Datasheet

200
150
100
50
0
-50
-100
-150
-200
OutputVoltageStability(ppm)
0 400200 600 800 1000 1200
Time(Hours)
1
2
3
6
5
4
+2.5V
0.47 Fm
+5V
R32C
V
BANDGAP
Vbe
1
-
+
Vbe
2
-
+
R
1
Q
2
NQ
1
I
REF3212, REF3220
REF3225, REF3230
REF3233, REF3240
SBVS058C –JUNE 2005– REVISED AUGUST 2011 www.ti.com
TYPICAL CHARACTERISTICS (continued)
At T
A
= +25°C, I
LOAD
= 0mA, V
IN
= +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 Q
1
and Q
2
are
typical connections required for operation of the
biased so that the current density of Q
1
is greater
REF32xx. A supply bypass capacitor of 0.47μF is
than that of Q
2
. The difference of the two
recommended.
base-emitter voltages (Vbe
1
– Vbe
2
) has a positive
temperature coefficient and is forced across resistor
R
1
. This voltage is amplified and added to the
base-emitter voltage of Q
2
, 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.
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