SPX5205
6/8
REV L
Application Information
The SPX5205 requires an output capacitor for device
stability. Its value depends upon the application circuit. In
general, linear regulator stability decreases with higher
output currents. In applications where the SPX5205 is
putting out less current, a lower output capacitance may
be sufficient. For example, a regulator sourcing only 10mA,
requires approximately half the capacitance as the same
regulator sourcing 150mA.
Bench testing is the best method for determining the proper
type and value of the capacitor since the high frequency
characteristics of electrolytic capacitors vary widely,
depending on type and manufacturer. A high quality 2.2μF
aluminum electrolytic capacitor works in most application
circuits, but the same stability often can be obtained with a
1μF tantalum electrolytic.
With the SPX5205 adjustable version, the minimum value of
output capacitance is a function of the output voltage. The
value decreases with higher output voltages, since closed
loop gain is increased.
Typical Applications Circuits
A 10nF capacitor on the BYP pin will significantly reduce
output noise but it may be left unconnected if the output
noise is not a major concern. The SPX5205 start-up speed
is inversely proportional to the size of the BYP capacitor.
Applications requiring a slow ramp-up of the output voltage
should use a larger CBYP. However, if a rapid turn-on is
necessary, the BYP capacitor can be omitted.
The SPX5205’s internal reference is available through the
BYP pin.
The Typical Application Circuit shown on page 1 represents
a SPX5205 standard application circuit. The EN (enable)
pin is pulled high (>2.0V) to enable the regulator. To disable
the regulator, EN < 0.4V.
The SPX5205 in Figure 13 illustrates a typical adjustable
output voltage configuration. Two resistors (R1 and R2) set
the output voltage. The output voltage is calculated using
the formula:
VOUT = 1.235V x (1 + R1/R2)
R2 must be >10 kΩ, and for best results, R2 should be
between 22 kΩ and 47kΩ.
+
+
GND
EN
Hi-ON
Lo-OFF
SPX5205
1
2
34
5
V
IN
V
OUT
R1
R2
ADJ
TOP View
5-pin Adjustable
Figure 13. Typical Adjustable Output Voltage