BQ76952: how to get the coefficient of temperature polynomial

Tan Haitao

Part Number: BQ76952

Hi,I use the excel get the two 4th order polynomial,first one is T°C = A4*(R4) + A3*(R3) + A2*(R2) + A1*R + A0 and another is R(Ω) = A4*(T4) + A3*(T3) + A2*(T2) + A1*T + A0

1. As you can see,the first one is not so good,is something wrong

2.How can I get the Coeff a1~a5 and Coeff b1~b4.The excel is the thermistor data I use, can you help me caculate the Coeff a1~a5 and Coeff b1~b4

T_R_table.xlsx

over 4 years ago

0 Matt Sunna over 4 years ago

TI__Guru* 81034 points

Hi Tan,

Thanks for providing your data. We will look into this and see if there is a way to improve the coefficients. I will update you with our feedback tomorrow.

Best regards,

Matt

0 -Terry over 4 years ago

TI__Expert 5090 points

Hi Haitao,

The polynomial used by the device is not just a simple T=f(R) polynomial, but I have used the R vs T data you loaded to generate a set of coefficients for you:

A = [-20768 28672 -12288 28672 4095];

B = [-24008 20662 -7729 4369];

For these, please use them with the Calibration:18K Temperature Model, and set adc0 = 11703.

When you test the result, please capture the reported temperature and the raw ADC counts for the pin you are using for the thermistor, in case further debug is needed. For example, if your thermistor is attached to the TS1 pin, then when testing please capture at each temperature the reported 0x70 TS1 Temperature() command data, along with the data from TS1 Counts, which is obtained using the 0x0076 DASTATUS6() subcommand. Data associated with other pins can be found in the commands 0x6A ~ 0x7A and the raw counts in 0x0076 DASTATUS6() ~ 0x0077 DASTATUS7() subcommands.

Thanks,

Terry