ADA4522-1ARMZ

Data Sheet ADA4522-1/ADA4522-2/ADA4522-4 55 V, EMI Enhanced, Zero Drift, Ultralow Noise, Rail-to-Rail Output Operational Amplifiers FEATURES ► ► ► ► ► ► ► ► ► PIN CONNECTION DIAGRAM Low offset voltage: 5 µV maximum Extremely low offset voltage drift: 22 nV/°C maximum Low voltage noise density: 5.8 nV/√Hz typical ► 117 nV p-p typical from 0.1 Hz to 10 Hz Low input bias current: 50 pA typical Unity-gain crossover: 3 MHz typical Single-supply operation: input voltage range includes ground and rail-to-rail output Wide range of operating voltages ► Single-supply operation: 4.5 V to 55 V ► Dual-supply operation: ±2.25 V to ±27.5 V Integrated EMI filters Unity-gain stable Figure 1. 8-Lead MSOP (RM Suffix) and 8-Lead SOIC (R Suffix) Pin Configuration For the ADA4522-1 and ADA4522-4 pin connections and for more information about the pin connections for these products, see the Pin Configurations and Function Descriptions section. APPLICATIONS ► ► ► ► ► ► Inductance, capacitance, and resistance (LCR) meter/ megohmmeter front-end amplifiers Load cell and bridge transducers Magnetic force balance scales High precision shunt current sensing Thermocouple/resistance temperature detector (RTD) sensors Programmable logic controller (PLC) input and output amplifiers Figure 2. Voltage Noise Density vs. Frequency, VSY = ±15 V GENERAL DESCRIPTION The ADA4522-1/ADA4522-2/ADA4522-4 are single/dual/quad channel, zero drift op amps with low noise and power, ground sensing inputs, and rail-to-rail output, optimized for total accuracy over time, temperature, and voltage conditions. The wide operating voltage and temperature ranges, as well as the high open-loop gain and very low dc and ac errors make the devices well suited for amplifying very small input signals and for accurately reproducing larger signals in a wide variety of applications. The ADA4522-1/ADA4522-2/ADA4522-4 performance is specified at 5.0 V, 30 V, and 55 V power supply voltages. These devices operate over the range of 4.5 V to 55 V, and are excellent for applications using single-ended supplies of 5 V, 10 V, 12 V, and 30 V, or for applications using higher single supplies and dual supplies of ±2.5 V, ±5 V, and ±15 V. The ADA4522-1/ADA4522-2/ADA4522-4 use on-chip filtering to achieve high immunity to electromagnetic interference (EMI). Table 1. Zero Drift Op Amps ( 50 kΩ, the current noise becomes the main contributor of the total input noise. Residual Ripple As shown in Figure 60, Figure 61, and Figure 62, the ADA4522-1/ ADA4522-2/ADA4522-4 have a flat noise spectrum density at lower frequencies and exhibits spectrum density bumps and peaks at higher frequencies. The largest noise bump is centered at 6 MHz; this bump is due to the decrease in the input gain at higher frequencies. This decrease is a typical phenomenon and can also be seen in other amplifiers. In addition to the noise bump, a sharp peak due to the chopping networks is seen at 4.8 MHz. However, this magnitude is significantly reduced by the offset and ripple correction loop. Its magnitude may be different with different amplifier units or with different circuitries around the amplifier. This peak can potentially be hidden by the noise bump and, therefore, may not be detected. Figure 76. Voltage Noise Density with Various Gains Figure 77 shows the voltage noise density of the ADA4522-1/ ADA4522-2/ADA4522-4 without and with post filters at different frequencies. The post filter serves to roll off the bandwidth before the switching frequency. In this example, the noise peak at 800 kHz is about 38 nV/√Hz. With a post filter at 80 kHz, the noise peak is reduced to 4.1 nV/√Hz. With a post filter at 8 kHz, the noise peak is lower than the noise floor and cannot be detected. The offset and ripple correction loop, designed to reduce the 4.8 MHz switching artifact, also creates a noise bump centered at 800 kHz and a noise peak on top of this noise bump. Although the magnitude of the bump is mostly constant, the magnitude of the 800 kHz peak is different from unit to unit. Some units may not exhibit the 800 kHz noise peak; however, for other units, peaks occur at multiple integrals of 800 kHz, such as 1.6 MHz or 2.4 MHz. These noise peaks, albeit small in magnitude, can be significant when the amplifier has a closed-loop frequency that is higher than the chopping frequency. To suppress the noise spike to a desired level, either configure the amplifier in a high gain configuration or apply a post filter at the output of the amplifier. Figure 76 shows the voltage noise density of the ADA4522-1/ ADA4522-2/ADA4522-4 in various gain configurations. Note that the higher the gain, the lower the available bandwidth is. The earlier bandwidth roll-off effectively filters out the higher noise spectrum. analog.com Figure 77. Voltage Noise Density with Post Filters Current Noise Density Figure 78 shows the current noise density of the ADA4522-1/ ADA4522-2/ADA4522-4 at unity gain. At 1 kHz, the current noise density is about 1.3 pA/√Hz. The current noise density is determined by measuring the voltage noise due to current noise flowing through a resistor. Due to the low current noise density of the amplifier, the voltage noise is usually measured with a high value resistor; in this case, a 100 kΩ source resistor is used. However, the source resistor interacts with the input capacitance of the amplifier and board, causing the bandwidth to roll off. Note that Figure 78 shows the current noise density rolling off much earlier than the unity-gain bandwidth; this roll-off is expected. Rev. G | 25 of 33 Data Sheet ADA4522-1/ADA4522-2/ADA4522-4 THEORY OF OPERATION Figure 78. Current Noise Density at Gain = 1 Figure 79. EMIRR vs. Frequency EMI REJECTION RATIO CAPACITIVE LOAD STABILITY Circuit performance is often adversely affected by high frequency EMI. When the signal strength is low and transmission lines are long, an op amp must accurately amplify the input signals. However, all op amp pins—the noninverting input, inverting input, positive supply, negative supply, and output pins—are susceptible to EMI signals. These high frequency signals are coupled into an op amp by various means, such as conduction, near field radiation, or far field radiation. For example, wires and printed circuit board (PCB) traces can act as antennas and pick up high frequency EMI signals. The ADA4522-1/ADA4522-2/ADA4522-4 can safely drive capacitive loads of up to 250 pF in any configuration. As with most amplifiers, driving larger capacitive loads than specified may cause excessive overshoot and ringing, or even oscillation. A heavy capacitive load reduces the phase margin and causes the amplifier frequency response to peak. Peaking corresponds to overshooting or ringing in the time domain. Therefore, it is recommended that external compensation be used if the ADA4522-1/ADA4522-2/ADA4522-4 must drive a load exceeding 250 pF. This compensation is particularly important in the unity-gain configuration, which is the worst case for stability. Amplifiers do not amplify EMI or RF signals due to their relatively low bandwidth. However, due to the nonlinearities of the input devices, op amps can rectify these out of band signals. When these high frequency signals are rectified, they appear as a dc offset at the output. The ADA4522-1/ADA4522-2/ADA4522-4 have integrated EMI filters at their input stage. To describe the ability of the ADA4522-1/ ADA4522-2/ADA4522-4 to perform as intended in the presence of electromagnetic energy, the electromagnetic interference rejection ratio (EMIRR) of the noninverting pin is specified in Table 2, Table 3, and Table 4 of the Specifications section. A mathematical method of measuring EMIRR is defined as follows: A quick and easy way to stabilize the op amp for capacitive load drive is by adding a series resistor, RISO, between the amplifier output terminal and the load capacitance, as shown in Figure 80. RISO isolates the amplifier output and feedback network from the capacitive load. However, with this compensation scheme, the output impedance as seen by the load increases, and this reduces gain accuracy. EMIRR = 20log(VIN_PEAK/ΔVOS) Figure 80. Stability Compensation with Isolating Resistor, RISO Figure 81 shows the effect on overshoot with different values of RISO. analog.com Rev. G | 26 of 33 Data Sheet ADA4522-1/ADA4522-2/ADA4522-4 THEORY OF OPERATION Figure 81. Small Signal Overshoot vs. Load Capacitance with Various Output Isolating Resistors analog.com Rev. G | 27 of 33 Data Sheet ADA4522-1/ADA4522-2/ADA4522-4 APPLICATIONS INFORMATION SINGLE-SUPPLY INSTRUMENTATION AMPLIFIER The extremely low offset voltage and drift, high open-loop gain, high common-mode rejection, and high power supply rejection of the ADA4522-1/ADA4522-2/ADA4522-4 make them excellent op amp choices as discrete, single-supply instrumentation amplifiers. Figure 82 shows the classic 3-op-amp instrumentation amplifier using the ADA4522-1/ADA4522-2/ADA4522-4. The key to high CMRR for the instrumentation amplifier are resistors that are well matched for both the resistive ratio and relative drift. For true difference amplification, matching of the resistor ratio is very important, where R5/R2 = R6/R4. The resistors are important in determining the performance over manufacturing tolerances, time, and temperature. Assuming a perfect unity-gain difference amplifier with infinite common-mode rejection, a 1% tolerance resistor matching results in only 34 dB of common-mode rejection. Therefore, at least 0.01% or better resistors are recommended. Figure 82. Discrete 3-Op-Amp Instrumentation Amplifier To build a discrete instrumentation amplifier with external resistors without compromising on noise, pay close attention to the resistor values chosen. RG1 and RG2 each have thermal noise that is amplified by the total noise gain of the instrumentation amplifier and, therefore, a sufficiently low value must be chosen to reduce thermal noise contribution at the output while still providing an accurate measurement. Table 10 shows the external resistors noise contribution referred to the output (RTO). Table 10. Thermal Noise Contribution Example Resistor Resistor Thermal Noise Value (kΩ) (nV/√Hz) Thermal Noise RTO (nV/√Hz) RG1 RG2 R1 R2 R3 R4 R5 R6 0.4 0.4 10 10 10 10 20 20 128.30 128.30 25.66 25.66 25.66 25.66 18.14 18.14 2.57 2.57 12.83 12.83 12.83 12.83 18.14 18.14 Note that A1 and A2 have a high gain of 1 + R1/RG1. Therefore, use a high precision, low offset voltage and low noise amplifier for A1 and A2, such as the ADA4522-1/ADA4522-2/ADA4522-4. Conversely, A3 operates at a much lower gain and has a different analog.com set of op amp requirements. Its input noise, referred to the overall instrumentation amplifier input, is divided by the first stage gain and is not as important. Note that the input offset voltage and the input voltage noise of the amplifiers are also amplified by the overall noise gain. Any unused channel of the ADA4522-1/ADA4522-2/ADA4522-4 must be configured in unity gain with the input common-mode voltage tied to the midpoint of the power supplies. Understanding how noise impacts a discrete instrumentation amplifier or a difference amplifier (the second stage of a 3-op-amp instrumentation amplifier) is important, because they are commonly used in many different applications. The Load Cell/Strain Gage Sensor Signal Conditioning Using the ADA4522-2 section and the Precision Low-Side Current Shunt Sensor section show the ADA4522-1/ADA4522-2/ADA4522-4 used as a discrete instrumentation or difference amplifier in an application. LOAD CELL/STRAIN GAGE SENSOR SIGNAL CONDITIONING USING THE ADA4522-2 The ADA4522-2, with its ultralow offset, drift, and noise, is well suited to signal condition a low level sensor output with high gain and accuracy. A weigh scale/load cell is an example of an application with such requirements. Figure 83 shows a configuration for a single-supply, precision, weigh scale measurement system. The ADA4522-2 is used at the front end for amplification of the low level signal from the load cell. Current flowing through a PCB trace produces an IR voltage drop; with longer traces, this voltage drop can be several millivolts or more, introducing a considerable error. A 1 inch long, 0.005 inch wide trace of 1 oz copper has a resistance of approximately 100 mΩ at room temperature. With a load current of 10 mA, the resistance can introduce a 1 mV error. Therefore, a 6-wire load cell is used in the circuit. The load cell has two sense pins, in addition to excitation, ground, and two output connections. The sense pins are connected to the high side (excitation pin) and low side (ground pin) of the Wheatstone bridge. The voltage across the bridge can then be accurately measured regardless of voltage drop due to wire resistance. The two sense pins are also connected to the analog-to-digital converter (ADC) reference inputs for a ratiometric configuration that is immune to low frequency changes in the power supply excitation voltage. The ADA4522-2 is configured as the first stage of a 3-op-amp instrumentation amplifier to amplify the low level amplitude signal from the load cell by a factor of 1 + 2R1/RG. Capacitors C1 and C2 are placed in the feedback loops of the amplifiers and interact with R1 and R2 to perform low-pass filtering. This filtering limits the amount of noise entering the Σ-Δ ADC. In addition, C3, C4, C5, R3, and R4 provide further common-mode and differential mode filtering to reduce noise and unwanted signals. Rev. G | 28 of 33 Data Sheet ADA4522-1/ADA4522-2/ADA4522-4 APPLICATIONS INFORMATION Figure 83. Precision Weigh Scale Measurement System PRECISION LOW-SIDE CURRENT SHUNT SENSOR Many applications require the sensing of signals near the positive or negative rails. Current shunt sensors are one such application and are mostly used for feedback control systems. They are also used in a variety of other applications, including power metering, battery fuel gauging, and feedback controls in industrial applications. In such applications, it is desirable to use a shunt with very low resistance to minimize series voltage drop. This configuration not only minimizes wasted power, but also allows the measurement of high currents while saving power. A typical shunt may be 100 mΩ. At a measured current of 1 A, the voltage produced from the shunt is 100 mV, and the amplifier error sources are not critical. However, at low measured current in the 1 mA range, the 100 μV generated across the shunt demands a very low offset voltage and drift amplifier to maintain absolute accuracy. The unique attributes of a zero drift amplifier provide a solution. Figure 84 shows a low-side current sensing circuit using the ADA4522-1/ADA4522-2/ADA4522-4. The ADA4522-1/ADA4522-2/ ADA4522-4 are configured as difference amplifiers with a gain of 1000. Although the ADA4522-1/ADA4522-2/ADA4522-4 have high CMRR, the CMRR of the system is limited by the external resistors. Therefore, as mentioned in the Single-Supply Instrumentation Amplifier section, the key to high CMRR for the system is resistors that are well matched from both the resistive ratio and relative drift, where R1/R2 = R3/R4. Any unused channel of the ADA4522-1/ADA4522-2/ADA4522-4 must be configured in unity gain with the input common-mode voltage tied to the midpoint of the power supplies. analog.com Figure 84. Low-Side Current Sensing Circuit PRINTED CIRCUIT BOARD LAYOUT The ADA4522-1/ADA4522-2/ADA4522-4 are high precision devices with ultralow offset voltage and noise. Therefore, take care in the design of the PCB layout to achieve optimum performance of the ADA4522-1/ADA4522-2/ADA4522-4 at the board level. To avoid leakage currents, keep the surface of the board clean and free of moisture. Properly bypassing the power supplies and keeping the supply traces short minimizes power supply disturbances caused by output current variation. Connect bypass capacitors as close as possible to the device supply pins. Stray capacitances are a concern at the outputs and the inputs of the amplifier. It is recommended that signal traces be kept at a distance of at least 5 mm from supply lines to minimize coupling. A potential source of offset error is the Seebeck voltage on the circuit board. The Seebeck voltage occurs at the junction of two dissimilar metals and is a function of the temperature of the junction. The most common metallic junctions on a circuit board are solder to board traces and solder to component leads. Figure 85 shows a cross section of a surface-mount component soldered to a PCB. A variation in temperature across the board (where TA1 ≠ TA2) causes a mismatch in the Seebeck voltages at the solder joints, thereby resulting in thermal voltage errors that degrade the performance of the ultralow offset voltage of the ADA4522-1/ ADA4522-2/ADA4522-4. Rev. G | 29 of 33 Data Sheet ADA4522-1/ADA4522-2/ADA4522-4 APPLICATIONS INFORMATION V of power supply, ISY+ remains at 1.55 mA per dual amplifier, but ISY− increases close to 2 mA in magnitude per dual amplifier. Figure 85. Mismatch in Seebeck Voltages Causes Seebeck Voltage Error In Figure 85, VSC1 and VSC2 are the Seebeck voltages due to solder to component at Junction 1 and Junction 2, respectively. VTS1 and VTS2 are the Seebeck voltages due to solder to trace at Junction 1 and Junction 2. TA1 and TA2 are the temperatures of Junction 1 and Junction 2, respectively. To minimize these thermocouple effects, orient resistors so that heat sources warm both ends equally. Where possible, it is recommended that the input signal paths contain matching numbers and types of components to match the number and type of thermocouple junctions. For example, dummy components, such as zero value resistors, can be used to match the thermoelectric error source (real resistors in the opposite input path). Place matching components in close proximity and orient them in the same manner to ensure equal Seebeck voltages, thus canceling thermal errors. Additionally, use leads that are of equal length to keep thermal conduction in equilibrium. Keep heat sources on the PCB as far away from amplifier input circuitry as is practical. Figure 86. Comparator Configuration A Figure 87. Comparator Configuration B It is highly recommended to use a ground plane. A ground plane helps distribute heat throughout the board, maintain a constant temperature across the board, and reduce EMI noise pickup. COMPARATOR OPERATION An op amp is designed to operate in a closed-loop configuration with feedback from its output to its inverting input. In contrast to op amps, comparators are designed to operate in an open-loop configuration and to drive logic circuits. Although op amps are different from comparators, occasionally an unused section of a dual op amp is used as a comparator to save board space and cost; however, this is not recommended for the ADA4522-1/ADA4522-2/ ADA4522-4. Figure 86 and Figure 87 show the ADA4522-1/ADA4522-2/ ADA4522-4 configured as a comparator, with 10 kΩ resistors in series with the input pins. Any unused channels are configured as buffers with the input voltage kept at the midpoint of the power supplies. The ADA4522-1/ADA4522-2/ADA4522-4 have input devices that are protected from large differential input voltages by Diode D5 and Diode D6, as shown in Figure 72. These diodes consist of substrate PNP bipolar transistors, and conduct whenever the differential input voltage exceeds approximately 600 mV; however, these diodes also allow a current path from the input to the lower supply rail, resulting in an increase in the total supply current of the system. Both comparator configurations yield the same result. At 30 analog.com Figure 88. Supply Current (ISY) per Dual Amplifier vs. Supply Voltage (VSY) (ADA4522-1/ADA4522-2/ADA4522-4 as a Comparator) Note that 10 kΩ resistors are used in series with the input of the op amp. If smaller resistor values are used, the supply current of the system increases much more. For more details on op amps as comparators, see the AN-849 Application Note, Using Op Amps as Comparators. USE OF LARGE SOURCE RESISTANCE The ADA4522-1/ADA4522-2/ADA4522-4 are designed to work with low value source resistance. Note that the amplifier has an ultralow voltage noise density of 6 nV/√Hz. A 1 kΩ resistor contributes 4 nV/√Hz; therefore, placing a 1 kΩ resistor at the input increases Rev. G | 30 of 33 Data Sheet ADA4522-1/ADA4522-2/ADA4522-4 APPLICATIONS INFORMATION total noise to 7.2 nV/√Hz. For this noise reason, it is recommended to avoid using large source resistance. Unity Gain Follower with Large Source Resistance When the ADA4522-1/ADA4522-2/ADA4522-4 are configured in a unity-gain follower configuration with a large source resistance and slow power supply ramp rate, the amplifier output may rail to the positive supply. Figure 89. Insert RF When Large RS is Used Workaround To avoid the amplifier output railing to the positive supply, implement one of the following actions (see Table 11 and Figure 89): Reduce the value of the source resistance (RS). ► Insert a feedback resistor (RF). ► Table 11. Amplifier Output Railing Workaround Recommendations Condition Recommendation 1.5 V ≤ VSY − VIN < 2.5 V 2.5 V ≤ VSY − VIN < 3.5 V VSY − VIN ≥ 3.5 V RF = 200 Ω or RF ≥ 50 RS, whichever is greater RS ≤ 200 Ω or RF ≥ 2 RS RS ≤ 500 Ω or RF ≥ 0.5 RS analog.com Rev. G | 31 of 33 Data Sheet ADA4522-1/ADA4522-2/ADA4522-4 OUTLINE DIMENSIONS Figure 90. 8-Lead Mini Small Outline Package [MSOP] (RM-8) Dimensions shown in millimeters Figure 91. 8-Lead Small Outline Package [SOIC_N] Narrow Body (R-8) Dimensions shown in millimeters and (inches) Figure 92. 14-Lead Small Outline Package [SOIC_N] Narrow Body (R-14) Dimensions shown in millimeters and (inches) analog.com Rev. G | 32 of 33 Data Sheet ADA4522-1/ADA4522-2/ADA4522-4 OUTLINE DIMENSIONS Figure 93. 14-Lead Thin Shrink Small Outline Package [TSSOP] (RU-14) Dimensions shown in millimeters Updated: December 21, 2021 ORDERING GUIDE Model1 Temperature Range Package Description Packing Quantity Package Option ADA4522-1ARMZ ADA4522-1ARMZ-R7 ADA4522-1ARMZ-RL ADA4522-1ARZ ADA4522-1ARZ-R7 ADA4522-1ARZ-RL ADA4522-2ARMZ ADA4522-2ARMZ-R7 ADA4522-2ARMZ-RL ADA4522-2ARZ ADA4522-2ARZ-R7 ADA4522-2ARZ-RL ADA4522-4ARUZ ADA4522-4ARUZ-R7 ADA4522-4ARUZ-RL ADA4522-4ARZ ADA4522-4ARZ-R7 ADA4522-4ARZ-RL -40°C to +125°C -40°C to +125°C -40°C to +125°C -40°C to +125°C -40°C to +125°C -40°C to +125°C -40°C to +125°C -40°C to +125°C -40°C to +125°C -40°C to +125°C -40°C to +125°C -40°C to +125°C -40°C to +125°C -40°C to +125°C -40°C to +125°C -40°C to +125°C -40°C to +125°C -40°C to +125°C 8-Lead MSOP 8-Lead MSOP 8-Lead MSOP 8-Lead SOIC 8-Lead SOIC 8-Lead SOIC 8-Lead MSOP 8-Lead MSOP 8-Lead MSOP 8-Lead SOIC 8-Lead SOIC 8-Lead SOIC 14-Lead TSSOP 14-Lead TSSOP 14-Lead TSSOP 14-Lead SOIC 14-Lead SOIC 14-Lead SOIC Tube, 50 Reel, 1000 Reel, 3000 Tube, 98 Reel, 1000 Reel, 2500 Tube, 50 Reel, 1000 Reel, 3000 Tube, 98 Reel, 1000 Reel, 2500 Tube, 96 Reel, 1000 Reel, 2500 Tube, 56 Reel, 1000 Reel, 2500 RM-8 RM-8 RM-8 R-8 R-8 R-8 RM-8 RM-8 RM-8 R-8 R-8 R-8 RU-14 RU-14 RU-14 R-14 R-14 R-14 1 Marking Code A3G A3G A3G A39 A39 A39 Z = RoHS Compliant Part. ©2015-2022 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. One Analog Way, Wilmington, MA 01887-2356, U.S.A. Rev. G | 33 of 33