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ZXSC380 Datasheet(PDF) 5 Page - Zetex Semiconductors |
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ZXSC380 Datasheet(HTML) 5 Page - Zetex Semiconductors |
5 / 10 page ZXSC380 Issue 1 - March 2007 5 www.zetex.com © Zetex Semiconductors plc 2007 Device description The ZXSC380 is non-synchronous PFM, DC-DC controller IC which, with a high performance internal transistor, for a high efficiency boost converter for use in single cell applications. A block diagram is shown in Figure 1. Figure 1 ZXSC380 Block diagram The on chip comparator forces the driver circuit and therefore the internal switching transistor to switch off when the voltage at ISENSE exceeds 20mV. This threshold is set by an internal reference circuit and divider. The voltage at ISENSE is taken from a current sense resistor connected in series with the emitter of the switching transistor. This resistor is chosen to give 20mV at ISENSE for an emitter current of 80mA. A monostable following the output of the comparator forces the turn-off time of the output stage to be typically 2.2 s. This ensures that there is sufficient time to discharge a significant proportion of the energy stored in the inductor coil before the next On period. With every On pulse the switching transistor is kept on until the voltage across the current-sense resistor exceeds the threshold of the ISENSE input. The On-pulse length, and therefore the switching frequency, is determined by the programmed peak current, the input voltage and the input to output voltage differential. See applications section for details. The Driver circuit supplies the internal switching transistor with a fixed drive current. To maximize efficiency the internal transistor is switched quickly, typically being switched off within 30ns. R1 R2 R SENSE + - + V REF GND I SENSE R1 R2 R SENSE + - + V REF GND I SENSE V CC V CC 1 2 3 V OUT V OUT |
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Similar Description - ZXSC380 |
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