ADS1225: output latched

Hailong,


I have heard of instances with repeated power up conditions. When this happens, it is possible that repeated power supply spiking can cause the digital to come up in a bad state.

The ADS1225 does have a power-on reset (POR) circuit that is used when power is first applied. This circuit holds the digital section in reset as the power comes up. This POR is basically an RC delay that holdes the device in reset for a time after the device is powered up. With repeated power-ups, this circuit may fail to hold the device in reset as the RC delay hasn't reset with each new repeated power-up.

Generally, we've recommended the supply be returned to 0V when powering the device up again. This allows the POR circuit to correctly trigger, without the problem of repeated power-ups holding some charge in the POR. In the past, some have reduced the bypass capacitors, or added some parallel resistance to quickly remove charge from the board so that the POR can reset easily.

Some of our newer devices have better POR circuits that were designed for cases of repeated power-ups. The ADS1220 is similar to the ADS1225, and should have a better POR circuit to prevent similar problems.


Joseph Wu

Hi Joseph,

I think we did not experience a repeated power up condition, I did check both supplies and they looks fine during the period, any input scenarios could cause the output latch to high (ffff)?

Thanks,

Hailong Xu  

see above

Hailong,


I don't know of any cases where the input could cause these types of problems. The only thing that I can think of is that the input is pulled so far high or low, that it causes a disruption in the power supplies. Any problems would be dependent on the system itself. However, I still think this would be unusual for the problem to come from any condition on the input.

I still think that the digital section may have been disrupted by a power supply glitch but I'd also check other possibilities. Normally, FFFFFFh would be the equivalent of -1d which is close to 0V input regardless of what the reference is. Have you checked the status of the reference? What is the reference voltage at the time, and what is the voltage at the input?


Joseph Wu