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Tiny, Precision Sensor Amplifier ICs Slash Current Needs, Extend Battery Life

March 30, 2021
The MAX41400 instrumentation and MAX40108 operational amps offer extremely low-current operation—lengthening battery life in sensor-centric front-end apps—along with ultra-low and stable input offset voltage and tiny size.

When it comes to sensor-based applications involving transducers such as thermocouples, RTDs, strain gauges, piezo devices, biosensors, and similar, the performance of the front-end amplifier is often the dominant factor in determining ultimate system precision, accuracy, and stability.

Addressing those apps is a pair of amplifiers from Maxim Integrated Products, beginning with the MAX41400, a low-power, high-precision instrumentation amplifier (in-amp or INA) with hardwired, pin-settable programmable gain from 10 to 250 V/V. The gain-setting resistors are located inside the device, thus minimizing gain-drift variations over the temperature range.

The amplifier also has internal EMI filters to protect from signal “disturbances” due to electromagnetic interference (EMI), with EMI rejection ratio (EMIRR) better than 100 dB at 1800 MHz and 2400 MHz and better than 90 dB at 400 MHz and 900 MHz. Common-mode rejection ratio (CMRR) is typically at least 120 to 130 dB depending on gain (the datasheet also gives worst-case minimum values at each gain value).

The MAX41400 features rail-to-rail CMOS inputs and outputs; a 28-kHz, 3-dB bandwidth at just 65 μA (typical) supply current, significantly increasing circuit run time compared to alternatives; and 25-μV (max) zero-drift input offset voltage over time and temperature, as shown by multiple graphs around this important parameter (see figure). The zero-drift feature eliminates the high 1/f noise typically associated with CMOS input amplifiers, making it useful for a wide variety of low-frequency measurement applications.

The MAX41400 operates from a 1.7- to 3.6-V power-supply voltage and is specified over the 40 to +125°C automotive temperature range. The detailed datasheet provides static and dynamic specifications and graphs, as expected, across a range of settings as well as important application details needed to maximum performance (with precision amplifiers, even slight “misunderstandings” in connection configuration can compromise performance).

Housed in a space-saving, 1.26- × 1.23-mm, 9-bump wafer-level package (WLP) with a 0.4-mm bump pitch as well as a 2.5- × 2-mm, 10-pin TDFN package, it’s priced at $0.95 (1,000 pieces). The links to its datasheet, its fully wired and ready-to-use MAX41400EVKIT# evaluation-board datasheet ($68), device model, and tools are here.

For the many applications where an in-amp isn’t the right amplifier topology, but a “regular” op amp is needed (such as signal-chain filtering or some analog front ends), the MAX40108 low-power, high-precision device is available. It operates down to 0.9 V. This space-saving amplifier in a nearly invisible 1.22- × 0.92-mm, 6-bump WLP with a 0.4-mm bump pitch targets portable, consumer, medical, and industrial applications.

It features rail-to-rail CMOS inputs and outputs, a gain bandwidth (GBW) product of 168 kHz, and a typical supply-current consumption of just 25.5 μA along with 1-μV (typical) zero-drift input offset voltage over time and temperature. The latter, as with the MAX41400 in-amp, helps reduce the 1/f noise.

The MAX40108 operates from a 0.9- to 3.6-V rail and is specified over the 40 to +125°C operating temperature range. It’s priced at $0.99 (1,000 pieces) and again, as with the MAX41400 in-amp, a ready-to-use evaluation board ($68), model, and tools are available; details are here.