Data Sheet ADR5040/ADR5041/ADR5043/ADR5044/ADR5045
Rev. C | Page 11 of 16
THEORY OF OPERATION
The ADR5040/ADR5041/ADR5043/ADR5044/ADR5045 use
the band gap concept to produce a stable, low temperature
coefficient voltage reference suitable for high accuracy data
acquisition components and systems. The devices use the physical
nature of a silicon transistor base-emitter voltage in the forward-
biased operating region. All such transistors have approximately a
−2 mV/°C temperature coefficient (TC), making them unsuitable
for direct use as a low temperature coefficient reference.
Extrapolation of the temperature characteristic of any one of
these devices to absolute zero (with the collector current
proportional to the absolute temperature), however, reveals that
its V
BE
approaches approximately the silicon band gap voltage.
Therefore, if a voltage develops with an opposing temperature
coefficient to sum the V
BE
, a zero temperature coefficient
reference results.
APPLICATIONS INFORMATION
The ADR5040/ADR5041/ADR5043/ADR5044/ADR5045 are
a series of precision shunt voltage references. They are designed
to operate without an external capacitor between the positive
and negative terminals. If a bypass capacitor is used to filter the
supply, the references remain stable.
For a stable voltage, all shunt voltage references require an
external bias resistor (R
BIAS
) between the supply voltage and the
reference (see Figure 19). The R
BIAS
sets the current that flows
through the load (I
L
) and the reference (I
IN
). Because the load
and the supply voltage can vary, the R
BIAS
needs to be chosen
based on the following considerations:
R
BIAS
must be small enough to supply the minimum I
IN
current
to the ADR5040/ADR5041/ADR5043/ADR5044/ADR5045,
even when the supply voltage is at its minimum value and
the load current is at its maximum value.
R
BIAS
must be large enough so that I
IN
does not exceed 15 mA
when the supply voltage is at its maximum value and the
load current is at its minimum value.
Given these conditions, R
BIAS
is determined by the supply
voltage (V
S
), the ADR5040/ADR5041/ADR5043/ADR5044/
ADR5045 load and operating current (I
L
and I
IN
), and the
ADR5040/ADR5041/ADR5043/ADR5044/ADR5045 output
voltage (V
OUT
).
INL
OUT
S
BIAS
II
VV
R
(3)
I
IN
+ I
L
R
BIAS
S
V
OUT
I
L
I
IN
ADR5040/ADR5041/
ADR5043/ADR5044/
ADR5045
06526-019
Figure 19. Shunt Reference
Precision Negative Voltage Reference
The ADR5040/ADR5041/ADR5043/ADR5044/ADR5045 are
suitable for applications where a precise negative voltage is desired.
Figure 20 shows the ADR5045 configured to provide a negative
output. Exercise caution in using a low temperature sensitive
resistor to avoid errors from the resistor.
R
BIAS
V
OUT
ADR5045
–5V
06526-020
V
CC
Figure 20. Negative Precision Reference Configuration
Stacking the ADR5040/ADR5041/ADR5043/ADR5044/
ADR5045 for User-Definable Outputs
Multiple ADR5040/ADR5041/ADR5043/ADR5044/ADR5045
devices can be stacked together to allow the user to obtain a
desired higher voltage. Figure 21a shows three ADR5045 devices
configured to give 15 V. The bias resistor, R
BIAS
, is chosen using
Equation 3, noting that the same bias current flows through all the
shunt references in series. Figure 21b shows three ADR5045
devices stacked together to give −15 V. R
BIAS
is calculated in the
same manner as before. Parts of different voltages can also be
added together; that is, an ADR5041 and an ADR5045 can be
added together to give an output of +7.5 V or −7.5 V, as desired.
Note, however, that the initial accuracy error is the sum of the
errors of all the stacked parts, as are the temperature coefficient
and output voltage change vs. input current.
R
BIAS
–15V
ADR5045
ADR5045
ADR5045
–V
DD
R
BIAS
+15V
DR5045
DR5045
DR5045
DD
(a) (b)
06526-021
Figure 21. ±15 V Output with Stacked ADR5045 Devices
