Eight low-cost op amps

If you're looking for an op amp for your latest design, you have a lot of choices. A leading distributor shows 34,000 items under that umbrella. Why not use the least expensive you can find, if it has reasonable specs. We'll have a look at how low you can go.

Now, there are op amps as low cost as $0.07 ea/1,000, but you, as a highly qualified engineer, would not want to use a low performance part when a few more cents would get you an excellent part, now would you?

I'm going to limit my coverage to those under $1. Let's see what we can get for that amount. I'm only going to look at single and dual versions, though you can get up to twelve in one package.

And, of course, there are a LOT of specs to look at for an op amp. I've always had a thing for common-mode rejection (CMRR) ratio. Find an amp with a good CMRR, and you'll find a good one overall. I sticking with better than 75-dB CMRR. Used to be that was a really good number. Now you can get 115 dB in a low-cost amp — as you will see — and if you pay a little more you can get 146 dB, minimum (see MAX44246, $1.89 ea/100). I'm also only picking 2 mV or less offset voltage, a slew rate between 1 and 20 V/µs (as I don't want to struggle with a really fast device), and input bias current under 200 nA.

Some older models, like a LM3904, come close to meeting the specs, but are intended for ±15-V operation and are not specified at lower voltages more typical these days. So, we leave them out, except for our very first pick. Note that specifications are specified at room temperature, unless otherwise notified.

The RC4558 from Texas Instruments is a dual device with the low-low price of just $0.085 ea/2,500. And, the specifications are not bad, but they are all done with a ±15 V and the lowest supply you can use is ±5 V. But this dual part is really low cost.

Number of Circuits	2
Input Bias Current	150 nA
Input Offset Voltage	0.5 mV typ 7.5 mV max
CMRR	90 dB typ
Slew Rate	1.7 V/µs
Gain Bandwidth Product	3 MHz
Input Noise Voltage	8 nV/√Hz
Current – Supply	2.5 mA
Supply Voltage	10 to 30 V, ±5 V to ±15 V
Operating Temperature	0°C to 70°C

The Texas Instruments OPA377 is a low-cost, low-noise amp with impressive specifications. At just $0.53 ea/3,000 we could call it a bargain. It has rail-to-rail outputs and is optimized for low-voltage single supply applications and is available in SC70-5, SOT23-5, and SO-8 packages.

Number of Circuits	1
Input Bias Current	0.2 pA
Input Offset Voltage	250 µV
CMRR	90 dB typ
Slew Rate	2 V/µs
Gain Bandwidth Product	5.5 MHz
Input Noise Voltage	7.5 nV/√Hz at 1 kHz
Supply Current	0.76 mA/channel typ, 1.05 mA max
Supply Voltage	2.2 to 5.5 V
Operating Temperature	-40° to 125°C

The TLE2022IDR from Texas Instruments is a dual low-current amp that costs $0.890 ea/2,500. This dual-supply device has of offset voltage drift of 0.005 μV/mo typ.

Number of Circuits	2
Input Bias Current	35 nA
Input Offset Voltage	150 µV typ, 600 µV max
CMRR	100 dB typ
Slew Rate	0.5 V/µs
Unity-Gain Bandwidth	2 MHz
Input Noise Voltage	19 nV/√Hz typ
Supply Current	450 µA typ, 600 µA max, at 5 V
Supply Voltage	±5 to ±15 V
Operating Temperature	−40° to 85°C.

The Texas Instruments LMV771MG is a rail-to-rail amp offered in the tiny SC70-5 package with extended temperature range and specifications given for power supplies of 2.7 or 5 V. Offset voltage temperature drift is given as −0.35 μV/°C, and the chip costs just $0.51 ea/1,000.

Number of Circuits	1
Input Bias Current	100 pA
Input Offset Voltage	0.25 typ, 0.85 mV max
CMRR	80 dB typ
Slew Rate	1.4 V/µs
Gain Bandwidth Product	3.5 MHz
Input Noise Voltage	7.5 nV/√Hz at 10 kHz
Supply Current	500 µA typ, 900 µA max
Supply Voltage	2.7 to 5.5 V
Operating Temperature	−40° to 125°C

The Analog Devices AD8605 precision, wide-temperature-range, low noise, CMOS, rail-to-rail amplifier is available in A SOT-23-5 or a wafer 5-ball WLCSP package. It features a 5-V/µs slew rate with a cost of only $0.72 ea/3,000.

Number of Circuits	1
Input Bias Current	1 pA max
Input Offset Voltage	20 µV typ, 300 µV max
CMRR	100 dB typ, 85 dB min
Slew Rate	5 V/µs
Gain Bandwidth Product	10 MHz
Input Noise Voltage	8 nV/√Hz typ. at 1 kHz
Supply Current	1 mA
Supply Voltage	2.7 to 5.5 V
Operating Temperature	−40° to 125°C

The Maxim MAX9614A is a low-offset-voltage 2.8-MHz-bandwidth op amp with wide temperature range. The device also features excellent RF immunity, making it excel in portable applications. The IC comes in a 6-pin SC70 1.25 x 2.0-mm package and is only $0.66 ea/2,500.

Number of Circuits	1
Input Bias Current	1.55 pA max
Input Offset Voltage	17 µV typ, 100 µV max
CMRR	95 dB typ, 80 dB min
Slew Rate	1.3 V/µs
Gain Bandwidth Product	2.8 MHz
Input Noise Voltage	28 nV/√Hz at 10 kHz
Supply Current	255 µA max
Supply Voltage	2.5 to 5.5 V
Operating Temperature	-40° to 125°C

The Maxim Max4475 is another wide-temperature-range amp and this one is automotive AECQ100 qualified. The chip costs $0.95 ea/2,500 and comes in SOT-23-6, µSOP, SO, and TDFN-EP packages.

Number of Circuits	1
Input Bias Current	1 pA typ, 150 pA max
Input Offset Voltage	70 μV typ, 350 μV max
CMRR	115 dB typ, 90 dB min
Slew Rate	3 V/µs
Gain Bandwidth Product	10 MHz
Input Noise Voltage	4.5 nV/√Hz at 1 kHz
Supply Current	2.5 ma typ, 4.4 ma max
Supply Voltage	2.7  to 5.5 V, ±1.35 to ±2.75 V
Operating Temperature	-40° to 125°C

And last, we have the LTC60 87 from Linear Technology , which is the fastest amp here. It has a shutdown current of 2.3 μA per amplifier, offset drift limited to 5 μV/°C max, and an output stage that swings within 30 mV of either supply rail. Available in 8-lead MSOP and 10-lead DFN packages, this chip costs $0.91 ea/1,000.

Number of Circuits	2
Input Bias Current	1 pA typ
Input Offset Voltage	330 µV typ, 750 µV max
CMRR	80 dB typ, 64 dB min
Slew Rate	7.2 V/μs
Gain Bandwidth Product	14 MHz typ
Input Noise Voltage	12 nV/√Hz at 1 KHz
Supply Current	1.05 mA/amplfier
Supply Voltage	2.7 to 5.5 V
Operating Temperature	-40° to 85°C and -40° to 125°C

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