Tool/software:
Hello,
I'm working on a custom board design using the BQ76952 for cell monitoring and want to connect NTC thermistors to several multifunction pins to measure external temperatures. I’ve attached a schematic excerpt below, showing the connections between the thermistors and the pins. CONN_TEMP_X is where the thermistor is connected. These thermistors are standard 10k NTCs (NCP15XH103F03RC).
I know that the technical reference manual does not indicate to use the external pull-up resistors (R99-R102). They can be removed easily though. I have removed R99 and I tried to use the temperature models to read actual temperature from that pin, but was not successful.
Here is what I've tried so far (remember that I removed the pull-up resistor R99 from TS1:
1st Case: 18K Temperature Model
Configuring TS1 Pin register as 0x07 (That is, pin for thermistor; thermistor temperature measurement, used for cell temperature protections; Calibration:18K Temperature Model; and 18 kΩ pull-up for thermistor measurement); and 18K Temperature Model coefficients left with default values, I get wrong "temperature" values from TS1 Temperature direct command:
TS1 Temperature: 3051 (raw, 0.1K), 31.95 [°C], when the current ambient temperature is around 25 [°C].
That is an offset error for starters, but there is a gain error too.
2nd Case: Custom Temperature Model
Configuring TS1 Pin register as 0x27 (That is, pin for thermistor; thermistor temperature measurement, used for cell temperature protections; Calibration:Custom Temperature Model; and 18 kΩ pull-up for thermistor measurement); and Custom Temperature Model parameters obtained from the TI tool:
Search complete, bestmaxerr = 0.5
bestA [A1 A2 A3 A4 A5] = [-19338 31696 -22024 31696 2801]
bestB [B1 B2 B3 B4] = [-13693 13993 -7183 4679]
Adc0 = 11703
I get also wrong temperature values from TS1 Temperature direct command:
TS1 Temperature: 3045 (raw, 0.1K), 31.35 [°C], when the current ambient temperature is around 25 [°C].
For now, I am configuring the pins as ADC inputs, and I am converting through an mcu the voltage measurement to the corresponding temperature. However, in this way I think I cannot use the under/overtemperature protections of the device. So, I have a couple of questions:
- Is there any problem you can spot either in the schematic or in the configuration I used in my tests?
- Is there another configuration I could try?
- What exactly is the input variable for the custom polynomial model?
- How is the device selecting between the first and second polynomials?
- Is it possible to use the pins as ADC inputs and still be able to use the temperature protections?
Any clarification or examples would be greatly appreciated — even undocumented behavior or internal guidance would help me move forward confidently. Thank you!
Federico