SAADC acquisition pulls down the acquisition voltage

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Hi,Master:

See below:

BAT + = 3.88V

a).When I removed the MCU:BAT_ADC = 2.556V

b).When I soldered the MCU:BAT_ADC = 2.28V,Why is there a 270mv voltage drop?

In the case of b):

1>.

When I only execute the following code in the program:

Configure the P003 pin as an input, not connected to the buffer, no pull-up and pull-down

Always cycling

Measured:BAT_ADC = 2.28V

2>.

When I only execute the following code in the program:

Configure the P003 pin as an input, not connected to the buffer, no pull-up and pull-down

Configure  AIN1 as SAADC channel

Always cycling

Measured:BAT_ADC = 2.28V

In the case of a):

Connect BAT_ADC to AIN1 on the official demo board,Measured:BAT_ADC = 2.556V

I think it should be a hardware design problem? How to find the answer?

Thanks.

[Kenneth]

Hi, all GPIOs cannot exceed >VDD+0.3V. In this case VDD is 1.95V, which means the maximum input level is 2.25V. I suggest to swap R191 and R192.

Best regards,
Kenneth

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Kenneth,thanks for you help! It is the answer to the problem.