ADR318 Analog Devices, Inc., ADR318 Datasheet - Page 10

• Manufacturer Part Number: ADR318
• Description: Precision Low Drift Sot-23 Voltage Reference With Shutdown
• Manufacturer: Analog Devices, Inc.

ADR318
APPLICATIONS
BASIC VOLTAGE REFERENCE CONNECTION
The circuit in Figure 18 illustrates the basic configuration for
the ADR318. Decoupling capacitors are not required for circuit
stability. The ADR318 is capable of driving capacitative loads
from 0 μF to 10 μF. However, a 0.1 μF ceramic output capacitor
is recommended to absorb and deliver the charge as is required
by a dynamic load.
PRECISION NEGATIVE VOLTAGE REFERENCE
WITHOUT PRECISION RESISTORS
A negative reference can be easily generated by combining the
ADR318 with an op amp. Figure 19 shows this simple negative
reference configuration. V
and therefore the negative reference can be taken directly from
the output of the op amp. The op amp should be a dual-supply,
low offset, rail-to-rail amplifier, such as the OP1177.
SHUTDOWN
INPUT
Figure 18. Voltage Reference Connection
0.1µF
–V
C
I
SS
Figure 19. Negative Reference
OP1177
OUT(F)
SHDN
V
V
IN
OUT(S)
V
V
ADR318
OUT(F)
OUT(S)
and V
ADR318
+V
GND
V
V
IN
DD
OUT(F)
GND
OUT(S)
SHDN
0.1µF
C
are at virtual ground
O
–VREF
OUTPUT
Rev. A | Page 10 of 12
GENERAL-PURPOSE 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 20, the ADR318 can be configured
as a precision current source. The illustrated circuit
configuration is a floating current source with a grounded load.
The reference output voltage is bootstrapped across R1 that sets
the output current into the load. With this configuration, circuit
precision is maintained for load currents in the range of the
reference supply current, typically 90 mA, to approximately 5 mA.
The supply current is a function of I
a given I
HIGH POWER PERFORMANCE WITH CURRENT LIMIT
In some cases, the user may want higher output current
delivered to a load and still achieve better than 0.5% accuracy
out of the ADR318. The accuracy for a reference is normally
specified with no load (see the Specifications section). However,
the output voltage changes with the load current.
The circuit in Figure 21 provides high current without
compromising the accuracy of the ADR318. The power bipolar
junction transistor (BJT) Q1 provides the required current, up
to 1 A. The ADR318 delivers the base drive to Q1 through the
force pin. The sense pin of the ADR318 is a regulated output
and is connected to the load.
SET
.
Figure 20. General-Purpose Current Source
SHDN
ADR318
+V
GND
V
U1
IN
DD
V
V
I
SY
OUT(F)
OUT(S)
(I
SET
0.1µF
)
R
L
ADJ
SET
I
R1
SY
I
OUT
and increases slightly at
= I
I
SET
SET
+ I
SV
(I
SET
)