Please advise me TI equivalents to:
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Hello Alex Baikov,
Here are the crosses using http://focus.ti.com/general/docs/searchgpn.tsp?newSearch=Y
The forum may have cut off some text, so see attachment.
|Manufacturer||Manufacturer GPN||TI GPN||Status||Description||Comments||Code **|
|National Semiconductor (NSC)||LF357||TLE2081||ACTIVE||High-Speed JFET-Input Operational Amplifier||Q: Same Functionality & Pinout|
|SGS-Thomson (SGS)||LF357||TLE2081||ACTIVE||High-Speed JFET-Input Operational Amplifier||Q: Same Functionality & Pinout|
|National Semiconductor (NSC)||LF357||TLE2071||ACTIVE||Low-Noise High-Speed JFET-Input Operational Amplifier||Q: Same Functionality & Pinout|
|Motorola (MOT)||LF357||OPA637||ACTIVE||Precision High-Speed Difet(R) Operational Amplifiers||F: Similar Functionality|
|Manufacturer||Manufacturer GPN||TI GPN||Orderable Match(es)||Status||Description||Comments||Code **|
|Analog Devices (ADI)||AD743||TLE2071||ACTIVE||Low-Noise High-Speed JFET-Input Operational Amplifier||Q: Same Functionality & Pinout|
|Analog Devices (ADI)||AD743||OPA132||ACTIVE||High Speed FET-Input Operational Amplifiers||Q: Same Functionality & Pinout|
|Analog Devices (ADI)||AD743||OPA134||ACTIVE||SoundPlus(TM) High Performance Audio Operational Amplifiers||Q: Same Functionality & Pinout|
|Analog Devices (ADI)||AD743||OPA627||View||ACTIVE||Precision High-Speed Difet(R) Operational Amplifiers||Av, CMMR, GBW, PSRR differ||Q: Same Functionality & Pinout|
We have new FET input op amps that are far superior to the old AD743 and LF357. Please check out the OPA140, OPA141 and OPA827. These new op amps provide excellent accuracy, lower noise and modern packages with much lower quiescent current.
Whoa! The fact that the question is about the AD743 and LF357 indicate the questioner knows a thing or two. These two parts are special to the designers of high-performance transimpedance amplifiers, or TIAs as we like to call them.
First, the AD743 has a quiet 2.9 nV/rt-Hz of noise (at 10kHz). This compares to 5.1 nV, 6.5 nV and 4.5 nV for your OPA140, OPA141 and OPA827, respectively. Sorry, Bruce, but if one's TIA has more than say 25pF of external capacitance, this means all three of your parts are decidedly inferior, and will make much more of the deadly high-frequency in = en-w-Cin noise than the vaunted AD743.
Analog Devices is deprecating the AD743, in part because they never offered an SMT version, and if you were smart you'd step up to the plate with a replacement to help those of us who are struggling to get along without it. Then you could claim to have a best-in-class part.
Now about the National Semi LF357. This part was not only inexpensive, it had only 3pF of input capacitance, and it offered 20MHz of bandwidth. It was perfect for cascode TIAs, and as Phil Hobbs wrote in his book, it is not replacable by any other current JFET opamp, at any price (note: its 12nV of noise doesn't matter in such applications). Your OPA140 and 141 offer only half the speed, at 11MHz, and they suffer from more than twice as much capacitance. That's very BAD for a cascode TIA. The OPA827 has 18MHz of bandwidth, close, but also suffers from more than twice the capacitance. Also BAD. Certainly not exemplary, as you claimed, Bruce.
Part of what made the LF357 great was, it was a decompensated opamp, with Gmin = 5. That's GOOD! Why not make a decompensated OPAxxx part?
Now that NSC is part of TI, maybe it's time to look at some of their best-in-class stuff, and consider what to do for the next two decades.
Thanks for your comments. Very interesting. I’ll partially retract my statement that the OPA827 and OPA140 are lower noise. To be honest, I was working from memory and I forgot about the low broadband noise of the AD743, but more on that later. You more accurately read between the lines. I see now that Alex has posted several questions on the OPT101 photodiode/amplifier so your assumption of a TIA may well be correct.
I have to admit that my recommendations were directed toward the most common objections to previous generation JFET op amps. The strongest exceptions are generally taken to the high quiescent current, limited input/output voltage ranges and large packages of older op amps. You have focused your assessments specifically on performance attributes important in some TIA applications. Our JFET op amps are used in a very wide range of applications so that is what triggered my response.
The AD743 is an interesting and rather specialized amplifier. When it was first released I recall puzzling over its high input bias current (400pA) for a JFET. And it burns high quiescent current (8.1mA) for its modest bandwidth (4.5MHz). Still, the AD743 has very low broadband noise and so, as you point out, with very high photodiode capacitance, it would have an advantage. The OPA827 is somewhat higher in broadband noise but lower input capacitance so it might be better suited for photodiodes of more moderate capacitance. General applications benefit from the lower quiescent current, wider bandwidth and lower input bias current of the OPA140 (1.8mA, 11MHz, 10pA) or OPA827 (4.8mA, 22MHz, 10pA). Furthermore, the OPA827 has lower flicker noise than the AD743; in many applications this is as or more important than the wideband noise.
The LF357 is an interesting case. You and I share an appreciation for decompensated amplifiers. They offer a great speed/current advantage. But our customers vote by placing orders. Unfortunately, you and I didn’t buy enough of them to sway the voting and we’ve all but given up making new ones. Our customers strongly prefer the unity-gain stable versions of the same amplifiers. My experience is in the Burr-Brown product line but my new colleagues confirm the same experience with LF356 vs. LF357. The LF356 is active and the LF357 is obsolete. If we could drum up interest we could make, for example, an OPA140-type design, decompensated, a bit higher noise and lower input capacitance. It would have wider bandwidth than the LF357, lower quiescent current, fit in modern packages, have better input/output voltage range and a host of other spec improvements.
The relatively new OPA140 and OPA827 have similar design tradeoffs to those made in our OPA627. The 23-year-old OPA627 is still extremely popular and very available. The LF357 and AD743 are now obsolete or not recommend for new designs. Customers have voted and the balanced performance tradeoffs made in the OPA627 across a wide range specs are well recognized.
One last point. We have a few old decompensated amplifiers. The OPA637, for example, is a decompensated OPA627. In spite of the lower sales of this special version, we will continue to support it. TI does not obsolete products for our mere convenience or low sales. At the same time, we try not to create new ones.
Thanks again for your comments and expert opinions.
Bruce (and others), this is an old thread, but I'd like to pick it up again. The OPA171 and its family are rather unique in being able to work to the rails, and especially the negative rail as a single-supply amplifier. Although the datasheet doesn't say, it appears to have JFET or MOS input transistors. I think you called it a FET amplifier, didn't you? Can you tell us, is it a JFET or a MOS-input amplifier? It has pretty low noise for its 3pF input capacitance, so I'd guess it's JFET (it seems if it had MOS or CMOS inputs, the area would have to be reasonably-large to get the 14nV/rt-Hz noise level, so it'd have more capacitance, right?). Is it partially FET and partially bipolar? It'd be nice to know more about its input stage, etc.
Why not tout this guy as a FET amplifier working to the rail(s)?
The OPA171 is CMOS. While we don't intend for this to be a secret, we wanted designers to judge it on its features and performance, not its fabrication process. It has capabilities that many engineers might find surprising for CMOS.
It has a dual input stage for rail-to-rail input behavior but we stop just short of calling it "rail-to-rail input." The feature bullet says "operates to positive rail." The distinction is that the upper 1.6V of the range at the top rail does not have the same common-mode rejection and bandwidth as the primary input stage. For many users, the performance distinction is subtle. Other IC manufacturers might call it rail-to-rail. It could have been designed to meet our full rail-to-rail standards but this was a product definition choice with some attendant trade-offs.
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