AD580
THEORY OF OPERATION
The AD580 family (AD580, AD581, AD584, AD589) uses the
+V IN
R8
R7
bandgap concept to produce a stable, low temperature coef-
ficient voltage reference suitable for high accuracy data acqui-
I 2 ? I 1
V OUT = V Z 1 +
R 4
R 5
= 2.5V
sition components and systems. The device makes use of the
underlying physical nature of a silicon transistor base-emitter
Q2
8A
Q1
A
R4
V Z = V BE + V 1
voltage in the forward-biased operating region. All such tran-
? V BE
R2
V BE (Q1)
R5
= V BE + 2
R 1
R 2
? V BE
ln 1
sistors have approximately a –2 mV/°C temperature coefficient,
unsuitable for use directly as a low TC reference. Extrapolation
of the temperature characteristic of any one of these devices to
2I 1 = I 1 + I 2
COM
R1
V 1 = 2
R 1
R 2
? V BE
= V BE + 2
= 1.205V
R 1 kT
R 2 q
J
J 2
absolute zero (with an emitter current propor-tional to the
absolute temperature), however, reveals that it will go to a V BE of
1.205 V at 0 K, as shown in Figure 3. Thus, if a voltage could be
Figure 4. Basic Bandgap-Reference Regulator Circuit
+E
developed with an opposing temperature coefficient to sum
with V BE to total 1.205 V, a 0 TC reference would result and
operation from a single, low voltage supply would be possible.
The AD580 circuit provides such a compensating voltage, V1 in
Q14
R12
R13
Q13
Q4
Figure 4, by driving two transistors at different current densities
and amplifying the resulting V BE difference (?V BE —which now
R8
R7
Q3
R6
Q7
has a positive TC). The sum, V Z , is then buffered and amplified
up to 2.5 V to provide a usable reference-voltage output. Figure
Q10
Q11
Q12
Q6
5 shows the schematic diagram of the AD580.
The AD580 operates as a 3-terminal reference, meaning that no
Q8
Q2
R3
Q9
Q1
Q15
C1
Q5
R10
R9
R4
2.5V
OUT
additional components are required for biasing or current
8A
A
setting. The connection diagram, Figure 6, is quite simple.
R2
R11
R5
R1
1.5
CONSTANT SUM = 1.205V
COM
–E
Figure 5. Schematic Diagram
1.205
1.0
FOR BOTH
DEVICES
4.5 ≤ V IN ≤ 30V
AD580
+E
E OUT
0.5
V BE VS. TEMPERATURE
FOR TWO TYPICAL
DEVICES (I E α T)
–E
LOAD
REQUIRED
COMPENSATION
Figure 6. Connection Diagram
0
–273 ° C
0K
–200 ° C
73K
–100 ° C
173K
VOLTAGE–
SAME DEVICES
0 ° C
273K
100 ° C
373K
VOLTAGE VARIATION VERSUS TEMPERATURE
Some confusion exists in the area of defining and specifying
TEMPERATURE
Figure 3. Extrapolated Variation of Base-Emitter Voltage with Temperature
(I E αT), and Required Compensation, Shown for Two Different Devices
reference voltage error over temperature. Historically, references
are characterized using a maximum deviation per degree
Centigrade; i.e., 10 ppm/°C. However, because of the
inconsistent nonlinearities in Zener references (butterfly or S
type characteristics), most manufacturers use a maximum limit
error band approach to characterize their references. This
technique measures the output voltage at 3 to 5 different
temperatures and guarantees that the output voltage deviation
will fall within the guaranteed error band at these discrete
temperatures. This approach, of course, makes no mention or
guarantee of performance at any other temperature within the
operating temperature range of the device.
Rev. B | Page 5 of 8
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