BQ27427: Need updated polynom for NTC Murata NCU15XH103F60RC

Hello Karl,

We will continue to work on your question, today is a national holiday, Memorial Day.

Thank you,
Alan

Thanks. Meanwhile I tried the following:

Connection

Our NTC is connected from BAT pin to GND, no other components are connected to the BAT net.

Excel file

I used this config file found in the forum:
/cfs-file/__key/communityserver-discussions-components-files/196/Analysis_5F00_Custom_5F00_External_5F00_Thermistor_5F00_Coeff_5F00_NewConfig_5F00_20111111.xlsx

from https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/971340/bq27426-check-on-coeff-for-ntc-ertj0er103j

NTC data

I entered the data for my NTC taken from
https://www.murata.com/products/productdata/8824151834654/NTHCG575.txt?1743059744000
To the excel file yellow fields.

Pull-up

I found that the pullup value for the similar gauge BQ27426 is set to 18k
BQ27427: NTC Curve Generation - Power management forum - Power management - TI E2E support forums

But this post says the pull-up is 10k
https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1361651/bq27427-ntc-curve-generation

The pull-up value is very unclear

Vadref

The Excel file says 2.5V, and "do not change this" but I found that I needed to change ADC ref to 1.8V to get the temperature value to be reasonable. I just guessed that it referred to the only regulated voltage it has, the internally regulated 1.8V.

Offset

There was a offset in temperature so I came to the same conclusion as in
BQ27427: The accuracy of temerparue measured function as external NTC on BQ27427 - Power management forum - Power management - TI E2E support forums   that I needed to ad a 5.7 degrees offset in the Ext Temp Offset register.

Accuracy

I have not yet done a controlled temperature test in climate chamber, but my bench test heating the NTC and having a reference shows that it follows the reference within one degree or similar.Tested about -15 to + 50 degrees C

Excel file output

This is the result of the solver as I have set it up:

Questions:

1. Am I using the correct excel file? Or is there a more recent one that is adapted to BQ27427?

2. Pull-up, what is the correct pullup value for BQ27427?

3. Vadref,  what is the correct Vadref value for BQ27427?

4. Offset, I guess the offset error of 5.5-6 degrees comes from something is not setup right in the excel file?!

B.R.

Karl

Sorry. I made a typo. The NTC connection is of course connected to BIN pin and GND.

I found the bq40z50 family Thermistor Coef Calculator in (+) BQ40z50 Thermistor Coefficients - Power management forum - Power management - TI E2E support forums via the thread BQ27427: NTC Curve Generation - Power management forum - Power management - TI E2E support forums

Is this the correct excel file to use for BQ27427?
I tested it and I get other registry values, need an offset of 6.5 degrees C and it measures faily similar to what I got from using the values from the first excel spreadsheet. 

The connection of the NTC looks more similar to BQ27427 in bq40z50 family Thermistor Coef Calculator.

Hello Karl,

This question has been assigned and will be reviewed.

Thank you,
Alan

Hello Karl,

The tools outputs the Ext a Coef and Ext b Coef which are suitable tor bq27427 as well. You should be able to use the BQ40z50 for BQ27427 as well. 

Ok. So what you are saying is that
1. I shall use the BQ40z50 excel file?
2. Or can "as well" use the Analysis_5F00_Custom_5F00_External_5F00_Thermistor_5F00_Coeff_5F00_NewConfig_5F00_20111111.xlsx ?

If I use Analysis_5F00_Custom_5F00_External_5F00_Thermistor_5F00_Coeff_5F00_NewConfig_5F00_20111111.xlsx, my questions are

2a. Pull-up, what is the correct pullup value for BQ27427?

2b. Vadref,  what is the correct Vadref value for BQ27427?2

2c  Offset, I guess the offset error of 5.5-6 degrees comes from something is not setup right in the excel file?!

3.
What about the offset of 5-6 degrees I see for both generated polynoms? Why is that not handled by the coefficients?
Is that excpected?
Van I expect the offset to be the same for each BQ27427, or will the offset be individual?

Hello Karl,

We have received your update and due to a back log of the queue we ask for some more time until we send a response.

Thank you,
Alan

Hello,

Please use the BQ40z50 excel file. All you need to do is to input in the yellow bellow. 



I am not familiar with Analysis_5F00_Custom_5F00_External_5F00_Thermistor_5F00_Coeff_5F00_NewConfig_5F00_20111111.xlsx