ADS131A04: Multiple device configuration setup (Synchronous Slave Mode)

Mago-san,

First, I assume they using three synchronous slaves controlled by a single master similar to figure 100 in the datasheet. It would be connected like this:

Here are the answers to the questions.

1. Yes with this configuration, you would need to program each of the devices separately, sending the initialization setup 3 times. The three devices have most of the SPI tied together, DIN, DOUT, and SCLK. However, the /CS is tied only to one device, and the /DONE for that device is used as the /CS for the next device. Only one device is programmed at a time, and they are programmed one after the other. Figure 101 shows only two devices, but I added some text to show that they are programmed separately, using the /DONE of device 1 to as the /CS of device 2.

2. The status word comes out on every single communication frame for the ADS131A04. Any time you read data, the status word will come before the data.

3. Using 3 devices, you would need to clock out 3 frames, each with 5 words. Here, I'm assuming dynamic frame size, with the CRC disabled. Each frame has a total 120 bits and three frames would be 360 bits. With an SCLK of 12.228MHz, you should be able to run the device as fast as 32kSPS, but any faster than that, the daisy chain would be to slow to clock out the data.

I would also note that the master must also have a synchronous clock. The master must be completely synchronous to the devices, and would be sending /DRDY pulses at exactly the data rate of the devices. Often, I recommend using a master device in asynchronous interrupt mode or in synchronous master mode, so that the /DRDY are properly generated for the slave devices.

Do you have more information about your customer's system? It would help to know what they are designing to give better recommendations.

Joseph Wu