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TPS40071 датащи(PDF) 7 Page - Texas Instruments |
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TPS40071 датащи(HTML) 7 Page - Texas Instruments |
7 / 30 page APPLICATION INFORMATION MINIMUM PULSE WIDTH SLEW RATE LIMIT ON VDD 15 9 16 13 12 10 ILIM HDRV SW LDRV VDD PGND TPS40070 C R VIN UDG−05058 + _ TPS40070 TPS40071 www.ti.com .................................................................................................................................................. SLUS582J – DECEMBER 2003 – REVISED APRIL 2009 The TPS40070 family of parts allows the user to construct synchronous voltage-mode buck converters with inputs ranging from 4.5 V to 28 V and outputs as low as 700 mV. Predictive gate drive circuitry optimizes switching delays for increased efficiency and improved converter output power capability. Voltage feed-forward is employed to ease loop compensation and provide better line transient response. A converter based on the TPS40070 operates as a single quadrant (source only) converter at all times. When the rectifier FET is on and the controller senses that current is near zero in the inductor, the rectifier FET is turned off, preventing the buildup of negative or reverse current in the inductor. This feature prevents the converter from pulling energy from its output and forcing that energy onto its input. Converters based on the TPS40071 operates as a two quadrant converter all the time (source and sink current). This is the controller of choice for most applications. The TPS4007x devices have limitations on the minimum pulse width that can be used to design a converter. Reliable operation is guaranteed for nominal pulse widths of 250 ns and above. This places some restrictions on the conversion ratio that can be achieved at a given switching frequency. Figure 2 shows minimum output voltage for a given input voltage and frequency. The regulator that supplies power for the drivers on the TPS40070/1 requires a limited rising slew rate on VDD for proper operation if the input voltage is above 10 V. If the slew rate is too great, this regulator can over shoot and damage to the part can occur. To ensure that the part operates properly, limit the slew rate to no more than 0.12 V/ µs as the voltage at VDD crosses 8 V. If necessary, an R-C filter can be used on the VDD pin of the device. Connect the resistor from the VDD pin to the input supply of the converter. Connect the capacitor from the VDD pin to PGND. There should not be excessive (more than a 200-mV) voltage drop across the resistor in normal operation. This places some constraints on ↔ the R-C values that can be used. Figure 1 is a schematic fragment that shows the connection of the R-C slew rate limit circuit. Equation 1 and Equation 2 give values for R and C that limits the slew rate in the worst case condition. Figure 1. Limiting the Slew Rate Copyright © 2003–2009, Texas Instruments Incorporated Submit Documentation Feedback 7 Product Folder Link(s): TPS40070 TPS40071 |
Аналогичный номер детали - TPS40071 |
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Аналогичное описание - TPS40071 |
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