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

R

1

Q

2

Q

1 I

N

+

Vbe

1

-

+

Vbe

2

-

V

BANDGAP

10

REF3112, REF3120, REF3125

REF3130, REF3133, REF3140

SBVS046D – DECEMBER 2003 – REVISED MARCH 2016

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Product Folder Links: REF3112 REF3120 REF3125 REF3130 REF3133 REF3140

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8 Detailed Description

8.1 Overview

The REF31xx is a family of series, CMOS, precision bandgap voltage references. The basic bandgap topology is

shown in Functional Block Diagram. Transistors Q1 and Q2 are biased such that the current density of Q1 is

greater than that of Q2. The difference of the two base-emitter voltages, Vbe1 – Vbe2, has a positive temperature

coefficient and is forced across resistor R1. This voltage is gained up and added to the base-emitter voltage of

Q2, which has a negative temperature coefficient. The resulting output voltage is virtually independent of

temperature. The curvature of the bandgap voltage, as shown in Figure 3, is due to the slightly nonlinear

temperature coefficient of the base-emitter voltage of Q2.

8.2 Functional Block Diagram

8.3 Feature Description

8.3.1 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 1.8 V, these references can be operated with a supply of

only 5 mV above the output voltage in an unloaded condition. For loaded conditions, a typical dropout voltage

versus load is shown in Typical Characteristics.

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 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 20.

Figure 20. Supply Current vs Supply Voltage