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AD7606-4 wrong conversion results

Question asked by ABuri on May 23, 2013
Latest reply on May 25, 2013 by ABuri

Hello everyone, I'm in need of some help.

 

I have encountered a problem during the usage of the AD7606-4. The read back conversion data via Serial Data Interface SPI (5.25 – 10.5 MHz with CPOL=0, CPHA =1) seems to be wrong.

 

For example if I applie a ~7.5 V voltage I receive ~0xBFAA (4.973V) which should be around ~0xDFDF. As well for 5 V I receive ~0x8008 (0.00244 V) which should be ~0xBFBE.

 

I am using the +-10V bipolar mode with external 2.5 V reference. VCC is 5 V while VDrive is 3.3 V. No oversampling applied. REFCAP voltage is around 4.57 V and REGCAP around 2.57 V.

 

A reset pulse (high active) of approx 60 nsec is applied after the power up to ensure the proper set up of the input range. After a pulse on CONVSTA/B, the microcontroller will be set into a wait loop until a falling edge on the BUSY is detected. Afterwards three data transitions will be made. For each of these CSn will be set low, then 16 Clock Cycles will be applied and CSn set back high again. After completion of these three transitions the cycle starts again by a new conversion start command.

 

You can find timing plots of CONVSTA/B, BUSY, CSn, CLK and SDO, as well as a schematic of the used AD7606-4 circuit in the attached pdf file.

 

Since the deadline is drawing near I’d be glad for any help on this matter.

 

Kind regards,

Alain Buri

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