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TK70002MCB Datasheet(PDF) 5 Page - TOKO, Inc |
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TK70002MCB Datasheet(HTML) 5 Page - TOKO, Inc |
5 / 7 page January 1999 TOKO, Inc. Page 5 TK70002 DEFINITION AND EXPLANATION OF TECHNICAL TERMS 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 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 P D /(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: 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 P D is the value when the thermal sensor is activated. A simple way to determine P D 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. DROPOUT VOLTAGE (V DROP) 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 (I OUT) 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 (I Q) The quiescent current is the current which flows through the ground terminal under no load conditions (I OUT = 0 mA) with V IN = 2.5 V and excludes the control pin current. STANDBY CURRENT (I STBY) Standby current is the current which flows into the solid state switch when the output is turned off by the control function (V CONT = 0 V). It is measured with VIN = 8 V. GROUND CURRENT (I GND) Ground current is the current which flows through the ground pin(s). It is defined as I IN - 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. 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. |
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