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APPLICATIONS INFORMATION

SUPPLY VOLTAGE

START-UP TIME

V

IN

REF33xx

GND

V

OUT

1.2V

Bandgap

BASIC CONNECTIONS

REF33xx

V

IN

V

OUT

V

OUT

V

IN

C

BYPASS

1 Fto10 F

(recommended)

m

m

C

L

0.1 Fto10 F

m

m

GND

Time(400 s/div)

m

V

IN

0.1 F

m

1 F

m

10 F

m

TEMPERATURE DRIFT

Drift=

V

V

-

OUTMAX

OUTMIN

V

TempRange

´

OUT

´ 10 (ppm)

6

(1)

REF3312,, REF3318

REF3320, REF3325

REF3330, REF3333

SBOS392A – AUGUST 2007 – REVISED SEPTEMBER 2007

The REF33xx is a family of low-power, precision

bandgap voltage references that are specifically

The REF33xx family of voltage references features

designed for excellent initial voltage accuracy with a

extremely

low

dropout

voltage,

except

for

the

high output current. Figure 17 shows a simplified

REF3312. The REF3312 has a minimum supply

block diagram of the REF33xx.

requirement of 1.8V. These references can be

operated with a supply 110mV above the output

voltage with a 5mA load (typical). For loaded

conditions, a typical dropout voltage versus load

If the supply voltage connected to the IN pin is rapidly

moved while the

REF33xx

is

connected

to

a

capacitive load, a reverse voltage may discharge

through the OUT pin and into the REF33xx device.

This voltage will not damage the REF33xx, provided

that it is less than or equal to 5V.

The REF33xx features an advanced start-up circuit.

Start-up time is almost independent of load (with a

Figure 17. REF33xx Simplified Block Diagram

0.1

μF to 10μF load). Upon start-up, the current boost

circuit forces the output voltage. When the preset

voltage is reached, the REF33xx switches to the

second stage of output circuitry to precisely set the

output voltage. Figure 19 shows the start-up time of

Figure 18 shows the typical connections for the

the REF3325 for three different capacitive loads. In

REF33xx. A recommended supply bypass capacitor

all three cases, the output voltage settles within 2ms.

ranging between 1

μF to 10μF is recommended. The

total capacitive load at the output must be between

0.1

μF to 10μF to ensure output stability.

Figure 18. Basic Connections

Figure 19. Start-Up Time

The REF33xx is designed for minimal drift error,

defined as the change in output voltage over

temperature. The drift is calculated using the box

method, as described in Equation 1:

8

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Product Folder Link(s): REF3312 REF3318 REF3320 REF3325 REF3330 REF3333