Datasheet

Data Sheet ADR5040/ADR5041/ADR5043/ADR5044/ADR5045
Rev. B | Page 11 of 16
THEORY OF OPERATION
The ADR504x family uses 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 charac-
teristic 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
V
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. Caution should be exercised 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 ADR504x for User-Definable Outputs
Multiple ADR504x parts 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
A
DR5045
A
DR5045
A
DR5045
V
DD
(a) (b)
06526-021
Figure 21. ±15 V Output with Stacked ADR5045 Devices