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Moteur de recherche de fiches techniques de composants électroniques |
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Moteur de recherche de fiches techniques de composants électroniques |
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TPS40200D Fiches technique(PDF) 9 Page - Texas Instruments |
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TPS40200D Fiches technique(HTML) 9 Page - Texas Instruments |
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9 / 39 page  www.ti.com GENERAL INFORMATION Overview Programming the Operating Frequency 105 . 0 C R 1 f RC RC SW ´ ´ = A 750 R V RC IN m £ (1) Synchronizing the Oscillator TPS40200 SLUS659 – FEBRUARY 2006 The TPS40200 is a non-synchronous controller with a built in 200-mA driver designed to drive high speed P-Channel FETS up to 500 kHz. Its small size combined with complete functionality makes the part both versatile and easy to use. The controller uses a low value current-sensing resistor in series with the input voltage and the power FET’s source connection to detect switching current. When the voltage drop across this resistor exceeds 100 mV, the part enters a hiccup fault mode at about 2% of the operating frequency. The part uses voltage feedback to an error amplifier that is biased by a precision 700-mV reference. Feed-forward compensation from the input keeps the PWM gain constant over the full input voltage range, eliminating the need to change frequency compensation for different input voltages. The part also incorporates a soft-start feature where the output follows a slowly rising soft-start voltage, preventing output-voltage overshoot. The operating frequency of the controller is determined by an external resistor RRC that is connected from the RC pin to VDD and a Capacitor attached from the RC pin to ground. This connection and the two oscillator comparators inside the IC, are shown in Figure 26. The oscillator frequency can be calculated from the following equation: Where : • fSW is the clock frequency • RRC is the timing resistor value in Ω • CRC is the timing capacitor value in F RRC must be kept large enough that the current through it does not exceed 750 µA when the internal switch (shown in Figure 26) is discharging the timing capacitor. This condition may be expressed by the following: Figure 26 shows the functional diagram of the TPS40200’s oscillator. When synchronizing the oscillator to an external clock, the RC pin must be pulled below 150 mV for 20 ns or more. The external clock frequency must be higher than the free running frequency of the converter as well. When synchronizing the controller, if the RC pin is held low for an excessive amount of time, erratic operation may occur. The maximum amount of time that the RC pin should be held low is 50% of a nominal output pulse, or 10% of the period of the synchronization frequency. Under circumstances where the input voltage is high and the duty cycle is less than 50%, a Schottky diode connected from the RC pin to an external clock may be used to synchronize the oscillator. The cathode of the diode is connected to the RC pin. The trip point of the oscillator is set by an internal voltage divider to be 1/10 of the input voltage. The clock signal must have an amplitude higher than this trip point. When the clock goes low, it allows the reset current to restart the RC ramp, synchronizing the oscillator to the external clock. This provides a simple, single-component method for clock synchronization. 9 Submit Documentation Feedback |
Numéro de pièce similaire - TPS40200D |
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Description similaire - TPS40200D |
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