TK11250CM Toko America, TK11250CM Datasheet - Page 17

• Manufacturer Part Number: TK11250CM
• Description: (TK112xxCM) Voltage Regulator
• Manufacturer: Toko America

PACKAGE POWER DISSIPATION (P
This is the power dissipation level at which the thermal
sensor is activated. The IC contains an internal thermal
sensor which monitors the junction temperature. When the
junction temperature exceeds the monitor threshold of
150 °C, the IC is shut down. The junction temperature rises
as the difference between the input power (V
output power (V
rise is greatly affected by the mounting pad configuration on
the PCB, the board material, and the ambient temperature.
When the IC mounting has good thermal conductivity, the
junction temperature will be low even if the power dissipation
is large. When mounted on the recommended mounting
pad, the power dissipation of the SOT23L-6 is increased to
600 mW. For operation at ambient temperatures over 25 °C,
the power dissipation of the SOT23L-6 device should be
derated at 4.8 mW/ °C. To determine the power dissipation
for shutdown when mounted, attach the device on the actual
PCB and deliberately increase the output current (or raise
the input voltage) until the thermal protection circuit is
activated. Calculate the power dissipation of the device by
subtracting the output power from the input power. These
measurements should allow for the ambient temperature of
the PCB. The value obtained from P
derating factor. The PCB mounting pad should provide
maximum thermal conductivity in order to maintain low
device temperatures. As a general rule, the lower the
temperature, the better the reliability of the device. The
thermal resistance when mounted is expressed as follows:
For Toko ICs, the internal limit for junction temperature is
150 °C. If the ambient temperature (T
January 2002 TOKO, Inc.
V IN
T
150 °C = 0
0
0
DEFINITION AND EXPLANATION OF TECHNICAL TERMS (CONT.)
jA
jA
j
= 0
= 125 °C / P
= 125 °C / P
jA
OUT
x P
x I
jA
D
OUT
x P
+ T
TK112xxC
) increases. The rate of temperature
D
D
GND
D
A
(°C / mW)
+ 25 °C
D
A
/(150 °C - T
D
) is 25 °C, then:
)
V OUT
IN
x I
IN
) and the
A
) is the
P
activated. A simple way to determine P
x I
falls as temperature rises. You should use the value when
thermal equilibrium is reached.
The range of usable currents can also be found from the
graph below.
Procedure:
1) Find P
2) P
3) Plot P
4) Connect P
a straight line.
5) In design, take a vertical line from the maximum
operating temperature (e.g., 75 °C) to the derating curve.
6) Read off the value of P
vertical line intersects the derating curve. This is taken as
the maximum power dissipation, D
The maximum operating current is:
D
IN
is the value when the thermal protection circuit is
when the output side is shorted. Input current gradually
D1
D PD
is taken to be P
P D
I
D1
OUT
D
against 25 °C
D1
= (D
to the point corresponding to the 150 °C with
PD(mW)
25
PD
5
2
/ (V
D
IN(MAX)
50
x (~0.8 - 0.9)
D
against the point at which the
T A (°C)
- V
75
4
OUT
100
PD
TK112xxCM
)
.
D
3
is to calculate V
150
Page 17
IN