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BQ76952EVM: 电池电压/温度NTC/电流采样精度评估相关问题

Part Number: BQ76952EVM

HI TI的工程师

如题

在手册中我已查找到ADC采样电池电压的精度,但手册中未给出用于温度NTC端口如 TS1 端口的ADC采样精度说明,是否可以将CELL端口的精度直接代入TS1 以及复用端口如 DDSG 等端口用于开发初期评估采样精度?

另一方面电流采样端口精度如何通过计算得出? 能否帮忙讲解下,十分感谢。

  • 您好,电流精度请参考下面内容

    You should choose your resistance based on your needs. Then adjust on the software from there, userA just adjusts the reported current. Lets assume the 10-A load current scenario and default configuration. At default, using a 1-mOhm resistor and userA of 1-mA, the reported current would be ~10000 with a 1-mA unit. Now, lets change the userA setting from 1-mA to 10-mA. The reported current now becomes ~1000 with a 10-mA unit (Assuming the device is calibrated).

    The formula for the LSB should be what's on the datasheet. Changing the CC Gain is what will affect your current reading the most, this is what you would need to adjust if you used a different sense resistor (The device is by default configured for a 1-mOhm sense resistor), or to calibrate the current for best accuracy.

    The resolution of the device would be 1.24/(5x2^15) = 7.6-uV. If using a 1-mOhm resistor and 1-mA for userA, this would correspond to a current resolution of ~7.6-mA. 

    温度精度请参考下面内容

    Temperature sampling occurs every 250ms. Please see below. More of this can be found in Improving temperature accuracy technical article.

  • 你好 非常感谢

    问题1

    1 LSB (16-bit mode, using CC1 filter) = VREF2 / (5 x 2N-1) ≈ 1.24 / (5 x 215) = 7.6µV

    1.24/(5x2^15) = 7.6-uV   利用这个公式假设我用0.5o电阻  那么得到的电流分辨率为 7.6uV/0.5 =15.2uA ?  库仑计可以这样用分辨率表示采样精度的对吗?

    问题2

    这个 公式中 1.24/(5x2^15)  5是代表什么含义? 与2的N-1 次方都是由CC1滤波器推算而来的吗? 

    问题3

    另外这个1.24的Vref在评估中是取固定值还是需要代入温漂如下图

    问题4

    此外库仑计的参数

     这和个参数如何理解?+- 22.3LSB?

    问题5

    另外对于NTC采样端口的ADC采样精度依然是在手册和资料中没有给出 例如LD  PACK+ CELL(X)都已明确给出, NTC 精度我个理解是 +-1度是一个很大的范围ADC采样精度已经远远高于它    内部上啦18K电阻 与外部10K NTC阻止可通过校准手段来达到+-1度 这样理解对吗? 

  • 您好

    1, 是的,上面公式是电流分辨率

    2,公式的详细参数介绍没有找到相关资料。

    3,Vref1 ~ 1.212 and Vref2 ~ 1.24. There will be marginal error when operating at different temperatures. This can be found in Figure 7-11 in the datasheet.

    4,请参考下面链接的内容

    https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/929608/bq76952-coulomb-counter-max-error?tisearch=e2e-sitesearch&keymatch=B%28CC_INL%29#

    5,BQ769x2_TemperatureRawCounts_Instructions (1).pdf