Data Sheet
ADR5040/ADR5041/ADR5043/ADR5044/ADR5045
THEORY OF OPERATION
V
S
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 VBE approaches approximately the
silicon band gap voltage. Therefore, if a voltage develops with
an opposing temperature coefficient to sum the VBE, a zero
temperature coefficient reference results.
R
I
+ I
L
BIAS
IN
V
OUT
I
L
I
IN
ADR5040/ADR5041/
ADR5043/ADR5044/
ADR5045
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.
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.
ADR5045
V
OUT
–5V
R
BIAS
For a stable voltage, all shunt voltage references require an
external bias resistor (RBIAS) between the supply voltage and the
reference (see Figure 19). The RBIAS sets the current that flows
through the load (IL) and the reference (IIN). Because the load
and the supply voltage can vary, the RBIAS needs to be chosen
based on the following considerations:
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,
RBIAS must be small enough to supply the minimum IIN current
R
BIAS, is chosen using Equation 3, noting that the same bias 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.
flows through all the shunt references in series. Figure 21b shows
three ADR5045 devices stacked together to give −15 V. RBIAS 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.
RBIAS must be large enough so that IIN 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, RBIAS is determined by the supply
voltage (VS), the ADR5040/ADR5041/ADR5043/ADR5044/
ADR5045 load and operating current (IL and IIN), and the
ADR5040/ADR5041/ADR5043/ADR5044/ADR5045 output
voltage (VOUT).
V
DD
R
ADR5045
ADR5045
ADR5045
BIAS
VS VOUT
RBIAS
(3)
+15V
IL IIN
ADR5045
ADR5045
ADR5045
–15V
R
BIAS
–V
DD
(a)
(b)
Figure 21. 15 V Output with Stacked ADR5045 Devices
Rev. B | Page 11 of 16
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