Datasheet OP184, OP284, OP484 (Analog Devices) - 17

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OP184/OP284/OP484
Resistor networks should be used in this circuit for R2 and R3 One measure of the performance of a voltage reference is its because they exhibit the necessary relative tolerance matching for capacity to recover from sudden changes in load current. While good performance. Matched networks also exhibit tight relative sourcing a steady-state load current of 1 mA, this circuit recovers resistor temperature coefficients for good circuit temperature to 0.01% of the programmed output voltage in 1.5 μs for a total stability. Trimming Potentiometer P1 is used for optimum dc change in load current of ±1 mA. CMR adjustment, and C1 is used to optimize ac CMR. With the
3V
circuit values as shown, Circuit CMR is better than 80 dB over the
3V R1
frequency range of 20 Hz to 20 kHz. Circuit referred-to-input
17.4kΩ 3 8
(RTI) noise in the 0.1 Hz to 10 Hz band is an impressively low
0.1µF 1/2 1 + 2.5V OP284
0.45 μV p-p. Resistor RP1 and Resistor RP2 serve to protect the
REF AD589 2 –
OP284 inputs against input overvoltage abuse. Capacitor C2 can
4
be included to the limit circuit bandwidth and, therefore, wide bandwidth noise in sensitive applications. The value of this capacitor should be adjusted, depending on the required closed-
R3 R2 P1 100kΩ 100kΩ 5kΩ
loop bandwidth of the circuit. The R4 to C2 time constant creates 053
RESISTORS = 1%, 100ppm/°C
a pole at a frequency equal to
POTENTIOMETER = 10 TURN, 100ppm/°C
00293- Figure 53. 2.5 V Reference That Operates on a Single 3 V Supply f ( dB) 1 3 = 2π R4C2
5 V ONLY, 12-BIT DAC SWINGS RAIL-TO-RAIL
The OP284 is ideal for use with a CMOS DAC to generate a
2.5 V REFERENCE FROM A 3 V SUPPLY
digitally controlled voltage with a wide output range. Figure 54 In many single-supply applications, the need for a 2.5 V reference shows a DAC8043 used in conjunction with the AD589 to gen- often arises. Many commercially available monolithic 2.5 V erate a voltage output from 0 V to 1.23 V. The DAC is actual y references require at least a minimum operating supply of 4 V. operating in voltage switching mode, where the reference is The problem is exacerbated when the minimum operating connected to the current output, IOUT, and the output voltage is supply voltage is 3 V. The circuit illustrated in Figure 53 is an taken from the VREF pin. This topology is inherently noninverting, example of a 2.5 V reference that operates from a single 3 V as opposed to the classic current output mode, which is inverting supply. The circuit takes advantage of the OP284 rail-to-rail and not usable in single-supply applications. input/output voltage ranges to amplify an AD589 1.235 V
5V
output to 2.5 V.
8 RP1 R1 2 1kΩ VDD R 3V 17.8kΩ RB + 3 V 1 DAC8043 V 5 1.23V I REF IN RP2 8 OUT 1kΩ 3 7 R3 5V – A2 VOUT 1.1k AD589 1 Ω 6 GND CLK SR1 LD A1 4 3 8 2 4 7 6 5 1/2 1 D R2 OP284 VOUT = (5V) 1.1kΩ 2 4096 R4 DIGITAL C1 10kΩ 4 CONTROL AC CMRR R1 TRIM 9.53kΩ 5pF TO 40pF C2 A1, A2 = 1/2 OP284 R3 R2 R4
054
P1 R4 232Ω 32.4Ω 100kΩ GAIN = 1 + 500Ω 1% 1% 1% R3
00293- 052
SET R2 = R3
Figure 54. 5 V Only, 12-Bit DAC Swings Rail-to-Rail
R1 + P1 = R4
00293- Figure 52. Single Supply, 3 V Low Noise Instrumentation Amplifier In this application, the OP284 serves two functions. First, it The low TCV buffers the high output impedance of the DAC VREF pin, which OS of the OP284 at 1.5 μV/°C helps maintain an output voltage temperature coefficient that is dominated by is on the order of 10 kΩ. The op amp provides a low impedance the temperature coefficients of R2 and R3. In this circuit with output to drive any fol owing circuitry. 100 ppm/°C TCR resistors, the output voltage exhibits a tempera- Second, the op amp amplifies the output signal to provide a rail- ture coefficient of 200 ppm/°C. Lower tempco resistors are to-rail output swing. In this particular case, the gain is set to 4.1 recommended for more accurate performance over temperature. so that the circuit generates a 5 V output when the DAC output is at full scale. If other output voltage ranges are needed, such as 0 V ≤ VOUT ≤ 4.095 V, the gain can be easily changed by adjusting the values of R2 and R3. Rev. J | Page 17 of 24 Document Outline Features Applications General Description Pin Configurations Table of Contents Revision History Specifications Electrical Characteristics Absolute Maximum Ratings Thermal Resistance ESD Caution Typical Performance Characteristics Applications Information Functional Description Input Overvoltage Protection Output Phase Reversal Designing Low Noise Circuits in Single-Supply Applications Overdrive Recovery Single-Supply, 3 V Instrumentation Amplifier 2.5 V Reference from a 3 V Supply 5 V Only, 12-Bit DAC Swings Rail-to-Rail High-Side Current Monitor Capacitive Load Drive Capability Low Dropout Regulator with Current Limiting 3 V, 50 Hz/60 Hz Active Notch Filter with False Ground Outline Dimensions Ordering Guide