BQ24072T: Problem with calculating the termistor values

Cajsa Fredriksson

Prodigy 60 points

Part Number: BQ24072T

Hi,

I want the BQ24072T to charge between 5°C and 40°C.

According to the sensor datasheet, R_Cold is 22.02kOhm and R_Hot is 5.827kOhm. I have calculated the following values:

R6: 31,7k (Used value is 31.6k)

R7: 20.3k

R8=100k

But when I use these values and adjust the resistance of the termistor (using a potentiometer), the charging will not stop until approximatery 30kOhm which is below 0°C according to the sensor datasheet.

(103AT, Beta=3435K, R25=10kOhm)

Are my calculated values wrong?

Thanks

over 5 years ago

0 Raheem over 5 years ago

TI__Mastermind 21590 points

Hello Cajsa,
What voltage did you measure on the TS pin when the device stops charging and what is the input voltage R6 is pulled up to?

0 Cajsa Fredriksson over 5 years ago in reply to Raheem

Prodigy 60 points

Thank you for answering.

The voltage on the TS pin is 1,4V when the charging stops.

The pull up voltage of R6 is 5,15V (Power adaptor input)

0 Raheem over 5 years ago in reply to Cajsa Fredriksson

TI__Mastermind 21590 points

Cajsa,
Can you run this test with actual resistors instead of a potentiometer. Try a 22.1k ohm resistor, 21.5k ohm resistor and 22.6k ohm and see if charging stops with any of those values.

0 Cajsa Fredriksson over 5 years ago in reply to Raheem

Prodigy 60 points

Hi Raheem,

I tested with the resistors and the charging stops with the 21.5k resistor. So now I know that it works. Thank you very much for your help!

Best Regards,

Cajsa

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BQ24072T: Problem with calculating the termistor values