Datasheet

ADP3309
Rev. C | Page 11 of 12
APPLICATION CIRCUITS
CROSSOVER SWITCH
The circuit in Figure 23 shows that two ADP3309s can be used
to form a mixed supply voltage system. The output switches
between two different levels selected by an external digital
input. Output voltages can be any combination of voltages from
the
Ordering Guide of the data sheet.
+
+
ADP3309-2.7
ADP3309-3.3
IN OUT
SD
IN OUT
SD
GND
GND
V
IN
= 4V TO 12V
4V
0V
OUTPUT SELECT
C1
1µF
C2
0.47µF
V
OUT
= 2.7V/3.3V
00141-023
Figure 23. Crossover Switch
HIGHER OUTPUT CURRENT
The ADP3309 can source up to 100 mA without any heat sink
or pass transistor. If higher current is needed, an appropriate
pass transistor can be used, as in
Figure 24, to increase the
output current to 1 A.
+
ADP3309-3.3
IN
OUT
SD
GND
V
IN
= 4V TO 8V
C1
47µF
C2
10µF
V
OUT
= 3.3V @ 1A
ERR
R1
50Ω
MJE253*
*AAVID531002 HE AT SINK IS USED
00141-024
Figure 24. Higher Output Current Linear Regulator
CONSTANT DROPOUT POST REGULATOR
The circuit in Figure 25 provides high precision with low
dropout for any regulated output voltage. It significantly
reduces the ripple from a switching regulator while providing a
constant dropout voltage, which limits the power dissipation of
the LDO to 30 mW. The ADP3000 used in this circuit is a
switching regulator in the step-up configuration.
+
ADP3309-3.3
IN OUT
SD
GND
V
IN
= 2.5V TO 3.5V
C3
2.2µF
V
OUT
= 3.3V @ 100mA
R1
120Ω
C1
100µF
10V
L1
6.8µF
D1
1N5817
ADP3000-ADJ
I
LIM
V
IN
SW1
FB
SW2GND
C2
100µF
10V
Q1
2N3906
R2
30.1kΩ
1%
R3
124kΩ
1%
Q2
2N3906
R4
274kΩ
00141-025
Figure 25. Constant Dropout Post Regulator