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SP6654ER Datasheet(PDF) 11 Page - Sipex Corporation |
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SP6654ER Datasheet(HTML) 11 Page - Sipex Corporation |
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11 / 17 page  11 Date: 2/1/05 SP6654 High Efficiency 800mA Synchronous Buck Regulator © Copyright 2005 Sipex Corporation For the typical SP6654 application circuit with inductor size of 10 µH, and KON of 2V*µsec, the SP6654 current ripple would be about 200mA, and inductor current reversal. This circuit along with the on-timer puts the converter into PFM mode and improves light load efficiency when the load current is less than half the inductor ripple current defined by KON/L. Shutdown/Enable Control The D0, D1 pins 4,5 of the device are logic level control pins that according to Table 1 shut down the converter when both are a logic low, or enables the converter when either are a logic high. When the converter is shut down, the power switches are opened and all circuit bias- ing is extinguished leaving only junction leak- age currents on supply pins 1 and 2. After pins 4 or 5 are brought high to enable the converter, there is a turn on delay to allow the regulator circuitry to reestablish itself. Power conversion begins with the assertion of the internal refer- ence ready signal which occurs approximately 150 µs after the enable signal is received. Power Good Indicator A power good indicator looks at the voltage on the feedback node. When this voltage is below 0.75V, the open drain NMOS on pin 3 sinks current to ground. Tying a resistor from pin 3 to VIN or VOUT creates a logic level power good indicator. PWRGD is forced low when in UVLO. External Feedback Pin The FB pin 6 is compared to an internal refer- ence voltage of 0.8V to regulate the SP6654 output. The output voltage can be externally programmed within the range +1.0V to +5.0V by tying a resistor from FB to ground and FB to VOUT (pin7). See the applications section for resistor selection information. Inductor Selection The SP6654 uses a specially adapted minimum on-time control of regulation utilizing a preci- sion comparator and bandgap reference. This adaptive minimum on-time control has the ad- vantage of setting a constant current ripple for a given inductor size. From the operations section it has been shown: Inductor Current Ripple, ILR ≈ KON L OPERATION: Continued APPLICATION INFORMATION would be fairly constant for different input and output voltages, simplifying the selection of com- ponents for the SP6654 power circuit. Other inductor values could be selected, as shown in Table 2 Components Selection. Using a larger value than 10 µH in an attempt to reduce output voltage ripple would reduce inductor current ripple and may not produce as stable an output ripple. For larger inductors with the SP6654, which has a peak inductor current of 1.25A, most 15 µH or 22 µH inductors would have to be larger physi- cal sizes, limiting their use in small portable applications. Smaller values like 6.8 µH would more easily meet the 1.25A limit and come in small case sizes, and the increased inductor |
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