MPC5744P ADC reference voltage

[lzheng]

Hi, according to the datasheet, ADC reference voltage is 3.3V or 5.0V with the recommended range of 3.15V to 5.25V according to Table 13. Is there any problem with the ADC reference voltage of 3.0V? 

It seems work fine but worry about performance issue when moving forward into production. 

Thanks,

Liping

[lzheng]

Thank you for your quick comments. I understood that the device will be stressed if it is beyond the maximum ratings. For  my case, it is different, my reference voltage is 3.0V which is slightly below the recommended value of 3.15V to 5.25V. It is well within the maximum ratings of -0.3V to 6.0V. Therefore, I am more concerned about whether there is any effect to the performance such as S/N ratio. My design was copied from previous design with MPC5643L which recommends the reference voltage of 3.0 to 3.63V or 4.5 to 5.5V. MPC5643L and MPC5744P are pin compatible and it was migrated per AN4624.  Are there any major changes of the ADC circuits between 5643L and 5744P? 

[lukaszadrapa · Accepted solution]

Hi @lzheng 

Well, it's assumed that users will use either 3.3V or 5V reference. Supply voltages also have some tolerance, so we do not recommend to use the reference at min or max value in order to have some safety margin. 3.0V on MPC5744P will not damage the device (it's still withing absolute maximum ratings) but is't out of operating conditions. The device was not characterized for this voltage level, so we can't provide more details about the differences. It will work without issues most likely but it's without our guarantees.

Regards,

Lukas

[lzheng]

Hi Lukas,

Thank you for your explanation. Although it still works fine without any known issue, per your suggestion, we will update the design for our production boards.

Regards,
Liping

[davidtosenovjan]

In such case the device would be operated out of specification, what’s not allowed.

There are several aspects:
1) Device may not work properly.
2) Even in case it would, the device will be stressed and device lifetime may be shortened.
3) User cannot apply warranty claim in case device is operated out of specification.