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

IN (V)

R1

Q

2

Q

1

+

Vbe

1

–

+

Vbe

2

–

Copyright © 2016, Texas Instruments Incorporated

11

REF2912, REF2920, REF2925

REF2930, REF2933, REF2940

www.ti.com

SBVS033C – JUNE 2002 – REVISED JUNE 2016

Product Folder Links: REF2912 REF2920 REF2925 REF2930 REF2933 REF2940

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Copyright © 2002–2016, Texas Instruments Incorporated

8 Detailed Description

8.1 Overview

The REF29xx is a series, CMOS, precision band-gap voltage reference. Its basic topology is shown in Functional

Block Diagram. The 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 coefficient. The resulting output voltage is virtually independent of temperature. The curvature of the

band-gap voltage, as seen in Figure 3, is due to the slightly nonlinear temperature coefficient of the base-emitter

voltage of Q2.

8.2 Functional Block Diagram

Figure 24. Simplified Schematic of Band-Gap Reference

8.3 Feature Description

8.3.1 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 1.8 V, the REF29xx can be operated with a supply of

only 1 mV above the output voltage in an unloaded condition. For loaded conditions, see Dropout Voltage vs

Load Current.

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 25.

Figure 25. Supply Current vs Supply Voltage