200

150

100

50

0

-50

-100

-150

-200

0

400

200

600

800

1000

1200

Time(Hours)

1

2

3

6

5

4

+2.5V

0.47 F

m

+5V

V

BANDGAP

Vbe

1

-

+

Vbe

2

-

+

R

1

Q

2

N

Q

1 I

REF3212, REF3220

REF3225, REF3230

REF3233, REF3240

SBVS058C

– JUNE 2005 – REVISED AUGUST 2011

www.ti.com

TYPICAL CHARACTERISTICS (continued)

At TA = +25°C, ILOAD = 0mA, VIN = +5V power supply, and REF3225 used for typical characteristics, unless otherwise noted.

LONG-TERM STABILITY

(32 Units)

Figure 19.

THEORY OF OPERATION

GENERAL DESCRIPTION

APPLICATION INFORMATION

The REF32xx is a family of CMOS, precision

The REF32xx does not require a load capacitor and

bandgap voltage references. Figure 20 shows the

is stable with any capacitive load. Figure 21 shows

basic bandgap topology. Transistors Q1 and Q2 are

typical connections required for operation of the

biased so that the current density of Q1 is greater

REF32xx. A supply bypass capacitor of 0.47

μF is

than

that

of

Q2. The difference of the two

recommended.

base-emitter voltages (Vbe1 – Vbe2) has a positive

temperature coefficient and is forced across resistor

R1. This voltage is amplified and added to the

base-emitter voltage of Q2, which has a negative

temperature coefficient. The resulting output voltage

is virtually independent of temperature.

Figure 21. Typical Operating Connections for the

REF3225

SUPPLY VOLTAGE

The REF32xx family of references features an

extremely low dropout voltage. With the exception of

the

REF3212,

which

has

a

minimum

supply

requirement

of

1.8V,

these

references

can

be

operated with a supply of only 5mV above the output

Figure 20. Simplified Schematic of Bandgap

voltage

in

an

unloaded

condition.

For

loaded

Reference

conditions, a typical dropout voltage versus load is

shown in the Typical Characteristic curves.

8

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© 2005–2011, Texas Instruments Incorporated