AD7980 in 4-WIRE CS MODE WITHOUT BUSY INDICATOR, How many AD7980 can be conected in this way? In datasheet, the example of this application is only two parts, if possible, connected three or more?

Hi Sara123 ,

Please refer to page 21 of the datasheet. It states that the 4-WIRE CS WITHOUT BUSY INDICATOR is a configuration when using multiple AD7980. Thus, you can use 2 or more AD7980.

Regards,

Jo

Hi NathanT，

Thanks for your reply，we have tested with 3 AD7980  to an SPI-cmpatible digital host. but there are some errors. would you mind giving the right timing diagram? By testing,the SDOs connected together can not get the right results. if seperated, it is ok. So it maybe somethings wrong,  Could you give the application example?

Thanks.

this one

other 

All SDOs are connected to Pull-up resistor

All SDO connection pull-down resistors

schematic diagram

The error occurred between two SDOs of AD7980 that did not send out data in 3 AD7980 system.   If only two AD7980 chips were used in the system, this problem would not occur. There will only be one AD7980 waiting to send data.

Hi woodjohn ,

You have stated that when you are using only two AD7980, you are able to get the proper output with a proper timing diagram, as per stated in the datasheet. May I request some screenshot from your scope if your configuration is two AD9780? So that I could properly assess your concern. And so that I could further assist you.

Regards,
Jo

We have holidays from June 22nd to June 24th and work on June 25th. I‘m glad to create some pictures of the two AD7980 systems. What kind of pictures would you like to see that are more useful. like I have sent picures?

Hi woodjohn ,

Pictures just like the one you have sent yesterday. Output of the system but just using two AD7980. So that I could properly assess your concern and so that I could further assist you.

Regards,

Jo

In 3 AD7980 systems, when AD7980A completes sending data, the SDOs of AD7980B and AD7980C will output data at the same time, which may cause conflicts. But in 2 AD7980 systems, when AD7980A completes sending data, only AD7980B is waiting. There are no problem with the 2 AD7980 systems. I don't know what I can do?

In 3 AD7980 systems, when AD7980A completes sending data, the SDOs of AD7980B and AD7980C will output data at the same time, which may cause conflicts. But in 2 AD7980 systems, when AD7980A completes sending data, only AD7980B is waiting. There are no problem with the 2 AD7980 systems. I don't know what I can do?

Hi woodjohn ,

I would suggest trying the configuration given in the datasheet. Connect all SDO of the AD7980 to a single data in of the host and configure each chip select (CS) to low sequentially. Which in your case, you have multiple data in for each SDO of AD7980. 

Let me know if this helped you in your concern so that I could further assist you. 

Regards,
Jo

I used the configuration provided in the datasheet first, just like the graph you provided, but it made an error and could not read back the correct AD conversion value. I suspect that 3 AD7980s cannot be used in this mode. In order to analyze the reasons, I separated the SDOs. Only SDOs is separated, everything else is the same. If there are no conflicts between the separated SDOs, they can be connected together. But I observed a conflict. The previous image shows the details of the observed conflict.

After separating the SDOs, I can read the correct AD conversion values. But the AD7980s that I did not read simultaneously output the highest bit of AD conversion results (estimated through analog signals). In this case, if SDO is connected together, an error will occur.

笔记

Hi woodjohn ,

You can try checking your configuration for chip select (CS). Make CS1 low if you will be using the AD7980_A from your set up. Then after using the first AD7980 make its CS high, before making CS2 low for AD7980_B. And so on.

Regards,
Jo

After separating the SDOs, I can read the correct AD conversion values from any of the three AD7980s. If two AD7980s are used(SDO connected together), the correct value can also be read from either one.This figure shows the application of CS.

Hi Woodjohn，if three AD7980s are used with SDO connected together , they can work well ?

Thanks.

It seems that there is a problem with my English, which has been the problem since the beginning. Three SDOs connected together have been unable to function properly. To find the reason, I separated the SDO and discovered a conflict. I want to see if anyone can prove me wrong. Find examples of three AD7980 SDO connections working properly together.

From the beginning until now, the problem has always existed. There has been no progress.

It has never worked well, and I don't believe it can work well.