REF2912, 2920, 2925, 2930, 2933, 2940

9

SBVS033B

www.ti.com

NOISE PERFORMANCE

The REF29xx generates noise less than 50

µV

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

10k

Ω

10k

Ω

+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

+

+

5

Ω

1

µF to 10µF

1

µF to

10

µF

3.3V

0.1

µF

V

IN

V+

V

S

Microcontroller

REF2933

GND