Datasheet AD780 (Analog Devices) - 6

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AD780 Data Sheet APPLYING THE AD780
The AD780 can be used without any external components to
100
achieve specified performance. If power is supplied to Pin 2 and Pin 4 is grounded, Pin 6 provides a 2.5 V or 3.0 V output depending on whether Pin 8 is left unconnected or grounded.
10
A bypass capacitor of 1 µF (+VIN to GND) should be used if the load capacitance in the application is expected to be greater than 1 nF. The AD780 in 2.5 V mode typical y draws 700 µA of Iq at 5 V. This increases by ~2 µA/V up to 36 V.
1 2 7 +VIN DNC COMPENSATION CAPACITOR, C2 (nF) VOUT 6 0.1
00841-006
1 DNC 0.1 1 10 100 AD780 LOAD CAPACITOR, C1 (
µ
F) RNULL TRIM 5 R POT
Figure 6. Compensation and Load Capacitor Combinations
3 TEMP O/P SELECT
C1 and C2 also improve the settling performance of the AD780
2.5V – DNC GND 3.0V – GND
when subjected to load transients. The improvement in noise
4 8
performance is shown in Figure 7, Figure 8, Figure 9, and Figure 10. 005
AMPLIFIER GAIN = 100 DNC = DO NOT CONNECT TO THIS PIN
00841- Figure 5. Optional Fine-Trim Circuit
100
µ
V 1s
Initial error can be nulled using a single 25 kΩ potentiometer
100 90
connected between VOUT, TRIM, and GND. This is a coarse trim with an adjustment range of 4%, and is only included here for compatibility purposes with other references. A fine trim can be implemented by inserting a large value resistor (e.g., 1 MΩ to 5 MΩ) in series with the wiper of the potentiometer (see Figure 5). The trim range, expressed as a fraction of the output, is simply
10 0%
greater than or equal to 2.1 kΩ/RNULL for either the 2.5 V or 3.0 V mode. The external nul resistor affects the overal temperature 00841-007
0.1 TO 10Hz
coefficient by a factor equal to the percentage of V OUT nulled. Figure 7. Standalone Noise Performance For example, a 1 mV (0.03%) shift in the output caused by the
NO AMPLIFIER
trim circuit, with a 100 ppm/°C null resistor, adds less than 0.06 ppm/°C to the output drift (0.03% × 200 ppm/°C, since the
20
µ
V 10ms
resistors internal to the AD780 also have temperature coefficients
100
of less than 100 ppm/°C).
90 NOISE PERFORMANCE
The impressive noise performance of the AD780 can be further improved, if desired, by adding two capacitors: a load capacitor (C1) between the output and ground, and a compensation
10
capacitor (C2) between the TEMP pin and ground. Suitable
0%
values are shown in Figure 6. 00841-008
10Hz TO 10kHz
Figure 8. Standalone Noise Performance Rev. I | Page 6 of 12 Document Outline Features Functional Block Diagram General Description Product Highlights Table of Contents Revision History Specifications Absolute Maximum Ratings Thermal Resistance Notes ESD Caution Theory of Operation Applying the AD780 Noise Performance Noise Comparison Temperature Performance Temperature Output Pin Temperature Transducer Circuit Supply Current Over Temperature Turn-On Time Dynamic Performance Line Regulation Precision Reference for High Resolution 5 V Data Converters 4.5 V Reference from 5 V Supply Negative (–2.5 V) Reference Outline Dimensions Ordering Guide