19-1468; Rev 1; 6/03 Micropower, Single-Supply, Rail-to-Rail, Precision Instrumentation Amplifiers The MAX4194–MAX4197 have rail-to-rail outputs and inputs that can swing to 200mV below the negative rail and to within 1.1V of the positive rail. All parts draw only 93µA and operate from a single +2.7V to +7.5V supply or from dual ±1.35V to ±3.75V supplies. These amplifiers are offered in 8-pin SO packages and are specified for the extended temperature range (-40°C to +85°C). See the MAX4198/MAX4199 data sheet for single-supply, precision differential amplifiers. Applications Medical Equipment Features ♦ +2.7V Single-Supply Operation ♦ Low Power Consumption 93µA Supply Current 8µA Shutdown Current (MAX4195/MAX4196/MAX4197) ♦ High Common-Mode Rejection: 115dB (G = +10V/V) ♦ Input Common-Mode Range Extends 200mV Below GND ♦ Low 50µV Input Offset Voltage (G ≥ +100V/V) ♦ Low ±0.01% Gain Error (G = +1V/V) ♦ 250kHz -3dB Bandwidth (G = +1V/V, MAX4194) ♦ Rail-to-Rail Outputs Ordering Information PART TEMP RANGE PIN-PACKAGE MAX4194ESA -40°C to +85°C 8 SO MAX4195ESA MAX4196ESA MAX4197ESA -40°C to +85°C -40°C to +85°C -40°C to +85°C 8 SO 8 SO 8 SO Thermocouple Amplifier Selector Guide 4–20mA Loop Transmitters Data-Acquisition Systems Battery-Powered/Portable Equipment Transducer Interface Bridge Amplifier PART SHUTDOWN GAIN (V/V) CMRR (dB) MAX4194 No Variable 95 (G = +1V/V) MAX4195 MAX4196 MAX4197 Yes Yes Yes +1 +10 +100 95 115 115 Pin Configurations TOP VIEW RG- 1 IN- 2 8 RG+ REF 1 7 VCC IN- 2 MAX4194 IN+ 3 6 OUT IN+ VEE 4 5 REF VEE 4 SO 3 MAX4195 MAX4196 MAX4197 8 SHDN 7 VCC 6 OUT 5 FB SO Rail-to-Rail is a registered trademark of Nippon Motorola, Ltd. ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. 1 MAX4194–MAX4197 General Description The MAX4194 is a variable-gain precision instrumentation amplifier that combines Rail-to-Rail® single-supply operation, outstanding precision specifications, and a high gain bandwidth. This amplifier is also offered in three fixed-gain versions: the MAX4195 (G = +1V/V), the MAX4196 (G = +10V/V), and the MAX4197 (G = +100V/V). The fixed-gain instrumentation amplifiers feature a shutdown function that reduces the quiescent current to 8µA. A traditional three operational amplifier configuration is used to achieve maximum DC precision. MAX4194–MAX4197 Micropower, Single-Supply, Rail-to-Rail, Precision Instrumentation Amplifiers ABSOLUTE MAXIMUM RATINGS Supply Voltage (VCC to VEE)..................................................+8V All Other Pins .................................. (VCC + 0.3V) to (VEE - 0.3V) Current into Any Pin..........................................................±30mA Output Short-Circuit Duration (to VCC or VEE)........... Continuous Continuous Power Dissipation (TA = +70°C) 8-Pin SO (derate 5.9mW/°C above +70°C).................. 471mW Operating Temperature Range ...........................-40°C to +85°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) ................................ +300°C Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (VCC = +5V, VEE = 0V, RL = 25kΩ tied to VCC/2, VREF = VCC/2, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER Supply Voltage Range SYMBOL CONDITIONS TYP MAX 2.7 7.5 Dual supplies ±1.35 ±3.75 UNITS VCC Inferred by PSR test Quiescent Current ICC VIN+ = VIN- = VCC/2, VDIFF = 0V 93 110 µA Shutdown Current ISHDN ISHDN = VIL, MAX4195/MAX4196/MAX4197 only 8 12 µA G = +1V/V, VCM = VCC/2, TA = +25°C ±100 ±450 G = +10V/V, VCM = VCC/2, TA = +25°C ±75 ±225 G = +100V/V, VCM = VCC/2, TA = +25°C ±50 ±225 G = +1000V/V, VCM = VCC/2, TA = +25°C ±50 G = +1V/V, VCM = VCC/2, TA = TMIN to TMAX ±100 ±690 G = +1V/V, VCM = VCC/2, TA = TMIN to TMAX ±75 ±345 G = +100V/V, VCM = VCC/2, TA = TMIN to TMAX ±50 ±345 Input Offset Voltage Input Offset Voltage Drift (Note 1) VOS TCVOS G = +1000V/V, VCM = VCC/2, TA = TMIN to TMAX ±50 G = +1V/V ±1.0 ±4.0 G ≥ +10V/V ±0.5 ±2.0 Input Resistance RIN VCM = VCC/2 Input Capacitance CIN VCM = VCC/2 Input Voltage Range VIN Inferred from CMR test DC Common-Mode Rejection VCM = VEE - 0.2V to VCC - 1.1V, TA = +25°C, ∆RS = 1kΩ (Note 1) Differential 1000 Common mode 1000 Differential 1 Common mode 4 VEE - 0.2 G = +1V 66 78 G = +10V 80 94 G = +100V 86 99 G = +1V 60 78 G = +10V 74 94 G = +100V 77 99 V µV µV/°C MΩ pF VCC - 1.1 V dB CMRDC VCM = VEE - 0.2V to VCC - 1.1V, TA = TMIN to TMAX, ∆RS = 1kΩ, (Note 1) 2 MIN Single supply _______________________________________________________________________________________ Micropower, Single-Supply, Rail-to-Rail, Precision Instrumentation Amplifiers (VCC = +5V, VEE = 0V, RL = 25kΩ tied to VCC/2, VREF = VCC/2, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS VCM = VEE + 0.2V to VCC - 1.1V, TA = +25°C, ∆RS = 1kΩ DC Common-Mode Rejection CMRDC VCM = VEE + 0.2V to VCC - 1.1V, TA = TMIN to TMAX, ∆RS = 1kΩ AC Common-Mode Rejection CMRAC Power-Supply Rejection Input Bias Current Input Bias Current Drift Input Offset Current Input Offset Current Drift PSR VCM = VEE + 0.2V to VCC - 1.1V, f = 120Hz TYP 78 95 G = +10V 93 115 G = +100V/V 95 115 G = +1000V/V 73 95 G = +10V 88 115 G = +100V/V 90 115 G = +1000V/V G = +1V 85 G = +10V 101 G = +100V 106 6 VCM = VCC/2 15 IOS VCM = VCC/2 ±1.0 TCIOS VCM = VCC/2 15 f = 10Hz 85 f = 100Hz 75 f = 10kHz 72 f = 0.1Hz to 10Hz 1.4 f = 10Hz 35 f = 100Hz 32 f = 10kHz 31 f = 0.1Hz to 10Hz 0.7 f = 10Hz 32 f = 100Hz 31 f = 10kHz 8.7 f = 0.1Hz to 10Hz in 2.4 f = 100Hz 0.76 f = 10kHz 0.1 RL = 25kΩ to VCC/2 Output Voltage Swing VOH, VOL RL = 5kΩ to VCC/2 dB dB 20 ±3.0 nA pA/°C nV/√Hz µVRMS nV/√Hz µVRMS nV/√Hz µVRMS pA/√Hz 16 VCC - VOH nA pA/°C 0.6 f = 10Hz f = 0.1Hz to 10Hz dB 120 VCM = VCC/2 G = +100V/V Input Noise Current 90 IB G = +10V/V UNITS 115 TCIB en MAX 115 G = +1V +2.7V ≤ VCC ≤ +7.5V; VCM = +1.5V; VOUT = +1.5V; VREF = +1.5V; RL = 25kΩ to +1.5V; G = +1V/V, +10V/V, +100V/V G = +1V/V Input Noise Voltage MIN G = +1V pARMS 30 100 VOL 30 100 VCC - VOH 100 200 VOL 100 200 mV _______________________________________________________________________________________ 3 MAX4194–MAX4197 ELECTRICAL CHARACTERISTICS (continued) MAX4194–MAX4197 Micropower, Single-Supply, Rail-to-Rail, Precision Instrumentation Amplifiers ELECTRICAL CHARACTERISTICS (continued) (VCC = +5V, VEE = 0V, RL = 25kΩ tied to VCC/2, VREF = VCC/2, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER Short-Circuit Current (Note 2) SYMBOL CONDITIONS MIN ISC Gain Equation Gain Error ±0.01 ±0.1 G = +10V ±0.03 ±0.3 G = +100V/V ±0.05 ±0.5 G = +1000V/V, MAX4194 ±0.5 G = +1V ±0.01 ±0.1 ±0.03 ±0.3 ±0.05 ±0.5 Capacitive-Load Stability MAX4194/MAX4195, G = +1V/V ±1 ±8 MAX4196/MAX4197 ±1 ±15 MAX4194 ±16 ppm/°C ±0.001 % 300 pF CL G = +1V/V -3dB Bandwidth BW-3dB VOUT ≤ 0.1VP-P, G = +10V/V VCM = VCC/2 G = +100V/V MAX4194 250 MAX4195 220 MAX4194 17 MAX4196 34 MAX4194 1.5 MAX4197 Slew Rate SR G = +1000V/V MAX4194 VOUT = 2VP-P, G = +1V/V G = +1V/V Settling Time tS 0.1%, VOUT = 2VP-P Total Harmonic Distortion THD Input Logic Voltage High VIH Input Logic Voltage Low VIL SHDN Input Current 4 % ±0.5 VEE + 0.1V ≤ VOUT ≤ VCC - 0.1V, VCM = VCC/2, G = +1V/V, +10V/V, +100V/V, +1000V/V Nonlinearity mA G = +1V TA = +25°C, VCM = VCC/2, G = +10V RL = 5kΩ, VEE + 0.2V ≤ VOUT G = +100V/V ≤ VCC - 0.2V G = +1000V/V, MAX4194 TC50kΩ UNITS 1+ (50kΩ/RG) TA = +25°C, VCM = VCC/2, RL = 25kΩ, VEE + 0.1V ≤ VOUT ≤ VCC - 0.1V 50kΩ Resistance Temperature Coefficient (Note 3) MAX ±4.5 MAX4194 only Gain Temperature Coefficient (Note 1) TYP kHz 3.1 0.147 0.06 0.05 G = +10V/V 0.04 G = +100V/V 5 G = +1000V/V 7 VOUT = 2VP-P, G = +1V/V, f = 1kHz V/µs ms 0.001 % VCC - 1.5 VEE < VSHDN < VCC ppm/°C V VCC - 2.5 V ±0.1 µA MAX4195/MAX4196/ MAX4197 only _______________________________________________________________________________________ Micropower, Single-Supply, Rail-to-Rail, Precision Instrumentation Amplifiers (VCC = +5V, VEE = 0V, RL = 25kΩ tied to VCC/2, VREF = VCC/2, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS Time to Shutdown tSHDN G = +1V/V, 0.1%, VOUT = +3V Enable Time From Shutdown tENABLE G = +1V/V, 0.1%, VOUT = +3.5V Power-Up Delay MIN TYP ms MAX4195/MAX4196/ MAX4197 only 0.5 ms 1 ms 0.5 ms VSHDN = VCC - 2.5V to VCC - 1.5V, G = +100V/V, 0.1%, VOUT = +3.5V tON/OFF UNITS 0.5 G = +1V/V, 0.1%, VOUT = +3.5V On/Off Settling Time MAX MAX4195/MAX4196/ MAX4197 only Note 1: Guaranteed by design. Note 2: Maximum output current (sinking/sourcing) in which the gain changes by less than 0.1%. Note 3: This specification represents the typical temperature coefficient of an on-chip thin film resistor. In practice, the temperature coefficient of the gain for the MAX4194 will be dominated by the temperature coefficient of the external gain-setting resistor. Typical Operating Characteristics (VCC = +5V, VEE = 0, RL = 25kΩ tied to VCC/2, TA = +25°C, unless otherwise noted.) MAX4195/MAX4196/MAX4197 SMALL-SIGNAL GAIN vs. FREQUENCY 1 0 -1 G = +1V/V -2 -3 G = +10V/V G = +100V/V 3 2 G = +1V/V 0 -1 G = +100V/V G = +10V/V -3 -4 -4 -5 -5 -6 1k 1 -2 1k 10k FREQUENCY (Hz) 100k 1M 100 10 -6 100 10k MAX4194 toc03 2 4 MAX4194 toc02-2 NORMALIZED GAIN (dB) 3 NORMALIZED GAIN (dB) MAX4194 toc01-1 4 0.1% SETTLING TIME vs. GAIN (VOUT = 2Vp-p) SETTLING TIME (µs) MAX4194 SMALL-SIGNAL GAIN vs. FREQUENCY 1 100 1k 10k FREQUENCY (Hz) 100k 1M 1 10 100 1k GAIN (V/V) _______________________________________________________________________________________ 5 MAX4194–MAX4197 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (continued) (VCC = +5V, VEE = 0, RL = 25kΩ tied to VCC/2, TA = +25°C, unless otherwise noted.) MAX4197 LARGE-SIGNAL PULSE RESPONSE (GAIN = +100V/V) MAX4194 LARGE-SIGNAL PULSE RESPONSE (GAIN = +100V/V) MAX4194 LARGE-SIGNAL PULSE RESPONSE (GAIN = +1V/V) MAX4194 toc06 MAX4194 toc05 MAX4194 toc04 INPUT (500mV/div) INPUT (5mV/div) INPUT (5mV/div) OUTPUT (500mV/div) OUTPUT (500mV/div) OUTPUT (500mV/div) 20µs/div 200µs/div 200µs/div MAX4194 SMALL-SIGNAL PULSE RESPONSE (GAIN = +1V/V) MAX4194 SMALL-SIGNAL PULSE RESPONSE (GAIN = +100V/V) MAX4197 SMALL-SIGNAL PULSE RESPONSE (GAIN = +100V/V) MAX4194 toc09 MAX4194 toc08 MAX4194 toc07 INPUT (50mV/div) INPUT (500µV/div) INPUT (500µV/div) OUTPUT (50mV/div) OUTPUT (50mV/div) OUTPUT (50mV/div) 200µs/div 200µs/div 20µs/div POWER-SUPPLY REJECTION vs. FREQUENCY G = +1V/V -30 -40 -50 -40 -60 CMR (dB) G = +10V/V -60 MAX4194 toc11 -20 COMMON-MODE REJECTION vs. FREQUENCY MAX4194 toc10 0 PSR (dB) MAX4194–MAX4197 Micropower, Single-Supply, Rail-to-Rail, Precision Instrumentation Amplifiers -80 G = +100V/V G = +1V/V -70 G = +10V/V -80 G = +100V/V -90 -100 -100 -120 G = +1000V/V -140 -120 1 10 100 1k FREQUENCY (Hz) 6 10k G = +1,000V/V -110 100k 10 100 1k FREQUENCY (Hz) _______________________________________________________________________________________ 10k 100k Micropower, Single-Supply, Rail-to-Rail, Precision Instrumentation Amplifiers MAX4195/MAX4196 TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY VOLTAGE-NOISE DENSITY vs. FREQUENCY G = +1V/V MAX4194 toc13 1.000 MAX4194 toc12 0.100 THD + NOISE (%) 100 G = +10V/V 10 0.010 MAX4196 G = +10V/V 0.001 G = +1V/V MAX4195 G = +100V/V G = +1000V/V 1 1 10 100 1k 10k 0 100k 1 10 1k 10k SUPPLY CURRENT vs. TEMPERATURE SUPPLY CURRENT vs. SUPPLY VOLTAGE 98 MAX4194 toc14 120 110 100 G = +1000V/V 96 SUPPLY CURRENT (µA) SUPPLY CURRENT (µA) 100 FREQUENCY (Hz) FREQUENCY (Hz) 90 MAX4194 toc15 VOLTAGE NOISE DENSITY (nV/÷Hz) 1,000 G = +100V/V 94 92 G = +1V/V, +10V/V 90 88 86 2 3 4 5 6 7 SUPPLY VOLTAGE (V) 8 84 9 10 35 60 85 8 6 4 INPUT BIAS CURRENT vs. TEMPERATURE 10 INPUT BIAS CURRENT (nA) MAX4194 toc16 10 SHUTDOWN CURRENT (µA) -15 TEMPERATURE (°C) MAX4195/MAX4196/MAX4197 SHUTDOWN CURRENT vs. TEMPERATURE 8 6 4 2 2 0 -40 -40 MAX4194TOC17 80 -15 10 35 TEMPERATURE (°C) 60 85 0 -40 -15 10 35 60 85 TEMPERATURE (°C) _______________________________________________________________________________________ 7 MAX4194–MAX4197 Typical Operating Characteristics (continued) (VCC = +5V, VEE = 0, RL = 25kΩ tied to VCC/2, TA = +25°C, unless otherwise noted.) Typical Operating Characteristics (continued) (VCC = +5V, VEE = 0, RL = 25kΩ tied to VCC/2, TA = +25°C, unless otherwise noted.) INPUT OFFSET CURRENT vs. TEMPERATURE MAX4197 -50 -100 MAX4195 -150 MAX4194TOC19 MAX4196 0 INPUT OFFSET VOLTAGE vs. TEMPERATURE 100 75 INPUT OFFSET VOLTAGE (µV) MAX4194TOC18 50 INPUT OFFSET CURRENT (pA) MAX4194–MAX4197 Micropower, Single-Supply, Rail-to-Rail, Precision Instrumentation Amplifiers MAX4197 50 MAX4196 25 0 -25 MAX4194 (G = +10V/V) -50 MAX4194 (G = +100V/V, G = +1000V/V) -75 MAX4195 -200 -40 -15 10 35 60 85 -100 -40 -15 TEMPERATURE (°C) 10 35 60 85 TEMPERATURE (°C) Pin Description PIN 8 FUNCTION MAX4195 MAX4196 MAX4197 NAME MAX4194 1, 8 — RG-, RG+ 5 1 REF Reference Voltage. Offsets output voltage. 2 2 IN- Inverting Input 3 3 IN+ Noninverting Input 4 4 VEE Negative Supply Voltage — 5 FB Feedback. Connects to OUT. 6 6 OUT Amplifier Output 7 7 VCC Positive Supply Voltage — 8 SHDN FUNCTION Connection for Gain-Setting Resistor Shutdown Control _______________________________________________________________________________________ Micropower, Single-Supply, Rail-to-Rail, Precision Instrumentation Amplifiers Input Stage The MAX4194–MAX4197 family of low-power instrumentation amplifiers implements a three-amplifier topology (Figure 1). The input stage is composed of two operational amplifiers that together provide a fixed-gain differential and a unity common-mode gain. The output stage is a conventional differential amplifier that provides an overall common-mode rejection of 115dB (G = VCC 25kΩ IN25kΩ 25kΩ RGOUT MAX4194 RG+ 25kΩ 25kΩ +10V/V). The MAX4194’s gain can be externally set between +1V/V and +10,000V/V (Table 1). The MAX4195/MAX4196/MAX4197 have on-chip gain-setting resistors (Figure 2), and their gains are fixed at +1V/V, +10V/V, and +100V/V, respectively. Input Voltage Range and Detailed Operation The common-mode input range for all of these amplifiers is VEE - 0.2V to VCC - 1.1V. Ideally, the instrumentation amplifier (Figure 3) responds only to a differential voltage applied to its inputs, IN+ and IN-. If both inputs are at the same voltage, the output is VREF. A differential voltage at IN+ (VIN+) and IN- (VIN-) develops an identical voltage across the gain-setting resistor, causing a current (I G ) to flow. This current also flows through the feedback resistors of the two input amplifiers A1 and A2, generating a differential voltage of: VOUT2 - VOUT1 = IG · (R1 + RG + R1) REF IN+ 25kΩ VEE Figure 1. MAX4194 Simplified Block Diagram VCC 25kΩ IN- FB 25kΩ 25kΩ RG 25kΩ SHDN MAX4195 MAX4196 MAX4197 REF 25kΩ VEE Figure 2. MAX4195/MAX4196/MAX4197 Simplified Block Diagram VOUT = (VIN+ - VIN-) · [(2 · R1) / RG] + 1 The common-mode input range is a function of the amplifier’s output voltage and the supply voltage. With a power supply of VCC, the largest output signal swing can be obtained with REF tied to VCC/2. This results in an output voltage swing of ±VCC/2. An output voltage swing less than full-scale increases the common-mode input range. * R1 = R2 = 25kΩ ** RG = INTERNAL TO MAX4195/MAX4196/MAX4197 RG = EXTERNAL TO MAX4194 R 2* VOUT1 VIN- The output voltage (V OUT ) for the instrumentation amplifier is expressed in the following equation: OUT 25kΩ IN+ where VOUT1 and VOUT2 are the output voltages of A1 and A2, RG is the gain-setting resistor (internal or external to the part), and R1 is the feedback resistor of the input amplifiers. IG is determined by the following equation: IG = (VIN+ - VIN-) / RG A1 R2* IG R 1* VIN+ - VIN- VOUT2 - VOUT1 RG** A3 OUT R1* VIN+ ( VOUT = (VIN+ - VIN-) · 1 + IG R2* A2 VOUT2 2R1 RG ) REF R2* Figure 3. Instrumentation Amplifier Configuration _______________________________________________________________________________________ 9 MAX4194–MAX4197 Detailed Description Table 1. MAX4194 External Gain Resistor Selection This disables the instrumentation amplifier and puts its output in a high-impedance state. Pulling SHDN high enables the instrumentation amplifier. CLOSEST RG (1%) CLOSEST RG (5%) (Ω) (Ω) Applications Information GAIN (V/V) +1 ∞* ∞* +2 49.9k 51k +5 12.4k 12k +10 5.62k 5.6k +20 2.61k 2.7k +50 1.02k 1.0k +100 511 510 +200 249 240 +500 100 100 +1,000 49.9 51 +2,000 24.9 24 +5,000 10 10 +10,000 4.99 5.1 *Leave pins 1 and 8 open for G = +1V/V. VCM vs. VOUT Characterization Figure 4 illustrates the MAX4194 typical common-mode input voltage range over output voltage swing at unitygain (pins 1 and 8 left floating), with a single-supply voltage of VCC = +5V and a bias reference voltage of VREF = VCC/2 = +2.5V. Points A and D show the full input voltage range of the input amplifiers (VEE - 0.2V to VCC - 1.1V) since, with +2.5V output, there is zero input differential swing. The other points (B, C, E, and F) are determined by the input voltage range of the input amps minus the differential input amplitude necessary to produce the associated VOUT. For the higher gain configurations, the VCM range will increase at the endpoints (B, C, E, and F) since a smaller differential voltage is necessary for the given output voltage. Setting the Gain (MAX4194) The MAX4194’s gain is set by connecting a single, external gain resistor between the two RG pins (pin 1 and pin 8), and can be described as: G = 1 + 50kΩ / RG where G is the instrumentation amplifier’s gain and RG is the gain-setting resistor. The 50kΩ resistor of the gain equation is the sum of the two resistors internally connected to the feedback loops of the IN+ and IN- amplifiers. These embedded feedback resistors are laser trimmed, and their accuracy and temperature coefficients are included in the gain and drift specification for the MAX4194. 5 COMMON-MODE INPUT VOLTAGE (V) MAX4194–MAX4197 Micropower, Single-Supply, Rail-to-Rail, Precision Instrumentation Amplifiers MAX4194/MAX4195 G = +1V/V REF = +2.5V/+1.5V 4 VCC = +5V/+3V VEE = 0 TA = +25°C A 3 B F C E 2 1 D 0.03 0 0 1 2 4.97 3 4 5 OUTPUT VOLTAGE (V) Figure 4. Common-Mode Input Voltage vs. Output Voltage Rail-to-Rail Output Stage The MAX4194–MAX4197’s output stage incorporates a common-source structure that maximizes the dynamic range of the instrumentation amplifier. The output can drive up to a 25kΩ (tied to VCC/2) resistive load and still typically swing within 30mV of the rails. With an output load of 5kΩ tied to VCC/2, the output voltage swings within 100mV of the rails. MAX4195 OUT AC-COUPLED (VDIFF = 2V, G = +1V/V) (500mV/div) Shutdown Mode The MAX4195–MAX4197 feature a low-power shutdown mode. When the shutdown pin (SHDN) is pulled low, the internal amplifiers are switched off and the supply current drops to 8µA typically (Figures 5a, 5b, and 5c). 10 SHDN (5V/div) 50µs/div Figure 5a. MAX4195 Shutdown Mode ______________________________________________________________________________________ Micropower, Single-Supply, Rail-to-Rail, Precision Instrumentation Amplifiers IN+ RISO VOUT INRL VEE RG = ∞ (MAX4194) (INTERNAL, MAX4195) VREF CL VREF SHDN (5V/div) Figure 6a. Using a Resistor to Isolate a Capacitive Load from the Instrumentation Amplifier (G = +1V/V) 50µs/div Figure 5b. MAX4196 Shutdown Mode INPUT (50mV/div) MAX4197 OUT AC-COUPLED (VDIFF = 20mV, G = +100V/V) (500mV/div) OUTPUT (50mV/div) SHDN (5V/div) 50µs/div 50µs/div Figure 5c. MAX4197 Shutdown Mode The accuracy and temperature drift of the RG resistors also influence the IC’s precision and gain drift, and can be derived from the equation above. With low RG values, which are required for high-gain operation, parasitic resistances may significantly increase the gain error. Figure 6b. Small-Signal Pulse Response with Excessive Capacitive Load (RL = 25kΩ, CL = 1000pF) INPUT (50mV/div) Capacitive-Load Stability The MAX4194–MAX4197 are stable for capacitive loads up to 300pF (Figure 6a). Applications that require greater capacitive-load driving capability can use an isolation resistor (Figure 6b) between the output and the capacitive load to reduce ringing on the output signal. However, this alternative reduces gain accuracy because RISO (Figure 6c) forms a potential divider with the load resistor. OUTPUT (50mV/div) 50µs/div Figure 6c. Small-Signal Pulse Response with Excessive Capacitive Load and Isolating Resistor (RISO = 75Ω, RL = 25kΩ, CL = 1000pF) ______________________________________________________________________________________ 11 MAX4194–MAX4197 VCC MAX4196 OUT AC-COUPLED (VDIFF = 200mV, G = +10V/V) (500mV/div) MAX4194–MAX4197 Micropower, Single-Supply, Rail-to-Rail, Precision Instrumentation Amplifiers Power-Supply Bypassing and Layout identical two-element strain gauges) to the inputs of the MAX4194. The bridge contains four resistors, two of which increase and two of which decrease by the same ratio. Good layout technique optimizes performance by decreasing the amount of stray capacitance at the instrumentation amplifier’s gain-setting pins. Excess capacitance will produce peaking in the amplifier’s frequency response. To decrease stray capacitance, minimize trace lengths by placing external components as close to the instrumentation amplifier as possible. For best performance, bypass each power supply to ground with a separate 0.1µF capacitor. With a fully balanced bridge, points A (IN+) and B (IN-) see half the excitation voltage (V BRIDGE ). The low impedance (120Ω to 350Ω) of the strain gauges, however, could cause significant voltage drop contributions by the wires leading to the bridge, which would cause excitation variations. Output voltage VOUT can be calculated as follows: VOUT = VAB · G where G = (1 + 50kΩ / RG) is the gain of the instrumentation amplifier. Since VAB is directly proportional to the excitation, gain errors may occur. Transducer Applications The MAX4194–MAX4197 instrumentation amplifiers can be used in various signal-conditioning circuits for thermocouples, PT100s, strain gauges (displacement sensors), piezoresistive transducers (PRTs), flow sensors, and bioelectrical applications. Figure 7 shows a simplified example of how to attach four strain gauges (two RG REFERENCE RG+ IN+ R VBRIDGE VAB = VIN+ - VINR RG- IN- REF B R µP VEE R = 120Ω - 350Ω A MAX144 ADC OUT VCC R Figure 7. Strain Gauge Connection to the MAX4194 ___________________Chip Information TRANSISTOR COUNT: 432 12 ______________________________________________________________________________________ Micropower, Single-Supply, Rail-to-Rail, Precision Instrumentation Amplifiers N E H INCHES MILLIMETERS MAX MIN 0.069 0.053 0.010 0.004 0.014 0.019 0.007 0.010 0.050 BSC 0.150 0.157 0.228 0.244 0.016 0.050 MAX MIN 1.35 1.75 0.10 0.25 0.35 0.49 0.19 0.25 1.27 BSC 3.80 4.00 5.80 6.20 0.40 SOICN .EPS DIM A A1 B C e E H L 1.27 VARIATIONS: 1 INCHES TOP VIEW DIM D D D MIN 0.189 0.337 0.386 MAX 0.197 0.344 0.394 MILLIMETERS MIN 4.80 8.55 9.80 MAX 5.00 8.75 10.00 N MS012 8 AA 14 AB 16 AC D C A B e 0 -8 A1 L FRONT VIEW SIDE VIEW PROPRIETARY INFORMATION TITLE: PACKAGE OUTLINE, .150" SOIC APPROVAL DOCUMENT CONTROL NO. 21-0041 REV. B 1 1 Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. 13 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products. MAX4194–MAX4197 Package Information (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.)