ADR01 Analog Devices, Inc., ADR01 Datasheet - Page 16

• Manufacturer Part Number: ADR01
• Description: Ultracompact Precision10 V/5 V/2.5 V/3.0 V Voltage References
• Manufacturer: Analog Devices, Inc.

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 result in less than
a 100 μV change in ΔV
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
voltage difference between V
V
GND pin to be the negative reference node. U2 should be a
precision op amp with a low offset voltage characteristic.
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 mA to 0.65 mA, limiting this circuit to general-purpose
applications.
OUT
OUT
to fall out of specification.
is at virtual ground, U2 closes the loop by forcing the
0.80
0.75
0.70
0.65
0.60
0.55
0.50
0.45
0.40
–50
1.9mV/°C
V
SAMPLE SIZE = 5
V
SET
IN
Figure 37. Voltage at TEMP Pin vs. Temperature
TEMP
= 15V
and I
–25
Figure 38. Temperature Monitoring
Q
. Although simple, I
U2
OUT
0
OP1177
15V
TEMPERATURE (°C)
(see Figure 38). Without buffering,
V+
V–
SET
OUT
V
OUT
25
IN
= (V
. Care must be taken to buffer the
and GND is 10.0 V. Because
OUT
50
ΔV
V
TEMP TRIM
ADR01/
ADR02/
ADR03/
ADR06
IN
− V
TEMP
GND
U1
Q
V
L
/ΔT 1.96mV/°C
varies typically from
OUT
)/R
75
SET
. I
100
V
L
O
is simply
125
Rev. J | Page 16 of 24
PRECISION CURRENT SOURCE WITH
ADJUSTABLE OUTPUT
Alternatively, a precision current source 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 Terminal B to Terminal W of the
digital potentiometer divided by R
where D is the decimal equivalent of the digital potentiometer
input code.
I
L
+12V
=
Figure 41. Programmable 0 mA to 5 mA Current Source
V
+5V TO +15V
ADR01/
ADR02/
ADR03/
ADR06
REF
R
SET
GND
×
V
V
TEMP TRIM
IN
Figure 40. Low Cost Current Source
ADR01/
ADR02/
ADR03/
ADR06
D
IN
I
GND
Figure 39. Negative Reference
Q
V
U1
–5V TO V
I
OUT
≈ 0.6mA
IN
V
OUT
–V
REF
R
V
TEMP TRIM
L
AD5201
0V TO (5V + V
ADR01/
ADR02/
ADR03/
ADR06
IN
SET
R
U2
OP1177
100k Ω
L
–12V
GND
+12V
U1
V+
V–
V
B
A
OUT
V
SET
L
I
I
SET
L
.
W
= I
L
U2
)
OP1177
= (V
SET
–15V
+15V
V+
V–
R
OUT
+ I
SET
R
Q
L
– V
1k Ω
1k Ω
L
)/R
V
SET
L
I
L
(1)