Datasheet AD780 (Analog Devices) - 7

link to page 7 link to page 7
Data Sheet AD780 2.0 2 7 +VIN DNC 1.6 VOUT 6 1 DNC 1.2 AD780 TRIM 5 0.8 3 TEMP C1 O/P SELECT 0.4 C2 2.5V – DNC ERROR (mV) GND 3.0V – GND 4 8 0
009
–0.4 DNC = DO NOT CONNECT TO THIS PIN
00841- Figure 9. Noise Reduction Circuit
–0.8
00841-011
–60 –40 –20 0 20 40 60 80 100 120 140 NOISE COMPARISON TEMPERATURE (
°
C)
Figure 11. Typical AD780BN Temperature Drift The wideband noise performance of the AD780 can also be expressed in ppm. The typical performance with C1 and C2 is
TEMPERATURE OUTPUT PIN
0.6 ppm; without external capacitors, typical performance is The AD780 provides a TEMP output (Pin 3) that varies linearly 1.2 ppm. with temperature. This output can be used to monitor changes This performance is, respectively, 7× and 3× lower than the in system ambient temperature, and to initiate calibration of the specified performance of the LT1019. system, if desired. The voltage VTEMP is 560 mV at 25°C, and the temperature coefficient is approximately 2 mV/°C.
NO AMPLIFIER
Figure 12 shows the typical VTEMP characteristic curve over
20
µ
V 10ms
temperature taken at the output of the op amp with a
100
noninverting gain of 5.
90 4.25 CIRCUIT CALIBRATED AT 25
°
C REFER TO FIGURE 13 4.00 3.75 ) 3.50 10 10mV PER
°
C OUT 0% 3.25 3.00 VOLTAGE (V 2.75
00841-010
10Hz TO 10kHz 2.50
Figure 10. Reduced Noise Performance with C1 = 100 µF, C2 = 100 nF
2.25 TEMPERATURE PERFORMANCE 2.00
00841-012 The AD780 provides superior performance over temperature by
–75 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (
°
C)
means of a combination of patented circuit design techniques, Figure 12. Temperature Pin Transfer Characteristic precision thin-film resistors, and drift trimming. Temperature performance is specified in terms of ppm/°C; because of Since the TEMP voltage is acquired from the band gap core nonlinearity in the temperature characteristic, the box test circuit, current pul ed from this pin has a significant effect on method is used to test and specify the part. The nonlinearity VOUT. Care must be taken to buffer the TEMP output with a takes the form of the characteristic S-shaped curve shown in suitable op amp, for example, an OP07, AD820, or AD711 (all Figure 11. The box test method forms a rectangular box around of which would result in less than a 100 µV change in VOUT). this curve, enclosing the maximum and minimum output voltages The relationship between ITEMP and VOUT is over the specified temperature range. The specified drift is equal to ∆VOUT = 5.8 mV/µA ITEMP (2.5 V Range) the slope of the diagonal of this box. or ∆VOUT = 6.9 mV/µA ITEMP (3.0 V Range) Rev. I | Page 7 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