BQ24210 Data Sheet Conflict? Thermister

Dan LaChance

Other Parts Discussed in Thread: BQ24210

Hello TI,

I have a question about selecting an NTC and divider resistor for the BQ24210. The datasheet seems to contradict itself.

It states that the thermistor bias output, Vtsb, is from 2.0V to 2.4V with a typical value of 2.2V. It then states that the voltage on the thermistor input for 45C, V45c is 18.6% of Vtsb. So V45c is anywhere from 0.372V to .4464V. It gives equation 13 for calculating the bias resistor Rt1 as Rt1 = 1/V45c * RTH(45C) – RTH(45C). Then later it uses this equation in an example application and somehow comes up with RT1 = 1 / (0.186) * 4911 Ω - 4911 Ω.

The value of V45c they came up with is somehow 0.186 which contradicts the rest of the datasheet.

Thanks,

Dan

over 9 years ago

0 Jing Zou over 9 years ago

TI__Mastermind 20570 points

Thanks for finding the error. We made a typo in the application section. It was supposed to be 1/(0.186*2.2)*4911-4911. We will update the datasheet accordingly.

0 Dan LaChance over 9 years ago in reply to Jing Zou

Expert 1770 points

Hello TI,

My customer came back this:

Actually,I think the previous equation (equation 13) is incorrect and the application information is correct.

You have a voltage divider at Vth between RT1 and RT. So VT = VTH * (RT / (RT+RT1). Then you have VT = 0.186*VTH. So 0.186*VTH = VTH * (RT / (RT+RT1). Cancelling out VTH and solving for RT1, you get RT1 = RT / 0.186 - RT.

Can TI verify?

Thanks,

Dan

0 Jing Zou over 9 years ago in reply to Dan LaChance

TI__Mastermind 20570 points

Dan,

I will look into this. Meanwhile, can you please provide info on the project? what is the application and volume?

0 Jing Zou over 9 years ago in reply to Jing Zou

TI__Mastermind 20570 points

I just confirmed the the customer's calculation is correct. We will update equation 13 in the datasheet.

Power management

Power management forum

BQ24210 Data Sheet Conflict? Thermister