APL5151/2/3/4
Thermal Protection
Thermal protection limits total power dissipation in the
device. When the junction temperature exceeds
T
J
=+150℃, the thermal sensor generates a logic sig-
nal to turn off the pass transistor and allows IC to
cool. When the IC’ junction temperature is down by
s
10℃, the thermal sensor will turn the pass transistor
on again, resulting in a pulsed output during continu-
ous thermal protection. Thermal protection is designed
to protect the APL5151/2/3/4 in the event of fault
conditions. For continuous operation, do not exceed
the absolute maximum junction temperature of
T
J
=+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 APL5151/2/3/4’
s
maximum power dissipation. The power dissipation
across the device is P
D
= I
OUT
(V
IN
-V
OUT
) and the maxi-
mum power dissipation is:
P
DMAX
= (T
J
-T
A
) / (θ
JC
+
θ
CA
)
where T
J
-T
A
is the temperature difference between the
junction and ambient air,
θ
JC
is the thermal resis-
tance of the package, and
θ
CA
is the thermal resis-
tance through the printed circuit board, copper traces,
and other materials to the ambient air.
The GND pin of the APL5151/2/3/4 provide an electri-
cal 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 the problem of over heat of IC.
Copyright
©
ANPEC Electronics Corp.
Rev. B.4 - May., 2005
12
www.anpec.com.tw
ANPEC [ ANPEC ELECTRONICS COROPRATION ]
