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I am using your CY8C5868 PSOC, use it sample lmt84(temperature sensor) P3.7 temperature as below configuration.
But FW can't capture stable value, use the scope capture the lmt84(temperature sensor) output signal is pull down in about 100KHZ. If I disconnet the output pin to P3.7, the lmt84 output signal is stable.
Based on the TI's LMT84 datasheet, this is a "medium" output impedance device (~5V/50uA = 100K ohms).
Most likely the issue you are seeing is that the SAR is a "medium" impedance input resource (~180K ohms). When the SAR is sampling, the input impedance affects the LMT84's output drive (which can only source 50uA).
When the LMT84's output impedance is combined with the PSoC's SAR input impedance, the "effective" input voltage will drop from the expected voltage from the LMT84's table.
As Vasanth indicated, using a OPAMP in the front of the SAR will help. (The input impedance of the OPAMP is about 10 Mohms)
Also, if you use the Delta-Sigma ADC with the input buffer enabled, you will also get about 10 Mohms input impedance.
Len "Engineering is an Art. The Art of Compromise."