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TK11690U Datasheet(PDF) 10 Page - TOKO, Inc |
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TK11690U Datasheet(HTML) 10 Page - TOKO, Inc |
10 / 14 page Page 10 December 1998 TOKO, Inc. TK116xxU 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 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 the radiation of heat is good, the device temperature will be low, even if the power loss is great. When mounted on the recommended mounting pad, the power dissipation of the SOT-89 package is 1000 mW. Derate the power dissipation at 8 mW/ °C for operation above 25 °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. The 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 = ΘjA 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 = Θ jA x PD + 25 °C Θ 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 the DEFINITION AND EXPLANATION OF TECHNICAL TERMS LINE REGULATION (Line Reg) Line regulation is the ability of the regulator to maintain a constant output voltage as the input voltage changes. The line regulation is specified as the input voltage is changed from V IN = VOUT(TYP) + 1 V to VIN = VOUT(TYP) + 6 V. LOAD REGULATION (Load Reg) Load regulation is the ability of the regulator to maintain a constant output voltage as the load current changes. It is a pulsed measurement to minimize temperature effects with the input voltage set to V IN = VOUT(TYP) +1 V. The load regulation is specified under three output current step conditions of 0 mA to 30 mA, 0 mA to 100 mA and 0 mA to 150 mA. DROPOUT 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 = VOUT(TYP) + 1 V at a chosen load current. When the output voltage has dropped 100 mV from the nominal, V IN - VOUT is the dropout voltage. This voltage is affected by load current and junction temperature. 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. 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. |
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