AD7124 Always reads zero. RDY/IDLE bit is always 1

Hi, 

Apologies. This is just a common steps I prefer to check if the ADC is converting and communicating properly with the MCU. Upon power up, can you pull /CS low and just monitor the DRDY pin if it is pulsing at correct ODR? 

Once you see it is pulsing, can you try to change the ODR settings and then see again if it is now pulsing at the new ODR? Then you can also check if you configure the ADC correctly by writing and reading to the same register. Once you confirm that the ADC is converting and that the SPI interface is good. Then we can go to the hardware debugging.

I'm sorry I'm kinda loaded now, but I will review this and come back to you if I find anything else. 

Thanks,

Jellenie

Hi Jellenie,

I have powered on the ADC, pulled /CS low, and DOUT/RDY remains high. 

I'm pretty sure something else is the issue. Maybe even the ADC is broken? I'd be surprised though.

My reasoning is that when I communicate with the device, it appears to be functioning correctly.

For example, the ID register reads back correctly. If I enable the MCLK_COUNT_EN bit in the ERROR_EN_REGISTER, the MCLK_COUNT register begins to update as expected. 

Hi 

If it remains high then it seems the ADC is not converting. Just to confirm the above suggestion is upon power up when ADC is at default config is that correct? 

Because I reviewed your register settings. It appears that your gain is set to 16. So if you have an input of 398mV then multiplying it with 16 will exceed and saturate the ADC. May I know why you used 1000uA? I am assuming you are using PT100 right? Have you seen this tool? This would help you check if the config is acceptable for ADC. Please have a look and let me know your feedback. 

https://www.analog.com/media/en/designtools/calculators/rtd_configurator_and_error_budget_calculator-rel1.0.0.exe 

Thanks,

Jellenie

Hi

>Just to confirm the above suggestion is upon power up when ADC is at default config is that correct? 

I've tried both in default config, and after configuration the current source. 

Right after boot, using the default values, and enabling all the errors, I see that the error register is 0xA880, showing that reference is not detected, and and both inputs are over voltage, and the analog LDO is not happy.

If I enable the current sources, all errors go away except the Analog LDO error (ALDO_PSM_ERR).

 I've looked at the tool. Thanks! I believe I should change my reference and headroom resistor 2K and 330 ohm respectively.

I also believe setting a gain of 8 and a current of 500uA is better.

Hi, 

Yes because I think the default config uses external reference and if your REFIN pins has no voltage because of the absence of IOUT then the ADC won’t convert which is the reason why DRDY remains high or low. 

We have here our recent released article regarding RTD application including the tool. Hope you find this helpful.

https://www.analog.com/media/en/analog-dialogue/volume-55/number-2/how-to-select-and-design-the-best-rtd-temperature-sensing-system.pdf 

Thanks,

Jellenie

Hi,

Thanks, that's a helpful guide. From reading it, my circuit is correct, with the exception that the reference resistor and headroom resistor need to be changed.

The error bit that is still set is ALDO_PSM_ERR. This won't go away no matter what I do. If I measure the analog LDO output, it's around 1.9V. Is this okay? This is what I'm the most stuck on, since even with correct reference voltages greater than 0.7V, or using an internal reference, this bit remains high. 

If I disable the monitoring, then the bit goes away, but I believe the error condition is still present, just hidden.

Hi, 

That is weird. Do you read the error registers consecutively and does the error flag remains as always or is it only appeared once? 

It is curious as you've mentioned that the LDO output is around 1.9V so that should be okay. I am wondering what might have causing this issue as the LDO output appears to be fine. Are you using Eval+ software or your own code? 

Thanks,

Jellenie

If I read it repeatedly, it remains. 

I am using my own software.

I've considered soldering the SPI pins from EVAL-SDP-CB1Z and using the Eval+ to talk to the device on my circuit board. 

Hi, 

I was thinking if this is just a bug somewhere. Are you having issues with your measurements? or everything appears to be normal? 

Let me see if I can double check this. I am currently wfh but when I get a chance this week I'll try if I can replicate the issue. 

Thanks,

Jellenie

Hi,

I'm wondering if the usage of the analog pins matters. In the app note CN0383, the "Multiple 3-wire RTD Configuration" shows the following:

My design on the other hand is using AIN0 and AIN3 for IOUT. Maybe this causes a problem. 

I'm going to be ordering a new board within a week or so, and I'll also pick a new Rref and RHeadroom.

Here's a screenshot of the Excel tool:

• Hi, 

No. The selection of AIN or IOUT pins is flexible. The above configuration is the configuration we used on our circuit note. It is also the default configuration we have used with our firmware example codes that will be also release soon. There’s no harm in changing these but I think using exactly the same config or external components we have used will just make your life easy. 

Thanks,

Jellenie

I've just received my new board which in theory is exactly the same as the eval board. However, I'm still seeing ALDO_PSM_ERR set, even though the voltages look good, and similar to what I reported earlier.

Any luck on replicated the issue on your end?

I've just received my new board which in theory is exactly the same as the eval board. However, I'm still seeing ALDO_PSM_ERR set, even though the voltages look good, and similar to what I reported earlier.

Any luck on replicated the issue on your end?

Hi, 

Yes, we have tested this on our side and we do not see this issue. The ALDO_PSM_ERR or DLDO_PSM_ERR does not flag since we have a valid LDO output of 1.9V and 1.8V respectively. Just a quick question, can you check if you also enabled the ALDO_PSM_TRIP_TEST_EN? Because if you do this will automatically set the ALDO_PSM_ERR bit as this is intended to check the power supply monitoring, so the input to the test circuitry is GND rather than the actual LDO output which makes the error bit flag. 

Thanks,

Jellenie

I checked my ERROR_EN bits, and was in fact setting the ALDO_PSM_TRIP_TEST_EN bit.

I cleared that, and the error goes away.

Now what I see is the !DRDY bit stay high, and DATA is always zero.  I

VREF is 2.6V

AIN1-AIN0 is 0.115 V

LDO outputs are 1.9 and 1.8.

I'll poke around and see if I can find out any other issues. 

Good to hear that it solved the issue. 

As for the other concern. When Data is always 0 do you see any other errors flag? 

May I know what's your gain setting for an input of 0.115V?

It is interesting that the pin stays high but the Data is always 0. 

Usually, when DOUT/RDY stops pulsing at any time and it stays high or low (even though the ADC is configured for continuous conversion mode), this indicates that the serial interface has become asynchronous (incorrect number of SCLK pulses, glitches on the SCLK line). 

And when Data remains high or low is usually cause by invalid reference, overrange or underrange input voltage. 

So again upon power up, with CS low, when you monitor the DRDY pin does it stay high or pulsing at correct ODR? Then again try to change the ODR by writing to the filter register then with /CS low monitor again the DRDY pin if it is pulsing at a new selected ODR. When you do this check please confirm that you have a valin reference and input voltage range. 

Thanks,

Thanks,

Jellenie