[AP1150ADSXX]

014011331-E-00

- 14 -

2014/10

11.6Board Layout

Figure 5. Layout（PCB Material: Glass epoxy (t=0.8mm)）

25

50

100

Pd(mW)

150C

500

0

0

(85C)

-4.0mW/C

Figure 6. Derating curve

Please do derating with 4.0mW/C at Pd=500mW and 25C or more. Thermal resistance (ja) is=250C/W.

The package loss is limited at the temperature that the internal temperature sensor works (about 150C).

Therefore, the package loss is assumed to be an internal limitation. There is no heat radiation characteristic of

the package unit assumed because of the small size. The device being mounted on the PCB carries heat away.

This value changes by the material and the copper pattern etc. of the PCB. The losses are approximately

500mW. Enduring these losses becomes possible in a lot of applications operating at 25C.

The overheating protection circuit operates when there are a lot of losses with the regulator (When outside

temperature is high or heat radiation is bad). The output current cannot be pulled enough and the output

voltage will drop when the protection circuit operates. When the junction temperature reaches 150C, the IC is

shut down. However, operation begins at once when the IC stops operation and the temperature of the chip

decreases.

・How to determine the thermal resistance when mounted on PCB

The thermal resistance when mounted is expressed as follows:

Tj=jaPd+Ta

Tj of IC is set around 150C. Pd is the value when the thermal sensor is activated.

If the ambient temperature is 25C, then:

150=jaPd+25

ja=125/Pd (C /mW)

on/off

Vout

Np