Precision instrumentation amplifier for use in, for example, BP monitors

Precision instrumentation amplifier for use in, for example, BP monitors

The AD8553 is a precision instrumentation amplifier featuring low noise, rail-to-rail output and a power-saving shutdown mode. The AD8553 also features low offset and drift coupled with high common mode rejection. In shutdown mode, the total supply current is reduced to less than 4 µA.

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Tel: 617/329-4700 World Wide Web Site: http://www.analog.com Fax: 617/326-8703 © Analog Devices, Inc., 2005 1.8V Auto-Zero In-Amp w/ Shutdown Preliminary Technical Data AD8553 FEATURES Low Offset Voltage: 25 µV max Low Input Offset Drift: 0.1 µV/°C max High CMRR: 120 dB min @ G=100 Low Noise: 0.7 µV p-p from 0.01Hz-10Hz Wide Gain Range: 1 to 10,000 Single Supply Operation: +1.8V to +5.5V Rail-to-Rail Output Shutdown capability APPLICATIONS Strain Gages Weigh Scales Pressure Sensors Laser Diode Control Loops Portable Medical Instruments Thermocouple Amplifiers GENERAL DESCRIPTION The AD8553 is a precision instrumentation amplifier featuring low noise, rail-to-rail output and a power-saving shutdown mode. The AD8553 also features low offset and drift coupled with high common mode rejection. In shutdown mode, the total supply current is reduced to less than 4 µA. Operation is fully specified from +1.8V to +5.5V. With low offset voltage of 25µV, offset voltage drift of 0.1µV/°C and voltage noise of only 0.7µV p-p (0.01Hz to 10 Hz), the AD8553 is ideal for applications where error sources cannot be tolerated. Precision instrumentation, position and pressure sensors, medical instrumentation, and strain gauge amplifiers benefit from the low noise, low input bias current, and high common mode rejection. The small footprint and low cost are ideal for high volume applications. The small package and low power consumption allow maximum channel density or minimum board size for space-critical equipment and portable systems. The AD8553 is specified over the industrial temperature range from -40°C to +85°C. The AD8553 is available in the lead-free 10-lead MSOP. 10-Lead MSOP (RMZ-10) AD8553 RGA VINP VO GND VINN RGB VCC VREF VFB ENABLE Rev. PrD PPrreelliimmiinnaarryy TTeecchhnniiccaall DDaattaa AD8553 ­ 2 ­ Rev. PrD ELECTRICAL SPECIFICATIONS(VS = 5V, VCM = 2.5V, VO =VREF = VCC/2, RL = 10k to GND, TA=25°C unless specified, G=1000 (R1 = 4k, R2 = 2M), G=100 (R1 = 3.92k, R2 = 196k), G=10 (R1 = 20k, R2 = 100k), G=1 (R1 = 200k,R2 = 100k)) Parameter Symbol Conditions Min Typ Max Units INPUT CHARACTERISTICS Input Offset Voltage Vos G = 1000 25 µV G = 100 25 µV G = 10 50 µV G = 1 350 µV vs. Temperature Vos/T G = 1000, -40°C TA +85°C 0.01 0.1 µV/°C G = 100, -40°C TA +85°C 0.01 0.1 µV/°C G = 10, -40°C TA +85°C 0.1 0.3 µV/°C G = 1, -40°C TA +85°C 0.7 3 µV/°C Input Bias Current IB 0.3 1 nA -40°C TA +85°C 2 nA Input Bias Current @ VREF 0.02 1 nA Input Operating Impedance Differential 75 || 2 M || pF Common-Mode 100 || 2 M || pF Input Voltage Range 0 3.35 V Common-Mode Rejection Ratio CMRR G = 100, VCM = 0V to 3.35V 120 140 dB -40°C TA +85°C 105 140 dB G=10, VCM = 0V to 3.35V 100 120 dB Gain Error G = 100, VCM = 12.125 mV, 0.25 % VO = 0.075V to 4.925V G = 10, VCM = 121.25mV, 0.5 % VO = 0.075V to 4.925V Gain tempco -40°C TA +85°C 50 ppm/°C Non-Linearity G = 100, VCM = 12.125mV, 0.006 % FS VO = 0.075V to 4.925V G=10, VCM = 121.25mV, 0.035 % FS VO = 0.075V to 4.925V VREF Range 0.8 4.2 V OUTPUT CHARACTERISTICS Output Voltage High VOH 4.925 V Output Voltage Low VOL 0.075 V POWER SUPPLY Power Supply Rejection Ratio PSRR G=100, Vs = 1.8V to 5.5V, VCM = 0V 100 120 dB G=10, Vs = 1.8V to 5.5V, VCM = 0V 90 106 dB Supply Current ISY IO = 0, VIN = 0V 1.1 1.3 mA -40°C TA +85°C 1.5 mA Supply Current Shutdown Mode ISD 2 4 µA ENABLE (pin) INPUTS Logic High Voltage VINH 2.4 V Logic Low Voltage VINL 0.8 V PPrreelliimmiinnaarryy TTeecchhnniiccaall DDaattaa AD8553 ­ 3 ­ Rev. PrD NOISE PERFORMANCE Voltage Noise en p-p f = 0.01 Hz to 10 Hz 0.7 µVp-p Voltage Noise Density en G = 100, f = 1 kHz 35 nV/Hz G = 10, f = 1kHz 150 nV/Hz Internal Clock Frequency 40 kHz Signal Bandwidth G = 1 to 1000 1* kHz (*500 Hz for x-grade samples) PPrreelliimmiinnaarryy TTeecchhnniiccaall DDaattaa AD8553 ­ 4 ­ Rev. PrD ELECTRICAL SPECIFICATIONS(VS = 1.8V, VCM = 0.1V, VO = VREF = VCC/2, RL = 10k to GND, TA=+25°C unless specified, G=1000 (R1 =4k, R2 = 2M), G=100 (R1 = 3.92k, R2 = 196k), G=10 (R1 =20k, R2 = 100k), G=1 (R1 =200k, R2 = 100k)) Parameter Symbol Conditions Min Typ Max Units INPUT CHARACTERISTICS Input Offset Voltage Vos G = 1000 30 µV G = 100 30 µV G = 10 60 µV G = 1 500 µV vs. Temperature Vos/T G = 1000, -40°C TA +85°C 0.1 0.5 µV/°C G = 100, -40°C TA +85°C 0.1 0.5 µV/°C G = 10 , -40°C TA +85°C 3 µV/°C G = 1, -40°C TA +85°C 10 µV/°C Input Bias Current IB 0.3 1 nA -40°C TA +85°C 2 nA Input Bias Current @ VREF 0.02 1 nA Input Operating Impedance Differential 75 || 2 M || pF Common-Mode 100 || 2 M || pF Input Voltage Range 0 0.15 V Common-Mode Rejection Ratio CMRR G=100, VCM = 0V to 0.15V 100 110 dB -40°C TA +85°C 86 dB G=10, VCM = 0V to 0.15V 86 95 dB Gain Error G = 100, VCM=4.125 mV, 0.35 % VO = 0.075V to 1.65V G = 10, VCM = 41.25mV, 0.5 % VO = 0.075V to 1.65V Gain tempco -40°C TA +85°C 50 ppm/°C Non-Linearity G= 100, VCM = 4.125mV, 0.015 % FS VO = 0.075V to 1.65V G=10, VCM = 41.25mV, 0.015 % FS VO = 0.075V to 1.65V VREF Range 0.8 1.0 V OUTPUT CHARACTERISTICS Output Voltage High VOH RL = 10k to GND 1.65 V Output Voltage Low VOL RL = 10k to GND 0.075 V POWER SUPPLY Power Supply Rejection Ratio PSRR G = 100, VS = 1.8V to 5.5V, VCM = 0V 100 120 dB Supply Current ISY IO = 0, VIN = 0V 0.9 1.2 mA -40°C TA +85°C 1.4 mA Supply Current Shutdown Mode ISD 2 4 uA_________ PPrreelliimmiinnaarryy TTeecchhnniiccaall DDaattaa AD8553 ­ 5 ­ Rev. PrD ENABLE (pin) INPUTS Logic High Voltage VINH 1.4 V Logic Low Voltage VINL 0.5 V NOISE PERFORMANCE Voltage Noise en p-p f = 0.01 Hz to 10 Hz 1 µVp-p Voltage Noise Density en G= 100, f = 1 kHz 45 nV/Hz G=10, f = 1kHz 180 nV/Hz Internal Clock Frequency 40 kHz Signal Bandwidth G=1 to 1000 1* kHz (*500 Hz for x-grade samples) ABSOLUTE MAXIMUM RATINGS Supply Voltage………………………………………………………………. +6V Input Voltage…………………………………………………………..+Vsupply Differential Input Voltage1………………………………………..±Vsupply Output Short-Circuit Duration to Gnd………………………… Indefinite Storage Temperature Range RM Package……………………………………………-65°C to +150°C Operating Temperature Range AD8553 …………………………………………………..-40°C to +85°C Junction Temperature Range RM Package……………………………………………-65°C to +150°C Lead Temperature Range (Soldering, 10 sec)…………………. +300°C Package Type JA 2 JC Units 10-Lead MSOP (RMZ) TBD TBD °C/W NOTES 1 Differential input voltage is limited to ±5.0 volts or the supply voltage, whichever is less. 2 JA is specified for the worst case conditions, i.e., JA is specified for device in socket for P-DIP packages; JAis specified for device soldered in circuit board for SOIC and TSSOP packages. ORDERING GUIDE Temperature Package Suffix Model Range Description AD8553ARMZ-R2 -40°C to +85°C 10-Lead MSOP RM-10 AD8553ARMZ-REEL -40°C to +85°C 10-lead MSOP RM-10 PPrreelliimmiinnaarryy TTeecchhnniiccaall DDaattaa AD8553 ­ 6 ­ Rev. PrD APPLICATIONS Typical Configuration Figures 1 and 2 show a typical AD8553 circuit configuration for an A/D converter application. + _ R1 R2 C2 5 7 6 2 9 4 1 10 100k 100k VS + 0.1uF VIN – VIN+ GND VOUT GND 300 1uF R3 C3 8 3 VS+ 0.1uF C4 Figure 1. Single-supply connection diagram PPrreelliimmiinnaarryy TTeecchhnniiccaall DDaattaa AD8553 ­ 7 ­ Rev. PrD + _ R1 R2 C2 5 7 6 2 9 4 1 10 VIN- VIN+ VOUT GND GND 300 1uF R3 C3 0.1uF 8 3 VS+ 0.1uF 0.1uF VS – Figure 2. Dual-supply connection diagram Gain Selection The gain of the AD8553 is set according to the following equation: G = 2*(R2/R1) For proper operation: (1) R1 > 3.92k (2) R1 > Vin / 13uA. Gain accuracy depends on the matching of the two external resistors. Any mismatch in resistor values results in a gain error. However, due to the current-mode operation of the AD8553, CMRR is not degraded because of resistor mismatch. Care should be taken when selecting and positioning the gain setting resistors. The resistors should be made of the same material and package style. Surface mount resistors are recommended. They should be positioned as close together as possible to minimize TC errors and feedback voltage errors. If resistor trimming is required to set a precise gain, trim resistor R2 only. Parasitic capacitance to pins 1 and 10 (resistor R1 connections) must be minimized. Reference Connection Unlike traditional three-opamp instrumentation amplifiers, parasitic resistance in series with the Vref pin (pin 7) does not degrade CMRR performance. This allows the AD8553 to attain its extremely high CMRR performance without the use of an external buffer amplifier driving the Vref pin. When using a single supply, the reference voltage can be set with a simple resistor voltage divider between the supply and ground (Figure 1). Capacitor C4 is recommended to filter supply noise. For optimal performance in single-supply applications, Vref should be set with a low-noise PPrreelliimmiinnaarryy TTeecchhnniiccaall DDaattaa AD8553 ­ 8 ­ Rev. PrD precision voltage reference (for example, from the ADC). In dual-supply applications, Vref can simply be connected to ground. Output Filtering Filter capacitor C2 is required to limit the amount of switching noise present at the output. The recommended bandwidth of the filter created by C2 and R2 is 1.5 kHz (AD8553 x-grade samples are 500 Hz). The user should first select R1 and R2 based on the desired gain, then select C2 based on the following formula: C2 = 1/(1500*2**R2) Another single-pole R-C filter on the output is recommended. A filter frequency of 1.5kHz is recommended (AD8553 x-grade samples are 500 Hz). This filter can also serve as an anti-aliasing filter if the AD8553 is used to drive an A/D converter. Maximizing Performance with a Proper Layout To achieve the maximum performance of the AD8553, care should be taken in the circuit board layout. The PC board surface must remain clean and free of moisture to avoid leakage currents between adjacent traces. Surface coating of the circuit board will reduce surface moisture and provide a humidity barrier, reducing parasitic resistance on the board. Care must be taken to minimize parasitic capacitance on pins 1 and 10 (resistor R1 connections). Traces from the IC to R1 should be kept symmetric and as short as possible. Excessive capacitance on these pins results in a gain error. This effect is most prominent at low gains (G