ADR827 Analog Devices, ADR827 Datasheet - Page 18

• Manufacturer Part Number: ADR827
• Description: 1.25V Low Power, Precision Reference and Op Amp
• Manufacturer: Analog Devices

Specifications of ADR827

• -3db Bandwidth: 1MHz
• Slew Rate: 0.5V/µs
• Vos: 100µV
• Ib: 10nA
• # Opamps Per Pkg: 1
• Input Noise (nv/rthz): 16nV/rtHz
• Vcc-vee: 2.7V to 30V
• Isy Per Amplifier: n/a
• Packages: SOP

ADR821/ADR827
APPLICATIONS INFORMATION
+2.5 V AND −2.5 V OUTPUTS (ADR821)
In many dual-supply applications, it is desirable to have ±2.5 V
references. Using the configuration shown in Figure 38, it is
possible to generate −2.5 V with the help of a +2.5 V reference,
an internal op amp, and 10 kΩ resistors. The supply voltages V+
and V− should be greater than +2.8 V and −2.8 V, respectively.
The op amp is configured as an inverting amplifier with a gain
of −1, which produces −2.5 V at the output of the op amp. The
output of the reference is fed to the amplifier inverting input.
Because the op amp has very low input offset voltage (500 μV
over the full temperature range) and the TC ratio of the
resistors is typically ±25 ppm/°C, the −2.5 V output is less than
7 mV away from the theoretical value.
2.5 V AND 5.0 V OUTPUTS (ADR821)
In many single-supply applications, it is desirable to have
multiple reference voltages. Using the configuration shown in
Figure 39, it is possible to generate 5.0 V with the help of a
2.5 V reference, an internal op amp, and resistors. V+ should
be kept at greater than 5.8 V and V− can be connected either
to ground or to negative supply. The output of the reference is
V+
V+
R
R
1
1
+IN
Figure 38. +2.5 V and −2.5 V Outputs
+IN
10kΩ
10kΩ
Figure 39. 2.5 V and 5.0 V Outputs
–IN
V–
V–
REF
REF
10kΩ
10kΩ
AMP_OUT
AMP_OUT
REF_OUT
REF_OUT
R
R
0.1µF
0.1µF
2
2
+2.5V
5.0V
–2.5V
2.5V
Rev. 0 | Page 18 of 20
fed to the amplifier noninverting input. The op amp is config-
ured as a noninverting amplifier with a gain of +2, which
produces 5 V at the output of the op amp. Using the guaranteed
maximum offset voltage over the temperature, and the typical
TC ratio of the resistors over the full temperature range, the
output is within 15 mV of the calculated value.
MULTIPLE 2.5 V OUTPUTS (ADR821)
On some boards, sensitive analog circuits, such as a VCO, exist
with noisy digital circuits. If the supply current requirements
are low (less than 3 mA), series references and op amps can be
used. Using the configuration shown in Figure 40, two different
2.5 V supplies can be created using a single ADR821. The supply
voltage V+ should be greater than 2.8 V and V− can be con-
nected to ground or a negative voltage. The op amp is configured
as a voltage follower with a gain of +1, which produces 2.5 V at
the output of the op amp. The output of the reference is fed
to the amplifier noninverting input. Because the op amp has
very low input offset voltage (500 μV maximum over the full
temperature range), the output voltage from the op amp section
tracks the reference voltage within 1 mV. For a dynamic load,
such as the reference input pin on some analog-to-digital
converters, the load should be connected to an op amp output
and the noise sensitive circuitry, such as a VCO, should be
connected to the reference output. If the dynamic load is con-
nected to the reference voltage, any perturbations appear as a
signal to the input of the voltage follower and appear on the
other output.
V+
R
1
+IN
10kΩ
Figure 40. Multiple 2.5 V Outputs
–IN
V–
REF
10kΩ
AMP_OUT
REF_OUT
0.1µF
2.5V
2.5V
R
2