I have a question about LPC521 follower, we are using it with MSP430F5438A, the input is 3.8V and after a resistor divider, 1.9V feed to LPC521 voltage follower. and output to a analog input pin ( p6.0 )of MSP430F5438A, I notice the reading from multimeter at the p6.0 and the ADC value have a 80mV to 100mV difference( ADC reading are higher than multimeter) . we have other ADC reading from p6.1(1.5V DC) and p6.2 which are very close to the multimeter readings, that prove the reference should be OK. it turns out MSP430F5438A ADC require the output side impedance smaller than 10K(see MSP430F5438A errata, ADC 27 work around). I think the voltage follower should have low output impedance. but I am not sure about this LPC521.
I also notice if add a 0.1uF cap bypass LPC521 follower output to ground, will make the ADC reading close to multimeter. could anyone explain why this cap can make this happen. it is a DC voltage, and from the scope the ripple is very low. less than 20mV.