REF2912, 2920, 2925, 2930, 2933, 2940

8

SBVS033A

www.ti.com

THEORY OF OPERATION

The REF29xx is a series, CMOS, precision bandgap voltage

reference. It’s basic topology is shown in Figure 1. The

voltage is gained up and added to the base-emitter voltage

voltage is virtually independent of temperature. The curvature

of the bandgap voltage, as seen in the typical curve, “Output

Voltage vs Temperature”, is due to the slightly nonlinear

The REF29xx features a low quiescent current, which is

extremely stable over changes in both temperature and

supply. The typical room temperature quiescent current is

42

µA, and the maximum quiescent current over temperature

is just 59

µA. Additionally, the quiescent current typically

changes less than 2.5

µA over the entire supply range, as

shown in Figure 3.

1

3

REF29xx

2

0.47

µF

V

IN

V

OUT

FIGURE 1. Simplified Schematic of Bandgap Reference.

FIGURE 2. Typical Connections for Operating REF29xx.

42.5

42.0

41.5

41.0

40.5

40.0

1

1.5

2

2.5

3

3.5

4

4.5

5

5.5

6

V

FIGURE 3. Supply Current vs Supply Voltage.

R

1

Q

2

Q

1

+

Vbe

1

–

+

Vbe

2

–

APPLICATION INFORMATION

The REF29xx does not require a load capacitor, and is stable

with any capacitive load. Figure 2 shows typical connections

required for operation of the REF29xx. A supply bypass

capacitor of 0.47

µF is recommended.

SUPPLY VOLTAGE

The REF29xx family of references features an extremely low

dropout voltage. With the exception of the REF2912, which

has a minimum supply requirement of 1.8V, the REF29xx

can be operated with a supply of only 1mV above the output

voltage in an unloaded condition. For loaded conditions, a

typical dropout voltage versus load is shown on the cover

page.

Supply voltages below the specified levels can cause the

REF29xx to momentarily draw currents greater than the

typical quiescent current. Using a power supply with a fast

rising edge and low output impedance easily prevents this.

THERMAL HYSTERESIS

Thermal hysteresis for the REF29xx is defined as the change

in output voltage after operating the device at 25

°C, cycling

the device through the specified temperature range, and

returning to 25

°C, and can be expressed as:

V

abs V

V

V

ppm

HYST

PRE

POST

NOM

=











 •

(

)

–

10

6

temperature cycling

been operated at 25

°C, cycled through specified

range –40

°C to +125°C and returned to operation at

25

°C

TEMPERATURE DRIFT

The REF29xx is designed to exhibit minimal drift error, defined

as the change in output voltage over varying temperature.

Using the ‘box’ method of drift measurement, the REF29xx

features a typical drift coefficient of 20ppm from 0

°C to 70°C—

the primary temperature range of use for many applications.

For industrial temperature ranges of –40

°C to 125°C, the

REF29xx family drift increases to a typical value of 50ppm.