LM2902: Strange waveform

[FAE] Andrew Wang

Part Number: LM2902

Hi Team,

I met a strange case when customer report using LM2902. I downloaded the newest model from TI.COM.

If connecting as below config, it can be seen the 10nF load shows a much slower slew rate, however if we change VBIAS 5V -> 0V, it went back to normal that is 10nF moving the fastest among 3 different loads - 10nF/100nF/1000nF, this is I think the correct result.

Any thoughts anout this strange behaviour? Thanks.

Andrew

Op-amp Stability Analysis (LM2902 - Time Domain).TSC Op-amp Stability Analysis (LM2902).TSC

over 4 years ago

0 Ron Michallick over 4 years ago

TI__Guru*** 149206 points

Andrew,

We will address this fully on Monday. The model that comes with TI-Tina works fine.

0 Ron Michallick over 4 years ago in reply to Ron Michallick

TI__Guru*** 149206 points

Andrew,

The newer model has a cross over delay code in it. see https://www.ti.com/lit/pdf/SLOA277 sections 4.3 through 4.5. This circuit caused the cross over code in the model to oscillate for a while. The code in model is good , but it not perfect. When using the older model (without this code) or adding a 18k resistor from output to either supply rail the issue will not occur. The resistor keeps the output current outside the cross over region. It also won't occur (more than once, 4us delay) in a real device.

Because of the Thanksgiving holiday in the U.S., TI E2E™ design support forum responses may be delayed from November 25 through December 2. Thank you for your patience.

Amplifiers

Amplifiers forum

LM2902: Strange waveform