ADP3309ART-2.85-R7 datasheet(11/12 Pages) AD

11 / 12 page

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

OUT

GND

VIN = 4V TO 12V

OUTPUT SELECT

1µF

0.47µF

VOUT = 2.7V/3.3V

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

OUT

GND

VIN = 4V TO 8V

47µF

10µF

VOUT = 3.3V @ 1A

ERR

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

OUT

GND

VIN = 2.5V TO 3.5V

2.2µF

VOUT = 3.3V @ 100mA

120Ω

100µF

10V

6.8µF

1N5817

ADP3000-ADJ

ILIM

VIN

SW1

SW2

GND

100µF

10V

2N3906

30.1kΩ

124kΩ

2N3906

274kΩ

Figure 25. Constant Dropout Post Regulator

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