Comparators: the lowest power you can get

Discrete comparators are still an essential element in electronic design. These days we often want to have the lowest power one available with “good” specs. We are going to look at a few good choices for this type of device.

There are quite a few important specs for comparators – quiescent supply current, offset voltage, speed, prop delay, input bias current, and supply voltage range, are perhaps the main ones. Next we need CMRR, operating temperature range, push-pull or open drain outputs, and how much current can the output handle. You might want rail-to-rail inputs and/or outputs. Oh yes, and cost and package type of course.

I am surprised at the number of manufactures making comparators. More than 16. Here are the main ones:

Let’s start with a reference device – the ancient LM339. Anyone know when this device first showed its pretty face? 1970 something, I think.

The LM331 is the single channel version and this IC from ON Semiconductor – an improved version called the LMV331 – has a supply current of 120 µA maximum, 60 µA typical over −40° to 85°C, an input offset voltage of 9 mV maximum, and a bias current of less than 1 nA typical at 25°C. Input common mode voltage range extends to ground, and, prop delay is 1.5 µs with a 10 mv overdrive. Not bad at all. On Semi also makes the NCS3402 dual nano-power open drain output comparator that takes only 470 nA/channel supply current.

Analog Devices

The ADCMP370 & 371 have high voltage (22 V) open drain or push-pull outputs. They feature rail-to-rail common-mode input range, are specified over –40° to 85°C, and come in a 5-lead SC70 package. Cost is $0.33 ea/3,000.

Micrel

The MIC841H is one of the top dogs in the low power race with 1.5 μA typical supply current. It features an internal ±1.25% reference, 10 nA input bias current over temperature, 10 μs propagation delay, and fixed 20 mV hysteresis on the MIC842 version. Packaging is SC-70 or TDFN, including a tiny 1.2 x 1.6 mm 4-pin, and you can choose a push – pull active high, push – pull active low, or open drain output. For some reason they do not have numbers for CMRR and V_offset on their spec sheets. It will cost you 49 cents ea/1,000.

Texas Instruments

The TI TLV3691 is another low power champ with a typical supply current of 75 nA at 6.5 V and a supply range of 0.9 to 6.5 V. The device comes in tiny DFN-6 (1 × 1 mm) or SC70-5 packages with a temperature range of –40° to 125°C. Input common-mode range extends 100 mV beyond both rails, the output is push – pull, response time is a not-real-fast 24 – 32 μs, input offset voltage is ±3 mV, and hysteresis is 17 mV. $0.56 ea/5,000.

Linear tech

The quiescent current of the LTC1540I is 0.68 µA at 5 V and over 40° to 85°C. The device features a 1.182 V reference (±2%), a push – pull output that can continuously source up to 40 mA, and 8-pin MSOP, SO and 3 x 3 mm DFN packages. Cost is $1.30 ea/2,500.

Microchip

The MCP6546 open-drain output comparator is a top low power contender with quiescent current of 600 nA. The devices V_OUT is 10 V maximum and propagation delay is 4 μs (typical, 100 mV overdrive). This IC has a chip select and 3.3 mv internal hysteresis. Industrial and -40° to 125°C extended temperature range versions are available. It will cost you only $0.34 ea/100, starting price.

A summary of low power comparator specifications