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AD1585BRT-REEL7 Fiches technique(PDF) 9 Page - Analog Devices

No de pièce AD1585BRT-REEL7
Description  2.5 V to 5.0 V Micropower, Precision Series Mode Voltage References
Download  16 Pages
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Fabricant  AD [Analog Devices]
Site Internet  http://www.analog.com
Logo AD - Analog Devices

AD1585BRT-REEL7 Fiches technique(HTML) 9 Page - Analog Devices

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AD1582/AD1583/AD1584/AD1585
–9–
REV. D
THEORY OF OPERATION
The AD1582/AD1583/AD1584/AD1585 family uses the band gap
concept to produce stable, low temperature coefficient voltage
references suitable for high accuracy data acquisition components
and systems. This family of precision references uses 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 band gap 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,
an almost zero TC reference can be developed. In the AD1582/
AD1583/AD1584/AD1585 simplified circuit diagram shown in
Figure 2, such a compensating voltage, V1, is derived by
driving two transistors at different current densities and
amplifying the resultant VBE difference (
∆V
BE, which has a positive
TC). The sum of VBE and V1(VBG) is then buffered and ampli-
fied to produce stable reference voltage outputs of 2.5 V, 3 V,
4.096 V, and 5 V.
R3
R4
VBE R2
R6
R5
VOUT
VIN
VBG
GND
V1
+
R1
+
Figure 2. Simplified Schematic
APPLYING THE AD1582/AD1583/AD1584/AD1585
The AD1582/AD1583/AD1584/AD1585 is a family of series
references that can be used for many applications. To achieve
optimum performance with these references, only two external
components are required. Figure 3 shows the AD1582 configured
for operation under all loading conditions. With a simple 4.7
µF
capacitor attached to the input and a 1
µF capacitor applied
to the output, the devices can achieve specified performance for
all input voltage and output current requirements. For best
transient response, add a 0.1
µF capacitor in parallel with the 4.7 µF
capacitor. While a 1
µF output capacitor can provide stable
performance for all loading conditions, the AD1582 can operate
under low (–100
µA < I
OUT < +100
µA) current conditions with
just a 0.2
µF output capacitor. The 4.7 µF capacitor on the input can
be reduced to 1
µF 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 3, these devices can be applied to any circuit
and provide superior low power solutions.
+
VOUT
1 F
1
2
VIN
4.7 F
3
AD1582/
AD1583/
AD1584/
AD1585
Figure 3. 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.
The error band guaranteed with the AD1582/AD1583/AD1584/
AD1585 family is the maximum deviation from the initial value at
25
°C. 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 +125°C.
Figure 4 shows the typical output voltage drift for the AD1582
and illustrates the methodology. The box in Figure 4 is bounded on
the x-axis by operating temperature extremes. It is bounded
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 +125
°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 produces curves similar to those in TPC 3 and Figure 4,
but output readings may vary depending upon the test methods
and test equipment used.
TEMPERATURE ( C)
–40
–20
0
20
40
60
80
100
120
2.504
2.502
2.496
2.494
2.492
2.500
2.498
Figure 4. Output Voltage vs. Temperature


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