REF3220AIDBVR datasheet(8/14 Pages) TI

8 / 14 page

REF3212,REF3220

REF3225,REF3230

REF3233,REF3240

SBVS058 −JUNE 2005

www.ti.com

TYPICAL CHARACTERISTICS (continued)

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

LONG−TERM STABILITY

(32 Units)

200

150

100

−50

−100

−150

−200

0400

200

600

800

1000

1200

Time (Hours)

THEORY OF OPERATION

The REF32xx is a family of CMOS, precision bandgap

voltage references. Figure 1 shows the basic bandgap

topology. Transistors Q1 and Q2 are biased so 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 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.

BANDGAP

Vbe

−

Vbe

−

1 I

Figure 1. Simplified Schematic of Bandgap

Reference

APPLICATION INFORMATION

The REF32xx does not require a load capacitor and is

stable with any capacitive load. Figure 2 shows typical

connections required for operation of the REF32xx. A

supply bypass capacitor of 0.47

µF is recommended.

+2.5V

0.47

µF

+5V

Figure 2. 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 voltage in an unloaded condition. For

loaded conditions, a typical dropout voltage versus load is

shown in the Typical Characteristic curves.

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