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AD7655 power on sequence?

Question asked by sprince on Jul 2, 2014
Latest reply on Jul 23, 2014 by sprince

Hello,

 

I'm designing a circuit with the AD7655 interfaced with dsPIC33F using 3 wire SPI interface. After powering up the BUSY output never goes low. I'm using 5V for AVDD & DVDD and 3.3V for OVDD.

 

I've been through the datasheet many times ( I know - keep reading) and haven't found anything about the start up sequence or what logic high is referenced to on the pins are.

I'm lost as to where the my error is however I'm sure it's something simple. The issue can be reproduced on different boards/ICs.   Any advice is greatly appreciated.


As of now I have nothing on the inputs and have ties the pins to:

 

A0                - 5V

BYTESWAP - DGND

A/B              - 5V

IMPULSE     - DGND

SER/PAR     - 5V

EXT/INT        - 5V

PD               - DGND

RESET        - DGND

REFA          - 2.5V

REFB          - 2.5V

REF            - 2.5V

REFGND     - DGND

CS              - GPIO1 (OGND)

RD              - GPIO2 (OGND)

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