AS3819
Application Hints
In general, linear regulator stability decreases with higher
output currents. In most applications the AS3815 is
operating at few milliamps. In these applications the output
capacitance can be further reduced. For example, when the
regulator is running at 10mA output current the output
capacitance value is half compared to the same regulator
that is running at 150mA.
The AS3819 requires an output capacitor for device stability.
The value required varies greatly depending upon the
application circuit. The high frequency characteristics of
electrolytic capacitors depend greatly on the type and also on
the manufacturer. Sometimes bench testing is the only means
to determine the proper capacitor type and value. The high
quality 2.2µF aluminum electrolytic capacitor covers all
general application circuits; this stability can be obtained with
a tantalum electrolytic value of 1µF.
With the AS3819 adjustable regulator, the minimum value
of output capacitance is a function of the output voltage.
The value decreases with higher output voltages, since the
closed loop gain is increased.
Typical Applications Circuits
The AS3819 provides access to the internal reference. A 10µF capacitor on the Ref BYP pin will provide a significant reduction in
output noise. This pin may be left unconnected if the output noise is not a major concern. The AS3819 start-up speed is inversely
proportional to the size of its capacitor. Applications requiring a slow ramp-up of output voltage should consider larger values of
CBYP. If the rapid turn-ON is necessary, omit bypass capacitor.
Figure 1 shows AS3819 standard application circuit. The EN (enable) pin is pulled high (>2.0V) to enable the regulator. To disable
the regulator, EN < 0.6V.
VIN
VOUT
5
1
2
3
+
GND
EN
AS3819
SOT-23
+
4
BYP
(Optn)
Hi-ON
Lo-OFF
Top View
Fig. 1
The AS3819 in figure 2 shows adjustable output voltage configuration. Two resistors set the output voltage. The formula for output
voltage is:
R1
VOUT = 1.235V x 1 +
R2
Resistor values are not critical as the Adj pin has high input impedance, for best results use resistors of 47kΩ or less. A capacitor for
Adj to ground will provide improved noise performance.
1
5
VIN
VOUT
2
+
GND
EN
R1
R2
+
AS3819
SOT-23
4
3
ADJ
Byp
Hi-ON
(Optn)
Lo-OFF
Top View
Fig. 2
Rev. 10/2/00
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