AD1582 Analog Devices, AD1582 Datasheet - Page 9

• Manufacturer Part Number: AD1582
• Description: 2.5V Micropower, Precisions Series Mode Voltage References
• Manufacturer: Analog Devices

THEORY OF OPERATION
The AD1582/AD1583/AD1584/AD1585 family uses the
“bandgap” concept to produce stable, low temperature coefficient
voltage references 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 V
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
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 V
a positive TC). The sum (V
and amplified to produce stable reference voltage outputs of
2.5 V, 3 V, 4.096 V, and 5 V.
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 3 shows the AD1582 config-
ured 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 will achieve specified perfor-
mance 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. While a 1 µF output capacitor will provide stable
performance for all loading conditions, the AD1582 can operate
under low (–100 µA < I
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.
V
BE
R3
R2
R1
+
–
V1
+
–
OUT
R4
BG
< 100 µA) current conditions with
) of V
BE
difference (∆V
BE
and V1 is then buffered
BE
BE
R5
R6
V
—which has
BG
BE
of a forward-
that, when
V
GND
V
OUT
IN
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 guaran-
teed to be 2.5 V ± 10 mV from –40°C to +85°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, 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 TPC 3 and Fig-
ure 4, but output readings may vary depending upon the test
methods and test equipment utilized.
AD1582/AD1583/AD1584/AD1585
2.510
2.509
2.508
2.507
2.506
2.505
2.504
2.503
2.502
2.501
–60
V
IN
4.7 F
–40
–20
3
0
TEMPERATURE – C
AD1582/
AD1583/
AD1584/
AD1585
20
40
1
2
1 F
60
80
V
OUT
+
–
100
120