SBOS392A – AUGUST 2007 – REVISED SEPTEMBER 2007
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APPLICATIONS INFORMATION
The REF33xx is a family of low-power, precision
bandgap voltage references that are specifically
designed for excellent initial voltage accuracy with a
high output current.
shows a simplified
block diagram of the REF33xx.
V
IN
SUPPLY VOLTAGE
The REF33xx family of voltage references features
extremely low dropout voltage, except for the
REF3312. The REF3312 has a minimum supply
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
graph is illustrated in
of the
Typical
Characteristics.
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.
REF33xx
V
OUT
Bandgap
1.2V
GND
START-UP TIME
The REF33xx features an advanced start-up circuit.
Start-up time is almost independent of load (with a
0.1μF 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.
shows the start-up time of
the REF3325 for three different capacitive loads. In
all three cases, the output voltage settles within 2ms.
Figure 17. REF33xx Simplified Block Diagram
BASIC CONNECTIONS
shows the typical connections for the
REF33xx. A recommended supply bypass capacitor
ranging between 1μF to 10μF is recommended. The
total capacitive load at the output must be between
0.1μF to 10μF to ensure output stability.
V
IN
V
IN
0.1
m
F
REF33xx
C
BYPASS
1
m
F to 10
m
F
(recommended)
V
IN
V
OUT
GND
V
OUT
C
L
0.1
m
F to 10
m
F
1V/div
1
m
F
10
m
F
Figure 18. Basic Connections
Time (400
m
s/div)
Figure 19. Start-Up Time
TEMPERATURE DRIFT
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
Drift =
V
OUTMAX
-
V
OUTMIN
V
OUT
´
Temp Range
´
10
6
(ppm)
(1)
8
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