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SI9176 Datasheet(PDF) 5 Page - Vishay Siliconix |
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SI9176 Datasheet(HTML) 5 Page - Vishay Siliconix |
5 / 17 page Si9176 Vishay Siliconix Document Number: 71753 S-41148—Rev. C, 14-Jun-04 www.vishay.com 5 FUNCTIONAL BLOCK DIAGRAM − + Error Amplifier − + PWM Comparator Voltage Reference, UVLO 2 MHz Oscillator To IC Bias PWM and Pulse Skipping Logic PMOS Current Sense VDD VIN FB AGND MODE SD PGND LX 2 MHz Oscillator Clamp REF Si9176 AGND DETAIL DESCRIPTION General The Si9176 is a high efficiency synchronous dc-dc converter that is ideally suited for lithium ion battery or three cell alkaline applications, as well as step-down of 3.3-V or 5.0-V supplies. The major blocks of the Si9176 are shown in the Functional Block Diagram. The 0.25-W internal MOSFETs switching at a frequency of 2-MHz minimize PC board space while providing high conversion efficiency and performance. The high frequency error-amplifier with built-in loop compensation minimizes external components and provides rapid output settling times of <30 ms. Sensing of the inductor current for control is accomplished internally without power wasting resistors. Start-Up When voltage is applied to VIN and VDD, the under-voltage lockout (UVLO) circuit prevents the oscillator and control circuitry from turning on until the voltage on the exceeds 2.4 V. With a typical UVLO hysteresis of 0.1 V, the converter operates continuously until the voltage on VIN drops below 2.3 V, whereupon the converter shuts down. This hysteresis prevents false start-stop cycling as the input voltage approaches the UVLO switching threshold. Start-up is always accomplished in PWM mode to ensure start-up under all load conditions. Switching to other modes of operation occurs according to the state of the MODE pin and the load current. The start-up sequence occurs after SD switches from LOW to HIGH with VIN applied, or after VIN rises above the UVLO threshold and SD is a logic HIGH. Mode Control (MODE) The MODE pin allows the user to control the mode of operation or to enable the Si9176 to automatically optimize the mode of operation according to load current. There are three different modes of operation as controlled by the MODE pin. Switching waveforms are shown in the Typical Switching Waveform sections, page 9. PWM Mode (MODE pin = HIGH) With the MODE pin in the logic HIGH condition, the Si9176 operates as a 2-MHz fixed frequency voltage mode converter. A NMOS synchronous rectification MOSFET transistor provides very high conversion efficiency for large load currents by minimizing the conduction losses. PWM mode provides low output ripple, fast transient response, and switching frequency synchronization. Output load currents can range from 0 to 600 mA. |
Similar Part No. - SI9176_04 |
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Similar Description - SI9176_04 |
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