LPC1778 ADC VREFP

[li_x]

Hello, I just noticed that we designed LPC1778 ADC VREFP for 3.0V, isolated and separated from VDDA 3.3V, but in LPC1778 datasheet VREFP is defined as " This should be the same voltage as VDDA, but should be isolated to minimize noise and error." Does that means VREFP should be the same voltage LEVEL as VDDA? From UM10470 user manual document, our software engineer pointed another sentence to me that "Measurement range VSS to VREFP (typically 3 V; not to exceed VDDA voltage level)" which looks like to say it's ok that VREFP is 3.0V different from VDDA 3.3V. Please help for a clarification. Thanks.

[Sabina_Bruce]

Hello Xiaoling,

As per the datasheet for the LPC1788, the VREFP should only be tied to the VDDA pin if you are not using the ADC or DAC module.

If you are then the values may range from  -0.5 to 4.6 V and as you mentioned above it should not exceed the VDDA voltage level. 

Essentially if you are using either ADC or DAC module then 3.0V is not a problem in your case.

Best Regards,

Sabina

[li_x]

Sabina,

Thank you for the reply. It does help.

Xiaoling