ADR381ART-REEL7 Analog Devices Inc, ADR381ART-REEL7 Datasheet - Page 12

• Manufacturer Part Number: ADR381ART-REEL7
• Description: VOLTAGE REFERENCE
• Manufacturer: Analog Devices Inc
• Series: ADR38r

Specifications of ADR381ART-REEL7

• Output Voltage: 2.5V
• Output Voltage Max: 2.5V
• Rohs Status: RoHS non-compliant
• Reference Type: Series
• Voltage - Output: 2.5V
• Tolerance: ±0.24%
• Temperature Coefficient: 25ppm/°C
• Voltage - Input: 2.8 ~ 18 V
• Number Of Channels: 1
• Current - Quiescent: 120µA
• Current - Output: 5mA
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: SOT-23-3, TO-236-3, Micro3™, SSD3, SST3
• Current - Cathode: -
• Other names: ADR381ART-REEL7; ADR381ART-REEL7TR

ADR380/ADR381
APPLICATIONS INFORMATION
STACKING REFERENCE ICs FOR ARBITRARY
OUTPUTS
Some applications may require two reference voltage sources,
which are a combined sum of standard outputs. The following
circuit shows how this stacked output reference can be
implemented:
Two ADR380s or ADR381s are used; the outputs of the individ-
ual references are simply cascaded to reduce the supply current.
Such configuration provides two output voltages: V
V
sum of this voltage and the terminal voltage of U2. U1 and U2
can be chosen for the two different voltages that supply the
required outputs.
While this concept is simple, a precaution is in order. Because
the lower reference circuit must sink a small bias current from
U2, plus the base current from the series PNP output transistor
in U2, the external load of either U1 or R1 must provide a path
for this current. If the U1 minimum load is not well-defined,
Resistor R1 should be used, set to a value that conservatively
passes 600 μA of current with the applicable V
that the two U1 and U2 reference circuits are locally treated as
macrocells, each having its own bypasses at input and output for
optimum stability. Both U1 and U2 in this circuit can source dc
currents up to their full rating. The minimum input voltage, V
determined by the sum of the outputs, V
dropout voltage of U2.
A NEGATIVE PRECISION REFERENCE WITHOUT
PRECISION RESISTORS
In many current-output CMOS DAC applications where the
output signal voltage must be of the same polarity as the
reference voltage, it is often required to reconfigure a current-
switching DAC into a voltage-switching DAC through the use
of a 1.25 V reference, an op amp, and a pair of resistors. Using
a current switching DAC directly requires an additional opera-
tional amplifier at the output to reinvert the signal. A negative
voltage reference is then desirable from the point that an additional
operational amplifier is not required for either reinversion
OUT2
Figure 27. Stacking Voltage References with the ADR380/ADR381
. V
V
IN
OUT1
0.1µF
0.1µF
C1
C3
is the terminal voltage of U1, while V
1
1
ADR380/
ADR380/
V
V
ADR381
ADR381
IN
IN
GND
GND
3
3
U2
U1
V
V
OUT
OUT
2
2
C2
1µF
C4
1µF
OUT2
OUT1
, plus the 300 mV
R1
3.9kΩ
across it. Note
V
V
OUT2
OUT2
OUT1
OUT1
is the
and
IN
Rev. C | Page 12 of 16
, is
(current-switching mode) or amplification (voltage-switching
mode) of the DAC output voltage. In general, any positive voltage
reference can be converted into a negative voltage reference
through the use of an operational amplifier and a pair of matched
resistors in an inverting configuration. The disadvantage to this
approach is that the largest single source of error in the circuit is
the relative matching of the resistors used.
The circuit in Figure 28 avoids the need for tightly matched
resistors with the use of an active integrator circuit. In this
circuit, the output of the voltage reference provides the input
drive for the integrator. The integrator, to maintain circuit
equilibrium, adjusts its output to establish the proper relation-
ship between the reference V
output voltage desired can be chosen by substituting for the
appropriate reference IC. A precaution should be noted with
this approach: although rail-to-rail output amplifiers work best
in the application, these operational amplifiers require a finite
amount (mV) of headroom when required to provide any load
current. The choice for the circuit’s negative supply should take
this issue into account.
V
PRECISION CURRENT SOURCE
Many times in low power applications, the need arises for a
precision current source that can operate on low supply voltages.
As shown in Figure 29, the ADR380/ADR381 can be configured
as a precision current source. The circuit configuration illustrated
is a floating current source with a grounded load. The reference
output voltage is bootstrapped across R
the output current into the load. With this configuration, circuit
precision is maintained for load currents in the range from the
reference supply current, typically 90 μA to approximately 5 mA.
Figure 28. Negative Precision Voltage Reference Using No Precision Resistors
IN
1µF
C1
0.1µF
V
IN
C2
1µF
C1
1
ADR380/
V
ADR381
IN
0.1µF
Figure 29. Precision Current Source
GND
3
U1
C2
V
OUT
1
2
100kΩ
V
ADR380/
ADR381
IN
R3
GND
3
OUT
U1
V
OUT
and GND. Thus, any negative
1kΩ
C3
1µF
R4
2
SET
A1
C3
1µF
ADJUST
1µF
(R1 + P1), which sets
C4
+5V
+V
–5V
–V
U2
OP195
I
SY
R1
P1
R
100Ω
I
L
OUT
R5
–V
REF