ADR370 Analog Devices, Inc., ADR370 Datasheet - Page 10

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

ADR370
12-BIT PRECISION PROGRAMMABLE CURRENT
SOURCE
By replacing the potentiometer in Figure 17 with a 12-bit
precision DAC, such as the AD5322, a higher precision
programmable current source can be achieved. Figure 18
illustrates the implementation of this circuit. The load current
can be determined with the following equation:
The compliance voltage should be kept low so that the supply
voltage to U2, between V
+5V
I
L
U1
V
=
IN
ADR370
V
R
SET
REF
Figure 18. 12-Bit Programmable Current Source
GND
(
×
1
V
+5V
4096
−
OUT
D
)
DD
U2
V
DD
and GND, does not fall below 2.5 V.
GND
V
IN
OP1177
V
O
VREF (1 – D2/N)
1
AD5322
U3
+5V
–5V
V+
V–
11
2
3
R
L
R
TOL ±0.05%
SET
I
L
V
L
Rev. B | Page 10 of 12
(6)
PRECISION BOOSTED OUTPUT REGULATOR
A precision voltage output with boosted current can be realized
with the circuit shown in Figure 19. In this circuit, V
maintained by the ADR370 at 2.048 V.
The ADR370 sources a maximum of 5 mA if the load current (I
is more than 5 mA, and if the current is furnished by the
transistor (Q1) and the input voltage supply (V
Q1 is turned on to regulate current as needed. R1 is required to
bias the base of Q1 and must be large enough to comply with
the supply current requirements of the ADR370. The supply
voltage can be as low as 4 V.
The maximum current output of this circuit is limited by the
power dissipation of the bipolar transistor, Q1.
Using the 2N3906 PNP transistor shown in
power supply (R
100 mA is drawn from the circuit, which limits the power
dissipation of Q1 to ~200 mW.
P
DISS
= (V
V
DD
10kΩ
Figure 19. Precision Boosted Output Regulator
DD
R1
L
− 2.048) × I
) should be chosen so that a maximum of
4V TO 12V
V
IN
ADR370
L
GND
V
OUT
R
Q1
Figure 19
L
2N3906
DD
).
I
L
O
and a 4 V
is
(7)
L
)