AD7986 External reference (Vref) typo? and connection queries

Document created by analog-archivist Employee on Feb 23, 2016
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using the AD7986 with an external reference configuration (with a +5V
ADR435 ref) with PDREF=high and REFIN=low.

first question is : how you connect my external reference buffer (AD8031) ?
The REF pin and the BVDD pin should be connected together to the output of the
external buffer (same potential) or the BVDD pin should be only connected to a
+5V power supply ? It's not really clear in the data sheet.

second question is :
Table 7 of the data sheet, VREF is equal to +5V and the FSR = +/-4.096V.

On the first page of the data sheet, the true differential analog input voltage
range is +/-VREF with VREF up to 5.0V.

With the external reference configuration , what is the max input voltage range
+/-5V or +/-4.096V ?

 

 
(Ans 1). For an external reference configuration (with a +5V). The external
reference buffer must be connected to the BVDD pin. This
is is stated in table 6, pin 19,20 descriptions column, (page 8, of datasheet
rev.B).

(Ans 2). Apologies, There appears a slight confusion here. Typically the
Common-Mode
Input Range VREF/2. see table 2.

Vref=5V in table 7 is a typo, it should be Vref=4.096V. The max input range is
+/-Vref for
the external reference.

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