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EVAL-AD7655EDZ in parallel output mode

Question asked by elcambuj on Jan 20, 2015
Latest reply on Feb 24, 2015 by elcambuj

Hi all!


We have bought the Evaluation board 76xx, with the AD7655 installed (EVAL-AD7655EDZ). We intend to feed the board with a signal to get it converted into bits using the parallel output capability of the chip and board. We have followed the indications of the evaluation board datasheet but probably we missed something because we do not get any data from the ADC (that is, data pins always show 0V).


Let us explain. Maybe someone could help us with this…


Configuration is as follows:

  • We have powered the analog block of the board using a ±12V and +5V, and the digital block using +5V. Grounds are different for the digital and analog blocks. The green led indicating that the chip is powered is on.
  • Jumpers are set at its default values because we intend to operate the board in the parallel mode.
  • The input signal that we are using as a test signal (to convert) is an oscillating voltage ranging from 0 to 4.5V and with a frequency of 1 MHz (frequencies of 1 kHz, 100 kHz have also been tested without success).
  • The signal is connected to the J1 port (we also tried J2 port without success).
  • We are not using the evaluation software.


What we measured is:

  • Data bits from the output interface: all are at 0V.
  • Test points tp3(SIG+), tp16(SIG-), tp1(BUSY), and tp8(CNVST): they show the expected signals according to the time diagrams on the datasheet.
  • Even we tested the ADC input pins: they have the expected inputs to the 7655 chip. However, no data was found at the output ports (aside from BUSY and EOC).
  • We have observed that pin 36 (DVDD) of the ADC is at 0V, whereas the 7655 datasheet indicates “Nominally at 5V”. However, pin 19 (also DVDD) is at +5V.


The questions are:

  1. 1- Is it correct that pin 36 is at 0V? (it seems that the evaluation board provides several functionalities but, according to 7655 datasheet, this pin should be at +5V).
  2. 2- Could it be that the 7655 is damaged?
  3. 3- Have we missed something?


Thanks in advance!