Datasheet

REF03
Rev. G | Page 7 of 12
APPLICATIONS
The REF03 provides a stable 2.5 V output voltage with minimal
dependence on load current, line voltage, or temperature. This
voltage is typically used to set an absolute reference point in
data conversion circuits, or in analog circuits such as log amps,
4 mA to 20 mA transmitters, and power supplies. The REF03 is
of particular value in systems requiring a precision reference
using a single 5 V supply rail.
Because an on-board operational amplifier is used to amplify
the basic band gap cell voltage to 2.5 V, supply decoupling is
critical to the transient performance of a voltage reference. The
supply line should be bypassed with a 10 µF tantalum capacitor
in parallel with a 0.01 µF to 0.1 µF ceramic capacitor for best
results, as shown in
Figure 15. The bypass capacitors should
be located as close to the reference as possible. Inadequate
bypassing can lead to instabilities.
Output bypass capacitors are not generally recommended. If
necessary for high frequency output impedance reduction, the
capacitance value used should be at least 1 µF.
If the V
TEMP
and TRIM pins are not in use, then they should be
left floating. However, when V
TEMP
is being used for temperature
compensation, it must be connected to a very high impedance
node in the circuit, such as a noninverting input of a buffer.
00372-015
V
TEMP
V
IN
GND
V
OUT
REF03
NC
NC
NC
TRIM
GND
0.1µF10µF
INPUT VOLTAGE
OUTPUT VOLTAGE
Figure 15. Basic Connections
GENERATING AN ADJUSTABLE BIPOLAR
VOLTAGE REFERENCE
There is often a requirement for an adjustable bipolar reference.
A simple method of generating such a reference is to connect
the output of the REF03 to an op amp in an adjustable gain
configuration, as shown in
Figure 16. The trimmable resistor
is then used to generate the desired output voltage from −2.5 V
to +2.5 V.
00372-016
REF03
V
IN
GND
V
+
V+
2
3
4
6
7
+15V
50kΩ
2
4
6
V
OUT
OP97
50kΩ
50kΩ
V
OUT
–2.5V TO +2.5V
Figure 16. Adjustable Bipolar Reference
GENERATING A −2.5 V REFERENCE
Often, there is a requirement for a negative reference voltage.
The simplest method of generating a −2.5 V reference with the
REF03 is to connect an op amp in a gain of −1 to the output, as
shown in
Figure 17. This provides both positive and negative
2.5 V references.
Figure 18 shows another method of obtaining
a negative reference, in which the current-output element is a
PNP transistor, with the REF03 in a servo loop to ensure that
the output remains 2.5 V below ground.
00372-017
REF03
V
IN
GND
V
+
V–
2
3
4
6
7
2
4
6
V
OUT
OP97
100kΩ
–2.5V
+2.5V
100kΩ
Figure 17. ±2.5 V Reference
00372-018
REF03
V
IN
GND
2
4
6
V
OUT
1kΩ
2kΩ
+5
V
–2.5V
–5V
2N2905
+6.2V
Figure 18. −2.5 V Reference