ADS1232: ads1232

Hello Bob,

Thank you for your prompt reply.

I am not using divider circuit to power ADC. I powered the ADC circuit directly through a LDO.  Now, AVDD=DVDD=REF=+5V.

At first, I checked without input to AIN+,AIN- pins with other condition such as SPEED=80 SPS, PDWN =high, internal oscillator(CLK/IN pin 3 to pulled down using 47K ohm). With this, the output was not pulsing.

With a followup test I connected input of 20mV with same configuration as above. If I probe the pin (DOUT ) again, ADC doesn't seem to respond, i.e, output not pulsing yet.

Not exactly sure where I'm stuck.

Hi Gobinath,

With the CLKIN pin pulled low, and if both AVDD and DVDD are at the nominal operating voltage, then when PDWN is pulled high the ADS1232 should start converting.  Verify that the SPEED, GAIN0, GAIN1 and A0 pins are not floating or in a float state.  These pins should be actively driven by the micro to either a high or low state.

After reviewing the schematic there may be an issue with the PDWN connection.  The micro should connect directly to this pin without extra components in the path. Try removing D6 and C5L (that's what it looks like in schematic screen shot) and replace R66 with a 0 Ohm resistor.  This allows direct control on the PDWN pin from the micro.  Hold the PDWN low until after the supplies have reached nominal operating voltage then pull PDWN high.  Wait approximately 100ms and then pulse the PDWN pin.  The low time of the pulse must be equal to or greater than 26us.  I would try a 100us pulse to make sure any line capacitance does not prevent the full low time required.

Best regards,

Bob B

Hello Bob,

I tried steps as you said, DOUT pin is  pulsing but not perfectly.

I have also attached waveform image. 

Input of ADC AIN+,AIN- (uni-polar signal) 1.6V, GAIN=1, SPEED=10SPS, PDWN(Controlling PDWN  directly from MCU) pin gets high after powering AVDD=DVDD=REF exactly 100ms .

I don't know where I getting problem in the circuit. Any help is much appreciated. 

Thank you.

Hi Gobinath,

It appears like the ADS1232 is now active, but the DRDY/DOUT pin is not going as low as it should.  Make sure you have a good ground connection.  Also make sure you are using the correct pin on the micro.  This should be an input pin and not an output pin on the micro.  If you are using an SPI peripheral, make sure you are connected to the MISO (or sometimes called SOMI) on the micro.

Best regards,

Bob B

Hi Bob B,

After much efforts in making this work, I'll let you know the signal that I get from each pin. Please let me know if any anomalies are present. Below listed signal levels are taken from the configuration we've discussed before.

The pins which I control form MCU such as A0, GAIN0, GAIN1, SPEED, PDWN are set to levels as specified in previous post.

Input to ADC is a unipolar signal of 2.2V going to AIN+ from a voltage divider whose I/P is 3.3V source.

Hi Gobinath,

Let the XTAL2 pin float and do not tie high or low.  Have you verified the issue with DRDY/DOUT?  This should be pulsing fully low every 100ms, but the scope shot you sent previously shows approximately 800ms distance between pulses and not going fully low.

If you are seeing 50Hz on the CAP pins, or if the signal is very noisy, then you are picking up noise from your signal source and wiring.  You should have an RC low-pass filter on the inputs to help limit the noise.

Do you have conversion results that you can show me?  Or are you still having issues capturing the conversion results?  You should make sure that you are converting at the proper conversion rate.  With the SPEED pin low, you should see the DRDY/DOUT pulsing at 100ms data rate.  You may need to adjust your scope so that you can clearly see this signal going low (to GND) and that the distance between pulses is maximized on the plot so that the trigger occurs at the beginning of the scope plot and that the horizontal settings are set low enough to clearly capture the pulses.

Best regards,

Bob B

Hi Bob,

Thank you for the detailed inputs. The following are our observations.

1. We have made sure that the PWRDWN pin does follow the sequence below.

Low (after reset) -> High (100ms) -> Low (100ms) -> Stays high forever then

2. We have put the required filters on the Vcc pins

3. We have given an input of about 1V

4. The gain is set to 2

5. Speed is set to Low

6. We have tried with both External Clk source of 4 MHz and Internal Clk source

After all the above settings we see that the DOUT pin stays high and does not pulse as suggested by you.

We are keeping the A0 pin to low, and providing the input in the 1st Channel

Could you please let us know what we may be missing. Bringing up the ADC is critical for us.

Also, is there a problem with probing the ADC pins directly, since in some cases we tried to do this as well.

Please let us know if we can provide more information for you, so you can suggest a solution for us.

Looking forward to hearing from you,

Thank you for your support and understanding.

Regards,

Gobinath/ Nambi

Hi Gobinath,

This is a very interesting situation.  The ADS1232 is actually one of the easiest Delta-Sigma ADCs to use as it is pin controlled (as opposed to register controlled).  All digital input pins must connect either logic high or logic low.  The digital input pins should not float.  This would include the following pins:

TEMP, A0, SCLK, SPEED, GAIN0, GAIN1, PDWN

In your original schematic TEMP was floating.  A floating input can put the device into uncertainty.  If the internal state is toggling due to the uncertainty, the conversion may restart almost continually and the conversion never actually completes.  This may be the cause of the issue you are seeing.

Make sure that the micro pin connected to DRDY/DOUT is configured as an input pin (MISO) and not an output pin (MOSI).

Also, both the AVDD and DVDD supplies need to be operating at nominal voltage before PDWN goes high initially.

If the ADS1232 is connected properly it should be converting, however there is also the possibility that the device is damaged.

Can you send me some pictures of your setup?  Often times more can be seen in a picture than in a word description.

Best regards,

Bob B