LM2904: May I ask if the anti-interference ability of our LM2904 varies among different batches.

Hello Gabriel,

LM2902 batch variability is greatest for improper input voltages, especially for inputs below the devices ground pin. It looks like the "noisy period" started with a negative pulse on blue. Which nodes are blue, pink and red?

Dear Ron

Blue is for PIN3 , red is for PIN2 , Yellow is for PIN1 output.

Should I add a first order RC filtering to reduce these 140K switch frequency .

Gabriel,

I see yellow at bottom and red in waveform. So they are the same ?

The noise has opposite polarity for noise. That makes me wonder if the 12V_RET points are all the same or if switching current makes them different. This  excessive noise may be a layout issue.

What is the noise on pin 4?

Dear Ron

Thanks for your suggestions !

The noise on pin 4 from the system 12V output ,both LM2904 GND and 12V output power PGND they are same PGND ,because of our LM2904 used to be a voltage control loop.

The customer VAPEL concern that only few bach of LM2904 could cause the LM2904 output not unstable ,why our LM2904 could be output difference is so great ?

Gabriel,

Here is a part of a tech days presentation on this topic.

A key point is this "All samples of the same die design will usually have the same results. However, depending on this fact is not a good design practice. Two die designs from same manufacturer might have different results.". 

LM2904 had had multiple product change notices over the decades, the last one a couple years ago, that can be different during this data sheet input voltage violation. 

Op amp phase reversal overview.pdf

Dear Ron

Thanks！

Customer wanna kown how we caculate the LM2904 CMRR ,could u help provide LM2904DR/LM2904DGKR CMRR caculate diagram or schmetic and Calculation formula ？

Gabriel,

The setup note is incorrect, that is a PSRR setup note

It should read VCM 0V to 3.5V with 5V supply at 25C.

CMRR is 20* log( 3.5V / ( [Vos@VCM=3.5V] - [VOS@VCM=0V] ) )

Basically the ratio of VCM change divided by change in input offset voltage.