參數(shù)資料
型號(hào)： TK11248A
廠商： TOKO Inc.
英文描述： VOLTAGE REGULATOR WITH ON/OFF SWITCH
中文描述： 調(diào)壓器ON / OFF開(kāi)關(guān)
文件頁(yè)數(shù)： 30/34頁(yè)
文件大小： 382K
代理商： TK11248A
Page 30
1-4-96
January, 1996 TOKO, Inc.
TK112xxA
DEFINITION AND EXPLANATION OF TECHNICAL TERMS
LINE REGULATION (LINE REG)
Line regulation is the relationship between change in
output voltage due to a change in input voltage.
LOAD REGULATION (LOAD REG)
Load regulation is the relationship between change in
output voltage due to a change in load current.
DROP OUT VOLTAGE (V
DROP
)
This is a measure of how well the regulator performs as the
input voltage decreases. The smaller the number, the
further the input voltage can decrease before regulation
problems occur. Nominal output voltage is first measured
when V
IN
= V
OUT
+ 1 at a chosen load current. When the
output voltage has dropped 100 mV from the nominal, V
IN
- V
OUT
is the dropout voltage. This voltage is affected by
load current and junction temperature.
OUTPUT NOISE VOLTAGE
This is the effective AC voltage that occurs on the output
voltage under the condition where the input noise is low and
with a given load, filter capacitor, and frequency range.
THERMAL PROTECTION
This is an internal feature which turns the regulator off when
the junction temperature rises above 150
°
C. After the
regulator turns off, the temperature drops and the regulator
output turns back on. Under certain conditions, the output
waveform may appear to be an oscillation as the output
turns off and on and back again in succession.
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 shutdown. The junction temperature rises
as the difference between the input power (V
IN
X I
IN
) and
the output power (V
OUT
X I
OUT
) increases. The rate of
temperature 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 great. When mounted on
the recommended mounting pad, the power dissipation of
the SOT-23L is increased to 400 mW. For operation at
ambient temperatures over 25
°
C, the power dissipation of
the SOT-23L device should be derated at 3.2 mW/
°
C. The
power dissipation of the SOT-89-5 package is 800 mW
when mounted as recommended. Derate the power dissi-
pation at 6.4 mW/
°
C for operation above 25
°
C. To
determine the power dissipation for shutdown when
mounted, attach the device on the actual PCB and deliber-
ately 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 PD/(150
°
C - T
A
) is the 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:
T
J
= 0
JA
X P
D
+ T
A
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 P
D
+ 25
°
C
0
JA
X P
D
= 125
°
C
0
JA
= 125
°
C/ P
D
P
D
is the value when the thermal sensor is activated. A
simple way to determine PD is to calculate V
IN
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 currents usable can also be found from the
graph below.
(mW)
PD
Dpd
25
50
75
T (°C)
150
3
6
5
4
Procedure:
1.) Find P
D
2.) P
D1
is taken to be P
D
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.
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