BQ79656EVM-021: How to convert GPIO read values to temperatures?

Florian Behlke

Part Number: BQ79656EVM-021

Hi,

i am using 7 NTC's at the GPIO ports 2 to 8 of the BQ79656EVM-021 board. I can read the voltage values but i am not sure how to convert them to actual Temperatures.I tried with the resistance/voltage divider formula but i am not sure about the size of the internal pullup resistor.

I connected the NTC at the GPIO Port and to ground over the J15 Connector. Is this right?
Can you help me with finding the temperature values from my GPIO voltages?

Thank You

Florian

over 1 year ago

0 Michelle Williams over 1 year ago

TI__Prodigy 540 points

Hi Florian,

On the BQ79656EVM, the J15 header is to connect cells or a cell simulator to the VC/CB pins on the device. You would need to use header J4 to use the onboard NTC (ERT-J1VG103GA). I would recommend looking up the datasheet for whichever NTC you are using since each NTC can have a different beta value & look-up table. Otherwise, there should not be any other pull up besides the 10k resistor on the EVM if the GPIO inputs are configured to ADC/OTUT inputs.

Sincerely,

Michelle W.

0 Florian Behlke over 1 year ago in reply to Michelle Williams

Prodigy 20 points

Hi Michelle,

but is it possible to connect external NTC to the board over the J4 header? I dont want to use the internal NTC at all. How do i have to connect the external NTC at the J4 Header?

Regards
Florian

0 Florian Behlke over 1 year ago in reply to Florian Behlke

Prodigy 20 points

Because if I connect my NTC at the GPIOX_R Pin and to ground it is always in a parallel circuit to the internal NTC. And this doesnt make any sense.

+1 Michelle Williams over 1 year ago in reply to Florian Behlke

TI__Prodigy 540 points

In that case, you would need to connect the NTCs to circuit like in the image like shown below. You can use jumper wire on J4 to connect the GPIOx to the NTC and use the TSREF testpoint to add the voltage reference off board. Below is highlighted which portion of J4 to connect to for the GPIOx node.

Sincerely,

Michelle W.

0 Florian Behlke over 1 year ago in reply to Michelle Williams

Prodigy 20 points

Thank you Michelle.

Power management

Power management forum

BQ79656EVM-021: How to convert GPIO read values to temperatures?