Probably a dumb question, I know I can find out myself, but the hours of googling that will take...Perhaps there is an opamp guru here that knows?
So for next project I figure why not a small battery powered thingy. Opamp based and I want to try very low power consumption and very small size, which is totally new to me.
Went looking at Mouser and Digikey trying to select which opamp. I know about some of the audio opamps, but not if there are any good ones that have very low power consumption.
Criteria:
Unity gain stable.
Low drift/offsets (precision class)
GBP 20MHz or more
SR > 8V/us
Small SMD, 5 or 6 pin SOT23 or similar. Pins on the outside, not under the package.
Any suggestions?
I am considering OPA322 or LT6233... ?
So for next project I figure why not a small battery powered thingy. Opamp based and I want to try very low power consumption and very small size, which is totally new to me.
Went looking at Mouser and Digikey trying to select which opamp. I know about some of the audio opamps, but not if there are any good ones that have very low power consumption.
Criteria:
Unity gain stable.
Low drift/offsets (precision class)
GBP 20MHz or more
SR > 8V/us
Small SMD, 5 or 6 pin SOT23 or similar. Pins on the outside, not under the package.
Any suggestions?
I am considering OPA322 or LT6233... ?
Go here and search, there are many such devices.
https://www.ti.com/amplifier-circuit/op-amps/products.html
https://www.ti.com/amplifier-circuit/op-amps/products.html
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You might want rail-to-rail opamps for battery use to get the most from the voltage.
Can you explain what you think "very low power" is in numbers + units?
GBP 20MHz or more won't help with low power consumption, low power opamps tend to have less bandwidth.
And power consumption is ultimately limited by load impedance and level.
Can you explain what you think "very low power" is in numbers + units?
GBP 20MHz or more won't help with low power consumption, low power opamps tend to have less bandwidth.
And power consumption is ultimately limited by load impedance and level.
Thnx for replies.
I am hoping for a 1-2mA at 3.3V. Do not need RR but it must swing > +-1Vp (2Vpp) but of course nice to have headroom over that.
I find many opamps to chose from and I can just pick one. But I was hoping there is a particular good one for audio.
I am hoping for a 1-2mA at 3.3V. Do not need RR but it must swing > +-1Vp (2Vpp) but of course nice to have headroom over that.
I find many opamps to chose from and I can just pick one. But I was hoping there is a particular good one for audio.
Whats the purpose? What are you driving. If you have a load thats 20 ma not much sense worying about an exta ma of bias. Is rail to rail more important?
*DEFINE* "thingy" 🙄
How dare you ask for answers without explaining your questions? 😕
And it took you reaching post #5 to add :"battery voltage 3.3V" which is *extreme* and Challenging 🙄
Based on what?
Thanks for replies. I will select from the tables at TI or Analog. I was just hoping for some legendary good low Is opamps. The 3v3 will be from an LDO obviously.
Don't think you'll find anything very high performance at 3.3V
I'd suggest the AD8655/8656 which is pretty good and will work at that low a voltage, but the current consumption is the expected 4mA per amp. That's the cost of decent performance.
For very low power I delved through my exotic opamps stash to find the MCP6274. Its another CMOS opamp, but only 0.17mA supply current. However you only get 2MHz GWP, 0.9V/µs slew rate and lots of voltage noise, and unknown amount of distortion. The PSRR starts dropping off from 30Hz upwards too, not nice at all.
MicroChip no doubt make something less extreme around the 1mA mark which might be what you need.
All of these devices are CMOS inputs, note, so they will have worse voltage noise specs than most audio opamps, and they will need full anti-static handling precautions to avoid damaging them too. Operating down at the 3V mark CMOS opamps have much the widest choice, but limitations.
I'd suggest the AD8655/8656 which is pretty good and will work at that low a voltage, but the current consumption is the expected 4mA per amp. That's the cost of decent performance.
You _do_ need rail-to-rail at 3.3V supply, and proper rail-to-rail at that, not marketing-guff type rail-to-rail. The AD8655 can drive to within 0.2V of each rail at 20mA output current, which is excellent.
For very low power I delved through my exotic opamps stash to find the MCP6274. Its another CMOS opamp, but only 0.17mA supply current. However you only get 2MHz GWP, 0.9V/µs slew rate and lots of voltage noise, and unknown amount of distortion. The PSRR starts dropping off from 30Hz upwards too, not nice at all.
MicroChip no doubt make something less extreme around the 1mA mark which might be what you need.
All of these devices are CMOS inputs, note, so they will have worse voltage noise specs than most audio opamps, and they will need full anti-static handling precautions to avoid damaging them too. Operating down at the 3V mark CMOS opamps have much the widest choice, but limitations.
That means you need rail-to-rail. Non-rail-to-rail swing to within about 2.5V of the rails or so.
Found this showing TIs newer opamps by series, with a one line description. Havent looked at new OAs for a while, looks like they have beev hard at work. U amp q currents, fento! amp bias, 180volt rails, and many other series for very specific uses.
Texas Instruments LM321 Series Newest Operational Amplifiers - Op Amps | Mouser Canada
Texas Instruments LM321 Series Newest Operational Amplifiers - Op Amps | Mouser Canada
Heres a low power, RtoR, low voltage, low distortion, audio OA that fits your bill.
https://www.ti.com/lit/ds/symlink/o...ll-mousermode-df-pf-null-wwe&ts=1592156716662
https://www.ti.com/lit/ds/symlink/o...ll-mousermode-df-pf-null-wwe&ts=1592156716662
thnx for suggestion, but needs to operate at 3.3V and swing at least +-1Vp at unity gain.
I am amazed that there are ckts that operate at 2.5V and are RRIO. But of course I have doubts regarding their sonics, but with tons of feedback I am not sure I will be able notice.
OPA322 is starting to warm my belly.
I am amazed that there are ckts that operate at 2.5V and are RRIO. But of course I have doubts regarding their sonics, but with tons of feedback I am not sure I will be able notice.
OPA322 is starting to warm my belly.
Shame about the 3.5V minimum, but its got good looking drive to 0.2V from the rails at that voltage. Wonder how well it works under-spec?
One thing to contemplate is a negative rail generator chip, so that your 3.3V can become +/-3.3V rails - these are switched capacitor devices line the MAX1680 and are pretty efficient (though you'll need to find a lower current one, the MAX1680 does upto 135mA out and takes several mA quiescent)
Well spotted. OPA1692 seems like a great device if you don't need CMRR. Gain margin seems good since they haven't gone overboard on the HF gain. Good price as well. Now just need a FET version....
I do have to wonder why one would need a 8 V/µs minimum slew rate spec for a measly 0.7 Vrms audio signal. Maximum expected signal slew rate would be a measly 0.13 V/µs. So I'd say shoot for around 1 V/µs with a bipolar input and 2 V/µs with a FET input part.
I would also prefer thinking in terms of dynamic range rather than voltage level. Voltage level is of interest to us at the input and output, not so much in between. 1-2 mA @ 3.3 V is not exactly likely to support huge dynamic range either way.
3.3 V operation shouldn't be too uncommon altogether. If in doubt, there always is the option of "cheating" with a (switched-capacitor based) inverter which should open up many more options. ON Semi's NCP1729 would be one such part. (Some passive cleanup is going to be a good idea by the looks of it.) Maxim makes entire headphone driver ICs with a corresponding converter integrated, like the MAX97220. You can also get ICs that'll generate a split voltage supply from a single voltage input, like the LM27762, but that one seems substantially oversized in this application.
I would also prefer thinking in terms of dynamic range rather than voltage level. Voltage level is of interest to us at the input and output, not so much in between. 1-2 mA @ 3.3 V is not exactly likely to support huge dynamic range either way.
3.3 V operation shouldn't be too uncommon altogether. If in doubt, there always is the option of "cheating" with a (switched-capacitor based) inverter which should open up many more options. ON Semi's NCP1729 would be one such part. (Some passive cleanup is going to be a good idea by the looks of it.) Maxim makes entire headphone driver ICs with a corresponding converter integrated, like the MAX97220. You can also get ICs that'll generate a split voltage supply from a single voltage input, like the LM27762, but that one seems substantially oversized in this application.
Ok. The thing is those specs are for a project at work... And sneaky me figure I might as well pick an opamp that happens to be good for audio as well. After the prototyping phase I can keep whatever I want and why not build something for audio out of that. So that explains the odd specs.