ADS1232: Abnormal reading but can't control the PWDN pin

Hello Lorenzo,

Welcome to the TI E2E community.

Can you describe 'abnormal' readings with a bit more detail.

1.  Does the ADC operate normally, but the readings are out of spec, such as a large gain error?

2.  Do the errors persist until another power-cycle, or do they eventually settle into normal readings?

3.  How long do you wait between power cycles; specifically power-on, power-off, power-on?

The internal power-on reset circuitry inside the ADS1232 may not correctly reset the device if the ADC is not in a power-down state for a least 60 seconds or longer before a power-up.  The fix for this behavior when running multiple power-cycles less than 60s is to follow the power-up timing sequence in figure 8-15 of the datasheet.  Unfortunately, this is the only way to force a proper reset of the device after a short power-cycle has occurred.  There is not another way using the Speed/SCLK/DRDY/DOUT pins to force an internal reset other than using the PWDN pin.

If you have very 'short' power dips, such as brown-out conditions, then adding a larger supply capacitor to maintain the voltage at the ADC during these transient events should help, but this will depend on the exact timing of the power-cycling in your system.

Regards,
Keith Nicholas
Precision ADC Applications

Hello Keith,

To answer your questions:

1. The most common issue we’ve observed is a significant gain increase after powering on, which in most cases is resolved with a brief power cycle. However, we’ve also seen rare instances of random, short bursts of high gain output (though this is less frequent).

2. It appears that a power cycle is the only way to resolve the problem.

3. The issue occurs both after powering on the board following an extended period of being off (e.g., 1 day) and after shorter durations (e.g., 10 seconds).

Apologies for not providing more detailed technical information, but we've only recently started noticing an increase in these issues with our latest batch of boards. Could there have been any changes in the manufacturing process of this component in recent years?

Our main concern is not with the short power cycles, but rather when the issue arises after the board has been powered off for an extended period (anywhere from 1 day to a week). It is crucial for us to ensure that this problem does not occur once the product is in the hands of our clients.
Thank you for your assistance.

Best regards,

Hi Lorenzo,

This does sound like a power-up reset issue.  Since you can also see this after the boards have been off for a long period of time, there may be a power-up ramp issue.  If the power supplies do not ramp up monotonically, with dips in the voltage, this could result in the failures that you are encountering.

If possible, please measure the supply voltages with a scope during power-up.

We do manufacture this device at two different locations, so there could be small shifts in device behavior depending on when you purchased the devices.

Regareds,
Keith

Hello Keith,

I conducted the measurements as requested. I tested boards both when the issue was present and when it was not, as well as boards that have never exhibited any issues. In all cases, I observed the same power-up ramp, as shown in the attached image.

Hello Lorenzo,

The power-up behavior looks good; no dips in either DVDD or AVDD.

You stated in your first post that PDWN is pulled-low; I assume you actually have it pulled high to DVDD, or the ADS1232 would be in power-down.  Keeping PDWN low until DVDD has stabilized should fix any power-up concerns, as long as DVDD is powered down for at least 1min before power-up.  You can add an RC circuit to PDWN to keep it low until DVDD has settled.  This is shown in the ADS1230 datasheet.

Based on your description, this seems to be only power-up related.  However, you may want to add 1nF common mode capacitors to each of the CAPP and CAPN pins as shown below, as this may help near 0 full scale.

Regards,
Keith