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SS6639-33CZBG 데이터시트(PDF) 8 Page - Silicon Standard Corp. |
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SS6639-33CZBG 데이터시트(HTML) 8 Page - Silicon Standard Corp. |
8 / 12 page www.SiliconStandard.com 8 of 12 SS6639 n PIN DESCRIPTIONS Pin 1: GND: Ground. Must be low impedance; solder directly to ground plane. Pin 2: VOUT: IC supply pin. Connect Vout to the regular output. Pin 3: EXT: Push-pull driver output for external power. Switch. n APPLICATION INFORMATION General Description The SS6639 PFM (pulse frequency modulation) controller IC combines a switch mode regulator, a push-pull driver, a precision voltage reference, and a voltage detector in a single monolithic device. It offers extremely low quiescent current, high efficiency, and very low gate-threshold voltage to ensure start-up with low battery voltage (0.8V typ.). Designed to maximize battery life in portable products, it minimizes switching losses by only switching as needed to service the load. PFM controllers transfer a discrete amount of energy per cycle and regulate the output voltage by modulating the switching frequency with a constant turn-on time. Switching frequency depends on load, input voltage, and inductor value and can range up to 100 KHz. When the output voltage drops, the error comparator enables the 100 kHz oscillator which turns the MOSFET on for around 7.5us and off for 2.5 µs. Turning on the MOSFET allows inductor current to ramp up, storing energy in the magnetic field. When the MOSFET turns off, the inductor forces current through the diode to the output capacitor and the load. As the stored energy is depleted, the current ramps down until the diode turns off. At this point, the inductor may ring due to residual energy and stray capacitance. The output capacitor stores charge when current flowing through the diode is high, and releases it when current is low, thereby maintaining a steady voltage across the load. As the load increases, the output capacitor discharges faster and the error comparator initiates cycles sooner, increasing the switching frequency. The maximum duty cycle ensures adequate time for energy transfer to the output during the second half of each cycle. Depending on the circuit, PFM controllers can operate in either discontinuous mode or continuous conduction mode. The continuous conduction mode means that the inductor current does not ramp to zero during each cycle. + V IN SW V OUT EXT I D I OUT Isw Ico I IN Discontinuous Conduction Mode Rev.2.01 6/26/2003 |
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