Synopsis for Investor: * The MAX4208/MAX4209H are small instrumentation amplifiers ideal for use in a wide range of applications: monitoring the power-supply currents in the core, ASIC, and microprocessor of laptop computers; in automotive and industrial applications; and in medical instrumentation. * These amplifiers feature the Company's patented indirect current-feedback architecture that allows customers to utilize the full dynamic range of input differential signals. * This indirect current-feedback architecture saves board space because it provides a true low-side sensing capability not offered by the common three- operational-amplifier approach.
The new autozeroing technology constantly measures and corrects the input offset voltage, thereby eliminating drift over time and temperature. The input offset voltage is 20 microvolts (max) at +25 degrees Celsius, and 40 microvolts (max) over the -40 degrees Celsius to +125 degrees Celsius temperature range. The technology's compact design allows the MAX4208/MAX4209H to fit in a small, 3mm x 5mm microMAX package, making them ideal 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.
Patented Design Allows Full Use of Input Common-Mode Range
The MAX4208/MAX4209H feature an innovative, two-transconductance-amplifier architecture (see Figure 1). This indirect current-feedback architecture allows customers to utilize 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.
The MAX4208/MAX4209H offer true ground sensing and an input common-mode voltage range of -0.1V to VDD - 1.3V. CMRR is guaranteed to be at least 106dB.
The devices' input stage uses CMOS transistors with 1pA (typ) input bias current. Input offset voltage is 20 microvolts (max) at +25 degrees Celsius, 30 microvolts (max) at +85 degrees Celsius, and 40 microvolts (max) over the -40 degrees Celsius to +125 degrees Celsius temperature range. The offset voltage distribution in Figure 2 shows that the devices' typical input offset voltage is less than 5 microvolts.
Impressive Amplifier Offset and Gain Error Performance
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 has a maximum gain error of +/-0.25% at +25 degrees Celsius, +/-0.3% up to +85 degrees Celsius, and +/-0.35% over the entire -40 degrees Celsius to +125 degrees Celsius temperature range. The gain error histogram in Figure 3 shows that the typical gain error is better than +/-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. The high-impedance inputs are optimized for small-signal differential voltages (+/-100mV). All devices operate from a single 2.85V to 5.5V supply (or +/-1.425V to +/-2.75V dual supplies) with ground-sensing capability and ultra-low, 1pA (typ) CMOS-input bias currents.
Applications Benefit from the New Technology
The benefits of using the MAX4208/MAX4209H amplifiers can be seen in a wide range of applications. A few examples follow.
1. Resistive and capacitive bridge-transducers that sense pressure and position in automotive and industrial applications (see Figure 4) 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, thus delivering better performance. The CMOS inputs also allow the part to interface to a wide variety of capacitive and other high-impedance sensors.
2. Figure 5 shows the MAX4209H used as an accurate low-side or low-voltage current-sense amplifier with extremely small sense voltages (10mV) 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.
3. MAX4208/MAX4209H can also be used in multiple medical-instrumentation applications such as cardiac monitors and defibrillators.
Samples of the MAX4208/MAX4209H are available now. The MAX4208 and MAX4209H are priced at $1.65 (1000-up, FOB USA). For more information please visit: http://www.maxim-ic.com/Autozero-Amps
*U.S. Patent #6,559,720.
Figure 1. http://www.maxim-ic.com/MAX4208/9-Fig1 Figure 2. http://www.maxim-ic.com/MAX4208/9-Fig2 Figure 3. http://www.maxim-ic.com/MAX4208/9-Fig3 Figure 4. http://www.maxim-ic.com/MAX4208/9-Fig4 Figure 5. http://www.maxim-ic.com/MAX4208/9-Fig5
Editors' Contact: Drew Ehrlich Public Relations 408-737-7600 Readers' Contact: Customer Service 1-800-998-8800