ADS7953: ADC is returning unexpected values

Przemyslaw Bielak

Part Number: ADS7953

Hello,

We are currently trying to get the ADC measurements from all 16 channels from ADS7953 chip - we are using ADS7953EVM board for testing purposes.

I tried to use the driver in Auto 1 mode, so the sent sequence looks like this:

- 0x8000 - enter Auto 1 program mode

- 0xFFFF - use all ADC channels

- 0x2C40 - send Auto 1 mode configuration

- 0x0000 in a loop - continue operating in Auto 1 mode

Here is the screenshot of all signal from logic analyzer:

If I understand the datasheet correctly, the ADS should be sending measurement data starting with 4 address bits and 12 data bits.

Could you please me if this situation is caused by wrong MOSI data, or is it some other problem?

Best regards,

Przemyslaw

over 6 years ago

0 Vishy Viswanathan over 6 years ago

TI__Mastermind 21685 points

Przemyslaw,

Can you test by sending Auto1 mode configuration command (0x2C40) at the beginning as well. See logic analyzer screen shots below.

Auto 1 Configuration and Programming commands

Channel Data

Let me know if this works for you.

Thanks,

Vishy

0 Przemyslaw Bielak over 6 years ago in reply to Vishy Viswanathan

Prodigy 70 points

Hello,

Unfortunately it did not help:

I am using ADS7953EVM board, so maybe the board connection is wrong. I connected:

P2.1 - CS

P2.3 - CLK

P2.4 - DGND

P2.11 - ADS data in

P2.13 - ADS data out - no pull up/down on processor side

J3.3 - A5V

J3.5 - DGND

J3.6 - AGND

J3.10 - D5V

All jumpers on board are in their default position except of W5, which is set to CS (CNTL).

Could you please check if this connection is correct?

Best regards,

Przemyslaw

0 Vishy Viswanathan over 6 years ago in reply to Przemyslaw Bielak

TI__Mastermind 21685 points

Przemyslaw,

The connections and jumper settings you list above look correct. Couple of comments

a) P2 pin 1 is not marked on the silk screen. Please note it's on the inside. Picture below shows my connections to P2.1(green), P2.3 (yellow), P2.11 (blue), P2.13(purple)

b) Also, on the ADS7953EVM silk screen, J3 is called out as P3. P3.1 is on the outside. See picture below

Also, do you have another EVM to try with?

Thanks,

Vishy

0 Przemyslaw Bielak over 6 years ago in reply to Vishy Viswanathan

Prodigy 70 points

Hello Vishy,

My connection is exactly the same as yours. The only difference is a connection to W4 jumper. On you photo, is it only a probe, or is it some voltage reference connected to that jumper?

Unfortunately we do not have any other EVM board to test, it was the only sample we received.

Thanks, Przemek

0 Vishy Viswanathan over 6 years ago in reply to Przemyslaw Bielak

TI__Mastermind 21685 points

Przemek,

I think I changed default setting of W4 to apply a known external voltage to CH0 input for testing channel 0 conversion. See below

Not sure why you are not seeing in D15:D12 conversion channel number. What SPI clock phase and polarity setup are you using: please try selecting clock phase high and clock polarity as low

Other option is to change the silicon on the board or get you a new EVM.

Thanks,

Vishy

0 Vishy Viswanathan over 6 years ago in reply to Vishy Viswanathan

TI__Mastermind 21685 points

Przemek,

Could you try testing in manual mode?

As an example, below I send 0x1880, 0x1900, and 0x1980 to read data from channel 1, channel 2 and channel 3. Channel 1 input = 1.25V, Channel 2 = channel 3 = 0.625V. See below logic analyzer capture of SPI exchange between ADS795x and MSP430: channel 1 data comes out in 3rd frame, channel 2 data comes out in 4th frame and channel 3 data comes out in 5th frame.

Just checking if any other mode works.

Thanks,

Vishy

0 Przemyslaw Bielak over 6 years ago in reply to Vishy Viswanathan

Prodigy 70 points

Vishy,

After sending Manual commands, the receive data still doesn't look correct:

The only difference I see between our signals, is that your MOSI data is split into 2x8 bits, but mine is 1x16 bits on one CS low signal. Do you thinks it can cause the problems I am facing?

Bests, Przemek

0 Vishy Viswanathan over 6 years ago in reply to Przemyslaw Bielak

TI__Mastermind 21685 points

Przemek,
I looked closely at your logic analyzer MISO data: looks like most of the time you are seeing echo of MOSI data in MISO. Could you double check your SPI connections to MCU?
MSP430 SPI peripheral uses byte buffers so you see the MOSI data split. It is perfectly fine sending 1x16bits as you do.
Thanks,
Vishy

0 Przemyslaw Bielak over 6 years ago in reply to Vishy Viswanathan

Prodigy 70 points

Hello Vishy,

You can see my connection on attached picture with cable description next to each cable.

I think it is correct, but could you also take a look?

Best regards,

Przemek

0 Vishy Viswanathan over 6 years ago in reply to Przemyslaw Bielak

TI__Mastermind 21685 points

Przemek,

These connections look fine. Not sure why you are not seeing at least channel number data. What's the SPI clock frequency?

Thanks,
Vishy

0 Przemyslaw Bielak over 6 years ago in reply to Vishy Viswanathan

Prodigy 70 points

Vishy,

The clock frequency is 1MHz. timings between signals also seems to ok according to the chip datasheet.

Best regards,

Przemek

0 Vishy Viswanathan over 6 years ago in reply to Przemyslaw Bielak

TI__Mastermind 21685 points

Przemek,
We are on the process of getting you a new EVM. Please let us know once you test with that.
Thanks,
Vishy

0 Przemyslaw Bielak over 6 years ago in reply to Vishy Viswanathan

Prodigy 70 points

Hello Vishy,
The second board arrived and after connecting it to our processor, I received the correct MISO data. Then, I switched to the old ADS board and it also worked. The problem was not the ADS chip itself, but a faulty cable used in previous configuration to connect the ADS board to our processor, which was broken under the insulation. Data sent by the ADS chip then couldn't be received by our processor.

Thank you very much for helping us during this problem.
It seemed that chip was working perfectly fine, but was unfortunately connected to other faulty element.

Best regards and thank you for your help,
Przemek

0 Vishy Viswanathan over 6 years ago in reply to Przemyslaw Bielak

TI__Mastermind 21685 points

Przemek,
Thanks a lot for your update. Let us know if you need any additional help.
Regards,
Vishy

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ADS7953: ADC is returning unexpected values