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

4V

0V

OUTPUT SELECT

C1

1µF

C2

0.47µF

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

C1

47µF

C2

10µF

ERR

R1

50Ω

MJE253*

*AAVID531002 HEAT SINK IS USED

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

C3

2.2µF

R1

120Ω

C1

100µF

10V

L1

6.8µF

D1

1N5817

ADP3000-ADJ

SW1

FB

SW2

GND

C2

100µF

10V

Q1

2N3906

R2

30.1kΩ

1%

R3

124kΩ

1%

Q2

2N3906

R4

274kΩ

Figure 25. Constant Dropout Post Regulator