Datasheet

ADR01/ADR02/ADR03/ADR06 Data Sheet
Rev. R | Page 16 of 20
12525 50 75 100
0.40
0.80
0.75
0.70
0.65
0.60
0.55
0.50
0.45
–25
0–50
V
IN
= 15V
SAMPLE SIZE = 5
V
TEMP
(V)
TEMPERATURE (°C)
Δ
V
TEMP
/ΔT ≈ 1.96mV/°C
02747-037
Figure 36. Voltage at TEMP Pin vs. Temperature
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
OUT
. Care must be taken to buffer the
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 ∆V
OUT
(see Figure 37). Without buffering,
even tens of microamps drawn from the TEMP pin can cause
V
OUT
to fall out of specification.
U2
15V
U1
ADR01/
ADR02/
ADR03/
ADR06
V
IN
V
OUT
TEMP
TRIM
GND
V
O
V–
V+
OP1177
V
TEMP
1.9mV/°C
V
IN
02747-038
Figure 37. Temperature Monitoring
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 23. As a result, a current source can be configured as
shown in Figure 38 where I
SET
= (V
OUT
− V
L
)/R
SET
. I
L
is simply
the sum of I
SET
and I
Q
. Although simple, I
Q
varies typically from
0.55 mA to 0.65 mA, limiting this circuit to general-purpose
applications.
ADR01/
ADR02/
ADR03/
ADR06
V
OUT
GND
V
IN
I
IN
I
SET
= (V
OUT
– V
L
)/R
SET
R
SET
I
Q
≈ 0.6mA
I
L
= I
SET
+ I
Q
V
L
R
L
02747-040
Figure 38. Low Cost Current Source
PRECISION CURRENT SOURCE WITH
ADJUSTABLE OUTPUT
Alternatively, a precision current source can be implemented
with the circuit shown in Figure 39. 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
SET
.
SET
REF
L
R
DV
I
×
=
(1)
where D is the decimal equivalent of the digital potentiometer
input code.
U2
+12V
–12V
W
B
A
U1
ADR01/
ADR02/
ADR03/
ADR06
V
IN
V
OUT
TEMP
TRIM
GND
V–
V+
OP1177
–5V TO V
L
AD5201
0V TO (5V + V
L
)
+12V
R
SET
1kΩ
R
L
I
L
V
L
1kΩ
100kΩ
02747-041
Figure 39. Programmable 0 mA to 5 mA Current Source
To optimize the resolution of this circuit, dual-supply op amps
should be used because the ground potential of ADR02 can
swing from −5.0 V at zero scale to V
L
at full scale of the
potentiometer setting.