Datasheet

REF2912, 2920, 2925, 2930, 2933, 2940
9
SBVS033B
www.ti.com
NOISE PERFORMANCE
The REF29xx generates noise less than 50µV
PP
between
frequencies of 0.1Hz to 10Hz, and can be seen in the Typical
Characteristic Curve,
0.1 to 10Hz Voltage Noise . The noise
voltage of the REF29xx increases with output voltage and
operating temperature. Additional filtering may be used to
improve output noise levels, although care should be taken
to ensure the output impedance does not degrade ac
performance.
LONG TERM STABILITY
Long term stability refers to the change of the output voltage
of a reference over a period of months or years. This effect
lessens as time progresses as is apparent by the long term
stability curves. The typical drift value for the REF29xx is
24ppm from 0-1000 hours, and 15ppm from 1000-2000
hours. This parameter is characterized by measuring 30
units at regular intervals for a period of 2000 hours.
LOAD REGULATION
Load regulation is defined as the change in output voltage
due to changes in load current. Load regulation for the
REF29xx is measured using force and sense contacts as
pictured in Figure 4. The force and sense lines tied to the
Output Pin
Meter
V
OUT
+
–
Sense Line
Force Line
Load
I
L
Contact and
Trace Resistance
FIGURE 4. Accurate Load Regulation of REF29xx.
contact area of the output pin reduce the impact of contact
and trace resistance, resulting in accurate measurement of
the load regulation contributed solely by the REF29xx. For
applications requiring improved load regulation, force and
sense lines should be used.
APPLICATION CIRCUITS
Negative Reference Voltage
For applications requiring a negative and positive reference
voltage, the OPA703 and REF29xx can be used to provide
a dual supply reference from a ±5V supply. Figure 5 shows
the REF2925 used to provide a ±2.5V supply reference
voltage. The low offset voltage and low drift of the OPA703
complement the low drift performance of the REF29xx to
provide an accurate solution for split-supply applications.
OPA703
REF2925
+5V
–5V
+5V
10kΩ
10kΩ
+2.5V
–2.5V
FIGURE 5. REF2925 Combined with OPA703 to Create
Positive and Negative Reference Voltages.
DATA ACQUISITION
Often data acquisition systems require stable voltage
references to maintain necessary accuracy. The REF29xx
family features stability and a wide range of voltages suitable
for most micro-controllers and data converters. See Figure 6
for a basic data acquisition system.
FIGURE 6. Basic Data Acquisition System 1.
ADS7822
V
CC
CS
D
OUT
DCLOCK
V
REF
+In
–In
GND
+
+
5Ω
1µF to 10µF
1µF to
10µF
3.3V
0.1µF
V
IN
V+
V
S
Microcontroller
REF2933
GND