LPC11E66 ADC Vref Different From VDDA Ramifications

[mikenn]

What's up NXP,

In the LPC11E66 user manual it is claimed the 12 bit adc will "give best performance" when Vref is the same as Vdda.  I am using Vref = 2.5V and Vdda = Vdd = 3.3V.  Both are well filtered.  Can someone please give more detail on what specific degradation(s) can be expected in my situation?

[mikenn]

What's up Xiangjun rong,

Please see UM10732 section 16.4 Pin description (page 305):

Remark: For best performance, select VREFP and VREFN at the same voltage levels as
VDDA and VSSA.

MikeN

[xiangjun_rong]

Hi,

As the Table 8. Static characteristics, the Vrefp voltage ranges from 2.4V to VDDA, I suppose it is okay to connect 2.5V to Vrefp with 10uF decoupling capacitor.

I have not seen anywhere that it is mentioned that "the 12 bit adc will "give best performance" when Vref is the same as Vdda. Can you tell us where the remark is written?

Hope it can help you

BR

Xiangjun rong

[mikenn]

What's up Xiangjun rong,

(sorry I placed this in the wrong spot)

Please see UM10732 section 16.4 Pin description (page 305):

Remark: For best performance, select VREFP and VREFN at the same voltage levels as
VDDA and VSSA.

MikeN

[xiangjun_rong · Accepted solution]

Hi,

Yes, I see the remark that the Vrep voltage must be vdda in order to get best performance for LPC11E6x in UM10732.pdf.

Unfortunately, I have asked AE team, we have not the test report, which can describe the ADC performance with different Vrefp voltage.

Sorry for not helping you

BR

Xiangjun Rong