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.

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.

Hello, may I ask if the problem has been resolved? Recently, I have been using the AD7980 chip and found that the sdo pin did not revert to a high impedance state after the sdi was pulled high as described in the manual. Instead, it took several tens of microseconds for it to revert back to a high impedance state. Have you encountered this situation?What is your sck frequency？

Hello, may I ask if the problem has been resolved? Recently, I have been using the AD7980 chip and found that the sdo pin did not revert to a high impedance state after the sdi was pulled high as described in the manual. Instead, it took several tens of microseconds for it to revert back to a high impedance state. Have you encountered this situation?What is your sck frequency？