Inaccurate sampling in S32K

[Hailong_Zeng]

The multimeter measures FUEL_SENSOR_1_CAPACITAL1 1.3 mV, but the actual value printed by the MCU serial port is 7mV.Is it the sampling network that's incorrect?

[PavelL]

Hello @Hailong_Zeng ,

I apologize for late response caused by Xmas vacations.

At first look, your C4116 and C4117 have low capacitance. Please refer to AN4373, Cookbook for SAR ADC Measurements - Application note (nxp.com) . E.g. for S32K3, necessary information (CS, CP1, CP2, RSW, RAD, ...) to calculate values of external components can be found in chapter 10.1 of S32K3 data sheet.

While you are sensing mV, I also recommend to have separate ground path for your signal from source to MCU. The ground path shall be separated in a way that no other current flows through this path.

Best regards,

Pavel