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LPCXpresso OM13058 LPC11U68 VREFN maximum voltage?

Question asked by dirtyd on Sep 8, 2016
Latest reply on Sep 12, 2016 by jeremyzhou

Is there a specification for maximum VREFN voltage? In the datasheet and user manual there are recommendations for best performance, but no hard limits except for the upper limit on VREFP.

 

From the user manual, page 304 :

"Remark: For best performance, select VREFP and VREFN at the same voltage levels as VDDA and VSSA. When selecting VREFP and VREFN different from VDDA and VSSA , ensure that the voltage midpoints are the same:
(VREFP-VREFN)/2 + VREFN = VDDA/2"

I am attempting to set VREFN at approximately 2.7V and VREFP at approximately 3.2V, for about 0.5V difference, using LM385 voltage references. VREFP pin is fine, I can connect either reference to it, but with VREFN pin it is pulled down to 0.85V. I can't see anything on the OM13058 schematic to explain this so I am wondering if it some kind of internal protection in the MCU itself?

 

Does anyone have any experience trying to use a similar high VREFN voltage?

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