charge current. Is input current dropping below this point? Input current and current to battery are about the same.

The TS pin has an off page connection, is it possible this pin is controlled by some other device?

0 shaffi ulla over 7 years ago in reply to Bill Johns

Prodigy 100 points

Hi John

The R1(ISET) is 15k (for 35mA ). R3(TS) is 10k NTC.

TS is not controlled by any other device.Resistor between CHG and Vout is 499 ohm,but recommended is 1.5k, does this effect the functionality.

Regards,
Shafi

0 Bill Johns over 7 years ago in reply to shaffi ulla

TI__Guru* 75656 points

Check the charge current during fast charge and what is decreases to near the end of charge.

0 shaffi ulla over 7 years ago in reply to Bill Johns

Prodigy 100 points

Hi John,

Charge current during fast charge is 35 mA,when battery reaches max voltage(i.e fully charged 4.2v) charge current at end of charge is 9 mA instead of 3.5 mA(10% of charge current ).Resistor connected to CHG is 499 ohm,but recommended is 1.5k, does this effect the functionality.

Regards,
Shafi

0 Bill Johns over 7 years ago in reply to shaffi ulla

TI__Guru* 75656 points

Hi Shafi
The additional current draw of the LEDs could be a problem. To reach end of charge current will need to decrease to 3.5mA and you are seeing 9mA. Try increasing the LED resistors to 1.5k or powering them from input voltage.

Power management

Power management forum

BQ21040: BQ21040