ADR370 Analog Devices, Inc., ADR370 Datasheet - Page 8

• Manufacturer Part Number: ADR370
• Description: Precision Low Power 2.048 V Sot-23 Voltage Reference
• Manufacturer: Analog Devices, Inc.

ADR370
THEORY OF OPERATION
The ADR370 uses the band gap concept to produce a stable, low
temperature coefficient voltage reference suitable for high
accuracy data acquisition components and systems. This device
makes use of underlying temperature characteristics of a silicon
transistor’s base-emitter voltage (V
operating region. Under this condition, all such transistors have
a −2 mV/°C temperature coefficient (TC) and a V
extrapolated to absolute zero, 0 K, (with collector current
proportional to absolute temperature) approximates the silicon
band gap voltage. By summing a voltage that has an equal and
opposite temperature coefficient of 2 mV/°C with a V
forward-biased transistor, an almost zero TC reference can be
developed. The simplified circuit diagram in
how a compensating voltage, V1, is achieved by driving two
transistors at different current densities and amplifying the
resulting V
sum (V
produce a stable reference voltage of 2.048 V at the output.
R3
R2
R1
BG
) of V
BE
difference (ΔV
V1
BE
and V1 is then buffered and amplified to
Figure 12. Simplified Schematic
R4
BE
, which has a positive TC). The
BE
) in the forward-biased
Figure 12 shows
R5
V
R6
DS
BE
V
V
GND
that, when
OUT
IN
BE
of a
Rev. B | Page 8 of 12
APPLYING THE ADR370
To achieve the specified performance, two external components
should be used in conjunction with the ADR370: a 4.7 μF
capacitor and a 1 μF capacitor. The 4.7 μF capacitor should be
applied to the input, and the 1 μF capacitor should be applied to
the output. Figure 13 shows the ADR370 with both the input
and output capacitors attached.
For further transient response optimization, an additional 0.1 μF
capacitor in parallel with the 4.7 μF input capacitor can be used.
A 1 μF output capacitor provides stable performance for all
loading conditions. The ADR370 can, however, operate under
low (−100 μA < I
0.2 μF output capacitor and a 1 μF input capacitor.
Figure 13. Typical Connection Diagram
OUT
C
4.7µF
C
1µF
IN
OUT
< +100 μA) current conditions with just a
V
V
IN
OUT
ADR370
GND