TK70002 Ver la hoja de datos (PDF) - Toko America Inc
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TK70002 Datasheet PDF : 7 Pages
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TK70002
DEFINITION AND EXPLANATION OF TECHNICAL TERMS
DROPOUT VOLTAGE (VDROP)
The output voltage decreases with the increase of output
current. It is dependent upon the load current and the
junction temperature. It measures the differential voltage
between the input voltage and the output voltage when the
input voltage is set to 2.5 V and the output current is set to
50 mA.
OUTPUT CURRENT (IOUT)
The rated output current is specified under the condition
where the output voltage drops 0.5 V below the no load
value. The input voltage is set to 2.5 V, and the current is
pulsed to minimize temperature effects.
QUIESCENT CURRENT (IQ)
The quiescent current is the current which flows through
the ground terminal under no load conditions (IOUT = 0 mA)
with VIN = 2.5 V and excludes the control pin current.
STANDBY CURRENT (ISTBY)
Standby current is the current which flows into the solid
state switch when the output is turned off by the control
function (VCONT = 0 V). It is measured with VIN = 8 V.
GROUND CURRENT (IGND)
Ground current is the current which flows through the
ground pin(s). It is defined as IIN - IOUT, excluding control
current.
ON/OFF CONTROL
High is “on” (referenced to ground). The input current is at
the pA level by connecting the control terminal to ground.
PACKAGE POWER DISSIPATION (PD)
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 (VIN x IIN)
and the output power (VOUT x IOUT) 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-23-6 is increased to 350 mW. For operation at
ambient temperatures over 25 °C, the power dissipation of
the SOT-23-6 device should be derated at 2.8 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 PD /(150 °C - TA) 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:
Tj = 0jA x PD + TA
For Toko ICs, the internal limit for junction temperature is
150 °C. If the ambient temperature (TA) is 25 °C, then:
REVERSE VOLTAGE PROTECTION
Reverse voltage protection prevents damage due to the
output voltage being higher than the input voltage. This
fault condition can occur when the output capacitor remains
charged and the input is reduced to zero, or when an
external voltage higher than the input voltage is applied to
the output side.
150 °C = 0jA x PD + 25 °C
0jA = 125 °C/ PD
PD is the value when the thermal sensor is activated. A
simple way to determine PD is to calculate VIN x IIN when
the output side is shorted. Input current gradually falls as
temperature rises. You should use the value when thermal
equilibrium is reached.
January 1999 TOKO, Inc.
Page 5
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