REV. B

ADP3300

–7–

Thermal Overload Protection

The ADP3300 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.

Under extreme conditions (i.e., high ambient temperature

and high power dissipation), where die temperature starts to rise

above 165

°C, the output current is reduced until die tempera-

ture 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:

PD = (8 – 3.3) 0.05 + 8

× 0.5 mA = 0.239 W

∆T = T

× θ

× 165 = 39.4

°C

With a maximum junction temperature of 125

°C, this yields a

maximum ambient temperature of 85

°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 thermal

resistance of the package.

Shutdown Mode

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

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

down to 0.3 V or below, 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 ADP3300 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 dropout

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.

APPLICATION CIRCUITS

Crossover Switch

The circuit in Figure 4 shows that two ADP3300s 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.

ADP3300-5.0

OUT

IN

GND

OUTPUT SELECT

5.0V

0V

SD

C1

1.0 F

ADP3300-3.3

OUT

IN

GND

SD

C2

0.47 F

+

+

Figure 4. Crossover Switch

Higher Output Current

If higher current is needed, an appropriate pass transistor can be

used, as in Figure 5, to increase the output current to 1 A.

MJE253*

C2

10 F

C1

47 F

R1

50

*AAVID531002 HEAT SINK IS USED

IN

OUT

ERR

GND

SD

ADP3300-5

+

Figure 5. High Output Current Linear Regulator