INA3 31 INA 233 1 INA331 INA2331 ® SBOS215B – DECEMBER 2001 – REVISED APRIL 2003 Low-Power, Single-Supply, CMOS INSTRUMENTATION AMPLIFIERS FEATURES APPLICATIONS ● ● ● ● ● ● ● DESIGNED FOR LOW COST HIGH GAIN ACCURACY: G = 5, 0.02%, 2ppm/°C GAIN SET WITH EXT. RESISTORS FOR > 5V/V LOW OFFSET VOLTAGE: ±250µV HIGH CMRR: 94dB DC, 50dB at 45kHz LOW BIAS CURRENT: 0.5pA BANDWIDTH, SLEW RATE: 2.0MHz, 5V/µs ● ● ● ● ● RAIL-TO-RAIL OUTPUT SWING: (V+) – 0.02V WIDE TEMPERATURE RANGE: –55°C to +125°C LOW QUIESCENT CURRENT: 490µA max/chan SHUT DOWN: 0.01µA MSOP-8 SINGLE AND TSSOP-14 DUAL PACKAGES ● INDUSTRIAL SENSOR AMPLIFIERS: Bridge, RTD, Thermocouple, Position ● PHYSIOLOGICAL AMPLIFIERS: ECG, EEG, EMG ● A/D CONVERTER SIGNAL CONDITIONING ● DIFFERENTIAL LINE RECEIVERS WITH GAIN ● FIELD UTILITY METERS ● PCMCIA CARDS ● AUDIO AMPLIFIERS ● COMMUNICATION SYSTEMS ● TEST EQUIPMENT ● AUTOMOTIVE INSTRUMENTATION DESCRIPTION The INA331 rejects line noise and its harmonics, because common-mode error remains low even at higher frequencies. The INA331 and INA2331 are rail-to-rail output, low-power CMOS instrumentation amplifiers that offer wide range, singlesupply operation as well as bipolar-supply operation. The INA331 family provides low-cost, low-noise amplification of differential signals with a low quiescent current of 415µA (dropping to 0.01µA when shutdown). Returning to normal operation within microseconds, this INA can be used for battery or multi-channel applications. Configured internally in a gain of 5V/V, the INA331 offers flexibility in higher gains by choosing external resistors. High bandwidth and slew rate makes the INA331 ideal for directly driving sampling Analog-to-Digital (A/D) converters as well as general-purpose applications. With high precision, low cost, and small packages, the INA331 outperforms discrete designs. Additionally, because they are specified for wide temperature range of –55°C to +125°C and operating range of –65°C to +150°C, they can be used in demanding industrial and automotive environments. R2 R1 RG G = 5 + (5R2/R1) INA2331 40kΩ INA331 10kΩ VREF 40kΩ Ch A 10kΩ A1 A3 VOUT A2 VIN– Ch B VIN+ V+ V– Shutdown Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet. Copyright © 2001-2003, Texas Instruments Incorporated PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. www.ti.com ELECTROSTATIC DISCHARGE SENSITIVITY ABSOLUTE MAXIMUM RATINGS(1) Supply Voltage, V+ to V– .................................................................... 7.5V Signal Input Terminals, Voltage(2) ..................... (V–) – 0.5V to (V+) + 0.5V Current(2) ..................................................... 10mA Output Short-Circuit(3) .............................................................. Continuous Operating Temperature .................................................. –55°C to +125°C Storage Temperature ...................................................... –65°C to +150°C Junction Temperature ...................................................................... 150°C Lead Temperature (soldering, 10s) ................................................. 300°C This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with appropriate precautions. Failure to observe proper handling and installation procedures can cause damage. NOTES: (1) Stresses above these ratings may cause permanent damage. Exposure to absolute maximum conditions for extended periods may degrade device reliability. (2) Input terminals are diode-clamped to the power-supply rails. Input signals that can swing more than 0.5V beyond the supply rails should be current limited to 10mA or less. (3) Short-circuit to ground, one amplifier per package. ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more susceptible to damage because very small parametric changes could cause the device not to meet its published specifications. PACKAGE/ORDERING INFORMATION PACKAGE-LEAD PACKAGE DESIGNATOR(1) TEMPERATURE RANGE SPECIFIED PACKAGE MARKING INA331IDGK MSOP-8 DGK –55°C to +125°C C31 INA331IDGKT Tape and Reel, 250 " " " " " INA331IDGKR Tape and Reel, 2500 INA331AIDGK MSOP-8 DGK –55°C to +125°C C31 INA331AIDGKT Tape and Reel, 250 " " " " " INA331AIDGKR Tape and Reel, 2500 INA2331AIPW TSSOP-14 PW –55°C to +125°C 2331A INA2331AIPWT Tape and Reel, 250 " " " " " INA2331AIPWR Tape and Reel, 2500 PRODUCT ORDERING NUMBER TRANSPORT MEDIA, QUANTITY Single Dual NOTE: (1) For the most current specifications and package information, refer to our web site at www.ti.com. PIN CONFIGURATION Top View INA2331 RGA 1 14 Shutdown A VIN–A 2 13 VOUTA VIN+A 3 12 REFA V– 4 11 V+ VIN+B 5 10 REFB VIN–B 6 9 VOUTB RGB 7 8 Shutdown B INA331 RG 1 8 Shutdown VIN– 2 7 V+ VIN+ 3 6 VOUT V– 4 5 REF MSOP-8 (DGK) Dual, TSSOP-14 (PW) 2 INA331, INA2331 www.ti.com SBOS215B ELECTRICAL CHARACTERISTICS: VS = +2.7V to +5.5V Boldface limits apply over the specified temperature range, TA = –55°C to 125°C. At TA = +25°C, RL = 10kΩ, G = 25, and VREF = VS /2, unless otherwise noted. INA331AIDGK INA2331AIPW INA331IDGK PARAMETER INPUT Input Offset Voltage, RTI Over Temperature Temperature Coefficient vs Power Supply vs Temperature Long-Term Stability Input Impedance Input Common-Mode Range Common-Mode Rejection –40°C to +85°C Over Temperature CONDITION VOS dVOS/dT PSRR MIN TYP MAX VS = +5V ±250 VS = +2.7V to +5.5V ±5 ±50 ±500 ±1.7 CMRR 0.35 0.55 90 77 72 1.5 3.8 94 ✻ ✻ 80 75 70 VCM = VS /2 ±0.5 ±0.5 IOS NOISE, RTI Voltage Noise: f = 10Hz f = 100Hz f = 1kHz f = 0.1Hz to 10Hz Current Noise: f = 1kHz UNITS ✻ ±1000 ±2.1 µV mV µV/°C µV/V µV/V µV/month Ω || pF V V dB dB dB dB dB ✻ ✱ ✻ ✻ ✻ ✻ 114 94 IB MAX ✻ ✻ Crosstalk, Dual INPUT BIAS CURRENT Bias Current Offset Current TYP ✱ ✻ ±200 ±220 ±0.4 1013 || 3 VS = 2.7V VS = 5V VS = 5V, VCM = 0.55V to 3.8V VS = 5V, VCM = 0.55V to 3.8V VS = 5V, VCM = 0.55V to 3.8V VS = 2.7V, VCM = 0.35V to 1.5V MIN ±10 ±10 ✻ ✻ ✻ ✻ pA pA RS = 0Ω eN iN GAIN(1) Gain Equation, Externally Set Range of Gain Gain Error vs Temperature Nonlinearity Over Temperature G>5 ±0.02 ±2 ±0.001 ±0.002 G=5 G=5 G = 25(2), VS = 5V, VO = 0.05 to 4.95 RL = 10kΩ G > 10 nV/√Hz nV/√Hz nV/√Hz µVp-p fA/√Hz ✻ G = 5 + (5R2/R1) 5 OUTPUT Output Voltage Swing from Rail(3) Over Temperature Capacitance Load Drive Short-Circuit Current ✻ ✻ ✻ ✻ ✻ 280 96 46 7 0.5 1000 ±0.1 ±10 ±0.010 ±0.015 50 25 50 See Typical Characteristics +48/–32 ✻ ✻ ✱ ✻ ✱ ✻ ✱ ✻ ✻ ✱ ✻ ✱ ✻ V/V % ppm/°C % of FS % of FS ✻ ✻ mV mV pF mA ✻ ✻ ✻ ✻ ✻ MHz V/µs µs µs µs FREQUENCY RESPONSE Bandwidth, –3dB Slew Rate Settling Time, 0.1% 0.01% Overload Recovery POWER SUPPLY Specified Voltage Range Operating Voltage Range Quiescent Current per Channel Over Temperature Shutdown Quiescent Current/Chan TEMPERATURE RANGE Specified Range Operating/Storage Range Thermal Resistance BW SR tS G = 25 VS = 5V, G = 25 G = 25, CL = 100pF, VO = 2V step 2.0 5 1.7 2.5 2 50% Input Overload G = 25 +2.7 +5.5 IQ VSD > 2.5(3) +2.5 to +5.5 415 ISD VSD < 0.8(3) 0.01 –55 –65 θJA MSOP-8, TSSOP-14 Surface Mount ✻ ✻ ✻ 490 600 1 +125 +150 150 ✻ ✻ ✻ ✻ ✻ ✱ ✻ ✻ ✻ ✻ V V µA µA µA °C °C °C/W ✻ Specifications same as INA331IDGK NOTES: (1) Does not include errors from external gain setting resistors. (2) Output voltage swings are measured between the output and power-supply rails. Output swings to rail only if G ≥ 10. Output does not swing to positive rail if gain is less than 10. (3) See typical characteristic “Percent Overshoot vs Load Capacitance.” (4) See typical characteristic “Shutdown Voltage vs Supply Voltage.” INA331, INA2331 SBOS215B www.ti.com 3 TYPICAL CHARACTERISTICS At TA = +25°C, VS = 5V, VCM = VS /2, RL = 10kΩ, and CL = 100pF, unless otherwise noted. COMMON-MODE REJECTION RATIO vs FREQUENCY GAIN vs FREQUENCY 80 120 70 60 50 80 Gain = 100 CMRR (dB) Gain (dB) 100 Gain = 500 40 Gain = 25 30 20 Gain = 5 10 0 60 40 20 –10 –20 0 10 100 1k 10k 100k 1M 10M 10 100 Frequency (Hz) POWER-SUPPLY REJECTION RATIO vs FREQUENCY Maximum Output Voltage (Vp-p) 90 80 70 PSRR (dB) 10k 100k MAXIMUM OUTPUT VOLTAGE vs FREQUENCY 6 100 60 50 40 30 20 10 0 VS = 5.5V 5 VS = 5.0V 4 3 VS = 2.7V 2 1 0 1 10 100 1k 10k 100 100k 10 100 1 10 100 1k 100k 1M 10M 10k 0.1 100k 2µV/div 1k INOISE (fA/√Hz) 100 10 10k 0.1Hz TO 10Hz VOLTAGE NOISE NOISE vs FREQUENCY 10k 1 1k Frequency (Hz) Frequency (Hz) VNOISE (nV/√Hz) 1k Frequency (Hz) 1s/div Frequency (Hz) 4 INA331, INA2331 www.ti.com SBOS215B TYPICAL CHARACTERISTICS (Cont.) At TA = +25°C, VS = 5V, VCM = VS /2, RL = 10kΩ, and CL = 100pF, unless otherwise noted. COMMON-MODE INPUT RANGE vs REFERENCE VOLTAGE OUTPUT SWING vs LOAD RESISTANCE 6 Output—Referred to Ground (V) 25 Swing to Rail (mV) 20 15 To Positive Rail 10 To Negative Rail 5 5 Outside of Normal Operation 4 3 2 1 0 0 0 10k 20k 30k 40k 0 50k 2 5 QUIESCENT CURRENT AND SHUTDOWN CURRENT vs POWER SUPPLY QUIESCENT CURRENT AND SHUTDOWN CURRENT vs TEMPERATURE IQ 400 350 IQ (µA) 300 250 200 150 100 ISD 50 0 3 3.5 4 4.5 5 600 550 500 450 400 350 300 250 200 150 100 50 0 IQ ISD –75 5.5 –50 –25 0 25 50 75 100 125 150 Temperature (°C) Supply Voltage (V) SHORT-CIRCUIT CURRENT vs POWER SUPPLY SHORT-CIRCUIT CURRENT vs TEMPERATURE 60 60 ISC+ ISC+ 50 50 40 40 ISC– ISC (mA) ISC (mA) 4 3 Input Common-Mode Voltage (V) 450 2.5 1 RLOAD (Ω) 500 IQ (µA), ISD (nA) REF Increasing 30 ISC– 30 20 20 10 10 0 0 2.5 3 3.5 4 4.5 5 5.5 –75 Supply Voltage (V) –25 0 25 50 75 100 125 150 Temperature (°C) INA331, INA2331 SBOS215B –50 www.ti.com 5 TYPICAL CHARACTERISTICS (Cont.) At TA = +25°C, VS = 5V, VCM = VS /2, RL = 10kΩ, and CL = 100pF, unless otherwise noted. SMALL-SIGNAL STEP RESPONSE (G = 100) 50mV/div 100mV/div SMALL-SIGNAL STEP RESPONSE (G = 5) 4µs/div SMALL-SIGNAL STEP RESPONSE (G = 5, CL = 1000pF) SMALL-SIGNAL STEP RESPONSE (G = 100, CL = 1000pF) 50mV/div 100mV/div 4µs/div 10µs/div SMALL-SIGNAL STEP RESPONSE (G = 100, CL = 4700pF) LARGE-SIGNAL STEP RESPONSE (G = 25) 1V/div 50mV/div 4µs/div 10µs/div 6 10µs/div INA331, INA2331 www.ti.com SBOS215B TYPICAL CHARACTERISTICS (Cont.) At TA = +25°C, VS = 5V, VCM = VS /2, RL = 10kΩ, and CL = 100pF, unless otherwise noted. PERCENT OVERSHOOT vs LOAD CAPACITANCE SETTLING TIME vs GAIN 100 60 Output 2Vp-p Differential Input Drive Output 100mVp-p Differential Drive 90 80 40 Overshoot (%) Settling Time (µs) 50 0.01% 30 20 G=5 70 60 50 40 G = 25 30 10 20 0.1% 10 0 0 1 10 100 10 1k 100 1k Gain (V/V) Load Capacitance (pF) SHUTDOWN VOLTAGE vs SUPPLY VOLTAGE SHUTDOWN TRANSIENT BEHAVIOR 10k 3 Operation in this Region is not Recommended 2.5 VSD 2 1V/div Shutdown (V) Normal Operation Mode 1.5 1 Shutdown Mode VOUT 0.5 Part Draws Below 1µA Quiescent Current 0 2.5 3 3.5 4 4.5 5 50µs/div 5.5 Supply Voltage (V) OFFSET VOLTAGE DRIFT PRODUCTION DISTRIBUTION OFFSET VOLTAGE PRODUCTION DISTRIBUTION 25 20 Percentage of Amplifiers (%) Percentage of Amplifiers (%) 18 20 15 10 5 16 14 12 10 8 6 4 2 0 –14 –13 –11 –10 –8 –7 –6 –4 –3 –1 0 1 3 4 6 7 8 10 11 13 14 –1.0 –0.9 –0.8 –0.7 –0.6 –0.5 –0.4 –0.3 –0.2 –0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 0 Offset Voltage (µV/°C) Offset Voltage (mV) INA331, INA2331 SBOS215B www.ti.com 7 TYPICAL CHARACTERISTICS (Cont.) At TA = +25°C, VS = 5V, VCM = VS /2, RL = 10kΩ, and CL = 100pF, unless otherwise noted. SLEW RATE vs TEMPERATURE INPUT BIAS CURRENT vs TEMPERATURE 8 10000 Input Bias Current (pA) 7 Slew Rate (V/µs) 6 5 4 3 2 1000 100 10 1 1 0 0.1 –75 –50 –25 0 25 50 75 100 125 150 –75 –50 –25 0 Temperature (°C) CHANNEL SEPARATION vs FREQUENCY 75 100 125 150 5 100 4 Output Voltage (V) Separation (dB) 50 OUTPUT VOLTAGE SWING vs OUTPUT CURRENT 120 80 60 40 3 25°C 125°C –55°C 2 1 20 0 0 1 10 100 1k 10k 100k 1M 10M 0 Frequency (Hz) 8 25 Temperature (°C) 5 10 15 20 25 30 35 40 45 50 55 60 Output Current (mA) INA331, INA2331 www.ti.com SBOS215B APPLICATIONS INFORMATION The INA331 is a modified version of the classic “two op amp” instrumentation amplifier, with an additional gain amplifier. Figure 1 shows the basic connections for the operation of the INA331 and INA2331. The power supply should be capacitively decoupled with 0.1µF capacitors as close to the INA331 as possible for noisy or high-impedance applications. The output is referred to the reference terminal, which must be at least 1.2V below the positive supply rail. OPERATING VOLTAGE The INA331 family is fully specified over a supply range of +2.7V to +5.5V, with key parameters tested over the temperature range of –55°C to +125°C. Parameters that vary significantly with operating conditions, such as load conditions or temperature, are shown in the Typical Characteristics. The INA331 may be operated on a single supply. Figure 2 shows a bridge amplifier circuit operated from a single +5V supply. The bridge provides a small differential voltage riding on an input common-mode voltage. G = 5 + 5 (R2 / R1 ) Short VOUT to RG for G = 5 R1 DESIRED GAIN (V/V) R2 5 10 50 100 RG 1 5 REF 40kΩ 10kΩ R2 R1 OPEN SHORT 100kΩ 100kΩ 10kΩ 90kΩ 10kΩ 190kΩ 40kΩ VIN– VIN+ 10kΩ A1 2 A3 6 VO = ((VIN+) – (VIN –)) • G A2 3 Also drawn in simplified form: 8 4 7 Shutdown VIN+ (For Single Supply) 0.1µF V+ 7 5 INA331 0.1µF 8 REF V– V+ Shutdown 3 VIN– 2 6 VOUT 1 4 V– RG FIGURE 1. Basic Connections. +5V Bridge Sensor VIN+ 3 V+ 7 REF(1) 5 INA331 Shutdown 8 VIN– 6 VOUT 1 2 4 V– RG NOTE: (1) REF should be adjusted for the desired output level, keeping in mind that the value of REF affects the common-mode input range. See Typical Characteristics. FIGURE 2. Single-Supply Bridge Amplifier. INA331, INA2331 SBOS215B www.ti.com 9 SETTING THE GAIN The ratio of R2 to R1, or the impedance between pins 1, 5, and 6, determines the gain of the INA331. With an internally set gain of 5, the INA331 can be programmed for gains greater than 5 according to the following equation: G = 5 + 5 (R2/R1) The INA331 is designed to provide accurate gain, with gain error less than 0.1%. Setting gain with matching TC resistors will minimize gain drift. Errors from external resistors will add directly to the error, and may become dominant error sources. how bias current path can be provided in the cases of microphone applications, thermistor applications, ground returns, and dc-coupled resistive bridge applications. When differential source impedance is low, the bias current return path can be connected to one input. With higher source impedance, two equal resistors will provide a balanced input. The advantages are lower input offset voltage due to bias current flowing through the source impedance and better high-frequency gain. V+ VIN+ 3 COMMON-MODE INPUT RANGE The upper limit of the common-mode input range is set by the common-mode input range of the second amplifier, A2, to 1.2V below positive supply. Under most conditions, the amplifier operates beyond this point with reduced performance. The lower limit of the input range is bounded by the output swing of amplifier A1, and is a function of the reference voltage according to the following equation: Shutdown 7 8 Microphone, Hydrophone, etc. REF 5 VIN– 2 47kΩ VB INA331 6 VOUT 1 4 V– RG (1) VOA1 = 5/4 VCM – 1/4 VREF V+ VIN+ 3 (See typical characteristics “Common-Mode Input Range vs Reference Voltage”). Shutdown 7 8 Transformer REF 5 INA331 VIN– 2 REFERENCE 6 VOUT 1 4 The reference terminal defines the zero output voltage level. In setting the reference voltage, the common mode input of A3 should be considered according to the following equation: VOA2 = VREF + 5 (VIN+ – VIN–) VB(1) Bridge Amplifier V– VEX V+ For ensured operation, V OA2 should be less than VDD – 1.2V. Bridge Sensor The reference pin requires a low-impedance connection. As little as 160Ω in series with the reference pin will degrade the CMRR to 80dB. The reference pin may be used to compensate for the offset voltage (see Offset Trimming section). The reference voltage level also influences the common-mode input range (see Common-Mode Input Range section). Center-tap RG provides bias current return VIN+ 3 Shutdown 7 8 REF 5 INA331 6 VOUT 1 VIN– 2 4 V– RG Bridge resistance provides bias current return NOTE: (1) VB is bias voltage within common-mode range, dependent on REF. INPUT BIAS CURRENT RETURN With a high input impedance of 1013Ω, the INA331 is ideal for use with high-impedance sources. The input bias current of less than 10pA makes the INA331 nearly independent of input impedance and ideal for low-power applications. For proper operation, a path must be provided for input bias currents for both inputs. Without input bias current paths, the inputs will “float” to a potential that exceeds common-mode range and the input amplifier will saturate. Figure 3 shows 10 FIGURE 3. Providing an Input Common-Mode Path. INA331, INA2331 www.ti.com SBOS215B SHUTDOWN MODE +5V The shutdown pin of the INA331 is nominally connected to V+. When the pin is pulled below 0.8V on a 5V supply, the INA331 goes into sleep mode within nanoseconds. For actual shutdown threshold, see typical characteristic “Shutdown Voltage vs Supply Voltage”. Drawing less than 2µA of current, and returning from sleep mode in microseconds, the shutdown feature is useful for portable applications. Once in ‘sleepmode’ the amplifier has high output impedance, making the INA331 suitable for multiplexing. 0.1µF VIN+ 3 V+ 7 5 INA331 8 REF VIN– 0.1µF Shutdown 6 VOUT 1 2 OPA340 VOUT 4 V– RG RAIL-TO-RAIL OUTPUT A class AB output stage with common-source transistors is used to achieve rail-to-rail output for gains of 10 or greater. For resistive loads greater than 10kΩ, the output voltage can swing to within 25 millivolts of the supply rail while maintaining low gain error. For heavier loads and over temperature, see the typical characteristic “Output Voltage Swing vs Output Current.” The INA331’s low output impedance at high frequencies makes it suitable for directly driving CapacitiveInput A/D converters, as shown in Figure 4. FIGURE 5. Output Buffering Circuit. Able to drive loads as low as 600Ω. V+ VIN+ 7 5 INA331 8 REF(1) V+ 7 3 8 REF VIN– 5 INA331 2 1 4 V– 6 VOUT Adjustable Voltage 12-Bits NOTE: (1) REF should be adjusted for the desired output level. The value of REF affects the common-mode input range. RG FIGURE 6. Optional Offset Trimming Voltage. fS < 100kHz INPUT PROTECTION FIGURE 4. INA331 Directly Drives Capacitive-Input, HighSpeed A/D Converter. OUTPUT BUFFERING The INA331 is optimized for a load impedance of 10kΩ or greater. For higher output current the INA331 can be buffered using the OPA340, as shown in Figure 5. The OPA340 can swing within 50mV of the supply rail, driving a 600Ω load. The OPA340 is available in the tiny MSOP-8 package. Device inputs are protected by ESD diodes that will conduct if the input voltages exceed the power supplies by more than 500mV. Momentary voltages greater than 500mV beyond the power supply can be tolerated if the current through the input pins is limited to 10mA. This is easily accomplished with input resistor RLIM, as shown in Figure 7. Many input signals are inherently current-limited to less than 10mA, therefore, a limiting resistor is not required. V+ OFFSET TRIMMING The INA331 is laser trimmed for low offset voltage. In the event that external offset adjustment is required, the offset can be adjusted by applying a correction voltage to the reference terminal. Figure 6 shows an optional circuit for trimming offset voltage. The voltage applied to the REF terminal is added to the output signal. The gain from REF to VOUT is +1. An op amp buffer is used to provide low impedance at the REF terminal to preserve good commonmode rejection. RLIM 3 VIN+ IOVERLOAD 10mA max REF 5 Shutdown 7 8 INA331 6 VOUT 1 2 VIN– 4 RLIM V– RG FIGURE 7. Sample Output Buffering Circuit. INA331, INA2331 SBOS215B RG OPA336 ADS7818 or ADS7822 VOUT 4 V– Shutdown 6 1 2 VIN– +5V VIN+ Shutdown 3 www.ti.com 11 OFFSET VOLTAGE ERROR CALCULATION FEEDBACK CAPACITOR IMPROVES RESPONSE The offset voltage (VOS) of the INA331IDGK is specified at a maximum of 500µV with a +5V power supply and the common-mode voltage at VS/2. Additional specifications for powersupply rejection and common-mode rejection are provided to allow the user to easily calculate worst-case expected offset under the conditions of a given application. For optimum settling time and stability with high-impedance feedback networks, it may be necessary to add a feedback capacitor across the feedback resistor, RF, as shown in Figure 8. This capacitor compensates for the zero created by the feedback network impedance and the INA331’s RG-pin input capacitance (and any parasitic layout capacitance). The effect becomes more significant with higher impedance networks. Also, RX and CL can be added to reduce highfrequency noise. Power-Supply Rejection Ratio (PSRR) is specified in µV/V. For the INA331, worst case PSRR is 200µV/V, which means for each volt of change in power supply, the offset may shift up to 200µV. Common-Mode Rejection Ratio (CMRR) is specified in dB, which can be converted to µV/V using the following equation: CMRR (in µV/V) = 10[(CMRR in dB)/–20] • V+ VIN+ 106 7 3 Shutdown 8 INA331 For the INA331, the worst case CMRR over the specified common-mode range is 90dB (at G = 25) or about 30µV/V This means that for every volt of change in common-mode, the offset will shift less than 30µV. These numbers can be used to calculate excursions from the specified offset voltage under different application conditions. For example, an application might configure the amplifier with a 3.3V supply with 1V common-mode. This configuration varies from the specified configuration, representing a 1.7V variation in power supply (5V in the offset specification versus 3.3V in the application) and a 0.65V variation in common-mode voltage from the specified VS/2. Calculation of the worst-case expected offset would be as follows: REF RX 6 5 VOUT CIN CL 1 VIN– 2 4 RG V– RIN RF RIN • CIN = RF • CF CF Where CIN is equal to the INA331’s input capacitance (approximately 3pF) plus any parastic layout capacitance. FIGURE 8. Feedback Capacitor Improves Dynamic Performance. It is suggested that a variable capacitor be used for the feedback capacitor since input capacitance may vary between instrumentation amplifiers, and layout capacitance is difficult to determine. For the circuit shown in Figure 8, the value of the variable feedback capacitor should be chosen by the following equation: Adjusted VOS = Maximum specified VOS + (power-supply variation) • PSRR + (common-mode variation) • CMRR VOS = 0.5mV + (1.7V • 200µV) + (0.65V • 30µV) = ±0.860mV RIN • CIN = RF • CF However, the typical value will be smaller, as seen in the Typical Characteristics. 12 Where CIN is equal to the INA331’s RG-pin input capacitance (typically 3pF) plus the layout capacitance. The capacitor can be varied until optimum performance is obtained. INA331, INA2331 www.ti.com SBOS215B APPLICATION CIRCUITS Filtering can be modified to suit application needs by changing the capacitor value of the output filter. MEDICAL ECG APPLICATIONS Figure 9 shows the INA331 configured to serve as a low-cost ECG amplifier, suitable for moderate accuracy heart-rate applications such as fitness equipment. The input signals are obtained from the left and right arms of the patient. The common-mode voltage is set by two 2MΩ resistors. This potential through a buffer provides optional right leg drive. LOW-POWER, SINGLE-SUPPLY DATA ACQUISITION SYSTEMS Refer to Figure 4 to see the INA331 configured to drive an ADS7818. Functioning at frequencies of up to 500kHz, the INA331 is ideal for low-power data acquisition. VR OPA336 1.6nF 0.1µF V+ 100kΩ VIN+ 3 Left Arm 100kΩ Right Arm 5 VIN– 2 INA331 1 V– 2MΩ 10kΩ 6 10kΩ OPA336 VOUT PUT VR 4 +5V 1MΩ 7 8 REF 1MΩ Shutdown RG 1MΩ 2MΩ 2kΩ VR = +2.5V 2kΩ OPA336 Right Leg FIGURE 9. Simplified ECG Circuit for Medical Applications. INA331, INA2331 SBOS215B www.ti.com 13 PACKAGE DRAWINGS DGK (R-PDSO-G8) PLASTIC SMALL-OUTLINE PACKAGE 0,38 0,25 0,65 8 0,08 M 5 0,15 NOM 3,05 2,95 4,98 4,78 Gage Plane 0,25 1 0°– 6° 4 3,05 2,95 0,69 0,41 Seating Plane 1,07 MAX 0,15 0,05 0,10 4073329/C 08/01 NOTES: A. B. C. D. 14 All linear dimensions are in millimeters. This drawing is subject to change without notice. Body dimensions do not include mold flash or protrusion. Falls within JEDEC MO-187 INA331, INA2331 www.ti.com SBOS215B PACKAGE DRAWINGS (Cont.) PW (R-PDSO-G**) PLASTIC SMALL-OUTLINE PACKAGE 14 PINS SHOWN 0,30 0,19 0,65 14 0,10 M 8 0,15 NOM 4,50 4,30 6,60 6,20 Gage Plane 0,25 1 7 0°– 8° A 0,75 0,50 Seating Plane 0,15 0,05 1,20 MAX PINS ** 0,10 8 14 16 20 24 28 A MAX 3,10 5,10 5,10 6,60 7,90 9,80 A MIN 2,90 4,90 4,90 6,40 7,70 9,60 DIM 4040064/F 01/97 NOTES: A. B. C. D. All linear dimensions are in millimeters. This drawing is subject to change without notice. Body dimensions do not include mold flash or protrusion not to exceed 0,15. Falls within JEDEC MO-153 INA331, INA2331 SBOS215B www.ti.com 15 PACKAGE OPTION ADDENDUM www.ti.com 3-Oct-2003 PACKAGING INFORMATION ORDERABLE DEVICE STATUS(1) PACKAGE TYPE PACKAGE DRAWING PINS PACKAGE QTY INA2331AIPWR ACTIVE TSSOP PW 14 2500 INA2331AIPWT ACTIVE TSSOP PW 14 250 INA331AIDGKR ACTIVE VSSOP DGK 8 2500 INA331AIDGKT ACTIVE VSSOP DGK 8 250 INA331IDGKR ACTIVE VSSOP DGK 8 2500 INA331IDGKT ACTIVE VSSOP DGK 8 250 (1) The marketing status values are defined as follows: ACTIVE: Product device recommended for new designs. LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect. NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design. PREVIEW: Device has been announced but is not in production. Samples may or may not be available. OBSOLETE: TI has discontinued the production of the device. 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