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参数资料
| 型号： | AD1587 |
| 厂商： | Analog Devices, Inc. |
| 英文描述： | Precision Shunt Mode Voltage References(微功耗,精密电压基准) |
| 中文描述： | 精密并联模式电压基准（微功耗，精密电压基准） |
| 文件页数： | 10/11页 |
| 文件大小： | 107K |
| 代理商： | AD1587 |
–8–
PRELIM. B, JUNE 96
AD1586/7/8/9
THEORY OF OPERATION
The AD1586/7/8/9 family uses the "bandgap" concept to produce
stable, low-temperature coefficient voltage references which are
suitable for high accuracy data-acquisition components and
systems. This family of precision references makes use of the
underlying temperature characteristics of a silicon transistor's
base-emitter voltage in the forward-biased operating region.
Under this condition, all such transistors have a -2 mV/
°C
temperature coefficient (TC) and a VBE that, when extrapolated
to absolute zero, 0
°K, (with collector current proportional to
absolute temperature) approximates the silicon bandgap voltage.
By summing a voltage that has an equal and opposite tempera-
ture coefficient of +2 mV/
°C with the VBE of a forward-biased
transistor, a zero TC reference can be developed. In the
AD1586/7/8/9 simplified circuit diagram shown in Figure 7, such
a compensating voltage, V1, is derived by driving two transistors
at different current densities and amplifying the resultant VBE
difference (
VBE - which has a positive TC). The sum (VBG) of
VBE and V1 is then scaled by the R5/R6 resistor network to
produce stable reference voltage outputs of 2.5V, 3V, 4.096V,
and 5V. To ensure that the bandgap cell and resistor network
maintain their required current levels, a buffer amplifier drives
an output transistor to sink any excess current.
TEMPERATUREPERFORMANCE
The AD1586/7/8/9 family of references are designed for applica-
tions where temperature performance is important. Extensive
temperature testing and characterization ensures that the device's
performance is maintained over the specified temperature range.
Some confusion exists, however, in the area of defining and
specifying reference voltage error over temperature. Historically,
references have been characterized using a maximum deviation
per degree centigrade, i.e., 50 ppm/
°C. However, because of the
inconsistent nonlinearities in standard zener references (such as
"S" type characteristics), most manufacturers use a maximum
limit error band approach to characterize their references. Using
this technique, the voltage reference output voltage error band is
specified by taking output voltage measurements at three or more
different temperatures.
The error band which is guaranteed with the AD1586/7/8/9
family is the maximum deviation from the initial value at +25
°C;
this method is of more use to a designer than the one which
simply gaurantees the maximum error band over the entire
temperature change. Thus, for a given grade of the AD1586/7/8/
9, the designer can easily determine the maximum total error
from inital accuracy plus temperature variation (e.g., for the
AD1586BRT, the initial tolerance is +/-2 mV, the temperature
error band is +/- 8 mV, thus the reference is guaranteed to be 2.5
V +/- 10 mV from -40
°C to +85 °C).
Figure 9 shows the typical output voltage drift for the AD1586
and illustrates the methodology. The box in Figure 9 is bounded
on the x-axis by operating temperature extremes, and on the y-
axis by the maximum and minimum output voltages observed
over the operating temperature range. The slope of the diagonal
drawn from the initial output value at +25
°C to the output
values at +85
°C and -40 °C determines the performance grade
of the device.
Duplication of these results requires a test system that is highly
accurate with stable temperature control. Evaluation of the
AD1586 will produce curves similar to those in Figures 3 and 9,
but output readings may vary depending upon the test methods
and test equipment utilized.
Figure 8. Typical Connection Diagram
(a)
(b)
Figure 8b shows a typical connection with the AD1586BRT
shunt reference. In this circuit, R
S is chosen for operation with a
minimum of 100
A quiescent current, a +1 mA load current
and a power supply tolerance of +/-10 %.
APPLYING THE AD1586
The AD1586/7/8/9 family of shunt references are simple to use in
virtually all applications. To operate the AD1586/7/8/9 family as
conventional shunt regulators (Figure 8a), an external series
resistor is connected between the supply voltage and the refer-
ence. For a given supply voltage the series resistor, R
S, deter-
mines the reverse current flowing through the AD1586/7/8/9.
The value of R
S must be chosen to maintain an acceptable
reverse current, I
R , while accomodating the expected variations
of the supply voltage, V
S, load current, IL, and the reverse
voltage, V
R.
The minimum value for Rs should then be chosen when I
L and
V
R are at their maximum and VS is at its minimum.
For the AD1586/7/8/9 family, the value of Rs should be large
enough to limit I
R to 10mA
when V
S is at its maximum and IL
and V
R are at their minimum.
The equations for selecting R
S is as follows:
R
S = ( VS - VR ) / ( IR + IL )
Figure 7. AD1586/7/8/9 Simplified Schematic
V+
-
+
R3
R2
R4
R1
V-
R6
R5
+
-
V1
V B G
V BE
Rs
VR
VOUT
+
-
Rs
VR
VOUT
+
-
IR
IL
IR + IL
VS
5V (3V) + 10 %
1.81 k
(180
)
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