REF01/REF02/REF03
Rev. K | Page 15 of 20
TEMPERATURE MONITORING
In addition to the optional TRIM function, the REF0x series of
references provides the ability to monitor changes in temper-
ature by way of tracking the voltage present at the TEMP pin.
The output voltage of this pin is taken directly from the band
gap core and, as a result, varies linearly with temperature. The
nominal voltage at the TEMP pin (V
TEMP
) is approximately
550 mV at 25°C, with a temperature coefficient (TCV
TEMP
) of
approximately 1.96 mV/°C. Refer to Figure 32 for a graph of
output voltage vs. temperature.
As an example, given these ideal values, a voltage change of
39.2 mV at the TEMP pin corresponds to a 20°C change in
temperature.
The TEMP function is provided as a convenience, rather than a
precise feature, of the reference. In addition, because the voltage
at the TEMP pin is taken directly from the band gap core, any
current injected into or pulled from this pin has a significant
effect on V
OUT
. As such, even tens of microamps drawn from the
TEMP pin can cause the output to fall out of regulation. Should
the designer wish to take advantage of this feature, it is neces-
sary to buffer the output of the TEMP pin with a low bias
current op amp, such as the AD8601 or AD8641. Any of these
op amps, if used as shown in Figure 36, causes less than a
100 µV change in V
OUT
.
U2
15V
U1
V
IN
V
OUT
TEMP TRIM
GND
V
O
V–
V+
AD8641
V
TEMP
1.9mV/°C
V
IN
00375-036
REF01/
REF02/
REF03
Figure 36. Temperature Monitoring
LONG-TERM STABILITY
One of the key parameters of the REF0x series of references is
long-term stability. Regardless of output voltage, internal testing
during development showed a typical drift of approximately
50 ppm after 1,000 hours of continuous, nonloaded operation
in a +25°C environment.
It is important to understand that long-term stability is not
guaranteed by design, and that the output from the device may
shift beyond the typical 50 ppm specification at any time, especially
during the first 200 hours of operation. For systems that require
highly stable output over long periods of time, the designer should
consider burning-in the devices prior to use to minimize the
amount of output drift exhibited by the reference over time. Refer
to the AN-713 Application Note for more information regarding
the effects of long-term drift and how it can be minimized.
BURN-IN
Burn-in, wherein the part is powered and allowed to operate
normally for an extended period of time, can be useful for
minimizing the effects of long-term drift. A sample burn-in
circuit is shown below in Figure 37.
00375-037
V
IN
V
OUT
GND
+18
–18V
+
10µF
+
10µF
10Ω
R
L
OPTIONAL
REF01/
REF02/
REF03
Figure 37. Burn-In Circuit
The part may be burned in with or without a constant resistive
load. The load current should not exceed 10 mA.
POWER DISSIPATION
The REF0x series of voltage references are capable of sourcing
up to 10 mA of load current at room temperature across the
rated input voltage range. However, when used in applications
subject to high ambient temperatures, the input voltage and
load current should be carefully monitored to ensure that the
device does not exceeded its maximum power dissipation
rating. The maximum power dissipation of the device can be
calculated via the following equation:
[]
W
JA
A
j
D
θ
TT
P
−
=
where:
P
D
is device power dissipation.
T
j
is device junction temperature.
T
A
is ambient temperature.
θ
JA
is package (junction-to-air) thermal resistance.
Because of this relationship, acceptable load current in high-
temperature conditions may be less than the maximum
current-sourcing capability of the device. In no case should
the part be operated outside of its maximum power rating as
doing so may result in premature failure or permanent damage
to the device.
