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Instrumentation amplifiers guarantee 20 microvolt max offset voltage

Sunnyvale, Calif. — Maxim Integrated Products has introduced the MAX4208 and MAX4209H instrumentation amplifiers that feature the company's patented current-feedback architecture, a spread-spectrum autozeroing technique. The new autozeroing technology constantly measures and corrects the input offset voltage, thereby eliminating drift over time and temperature, said Maxim.

The technology's compact design allows the MAX4208/MAX4209H devices to fit in a small 3 x 5-mm microMAX package, making them suitable for use in a wide range of applications. The amplifiers can monitor the low-voltage, power-supply currents of the core, ASIC and microprocessor in laptop computers. The amplifiers are also used in automotive, industrial, and medical instrumentation.

The MAX4208/MAX4209H devices feature a two-transconductance-amplifier architecture (see Figure 1). This indirect current-feedback architecture allows customers to use the full dynamic range of input differential signals, even when the common-mode voltages are close to, or below, ground. This true low-side sensing capability is not offered by the common three-operational-amplifier approach, said Maxim.

The MAX4208/MAX4209H devices also offer true ground sensing and an input common-mode voltage range of -0.1 V to VDD – 1. 3V. CMRR is guaranteed to be at least 106 dB. The devices' input stage uses CMOS transistors with 1 pA (typ) input bias current. Input offset voltage is 20 microvolts (max) at +25°C, 30 microvolts (max) at +85°C, and 40 microvolts (max) over the -40°to +125°temperature range. The offset voltage distribution in Figure 2 shows that the devices' typical input offset voltage is less than 5 microvolts.

The MAX4208 features an adjustable gain, with the gain set by the ratio of two external resistors (G = 1 + R2/R1). The MAX4209H uses internal laser-trimmed resistors to set a fixed gain of 100x. The MAX4209H offers a maximum gain error of plusmn;0.25% at +25°C, plusmn;0.3% up to +85°C, and plusmn;0.35% over the entire -40°C to +125°C temperature range. The gain error histogram in Figure 3 shows that the typical gain error is better than plusmn;0.1%.

The MAX4208/MAX4209H also include an autozero reference-buffer amplifier (see Figure 1), which allows the output to be level-shifted to VDD/2 using a simple resistor-divider or an external reference input with minimum loading error. This buffer increases system accuracy and is useful for bipolar signals in single-supply applications, said Maxim. The high-impedance inputs are optimized for small-signal differential voltages (±100 mV). All devices operate from a single 2.85-V to 5.5-V supply (or plusmn;1.425 V to plusmn;2.75 V dual supplies) with ground-sensing capability and ultra-low, 1pA (typ) CMOS-input bias currents.

Product notes: Figure 1: two-transconductance-amplifier architecture
Figure 2: offset voltage distribution
Figure 3: gain error histogram

Applications: Figure 4: Resistive and capacitive bridge-transducers that sense pressure and position in automotive and industrial applications can be amplified and used to drive analog-to-digital converters (ADCs). The low-offset voltages and low-offset drift allow large gains to be used with small DC error, delivering better performance, said Maxim. The CMOS inputs also allow the part to interface to a variety of capacitive and other high-impedance sensors.
Figure 5: The MAX4209H can be used as an accurate low-side or low-voltage current-sense amplifier with extremely small sense voltages (10 mV) and small sense resistors. This design is used in laptops to monitor current in the core, ASIC, and microprocessor. The low Vsense voltage drop reduces power dissipation in sense resistors to minimize hot spots, which leads to better efficiency, said Maxim.

Pricing: The MAX4208 and MAX4209H are priced at $1.65 (1000-up, FOB USA).
Availability: Samples of the MAX4208/MAX4209H are available now.
Product information: Autozero amplifiers
Datasheet: MAX4208 and MAX4209H

Maxim Integrated Products , 1-800-998-8800, www.maxim-ic.com

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