ADR02 AD [Analog Devices], ADR02 Datasheet - Page 16

• Manufacturer Part Number: ADR02
• Description: Ultracompact Precision10 V/5 V/2.5 V/3.0 V Voltage References
• Manufacturer: AD [Analog Devices]

ADR01/ADR02/ADR03/ADR06
The TEMP function is provided as a convenience rather than a
precise feature. Because the voltage at the TEMP node is
acquired from the band gap core, current pulling from this pin
has a significant effect on V
TEMP output with a suitable low bias current op amp, such as
the AD8601, AD820, or OP1177, all of which would result in
less than a 100 µV change in ∆V
buffering, even tens of microamps drawn from the TEMP pin
can cause V
NEGATIVE REFERENCE
Without using any matching resistors, a negative reference can
be configured as shown in Figure 39. For the ADR01, the volt-
age difference between V
at virtual ground, U2 closes the loop by forcing the GND pin to
be the negative reference node. U2 should be a precision op
amp with a low offset voltage characteristic.
0.80
0.75
0.70
0.65
0.60
0.55
0.50
0.45
0.40
–50
1.9mV/
V
SAMPLE SIZE = 5
OUT
IN
Figure 37. Voltage at TEMP Pin vs. Temperature
5 V TO 15 V
V
= 15V
TEMP
–25
to fall out of specification.
o
C
Figure 38. Temperature Monitoring
Figure 39. Negative Reference
0
–V
U2
REF
OP1177
OUT
TEMPERATURE (
TEMP TRIM
V
15V
ADR01/
ADR02/
ADR03/
ADR06
IN
OUT
V+
V–
25
and GND is 10 V. Because V
GND
V
U1
IN
. Care must be taken to buffer the
V
OUT
OUT
50
∆V
(see Figure 38). Without
TEMP
o
V
TEMP TRIM
U2
OP1177
C)
–15V
ADR01/
ADR02/
ADR03/
ADR06
IN
+15V
GND
/∆T 1.96mV/
V+
V–
U1
75
V
OUT
100
o
C
V
O
125
OUT
is
Rev. F | Page 16 of 20
LOW COST CURRENT SOURCE
Unlike most references, the ADR01/ADR02/ADR03/ADR06
employ an NPN Darlington in which the quiescent current
remains constant with respect to the load current, as shown in
Figure 24. As a result, a current source can be configured as
shown in Figure 40 where I
the sum of I
0.55 to 0.65 mA, limiting this circuit to general-purpose
applications.
PRECISION CURRENT SOURCE WITH
ADJUSTABLE OUTPUT
A precision current source, on the other hand, can be
implemented with the circuit shown in Figure 41. By adding a
mechanical or digital potentiometer, this circuit becomes an
adjustable current source. If a digital potentiometer is used, the
load current is simply the voltage across terminals B to W of the
digital potentiometer divided by R
where D is the decimal equivalent of the digital potentiometer
input code.
I
L
+12 V
=
V
Figure 41. Programmable 0 to 5 mA Current Source
SET
REF
R
ADR01/
ADR02/
ADR03/
ADR06
SET
and I
×
V
TEMP TRIM
GND
V
ADR01/
ADR02/
ADR03/
ADR06
Figure 40. Low Cost Current Source
IN
D
IN
GND
I
Q
U1
Q
–5V TO V
. Although simple, I
V
V
I
OUT
OUT
IN
0.6mA
L
AD5201
0V TO (5V + V
SET
U2
OP1177
R
100kΩ
–12V
+12V
SET
R
= (V
V+
V–
L
A
B
SET
OUT
V
W
L
.
L
)
I
I
L
SET
– V
= I
R
Q
= 10V/R
SET
SET
R
L
varies typically from
)/R
L
+ I
1kΩ
1kΩ
Q
SET
SET
V
. I
L
L
I
L
is simply
(1)