參數(shù)資料
型號: AD1584BRT
英文描述: Voltage Reference
中文描述: 電壓基準(zhǔn)
文件頁數(shù): 8/12頁
文件大?。?/td> 167K
代理商: AD1584BRT
AD1582/AD1583/AD1584/AD1585
–8–
REV. A
THEORY OF OPERATION
The AD1582/AD1583/AD1584/AD1585 family uses the
“bandgap” concept to produce stable, low temperature coeffi-
cient voltage references suitable for high accuracy data acquisi-
tion 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 V
BE
that, when
extrapolated to absolute zero, 0
°
K, (with collector current propor-
tional to absolute temperature) approximates the silicon bandgap
voltage. By summing a voltage that has an equal and opposite
temperature coefficient of +2 mV/
°
C with the V
BE
of a forward-
biased transistor, a zero TC reference can be developed. In the
AD1582/AD1583/AD1584/AD1585 simplified circuit diagram
shown in Figure 8, such a compensating voltage, V1, is derived
by driving two transistors at different current densities and
amplifying the resultant V
BE
difference (
V
BE
—which has a
positive TC). The sum (V
BG
) of V
BE
and V1 is then buffered
and amplified to produce stable reference voltage outputs of
2.5 V, 3 V, 4.096 V, and 5 V.
R3
R4
V
BE
R2
R6
R5
V
OUT
V
IN
V
BG
GND
V1
+
R1
+
Figure 8. Simplified Schematic
APPLYING THE AD1582/AD1583/AD1584/AD1585
The AD1582/AD1583/AD1584/AD1585 is a family of series
references that can be utilized for many applications. To achieve
optimum performance with these references, only two external
components are required. Figure 9 shows the AD1582 config-
ured for operation under all loading conditions. With a simple
4.7
μ
F capacitor attached to the input and a 1
μ
F capacitor
applied to the output, the devices will achieve specified perfor-
mance for all input voltage and output current requirements.
For best transient response, add a 0.1
μ
F capacitor in parallel with
the 4.7
μ
F. While a 1
μ
F output capacitor will provide stable
performance for all loading conditions, the AD1582 can operate
under low (–100
μ
A < I
OUT
< 100
μ
A) current conditions with
just a 0.2
μ
F output capacitor. The 4.7
μ
F capacitor on the input
can be reduced to 1
μ
F in this condition.
Unlike conventional shunt reference designs, the AD1582/
AD1583/AD1584/AD1585 family provides stable output
voltages at constant operating current levels. When properly
decoupled, as shown in Figure 9, these devices can be applied to
any circuit and provide superior low power solutions.
+
V
IN
V
OUT
1 F
4.7 F
1
2
3
Figure 9. Typical Connection Diagram
TEMPERATURE PERFORMANCE
The AD1582/AD1583/AD1584/AD1585 family of references is
designed for applications 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 guaranteed with the AD1582/AD1583/AD1584/
AD1585 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 guarantees the maximum error band over the
entire temperature change. Thus, for a given grade of the
AD1582/AD1583/AD1584/AD1585, the designer can easily
determine the maximum total error by summing initial accuracy
and temperature variation (e.g., for the AD1582BRT, 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 10 shows the typical output voltage drift for the AD1582
and illustrates the methodology. The box in Figure 10 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
AD1582 will produce curves similar to those in Figures 4 and
10, but output readings may vary depending upon the test
methods and test equipment utilized.
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