©2005 Fairchild Semiconductor Corporation

www.fairchildsemi.com

FOD3180 Rev. 1.0.6

11

Reflow Profile

Output Power Derating

T

he maximum package power dissipation is 295mW. The

package is limited to this level to ensure that under normal

operating conditions and over extended temperature

range that the semiconductor junction temperatures do

not exceed 125°C. The package power is composed of

three elements; the LED, static operating power of the

output IC, and the power dissipated in the output power

MOSFET transistors. The power rating of the output IC is

250mW. This power is divided between the static power of

6mA. This maximum condition is valid over the opera-

tional temperature range of -40°C to +100°C. Under these

maximum operating conditions, the output of the power

MOSFET is allowed to dissipate 100mW of power.

The absolute maximum output power dissipation versus

ambient temperature is shown in Figure 12. The output

driver is capable of supplying 100mW of output power

over the temperature range from -40°C to 87°C. The out-

put derates to 90mW at the absolute maximum operating

temperature of 100°C.

The output power is the product of the average output

peak

current flowing in the output. The duty factor is

the ratio of the ‘on’ time of the output load current divided

2.0

Ω results in an average output load current of 200mA.

The load duty factor is a ratio of the average output time

of the power MOSFET load circuit and period of the driv-

ing frequency.

The maximum permissible, operating frequency is deter-

mined by the load supplied to the output at its resulting

output pulse width. Figure 13 shows an example of a

0.03µF gate to source capacitance with a series resis-

tance of 8.50

Ω. This reactive load results in a composite

average pulse width of 1.5µs. Under this load condition it

is not necessary to derate the absolute maximum output

current until the frequency of operation exceeds 63kHz.

• Peak reflow temperature: 260 C (package surface temperature)

• Time of temperature higher than 183 C for 160 seconds or less

• One time soldering reflow is recommended

245 C, 10–30 s

Time (Minute)

0

300

250

200

150

100

50

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

Time above 183C, <160 sec

Ramp up = 2–10C/sec

260 C peak

Fig. 12 Absolute Maximum Power Dissipation

vs. Ambient Temperature

-40

-20

0

20

40

60

80

100

0.15

0.1

0.05

0

LED Power = 45mW

F – FREQUENCY (kHz)

0

0.5

1

1.5

2

2.5

110

100

Fig. 13 Output Current Derating vs. Frequency

Load = .03µF +8.5Ω

LED Duty Factor = 50%

Output Pulse Width = 1.5µs