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TPS40070 Fiches technique(PDF) 8 Page - Texas Instruments |
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TPS40070 Fiches technique(HTML) 8 Page - Texas Instruments |
8 / 30 page C u V IN * 8 V R SR (1) R t 0.2 V f SW Q g(TOT) ) IDD (2) SETTING THE SWITCHING FREQUENCY (PROGRAMMING THE CLOCK OSCILLATOR) R T + 1 f SW(kHz) 17.82 10*6 * 23 kW (3) 100 1.5 0.5 1000 200 300 400 500 600 700 800 900 1.0 3.0 2.0 2.5 4.5 3.5 4.0 5.0 MINIMUM OUTPUT VOLTAGE vs FREQUENCY fOSC - Oscillator Frequency - kHz VIN = 28 V VIN = 24 V VIN = 18 V VIN = 15 V VIN = 12 V VIN = 10 V VIN = 8 V VIN = 5 V fSW - Switching Frequency - kHz SWITCHING FREQUENCY vs TIMING RESISTANCE 0 100 0 200 400 600 800 1000 200 300 400 500 600 PROGRAMMING THE RAMP GENERATOR CIRCUIT AND UVLO TPS40070 TPS40071 SLUS582J – DECEMBER 2003 – REVISED APRIL 2009 .................................................................................................................................................. www.ti.com where • V VIN is the final value of the input voltage ramp • f SW is the switching frequency • Q g(TOT) is the combined total gate charge for both upper and lower MOSFETs (from MOSFET data sheet) • I DD is the TPS4007x input current (3.5 mA maximum) • SR is the maximum allowed slew rate [12×104] (V/s) The TPS4007x has independent clock oscillator and PWM ramp generator circuits. The clock oscillator serves as the master clock to the ramp generator circuit. Connecting a single resistor from RT to ground sets the switching frequency of the clock oscillator. The clock frequency is related to RT by: Figure 2. Figure 3. The ramp generator circuit provides the actual ramp used by the PWM comparator. The ramp generator provides voltage feed-forward control by varying the PWM ramp slope with line voltage, while maintaining a constant ramp magnitude. Varying the PWM ramp directly with line voltage provides excellent response to line variations since the PWM does not have to wait for loop delays before changing the duty cycle. (See Figure 9). The PWM ramp must reach approximately 1 V in amplitude during a clock cycle, or the PWM is not allowed to start. The PWM ramp time is programmed via a single resistor (RKFF) connected from KFF VDD. RKFF , VSTART and RT are related by (approximately): 8 Submit Documentation Feedback Copyright © 2003–2009, Texas Instruments Incorporated Product Folder Link(s): TPS40070 TPS40071 |
Numéro de pièce similaire - TPS40070 |
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Description similaire - TPS40070 |
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