REF3112, 3120, 3125, 3130, 3133, 3140

7

SBVS046A

www.ti.com

THEORY OF OPERATION

The REF31xx is a family of series, CMOS, precision bandgap

voltage references. The basic bandgap topology is shown in

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

resulting output voltage is virtually independent of temperature.

100

µA, and the maximum quiescent current over temperature

is just 135

µA. The quiescent current typically changes less

than 2

µA over the entire supply range, as shown in Figure 3.

1

3

REF31xx

2

0.47

µF

V

IN

V

OUT

FIGURE 1. Simplified Schematic of Bandgap Reference.

FIGURE 2. Typical Connections for Operating REF31xx.

FIGURE 3. Supply Current vs Supply Voltage.

R

1

Q

2

Q

+

Vbe

1

–

+

Vbe

2

–

V

BANDGAP

APPLICATION INFORMATION

The REF31xx does not require a load capacitor and is stable

with any capacitive load. Figure 2 shows typical connections

required for operation of the REF31xx. A supply bypass

capacitor of 0.47

µF is recommended.

SUPPLY VOLTAGE

The REF31xx family of references features an extremely low

dropout voltage. With the exception of the REF3112, which

has a minimum supply requirement of 1.8V, these references

can be operated with a supply of only 5mV above the output

voltage in an unloaded condition. For loaded conditions, a

typical dropout voltage versus load is shown in the typical

curves.

The REF31xx features a low quiescent current, which is

extremely stable over changes in both temperature and

supply. The typical room temperature quiescent current is

Supply voltages below the specified levels can cause the

REF31xx to momentarily draw currents greater than the

typical quiescent current. This can be prevented by using a

power supply with a fast rising edge and low output impedance.

THERMAL HYSTERESIS

Thermal hysteresis for the REF31xx 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. It can be expressed as:

V

abs V

V

V

ppm

HYST

PRE

POST

NOM

=











 •

(

)

–

10

6

temperature cycling

has been cycled through the specified temperature

range of –40

°C to +125°C and returned to 25°C.

TEMPERATURE DRIFT

The REF31xx is designed to exhibit minimal drift error, defined

as the change in output voltage over varying temperature. The

drift is calculated using the “box” method which is described by

the following equation:

VV

V

TemperatureRange

ppm

OUTMAX

OUTMIN

OUT

–

•

•









10

6

The REF31xx features a typical drift coefficient of 5ppm from

0

°C to 70°C—the primary temperature range for many

applications. For the industrial temperature range of –40

°C to

125

°C, the REF31xx family drift increases to a typical value of

10ppm.

QUIESCENT CURRENT vs POWER SUPPLY

100.5

100.0

99.5

99.0

98.5

98.0

1.5

Power Supply (V)

2.5

3.5

4.5

5.5