EVAL-INAMP-ICF-RMZ User Guide UG-513 One Technology Way • P.O. Box 9106 • Norwood, MA 02062-9106, U.S.A. • Tel: 781.329.4700 • Fax: 781.461.3113 • www.analog.com Evaluating the AD8237 Micropower, Zero Drift, True Rail-to-Rail Instrumentation Amplifier and the AD8420 Wide Supply Range, Micropower, Rail-to-Rail Instrumentation Amplifier FEATURES jumpers are included for added convenience. The board also offers an SMA/SMB outline at the input and output for best signal integrity. Simple evaluation of AD8237 and AD8420 SMA/SMB or vector test pin inputs and outputs Bandwidth mode selection switch for AD8237 Shipped with AD8420ARMZ and AD8237ARMZ Users can add their own end-launch SMA/SMB connector to interface the evaluation board with complementary tools, such as an analog-to-digital converter (ADC) evaluation board, available from Analog Devices, Inc. To get started with this evaluation board, see the Quick Start for the EVAL-INAMP-ICF-RMZ Board section. APPLICATIONS Quick, easy product evaluation and characterization Pads for common surrounding components Interface to other evaluation tools BASIC OPERATION GENERAL DESCRIPTION The EVAL-INAMP-ICF-RMZ allows users the option of evaluating the AD8237 or the AD8420 indirect current feedback (ICF) instrumentation amplifier individually or connected to an adjacent board in an application. This evaluation board ships with both instrumentation amplifiers in surface-mount MSOP packages. The evaluation board is arranged so that the user can easily adjust the gain resistors and common discrete components surrounding the part. A bandwidth mode switch for the AD8237 and reference The AD8237 and AD8420 series in-amps convert a differential input signal to a gained single-ended output signal with respect to a reference voltage. The board connects the user-provided power supplies to pins of the integrated circuit and ground to the board. The differential signal is applied between the +IN and −IN pins of the in-amp, while the signal output appears between the VOUT pin and the REF pin of the in-amp. Figure 2 shows the component layout and the location of the connections for the EVAL-INAMP-ICF-RMZ printed circuit board (PCB). 11214-001 DIGITAL PHOTOGRAPH OF THE EVAL-INAMP-ICF-RMZ Figure 1. EVAL-INAMP-ICF-RMZ Evaluation Board, Primary Side PLEASE SEE THE LAST PAGE FOR AN IMPORTANT WARNING AND LEGAL TERMS AND CONDITIONS. Rev. 0 | Page 1 of 8 UG-513 EVAL-INAMP-ICF-RMZ User Guide TABLE OF CONTENTS Features .............................................................................................. 1 Quick Start for the EVAL-INAMP-ICF-RMZ Board ...................4 Applications ....................................................................................... 1 Circuit Options ..............................................................................4 General Description ......................................................................... 1 Reference ........................................................................................6 Basic Operation................................................................................. 1 Input ................................................................................................6 Digital Photograph of the EVAL-INAMP-ICF-RMZ .................. 1 Output .............................................................................................7 Revision History ............................................................................... 2 EVAL-INAMP-ICF-RMZ Schematic and User Options ............. 3 User Options ................................................................................. 3 REVISION HISTORY 2/13—Revision 0: Initial Version Rev. 0 | Page 2 of 8 EVAL-INAMP-ICF-RMZ User Guide UG-513 EVAL-INAMP-ICF-RMZ SCHEMATIC AND USER OPTIONS VCC C4 0.1µF VEE C5 0.1µF S1 5 C1 R1 +IN 1 2 U1 C3 R2 –IN 3 VINN OUT 4 + VINP C2 FB – REF VOUTP 8 7 RF 6 CF1 FB1 R3 VEE RG GND1 + C7 10µF + GND2 GND R5 FB2 REF R4 W1 C6 10µF W2 VOUTN 11214-002 VCC Figure 2. EVAL-INAMP-ICF-RMZ Schematic Diagram USER OPTIONS Table 1. Jumpers and Switches Jumper W1 Function REF to GND W2 VOUTN select S1 Pin 1 select Description REF is shorted to ground through W1 solder jumper. Remove W1 to drive REF with a voltage other than ground. Determines what voltage is at VOUTN. If REF is being driven to level-shift the output but GND must be passed to an adjacent board through the SMA/SMB, remove the solder jumper and set W2 to GND. Otherwise, it can be left as-is. Bandwidth mode setting for the AD8237. If the switch toggle is moved to the right (LO), Pin 1 is shorted to VEE (AD8237 low bandwidth mode). If the switch toggle is moved to the left position (HI), Pin 1 is shorted to VCC (AD8237 high bandwidth mode). For the AD8420, the best frequency response is obtained if S1 is set to LO (Pin 1 is shorted to VEE). Factory Setting Shorted REF LO (−VS) Table 2. Input/Output I/O VCC VEE GND +IN/VINP −IN/VINN OUT/VOUTP FB1/FB2 REF VOUTN Function Positive supply voltage rail of the in-amp. Negative supply voltage rail of the in-amp. Ground connection for the board. Connect to power supply ground. GND1, GND2, and GND pins are all connected to board ground. Positive input of the in-amp (vector pin/SMA). Negative input of the in-amp (vector pin/SMA). Output of the in-amp (vector pin/SMA). Feedback input for the in-amp. Two pins are provided to simplify gain setting with leaded resistors on press mount sockets. External reference input for the in-amp. W1 must be removed before driving REF with a voltage source. Selectable reference or ground SMA output (see W2 in Table 1). Table 3. Suggested Accessories Reference Designation SMA Jack SMA Plug SMB Jack SMB Plug Press mount socket Part Side launch 0.062” board thickness, such as the EMERSON 142-0701-851 (Digi-Key J658-ND) Side launch 0.062” board thickness, such as the EMERSON 142-0801-811 (Digi-Key J10131-ND) Side launch 0.062” board thickness, such as the EMERSON 131-3701-801 (Digi-Key J10107-ND) Recommend above jack and adapter, such as the Amphenol Connex 142246 (Digi-Key ACX1479-ND) Plugs onto the vector test pin, such as the Cambion 450-4352-01-03-10 (Newark 40F6130). Can be used for inputs and outputs or through-hole gain setting resistors. Rev. 0 | Page 3 of 8 UG-513 EVAL-INAMP-ICF-RMZ User Guide QUICK START FOR THE EVAL-INAMP-ICF-RMZ BOARD VCC 10µF 3. 4. Single-Supply Range 1.8 V to 5.5 V 2.7 V to 36 V Dual-Supply Range ±0.9 V to ±2.75 V ±2.7 V1 to ±18 V For VCM, VREF = 0 V. The ±1.35 V supply may be used with VCM and VREF at VEE. Table 6. Input Range Part Number AD8237 AD8420 1 2 R2 3 Input Range (+IN, –IN, FB, and REF) VEE − 0.3 V to VCC + 0.3 V VEE − 0.15 V to VCC − 2.2 V 5 + 1 4 DUT – 10µF 0.1µF OUT 8 FB REF 7 RF VOUTP 0Ω + VOUT 6 RG OPEN REF – W1 W2 VOUTN Figure 3. Default Connection Diagram Table 5. Supply Voltage Range 1 0Ω Purpose REF tied to ground Ensures proper setting for AD8237 Install the desired component in the MSOP footprint. Connect the supply voltages within the ranges shown in Table 5 to VCC and VEE, and connect the power supply ground return to GND. Drive the inputs with a signal within the listed input range shown in Table 6. Ensure that the expected output signal (default configuration: VOUT = V+IN − V−IN) is within the supplies. Measure the output on a multimeter or oscilloscope. The output voltage is the voltage measured between VOUT (OUT) and VREF (REF). The default configuration is a gain of 1 with REF shorted to the board ground. The output can drive another device, such as another amplifier or an ADC. Part Number AD8237 AD8420 R1 2 0Ω –IN Follow Step 1 through Step 4 to get started using the EVALINAMP-ICF-RMZ evaluation board (see Figure 3). 1. 2. +IN VINN Table 4. Factory Setting Connection W1 Soldered S1 set to LO S1 0.1µF SMA/SMB CONNECTORS NOT INSTALLED VINP VEE 11214-003 The quick start instructions in this section assume that the evaluation board is in its default condition as is shown in Table 4. The values provided are intended to simplify the process of getting started and of checking functionality. Consult the AD8237 data sheet and the AD8420 data sheet for more detailed and up-to-date information on these instrumentation amplifiers. Differential Input Limit1 ±(VS − 1.2)2 ±1 V Defined as the maximum voltage between +IN and −IN for the valid output. For example, if VCC = 2.5 V and VEE = −2.5 V, the differential input limit is ±3.8 V. CIRCUIT OPTIONS Using a Single Supply The EVAL-INAMP-ICF-RMZ can be used in single-supply mode by shorting the VEE pin to ground and connecting the single power supply between VCC and ground. Both the AD8237 and the AD8420 can operate with the inputs and the reference pin at ground on a single supply; however, because the output cannot swing all the way to ground, there must be a positive input signal. For this reason, in many single-supply circuits, it is necessary to remove W1 and drive the reference pin with a higher voltage, such as midsupply. See the Reference section for more details. Changing the Gain The EVAL-INAMP-ICF-RMZ board defaults to a gain of 1 because of the 0 Ω resistor at RF. Removing the 0 Ω resistor and installing 0805-sized resistors at RF and RG creates the following transfer function: VOUT = G(V+IN − V−IN) + VREF where G = 1 + (RF/RG). Table 7. Suggested 1% Resistor Values for Various Gains RF (kΩ) Short 49.9 80.6 90.9 95.3 97.6 100 200 499 1000 RG (kΩ) None 49.9 20 10 5 2 1 1 1 1 Gain 1.00 2.00 5.03 10.09 20.06 49.8 101 201 500 1001 While the ratio of RF to RG sets the gain, the designer determines the absolute value of the resistors. Larger values reduce power consumption and output loading; smaller values limit the FB input bias current or offset current error. For best performance, keep (RF + RG) || RL ≥ 20 kΩ. Rev. 0 | Page 4 of 8 EVAL-INAMP-ICF-RMZ User Guide UG-513 Compensating Errors from the FB Pin Bias Current and Input Impedance RFI Filtering Cutting the trace between the R4 pads and placing a resistor of RF || RG in R4 limits errors from the FB pin bias current (see Figure 4). At higher gains, this resistor can be the same value as RG. Although the offset current of the AD8237 is the same as the bias current, this resistor still helps to compensate the error due to the common-mode input resistance and is therefore recommended. An RFI filter is formed by R1 and R2 with C1, C2, and C3. RFI signals can be filtered with a low-pass RC network placed at the input of the instrumentation amplifier, such as the one shown in Figure 6, where C1 = C2 = CC, C3 = CD, and R1 = R2 = R. The filter limits the input signal bandwidth according to the following relationship: FilterFrequency DIFF = +IN VOUT IB+ FilterFrequency CM = AD8420 FB IBF REF –IN RF where CD ≥ 10 CC. IBR RG R4 = RF||RG RF RG VCC VREF R 20kΩ 1% Figure 4. Cancelling Out Error from FB Input Bias Current RS R CD 20kΩ 3300pF 1% RIN VIN FB R3 RF IF RF||RG + R3 = RS, VOUT = VIN × (1 + RF ) RG 11214-005 RG –IN CC 330pF 5% RG RF 10µF 0.1µF VEE CD affects the differential signal, and CC affects the common-mode signal. Values of R and CC are chosen to minimize out of band RFI at the expense of reduced signal bandwidth. Mismatch between the R × CC at the positive input and the R × CC at the negative input degrades the CMRR of the in-amp. By using a value of CD that is at least one magnitude larger than CC, the effect of the mismatch is reduced and performance is improved. VOUT RIN REF –IN VOUT AD8420 Figure 6. RFI Filtering RIN RS + RIN AD8237 +IN CC 330pF 5% +IN If the source resistance is well known, setting the parallel combination of RF and RG equal to RS can be used to cancel differential input impedance errors. If practical resistor values force the parallel combination of RF and RG to be less than RS, cut the trace between the R3 pads and insert a resistor to make up for the difference. V+IN = VIN × 10µF 0.1µF 11214-004 G=1+ 1 2πRC C 11214-006 IB– 1 2πR(2C D + C C ) The AD8237 has an internal RFI filter that is sufficient for most applications. Nonetheless, an external RFI filter can be added if additional immunity is necessary. Figure 5. Canceling Input Impedance Errors Mode Switch By default, S1 is switched to the right (LO). For AD8237, this corresponds to low bandwidth mode. In low bandwidth mode, AD8237 is unity-gain stable and has a gain bandwidth product of 200 kHz. For gains greater than or equal to 10, S1 can be switched to the left (HI) to put the AD8237 in high bandwidth mode, which has a gain bandwidth product of 1 MHz. In high bandwidth mode, AD8237 is not stable for gains less than 10. R1 and R2 can also be used for input protection or to simulate the source resistance expected in an application. Alternatively, input attenuators can be formed with R1 and a resistor in the place of C1, and/or R2 and a resistor in the place of C2. A differential attenuator can be formed with R1, a resistor in the C3 position, and R2. For the AD8420, Pin 1 is listed as a no connect pin; however, it is high impedance and may be shorted to either supply. Setting S1 to LO matches the parasitic capacitance at the inputs, allowing the best common-mode rejection ratio (CMRR) vs. frequency. Rev. 0 | Page 5 of 8 UG-513 EVAL-INAMP-ICF-RMZ User Guide Other Board Options INPUT A capacitor in CF1, which is parallel with RF, can be used to reduce the gain at high frequencies and therefore reduce noise. Do not leave the in-amp inputs floating, that is, without a dc return path for the bias current. This often occurs when the inputs are connected to a transformer, a thermocouple, or a pair of series capacitors. The inputs must have a dc path to ground, as shown in Figure 7 and Figure 8. If R5 is installed instead of RG, the following transfer function results: VOUT = G(V+IN − V−IN + VREF) The circuit shown in Figure 8 has series capacitors, C, between the signal generator and the input. The series capacitors act as an open circuit at dc; therefore, they prevent a dc current from flowing into the input transistors of the in-amp. Two 10 kΩ resistors are used between the inputs of the in-amp and ground to provide the necessary current path. Closely match the resistors and capacitors in the positive and negative signal path to optimize CMRR. Where G = 1 + (RF/R5) In this case, VOUT is measured with respect to ground. This transfer function can be useful in certain cases, such as electrocardio gram (ECG) circuits that require high gain and dc removal. This configuration on the evaluation board is generally most useful when a dual supply is used. See the Applications Information section for the AD8420 data sheet or the AD8237 data sheet for more information. REFERENCE The reference level of the instrumentation amplifier can be set by driving the REF pin with an amplifier or voltage reference, a dc source, or even a resistor divider (see the AD8420 data sheet or the AD8237 data sheet for further information). By default, W1 is in place and REF is shorted to ground. If a reference voltage other than ground is used, remove the solder from W1 before driving REF with the reference voltage, as shown in Figure 7. VCC 10µF S1 0.1µF 5 2 +IN + 3 0.1µF 10µF 4 OUT 8 FB REF 6 – +COM 1 DUT 100mV p-p, 1kHz –IN OSCILLOSCOPE 7 RF RG 97.6kΩ 2.49kΩ REF W1 11214-007 5V VEE 2.5V Figure 7. Using an External Voltage Source to Set the Reference Level (See Encircled) VCC VEE OSCILLOSCOPE S1 0.1µF 5 C 2 +IN + –IN 3 10kΩ – 4 REF 6 10kΩ 10µF +COM 1 DUT C 0.1µF OUT 8 FB 7 RF RG REF 11214-008 10µF W1 Figure 8. AC Input Coupling, Using a Resistive DC Return Path Rev. 0 | Page 6 of 8 EVAL-INAMP-ICF-RMZ User Guide UG-513 VCC Measure the output voltage by monitoring the voltage between the OUT and REF tie points of the board, as shown in Figure 9. If an external voltage reference is used, the output can be measured, referred to ground, as shown in Figure 7. The evaluation board offers two SMA/SMB outlines at the output, VOUTP and VOUTN. The cable shields for VOUTP and VOUTN are both connected to ground. The voltage in the signal conductor of VOUTN is selectable by Solder Jumper W2. By default, the output voltage at VOUTN is VREF. If the REF pin is being driven but ground must be passed to the next stage, such as a pseudo-differential ADC, the default solder jumper can be removed, and VOUTN can be shorted to ground. Take care that the voltage source driving REF does not become inadvertently shorted to ground during this process. 10µF 2 + Rev. 0 | Page 7 of 8 3 – 0.1µF 10µF +COM 1 4 DUT –IN OSCILLOSCOPE S1 0.1µF 5 +IN VEE OUT 8 FB REF 6 7 RF RG REF W1 Figure 9. Correct Output Connection Using the REF Pin 11214-009 OUTPUT UG-513 EVAL-INAMP-ICF-RMZ User Guide NOTES ESD Caution ESD (electrostatic discharge) sensitive device. Charged devices and circuit boards can discharge without detection. Although this product features patented or proprietary protection circuitry, damage may occur on devices subjected to high energy ESD. Therefore, proper ESD precautions should be taken to avoid performance degradation or loss of functionality. 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Customer agrees that it will not directly or indirectly export the Evaluation Board to another country, and that it will comply with all applicable United States federal laws and regulations relating to exports. GOVERNING LAW. This Agreement shall be governed by and construed in accordance with the substantive laws of the Commonwealth of Massachusetts (excluding conflict of law rules). Any legal action regarding this Agreement will be heard in the state or federal courts having jurisdiction in Suffolk County, Massachusetts, and Customer hereby submits to the personal jurisdiction and venue of such courts. The United Nations Convention on Contracts for the International Sale of Goods shall not apply to this Agreement and is expressly disclaimed. ©2013 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. UG11214-0-2/13(0) Rev. 0 | Page 8 of 8