ADR121 Analog Devices, Inc., ADR121 Datasheet - Page 17

• Manufacturer Part Number: ADR121
• Description: Precision, Micropower Ldo Voltage References In Tsot
• Manufacturer: Analog Devices, Inc.

APPLICATIONS
BASIC VOLTAGE REFERENCE CONNECTION
The circuit in Figure 4 illustrates the basic configuration for the
ADR12x family voltage reference.
STACKING REFERENCE ICs FOR ARBITRARY
OUTPUTS
Some applications may require two reference voltage sources
that are a combined sum of the standard outputs. Figure 50
shows how this stacked output reference can be implemented.
Two reference ICs are used and fed from an unregulated input,
V
which provide two output voltages, V
terminal voltage of U1, while V
and the terminal of U2. U1 and U2 are chosen for the two
voltages that supply the required outputs (see Table 6). For
example, if U1 and U2 are ADR127 and V
1.25 V and V
IN
. The outputs of the individual ICs are connected in series,
INPUT
Figure 49. Basic Configuration for the ADR12x Family
OUT2
INPUT
Figure 50. Stacking References with ADR12x
+
0.1µF
is 2.5 V.
+
+
0.1µF
0.1µF
1
2
3
NC
GND
V
IN
1
2
3
1
2
3
ADR12x
NC
GND
V
NC
GND
V
IN
IN
ADR12x
ADR12x
OUT2
V
OUT
NC
NC
V
V
is the sum of this voltage
OUT
OUT
NC
NC
NC
NC
6
5
4
OUT1
6
5
4
6
5
4
+
and V
IN
0.1µF
OUTPUT
≥ 3.95 V, V
+
+
OUTPUT1
OUTPUT2
0.1µF
0.1µF
OUT2
. V
OUT1
OUT1
is the
is
Rev. 0 | Page 17 of 20
Table 6. Required Outputs
U1/U2
ADR127/ADR121
ADR127/ADR125
ADR121/ADR125
NEGATIVE PRECISION REFERENCE WITHOUT
PRECISION RESISTORS
A negative reference is easily generated by adding an op amp,
A1, and is configured as shown in Figure 51. V
ground and, therefore, the negative reference can be taken
directly from the output of the op amp. The op amp must be
dual-supply, low offset, and rail-to-rail if the negative supply
voltage is close to the reference output.
GENERAL-PURPOSE CURRENT SOURCE
In low power applications, the need can arise for a precision
current source that can operate on low supply voltages. The
ADR12x can be configured as a precision current source (see
Figure 52). The circuit configuration shown is a floating current
source with a grounded load. The reference’s output voltage is
bootstrapped across R
load. With this configuration, circuit precision is maintained for
load currents ranging from the reference’s supply current,
typically 85 μA, to approximately 5 mA.
–V
+V
+V
REF
DD
DD
Figure 52. ADR12x Trim Configuration
Figure 51. Negative Reference
SET
1
2
3
ADR121/ADR125/ADR127
, which sets the output current into the
NC
GND
V
IN
ADR12x
AD8603
1
2
3
–V
I
SY
NC
GND
V
V+
V–
DD
IN
ADR127
V
–
+
OUT
V
1.25 V
1.25 V
2.5 V
NC
NC
OUT2
2
3
0.1µF
6
5
4
V
R1
RL
OUT
NC
NC
1kŸ
P1
6
5
4
I
SET
OUT1
is at virtual
V
3.75 V
6.25 V
7.5 V
OUT1