AD7656: Is it possible to read 2 channels as opposed to all 6

Question Is it possible to collect only the results from V1 and V2 (because of time constraints) and then cancel the transmission? Answer You can clock out the first two results then stop the serial interface data transfer. At the end of the next conversion all 6 results registers will get over written with new values.

burned out issue of AD7656

Question I use +/-15V power supply for AD7656, but it sometimes burn out. Answer AD7656 broken issue is may caused by over voltage first, then over current. The over voltage is because some high frequency spike on +/-15V power supply. use only +/-12V power supply to reserve enough headroom

AD7656: RC between AVcc and DVcc

Question We are looking for a bit more info on the RC that should be placed between AVcc and DVcc when using a single supply. Which direction should the RC flow? Answer I believe that a small value resistor e.g 10 Ohms should be sufficient to separate the digital noise on the digital supply from the analog supply pins. The system's analogue supply should be connected directly to the AVDD and the resistor to DVDD should be tapped off at a point which minimises the path shared by AVDD and DVDD supplies.

Part number of the EMC Filter in the AD7656EVB

Question Would you please tell me the part number of the EMC Filter in the AD7656EVB? Answer The part number of EMC filter is Murata NFE61PT102E1H9L and can be sourced from Farnell. (Farnell code is : 9528202)

AD7656/AD7656-1 - problems even after RESET

Q: I have given the AD7656/AD7565-1 a RESET and a valid CONVST signal but I periodically get strange and repeatable data. I have factored out noise from input and timing issue during my debug. What else could I be missing? A : Ensure a stable reference (if external is used) and proper decoupling. Avoid running digital lines under the devices because doing so couples noise onto the die.

AD7656/AD7656-1 - need for RESET

Q: Do I need to reset the AD7656/AD7656-1 after each sample? A: In all modes, the parts should receive a RESET pulse after power-up. After the RESET has been applied, the part should convert normally.

AD7656/ AD7656-1 - grounding considerations

Q: Are there special grounding considerations for the AD7656/AD7656-1? A: At least one ground plane should be used. It can be common or split between the digital and analog sections. In the case of the split plane, join the digital and analog ground in only one place, preferably underneath the AD7656/AD7656-1, or at least as close as possible to the part. Multiple connections are acceptable as long as the multiple connection mimics a solid GND plane.

Difference between AD7656 and AD7656-1

Q: What are the similarities and differences between AD7656 and AD7656-1? A: The AD7656-1 is a pin to pin and software compatible upgrade to the AD7656. The AD7656-1 has reduced decoupling requirements and reduced bill of materials cost compared with the AD7656. Both parts contain low noise, wide bandwidth, track-and-hold amplifiers but differ in full power bandwidth. The AD7656 can handle input frequencies up to 12 MHz, the AD7656-1 can handle up to 4.5 MHz. Functionality-wise, the only difference is that the AD7656 can work with a 2.5V or 3V reference whereas the AD7656-1 can only accept a 2.5V reference. There are AC/DC specification differences that could affect calibration routines – please refer to the datasheet specification table for more information.

My question is the same, but for two different devices, AD974 and AD7656.

Q My question is the same, but for two different devices, AD974 and AD7656. I want an input range of at least +/-5V, and from what I understand from the datasheets, I can use both of the devices as single ended, i.e. I can use the four inputs on the AD974 for four different signals and still have an input range of +/-10V and the same for the AD7656, I can use the six inputs for six different signals and still have an input range of +/-5V. so my question is quite simple, can I use the devices with bipolar inputs and still get an input range of +/-5V respectively +/- 10V?? A To answer your question yes you can use the devices with bipolar inputs, AD974 only have bipolar +/-10V input range, input range for the AD7656 is Vin = +/-5V or +/-10V depending on the range pin referenced to ground. NB: The supplies Vdd and Vss must always greater or equal to the input swing.

In Your data sheet for the AD7856ARS page 7. Pin 7 CREF1, it says 470n NP0. Is this correct? We cant find such high value with NP0.

Q In Your data sheet for the AD7856ARS page 7. Pin 7 CREF1, it says 470n NP0. Is this correct? We cant find such high value with NP0. A The recommendation that the 470nF capacitor be an NPO type is not really required in practice. We have achieved specified performance without an NPO capacitor in place. The reason for the dual decoupling capacitors is to effectively decouple the high frequency bursts of charge which arise in the DAC. So the absolute value of the capacitor is not so important. Any 470nF ceramic capacitor with low ESR, ESL is suitable. The designation of a capacitor as NPO means that it's value does not have a significant positive or negative temperature coefficient. We originally thought that the high equivalent series resistance of high value ceramic capacitors could cause a problem but this turned out not to be the case.

AD7656: power and decoupling caps requirements

Q What are the power and decoupling caps requirements for the AD7656? A As you can see from the figures below the static current drawn by the AD7656 is the same as the operational current this is as a result of the comparator used on the AD7656, the comparator draws more current during track mode. The VDD and VSS supplies are only used for the track and hold switches on the analog input and they don’t require much current, at 250 ksps they require 250 uA each. These supplies will draw little current when in power down. The Avcc supply takes most of the current as this is the supply used for the Ad7656 cores. This is the supply that is used for the conversion process. Here is the min decoupling that the part requires AVCC pins 46/47 - 100uf poly tantalum. AVCC pins 43/44 - 100uf poly tantalum. AVCC pins 34/35 - 100uf poly tantalum. VDD pin 31 - 10uf tantalum. VSS pin 30 - 10uf tantalum. Vdrive pin 9 - 10uf tantalum. AVCC pin 60 - 10uf tantalum. AVCC pin 50 - 10uf tantalum. Refcap A/B/C pins 54/56/58 - 10uf tantalum. Refin/Refout pin 51- 10uf tantalum. However the 8 Avcc pins can alternatively be decoupled with a 10 uF and 0.1 uF pair on each pin. Its important that the customer pays particular attention to the Avcc layout and decoupling as this is the supply for the AD7656 core and conversion. Attachments: AD7656_DecouplingRequirement.docx

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Products Mentioned

AD7656A-1 Production
The AD7656A-1 is a reduced decoupling pin- and software-compatible version of AD7656A. The AD7656A-1 contains six 16-bit, fast, low power successive approximation...
Datasheet
AD7656A-1 on Analog.com

AD7656-1 Production
The AD7656-1 / AD7657-1Â / AD7658-1Â are reduced decoupling pin- and software-compatible versions of AD7656Â / AD7657Â / AD7658. The AD7656-1 / AD7657...
Datasheet
AD7656-1 on Analog.com