AD5421 Analog Devices, AD5421 Datasheet
AD5421
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AD5421 Summary of contents
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... The AD5421 is guaranteed monotonic to 16 bits. It provides 0.0015% integral nonlinearity, 0.0012% offset error, and 0.0006% gain error under typical conditions. The AD5421 is available in a 28-lead TSSOP and a 32-lead LFCSP specified over the extended industrial temperature range of −40°C to +105°C. FUNCTIONAL BLOCK DIAGRAM ...
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... AD5421 TABLE OF CONTENTS Features .............................................................................................. 1 Applications ....................................................................................... 1 General Description ......................................................................... 1 Functional Block Diagram .............................................................. 1 Revision History ............................................................................... 2 Specifications ..................................................................................... 3 AC Performance Characteristics ................................................ 8 Timing Characteristics ................................................................ 8 Absolute Maximum Ratings .......................................................... 10 Thermal Resistance .................................................................... 10 ESD Caution ................................................................................ 10 Pin Configuration and Function Descriptions ........................... 11 Typical Performance Characteristics ........................................... 13 Terminology .................................................................................... 19 Theory of Operation ...................................................................... 20 Fault Alerts .................................................................................. 20 External Current Setting Resistor ............................................ 21 Loop Current Range Selection ...
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... C grade % FSR C grade 25° FSR B grade % FSR B grade 25°C A ppm FSR Drift after 1000 hours FSR C grade % FSR B grade LSB Guaranteed monotonic % FSR % FSR T = 25°C A ppm FSR/°C % FSR % FSR T = 25°C A AD5421 = 125° 125°C A ...
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... AD5421 Parameter 1 Gain Error TC 3 Full-Scale Error Full-Scale Error TC 3 Downscale Alarm Current Upscale Alarm Current OUTPUT CHARACTERISTICS 3 Loop Compliance Voltage 4 Loop Current Long-Term Stability Loop Current Error vs. REG Load OUT Current Resistive Load Inductive Load Power Supply Sensitivity Output Impedance ...
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... Assuming 4 mA flowing in the loop and during HART communications mA mV/mA Measured and 3 mA loads SCLK, SYNC , SDIN, LDAC IODV = 1 IODV = 3 IODV = 5 μA Per pin pF Per pin V V μ °C Fault removed when temperature ≤ 125°C AD5421 ...
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... Temperature range: −40°C to +105°C; typical at +25°C. 2 Total unadjusted error is the total measured error (offset error + gain error + linearity error + output drift over temperature) after factory calibration of the AD5421. System level total error can be reduced using the offset and gain registers. ...
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... Total unadjusted error is the total measured error (offset error + gain error + linearity error + output drift over temperature) after factory calibration of the AD5421. System level total error can be reduced using the offset and gain registers. = 250 Ω; external NMOS connected; all loop current ranges; ...
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... AD5421 AC PERFORMANCE CHARACTERISTICS Loop voltage = 24 V; REFIN = 2.5 V external; R Table 3. Parameter 1 DYNAMIC PERFORMANCE Loop Current Settling Time Loop Current Slew Rate AC Loop Voltage Sensitivity Temperature range: −40°C to +105°C; typical at +25°C. 1 TIMING CHARACTERISTICS Loop voltage = 24 V; REFIN = 2.5 V external; R Table 4. Parameter ...
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... Figure 2. Serial Interface Timing Diagram D16 D15 D0 D23 UNDEFINED DATA SPECIFIED REGISTER DATA CLOCKED OUT Figure 3. Readback Timing Diagram Rev Page D16 D15 D0 NOP OR REGISTER ADDRESS D15 D0 AD5421 ...
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... AD5421 ABSOLUTE MAXIMUM RATINGS T = 25°C, unless otherwise noted. Transient currents 100 mA do not cause SCR latch-up. Table 6. Parameter Rating REG to COM −0 + REG to COM −0 +14 V OUT Digital Inputs to COM, −0 RANGE0, RANGE1 ...
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... Digital Input Pins. These two pins select the loop current range (see the Loop Current Range Selection section). Rev Page AD5421 SDIN PIN 1 LDAC 2 23 LOOP– INDICATOR FAULT AD5421 COM TOP VIEW (Not to Scale REFOUT1 ...
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... This pin can be used for general-purpose voltage monitoring, but it is intended for monitoring of the loop supply voltage. Connecting the loop voltage to this pin via a 20:1 resistor divider allows the AD5421 to monitor and feedback the loop voltage. The AD5421 also generates an alert if the loop voltage is close to the minimum operating value (see the Loop Voltage Fault section) ...
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... LOOP EXT V 0 4mA TO 20mA RANGE INT V = 250Ω R LOAD INT V MIN INL – –40 TEMPERATURE (°C) Figure 11. Integral Nonlinearity Error vs. Temperature AD5421 , INT R REF SET , EXT R REF SET , INT R REF SET , EXT R REF SET INT R REF SET ...
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... AD5421 0.5 0.4 0.3 MAX DNL 0.2 0.1 0 –0.1 MIN DNL –0.2 –0.3 –0.4 –0.5 –40 – TEMPERATURE (°C) Figure 12. Differential Nonlinearity Error vs. Temperature 0.04 0.03 0.02 0.01 0 –0. 24V LOOP –0.02 4mA TO 20mA RANGE = 250Ω R LOAD –0.03 EXT NMOS EXT V , INT R REF SET –0.04 EXT V , EXT R REF ...
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... Figure 22. Loop Current Error vs. REG Load Current OUT –2 V LOOP –4 EXT NMOS EXT V I –6 LOOP R LOAD T = 25°C A – TIME (Seconds) Figure 23. Loop Current Noise, 0 Bandwidth AD5421 80 100 4.0 4.5 5.0 = 24V REF = 4mA = 250Ω ...
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... AD5421 1 24V I = 4mA 1.33mV p-p LOOP LOOP = 500Ω EXT NMOS R 0.2mV rms 0.8 LOAD INT 25°C REF A 0.6 0.4 0.2 0 –0.2 –0.4 –0.6 –0.8 –1.0 0 0.1 0.2 0.3 0.4 0.5 0.6 TIME (Seconds) Figure 24. Loop Current Noise, 500 kHz Bandwidth (HART Bandwidth) 6 FALLING RISING 1 0 –40 – ...
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... EXT NMOS T = 25°C A – TIME (Seconds 24V LOOP EXT NMOS T = 25° REFOUT1 LOAD CURRENT (mA) Figure 35. REFOUT1 Voltage vs. Load Current AD5421 0 –50 –100 –150 –200 –250 –1 –2 –3 –4 – ...
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... AD5421 2.5012 60 DEVICES SHOWN 2.5010 2.5008 2.5006 2.5004 2.5002 2.5000 2.4998 2.4996 2.4994 –40 – TEMPERATURE (°C) Figure 36. REFOUT1 Voltage vs. Temperature, 60 Devices Shown (C Grade Device TEMPERATURE COEFFICIENT (ppm/°C) Figure 37. REFOUT1 Temperature Coefficient Histogram (C Grade Device 100 MEAN TC = 1.5ppm/° ...
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... REF_MIN over the total temperature range the nominal reference output voltage, 2.5 V. REF_NOM Temp_Range is the specified temperature range (−40°C to +105°C). Rev Page AD5421 pins for which the output IN V REF_MIN 6 × ...
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... The 8-bit FCS is appended to the end of the data-word, and 32 data bits are sent to the AD5421 before SYNC is taken high. If the check is valid, the data is accepted. If the check fails, the FAULT pin is asserted and the PEC bit of the fault register is set. ...
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... AD5421 and the loop power supply. The use of this device keeps the voltage drop across the AD5421 at approximately 12 V, limiting the worst-case on-chip power dissi- pation to 288 mW (12 V × 288 mW). If the AD5421 is . connected directly to the loop supply as shown in Figure 42, the ...
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... LOOP VOLTAGE REGULATOR The on-chip voltage regulator provides a regulated voltage out- put to supply the AD5421 and the remainder of the transmitter circuitry. The output voltage range is from 1 and is selected by the states of three digital input pins (see Table 10). The regulator output is accessed at the REG Table 10 ...
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... Data Sheet POWER-ON DEFAULT The AD5421 powers on with all registers loaded with their default values and with the loop current in the alarm state set to 3 22.8 mA/24 mA (depending on the state of the ALARM_ CURRENT_DIRECTION pin and the selected range). The AD5421 remains in this state until it is programmed with new values ...
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... AD5421 Figure 48 shows the circuit diagram for this measurement. The 47 nF and 168 nF capacitor values for C adequate filtering of the digital steps, ensuring that they do not cause interference. REG IN AD5421 LOOP– C COM IN 168nF 47nF FROM HART MODEM Figure 48. Circuit Diagram for Figure 47 ...
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... If packet error checking on the SPI interface is required using cyclic redundancy codes, an additional eight bits must be written to the AD5421, creating a 32-bit serial interface. In this case, 32 bits are written to the AD5421 before SYNC is brought high. INPUT SHIFT REGISTER The input shift register is 24 bits wide (32 bits wide if CRC error checking of the data is required) ...
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... AD5421 DAC REGISTER The DAC register is a read/write register and is addressed as described in Table 11. The data programmed to the DAC register determines the loop current, as shown in the Ideal Output Transfer Function section and in Table 15. Ideal Output Transfer Function The transfer function describing the relationship between the data programmed to the DAC register and the loop current is expressed by the following three equations ...
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... Table 17. Control Register Bit Descriptions Control Bits Description SPI watchdog The T0, T1, and T2 bits allow the user to program the watchdog timeout period. The watchdog timer is reset when a valid timeout write to any AD5421 register occurs or when a NOP command is written ...
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... This bit is cleared when the temperature returns below approximately 125°C. Temp 100°C No This bit is set high to indicate an increasing temperature of the AD5421. This bit is set if the die temperature of the AD5421 exceeds approximately 100°C. This bit is cleared when the temperature returns below approximately 85°C. V ...
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... Digital Offset Adjustment (LSBs) +32767 +32766 … −1 … −32767 −32768 D10 16-bit gain adjust data Digital Gain Adjustment at Full-Scale Output (LSBs) 0 −1 … −32767 −32768 −32769 … −65534 −65535 Rev Page AD5421 LSB D0 LSB D0 ...
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... AD5421 Transfer Function Equations with Offset and Gain Adjust Values When the offset adjust and gain adjust register values are taken into account, the transfer equations can be expressed as follows. For the output range, the loop current can be expressed as follows: ...
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... MCU Figure 49. AD5421 Application Diagram for HART Capable Smart Transmitter DETERMINING THE EXPECTED TOTAL ERROR The AD5421 can be set number of different configu- rations, each of which achieves different levels of accuracy, as described in Table 1 and Table 2. With the internal voltage reference and internal ...
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... To reduce this error value further, a voltage reference and R resistor with lower TC specifications must be chosen. THERMAL AND SUPPLY CONSIDERATIONS The AD5421 is designed to operate at a maximum junction temp- erature of 125°C. To ensure reliable and specified operation over the lifetime of the product important that the device not be operated under conditions that cause the junction temperature to exceed this value ...
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... PAD 3. 0.25 MIN FOR PROPER CONNECTION OF THE EXPOSED PAD, REFER TO THE PIN CONFIGURATION AND FUNCTION DESCRIPTIONS SECTION OF THIS DATA SHEET. 5.55 5.50 5.45 3.05 EXPOSED 3.00 PAD (Pins Up) 2.95 FOR PROPER CONNECTION OF 0.25 THE EXPOSED PAD, REFER TO THE PIN CONFIGURATION AND FUNCTION DESCRIPTIONS 0.75 SECTION OF THIS DATA SHEET. 0.60 0.45 AD5421 ...
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... AD5421BCPZ-REEL7 −40°C to +105°C AD5421BREZ −40°C to +105°C AD5421BREZ-REEL −40°C to +105°C AD5421BREZ-REEL7 −40°C to +105°C AD5421CREZ −40°C to +105°C AD5421CREZ-RL −40°C to +105°C AD5421CREZ-RL7 −40°C to +105°C EVAL-AD5421SDZ Z = RoHS Compliant Part. 1 ...
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... Data Sheet NOTES Rev Page AD5421 ...
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... AD5421 NOTES ©2011 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D09128-0-12/11(C) Rev Page Data Sheet ...