Datasheet AD780 (Analog Devices) - 8

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AD780 Data Sheet
Notice how sensitive the current dependent factor on V
0.85
OUT is. A large amount of current, even in tens of microamps, drawn
–55
°
C
from the TEMP pin can cause the VOUT and TEMP output to fail.
0.80
The choice of C1 and C2 was dictated primarily by the need for
+25
°
C
a relatively flat response that rolled off early in the high frequency
0.75
noise at the output. However, there is considerable margin in
+125
°
C
the choice of these capacitors. For example, the user can actual y put a huge C2 on the TEMP pin with none on the
0.70
output pin. However, one must either put very little or a lot of capacitance at the TEMP pin. Intermediate values of capacitance
QUIESCENT CURRENT (mA) 0.65
can sometimes cause oscillation. In any case, the user should follow the recommendation in Figure 6.
0.60
00841-014
4 36 TEMPERATURE TRANSDUCER CIRCUIT INPUT VOLTAGE (V)
The circuit shown in Figure 13 is a temperature transducer that Figure 14. Typical Supply Current over Temperature amplifies the TEMP output voltage by a gain of a little over +5 to
TURN-ON TIME
provide a wider ful -scale output range. The digital potentiometer can be used to adjust the output so it varies by exactly 10 mV/°C. The time required for the output voltage to reach its final value within a specified error band is defined as the turn-on settling To minimize resistance changes with temperature, resistors with time. The two major factors that affect this are the active circuit low temperature coefficients, such as metal film resistors, settling time and the time for the thermal gradients on the chip should be used. to stabilize. Typical settling performance is shown in Figure 15.
5V
The AD780 settles to within 0.1% of its final value within 10 µs.
2 +VIN VIN 5V TEMP 3 10mV/
°
C AD820 0V 1
µ
F AD780 GND V R OUT B RF 4 1.27k
Ω
2.500V 6.04k
Ω
(1%) (1%) 2.499V RBP 200
Ω
2.498V
00841-013 00841-015 Figure 13. Differential Temperature Transducer
10
µ
s/DIV SUPPLY CURRENT OVER TEMPERATURE
Figure 15. Turn-On Settling Time Performance The quiescent current of the AD780 varies slightly over temperature and input supply range. The test limit is 1 mA over the industrial and 1.3 mA over the military temperature range. Typical performance with input voltage and temperature variation is shown in Figure 14. Rev. I | Page 8 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