Datasheet

Data Sheet ADR4520/ADR4525/ADR4530/ADR4533/ADR4540/ADR4550
Rev. 0 | Page 31 of 32
APPLICATIONS INFORMATION
BASIC VOLTAGE REFERENCE CONNECTION
The circuit shown in Figure 94 illustrates the basic configuration
for the ADR4520/ADR4525/ADR4530/ADR4533/ADR4540/
ADR4550 family of voltage references.
Figure 94. ADR4520/ADR4525/ADR4530/ADR4533/ADR4540/ADR4550
Simplified Schematic
INPUT AND OUTPUT CAPACITORS
Input Capacitors
A 1 μF to 10 μF electrolytic or ceramic capacitor can be connected
to the input to improve transient response in applications where
the supply voltage may fluctuate. An additional 0.1 μF ceramic
capacitor should be connected in parallel to reduce supply noise.
Output Capacitors
An output capacitor is required for stability and to filter out low
level voltage noise. The minimum value of the output capacitor
is shown in Table 12.
Table 12. Minimum C
OUT
Value
Part Number Minimum C
OUT
Value
ADR4520, ADR4525 1.0 µF
ADR4530, ADR4533,
ADR4540, ADR4550
0.1 µF
An additional 1 μF to 10 μF electrolytic or ceramic capacitor can be
added in parallel to improve transient performance in response to
sudden changes in load current; however, the designer should keep
in mind that doing so will increase the turn-on time of the device.
LOCATION OF REFERENCE IN SYSTEM
The ADR4520/ADR4525/ADR4530/ADR4533/ADR4540/
ADR4550 reference should be placed as close to the load as possible
to minimize the length of the output traces and, therefore, the error
introduced by the voltage drop. Current flowing through a PCB
trace produces an IR voltage drop; with longer traces, this drop
can reach several millivolts or more, introducing considerable
error into the output voltage of the reference. A 1 inch long, 5 mm
wide trace of 1 ounce copper has a resistance of approximately
100 mΩ at room temperature; at a load current of 10 mA, this
can introduce a full millivolt of error.
SAMPLE APPLICATIONS
Bipolar Output Reference
Figure 95 shows a bipolar reference configuration. By connecting
the output of the ADR4550 to the inverting terminal of an
operational amplifier, it is possible to obtain both positive and
negative reference voltages. R1 and R2 must be matched as closely
as possible to ensure minimal difference between the negative
and positive outputs. Resistors with low temperature coefficients
must also be used if the circuit is used in environments with large
temperature swings; otherwise, a voltage difference develops
between the two outputs as the ambient temperature changes.
Figure 95. ADR4550 Bipolar Output Reference
Boosted Output Current Reference
Figure 96 shows a configuration for obtaining higher current
drive capability from the ADR4520/ADR4525/ADR4530/
ADR4533/ADR4540/ADR4550 references without sacrificing
accuracy. The op amp regulates the current flow through the
MOSFET until V
OUT
equals the output voltage of the reference;
current is then drawn directly from V
IN
instead of from the
reference itself, allowing increased current drive capability.
Figure 96. Boosted Output Current Reference
Because the current-sourcing capability of this circuit depends only
on the I
D
rating of the MOSFET, the output drive capability can
be adjusted to the application simply by choosing an appropriate
MOSFET. In all cases, the V
OUT
pin should be tied directly to the
load device to maintain maximum output voltage accuracy.
10203-054
V
IN
GND
V
REF
BAND GAP
V
IN
+15V
–15V
–5V
+5V
ADA4000-1
0.1µF1µF
0.1µF
R1
10kΩ
R2
10kΩ
R3
5kΩ
ADR4550
V
IN
V
OUT
GND
2
6
4
10203-055
10203-056
C
L
C
L
0.1µF
2N7002
AD8663
V
IN
U6
V
OUT
+16V
0.1µF1µF
R1
100Ω
R
L
200Ω
ADR4520/ADR4525/
ADR4530/ADR4533/
ADR4540/ADR4550
V
IN
V
OUT
GND
2 6
4
PART
NUMBER
MINIMUM
C
L
ADR4520,
ADR4525
1.0µF
ADR4530,
ADR4533,
ADR4540,
ADR4550
0.1µF