LME49710 missing data in datasheet


Paid Member
2002-03-29 5:19 am
This is, IMNSHO, one of the poorer occidental datasheets I have seen. All the distortion graphs are essentially meaningless and 3 or 4 would have sufficed to get the point across. It is hard to determine from the spec table which, of any, specs are actually measured (notes 7.8). Sure, there are mins and maxes, but there are a bunch of weaselwords that essentially say "we may not actually test any of this stuff".

Still, the family is supposed to be good and I look forward to trying them.
Yes, per an email from Bob Pease, you can use the LM4562 curves for the LME part. I was interested in this because I wanted to compare the plot with that for the OPA627. It's a bit annoying because they're done upside down to each other, but it looks like the 627 has significantly more phase margin. Sonically, I don't find much difference between them, but wondered if something could account for the strong opinions people seem to have. IMO, because the National parts are 55MHz parts, albeit very well behaved 55MHz parts, casual construction techniques invite all sorts of problems. Good local HF bypassing is essential, ground planes are desirable, and if you send RF in, you can bet amplified RF will be coming out! OTOH, used properly, there isn't much that can better the National parts.
I'm using them in relatively high speed integrators as part of the error amplifier circuitry in a close cousin to the Jung super regulator topology. Once the initial problems were sorted out they seem quite stable, are low noise, have low dc offset, and drift, and lots of open loop gain at dc for good accuracy closed loop. (Good bandwidth for ac performance as well.)

I have a pair of metal can LME49720 I'm going to try at some point. Oddly enough this seems to be one of the few parts National still offers in TO-8 cans - must be for the far eastern market where there seems to be a premium placed on these parts.

I've used lots of LM4562 over the past year modding my two sacd players, and a Zhaolu 2.5A dac - they are definitely quite good sounding compared to any other op-amp I have tried lately.
Low level HF oscillation due to very high open loop gain, slow bipolar power transistor pass element, and my large capacitive load. Just a typical high performance power supply design problem, was easily fixed once understood. Great overall performance. Good ac amplifiers and shunt capacitance don't mix well without proper precautions - this will not be a problem in normal use as an audio op-amp.