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参数资料
| 型号： | TK740SIL-2727 |
| 厂商： | TOKO INC |
| 元件分类： | 固定正电压多路输出LDO稳压器 |
| 英文描述： | DUAL OUTPUT, FIXED POSITIVE LDO REGULATOR, PDSO8 |
| 封装： | SOT-23, 8 PIN |
| 文件页数： | 14/29页 |
| 文件大小： | 584K |
| 代理商： | TK740SIL-2727 |
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January 22, 2002 TOKO, Inc.
Page 21
TK740xxL
DEFINITION AND EXPLANATION OF TECHNICAL TERMS (CONT.)
PACKAGE POWER DISSIPATION (P
D)
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
IN x IIN) and the
output power (V
OUT x IOUT) increases. The rate of tempera-
ture rise is greatly affected by the mounting pad configura-
tion 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 recom-
mended mounting pad, the power dissipation of the
SOT23L-8 is increased to 600 mW. For operation at
ambient temperatures over 25 °C, the power dissipation of
the SOT23L-8 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
D /(150 °C - TA) is the derating factor. The
PCB mounting pad should provide maximum thermal con-
ductivity 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:
T
j = 0jA x PD + TA
For Toko ICs, the internal limit for junction temperature is
150 °C. If the ambient temperature (T
A) is 25 °C, then:
150 °C = 0
jA x PD + 25 °C
0
jA = 125 °C / PD
0
jA = 125 °C / PD (°C / mW)
P
D is the value when the thermal protection circuit is
activated. A simple way to determine P
D is to calculate VIN
x I
IN when the output side is shorted. Input current gradually
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
D
2) P
D1 is taken to be PD x (~0.8 - 0.9)
3) Plot P
D1 against 25 °C
4) Connect P
D1 to the point corresponding to the 150 °C with
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
D against the point at which the
vertical line intersects the derating curve. This is taken as
the maximum power dissipation, D
PD.
The maximum operating current is:
I
OUT = (DPD / (VIN(MAX) - VOUT)
Pd
25
50
75
150
TA (°C)
3
PD(mW)
5
0
100
2
4
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