UC1526: CMRR

Ajay,

Why do you need to measure this parameter and are there also other parameters you are trying to verify? Can you share your test methodology and results you are seeing which are not agreeing with the data sheet?

I will check and get back to you. Most likely, because this is a legacy PWM controller, we may not directly measure the CMRR at test but "guarantee by design." However, when this is the case we normally specify this as a footnote and this is not shown in the UC1526 data sheet. We do mention Rs<12kΩ in the data sheet test conditions. I will need to ask my Test Engineering colleagues about the test setup and then confirm if the schematics, test docs are still available since this procedure originated many years ago with Unitrode.

Regards,

Steve M

Hi Steve,

Thank you very much for the quick reply. I am required to test this device to the SMD 8551501VA. I have every test passing except CMRR. Please see my CMRR test circuit below. At VCM = 0V the Vos = 14mV, and at VCM = 5.2V the Vos = -16mV. That’s a CMRR of about 45 dB. I would normally use a false summing junction to test CMRR, but this device prohibits access to supplies of the error amp so they cannot be shifted for testing. I appreciate any guidance you and your test engineering colleagues can provide!

Thanks,

Ajay Sequeira

Ajay,

Unfortunately due to the age of this device and the fact that it is not using a test platform that is common to most TI devices, I am unable to share a test schematic with you. It may be possible that the CMRR parameter was bench tested and characterized on a few wafers at the beginning of it's life cycle but how and if this was done is not known.  

Regards,

Steve M

Steve,

Thanks for checking. One more question though, would you happen to see any issues with my test circuit that I provided above? 

Ajay Sequeira