APL5501/2/3
Thermal Protection
Thermal protection limitstotal power dissipation inthe
device. When the junction temperature exceeds
TJ=+150℃, the thermal sensor generates a logic sig-
nal to turn off the pass transistor and allows IC to
cool. When the IC’s junction temperature is down by
10℃, the thermal sensor will turn the pass transistor
on again, resulting in a pulsed output during continu-
ousthermal protection. Thermalprotectionisdesigned
to protect the APL5501/2/3 in the event of fault
conditions. For continuous operation, do not exceed
the absolute maximum junction temperature of
TJ=+150℃.
Operating Region and Power Dis-
sipation
The thermal resistance of the case to circuit board,
and the rate of air flow all control the APL5501/2/3’s
maximum power dissipation. The power dissipation
across the device is PD = IOUT (VIN-VOUT) and the maxi-
mum power dissipation is:
PDMAX = (TJ-TA) / (θJC + θCA)
where TJ-TA isthetemperaturedifference betweenthe
junction and ambient air, θJC is the thermal resis-
tance of the package, andθCA is the thermal resis-
tance throughthe printed circuit board, copper traces,
and other materials to the ambient air.
The GND pin of the APL5501/3 provide an electrical
connection to ground and channeling heat away. If
power dissipation is large, connect the GND pin to
ground using a large pad or ground plane, can im-
prove theproblem of over heat of IC.
Copyright ã ANPEC Electronics Corp.
12
www.anpec.com.tw
Rev. B.2 - May., 2005
ANPEC [ ANPEC ELECTRONICS COROPRATION ]
