ADS8688： ADS8688 command order

Dale Li said:

Hello user6482702,

The command 0x8500 is used to reset the ADC, it doe not select any channel for an effective conversion. Please use other commands, for instance, 0xC000 to select Channel 0 for conversion.

If it still does not work, please

1. check if the voltage on both REFIO and REFCAP pin is 4.096V
2. provide your timing plot for /CS,SCLK, SDI and SDO captured with an oscilloscope
3. provide your schematic to check.

Thanks & regards,

Dale

Thank you for your reply.

green：sclok

blue：cs

red：SDI

Yellow：SDO

Paste the oscilloscope image below

Hello,

Have you checked the voltage on the REF pins? Can you provide your schedule?

Please use CPOL=0, CPHA=1 for your SPI configuration and check again.

Thanks&regards,

Dale

It will be a circuit diagram.

It does not work.
Should the command just send 0xc000?

The voltage on the REF pin is 4.096V.

I used to put 5v. Will the tip break?

It does not work.
Should the command just send 0xc000?

Hello user6482702,

You connect the /RST/RD pin 2 to the DGND and the ADC is under power down state, this is the key reason why the ADC does not have any reaction. This pin can be tied to the DVDD with a pull-up resistor.

Other issues in your schematic:

1. DAISY pin 3 should be tied to the DGND since you have only one ADC.

2. DGND and AGND should share a same solid ground plane, I did not see any connection between them in your schematic.

3. A RC filter is recommended on each ADC's input, the series resistor can limit current and protect the ADC. See the EVM User's Guide.

4. The 10uF capacitor CC019 should not be shared, REFIO and REFCAP require a dedicated capacitor for each pin. Also, ceramic capacitors are good for them.

0xC000 is the correct command for data conversion on CH0, however you need 16 more SPI clocks to retrieve the data in the same frame.

5V definitely is not in the normal reference range(4.046~4.146 specified in the datasheet). From your schematic, you are using the internal reference by connecting /REFSEL to the ground, this is good.

Regards,

Dale

Thank you very much. After fixing it, it worked.

However, only 0-2.5V can be sampled.
I want to sample ± 2.5v.
Do I need to send commands programmatically?