Hello
Could you help us confirm if you have used an example for the ADC as a base? If so, indicate which;
Have you configured the input ADC Channel 0 and Input Select Register as 3 so you can select temperature sensor?
For more detailed information, kindly refer to Chapter 44.6.2 in LPC546xx User manual[UM10912]
If you could bring more details about, how did you configure the ADC temperature sensor, please.
According to LPC546xx Product data sheet Chapter 7.22,
"After power-up, the temperature sensor output must be allowed to settle to its stable value before it can be used as an accurate ADC input. For an accurate measurement of the temperature sensor by the ADC, the ADC must be configured in single-channel burst mode. The last value of a nine-conversion (or more) burst provides an accurate result." Therefore, it could be that your Temperature sensor is not settle yet or you need to make more conversions in single channel burst mode.
You also should consider optimize the ADC external circuit to minimize the ADC error related to external environment.
This Application Note can help you in How to Increase the Analog-to-Digital Converter Accuracy in an Application
Best Regards, Luis
