ADP3307

–7–

REV. 0

+

C1

1 F

ADP3307-3.3

NR

OUT

ERR

ON

OFF

SD

GND

330k

IN

C2

4.7 F

+

R1

10nF

Figure 21. Noise Reduction Circuit

Thermal Overload Protection

The ADP3307 is protected against damage due to excessive

power dissipation by its thermal overload protection circuit,

which limits the die temperature to a maximum of 165

°C. Un-

der extreme conditions (i.e., high ambient temperature and

power dissipation), where die temperature starts to rise above

165

°C, the output current is reduced until the die temperature

has dropped to a safe level. Output current is restored when the

die temperature is reduced.

Current and thermal limit protections are intended to protect

the device against accidental overload conditions. For normal

operation, device power dissipation should be externally limited

so that junction temperatures will not exceed 125

°C.

Calculating Junction Temperature

Device power dissipation is calculated as follows:

× 2 mA = 0.231 W

∆T = T

With a maximum junction temperature of 125

°C, this yields a

maximum ambient temperature of ~72

°C.

Printed Circuit Board Layout Consideration

Surface mount components rely on the conductive traces or

pads to transfer heat away from the device. Appropriate PC

board layout techniques should be used to remove heat from the

immediate vicinity of the package.

The following general guidelines will be helpful when designing

a board layout:

1. PC board traces with larger cross section areas will remove

more heat. For optimum results, use PC boards with thicker

copper and wider traces.

2. Increase the surface area exposed to open air so heat can be

removed by convection or forced air flow.

3. Do not use solder mask or silkscreen on the heat dissipating

traces because it will increase the junction-to-ambient ther-

mal resistance of the package.

Shutdown Mode

Applying a TTL high signal to the shutdown pin or tying it to

the input pin will turn the output ON. Pulling the shutdown pin

down to a TTL low level or tying it to ground will turn the

output OFF. In shutdown mode, quiescent current is reduced

to less than 1

µA.

Error Flag Dropout Detector

The ADP3307 will maintain its output voltage over a wide

range of load, input voltage and temperature conditions. If the

output is about to lose regulation, for example, by reducing the

supply voltage below the combined regulated output and drop-

out voltages, the

ERR pin will be activated. The ERR output is

an open collector that will be driven low.

Once set, the

ERRor flag’s hysteresis will keep the output low

until a small margin of operating range is restored either by

raising the supply voltage or reducing the load.

APPLICATIONS CIRCUITS

Crossover Switch

The circuit in Figure 22 shows that two ADP3307s 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.

ADP3307-2.7

ADP3307-3.3

+

OUT

IN

SD

GND

+

IN

OUT

SD

GND

C1

1.0 F

C2

0.47 F

OUTPUT SELECT

4V

0V

Figure 22. Crossover Switch

Higher Output Current

The ADP3307 can source up to 100 mA without any heatsink

or pass transistor. If higher current is needed, an appropriate

pass transistor can be used, as in Figure 23, to increase the

output current to 1 A.

ADP3307-3.3

OUT

IN

SD

GND

+

MJE253*

C1

47 F

C2

10 F

*AAVID531002 HEAT SINK IS USED

ERR

R1

50

Figure 23. High Output Current Linear Regulator