EVAL-AD7746EBZ, how to use the second channel

#1

Hi ,

I am doing test on the AD7746 evaluation board and run into a puzzle. The datasheet says, to test CIN2, which is the second input channel, the capacitive length sensor should be disabled by disconnecting the two 0 Ohm SMD resistors, R1 & R2. I was able to locate R1 and R2, and I marked them in the photo (attached), but I do not know how to disconnect them. they do not look like jumpers.

I chatted with a guy online and was told that R1 and R2 are both small 0201 jumper resistors that would need to be desoldered from the board. They’re not designed or intended for easy-on, easy-off removal.

The thing is that they are too tiny, as small as approximately 2 mm in size, it is very difficulty for a common user to desolder the resistors without damage them, and doing so will make it not returnable if test result does not satisfy user.

Can someone please take a look and give me some suggestions?

Best regards,
Gu

#2

I tried to upload a photo of the board, but a message says new user is not allowed to upload attachment. This is my first post here, do not know how to upload file.

#3

Hello, Gu. I’m looking into this with a few colleagues and will relay my findings. Hopefully in the interim someone more versed in this device can assist.

#4

R1 and R2 are indeed surface mount resistors, in an 0603 (1608 metric) package.

The reason evaluation boards are produced is to offer potential users of the featured component-level device(s) a convenient means of evaluating the performance of said device(s) in the context of a known design; it saves a user the trouble of having to design and build their own evaluation platform, and the uncertainty of whether the observed performance is due to the device or their own board design.

The cost of an evaluation board is a fee for this convenience; regardless of whether or not a user is satisfied with device performance, the cost of an evaluation board is not refundable unless it is determined to be damaged or defective at the time of delivery.

#5

#6

Hi Rick,
Thank you for your reply.
The board is designed for evaluation of two channels, and testing the
second channel, CIN2, is a very important part of the evaluation, it
supposed to be designed with two jumpers linking to the two resistors
for easy removal and evaluation.

Gu

#7

I’m in contact with our Analog specialist to check into this and get confirmation of the issue from ADI. In the interim, unfortunately all I can really say is that SMT resistors aren’t meant to be pulled on and off the board freely. Why Analog designed the board this way, I hope we can find out for you. If you’re concerned over desoldering processes potentially damaging the rest of the board, you may be able to simply pry these resistors off with a pick. They would not go back on again once so pried, unfortunately.

#8

Hi Matt,

Thank you for your effort to address the issue.

I have found more problem with the AD7746 board and also posted it on
ADI’s engineering zoon already.
https://ez.analog.com/data_converters/precision_adcs/f/q-a/110561/ad7746-precision-and-repeat-ability

Could you please also Help with the issues? I will not pry the resistors
for testing CIN2 before the CIN1 test is acceptable.

Regards,
Gu