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CM9130-01QE Datasheet(PDF) 7 Page - California Micro Devices Corp |
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CM9130-01QE Datasheet(HTML) 7 Page - California Micro Devices Corp |
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7 / 12 page  © 2006 California Micro Devices Corp. All rights reserved. 04/26/06 490 N. McCarthy Blvd., Milpitas, CA 95035-5112 l Tel: 408.263.3214 l Fax: 408.263.7846 l www.cmd.com 7 CM9130 PRELIMINARY The 1.5x mode employs a fractional charge pump. The charge pump uses two phases from the internal oscil- lator to drive switches that are connected to the bucket capacitors, C1 and C2, as shown in Figure 1 In the first switch position, the bucket capacitors are connected in series and each are charged from VIN to a voltage of VIN/2. The next phase changes the switch positions so that C1 and C2 are in parallel, and places them on top of VIN. The resulting voltage across COUT is then VIN+1/2VIN = 1.5 x VIN. Figure 1. Switch Operation The CM9130 has over-temperature and over-current protection circuitry to limit device stress and failure dur- ing short circuit conditions. An overcurrent condition will limit the output current (approximately 400~600mA) and will cause the output voltage to drop, until automat- ically resetting after removal of the excessive current. Over-temperature protection disables the IC when the junction is about 135 °C, and automatically turns on the IC when the junction temperature drops by approxi- mately 15 °C. Efficiency A conventional charge pump with a fixed gain of 2x will usually develop more voltage than is needed to drive paralleled white LEDs from Li-Ion sources. This exces- sive gain develops a higher internal voltage, reducing system efficiency and increasing battery drain in porta- ble devices. A fractional charge pump with a gain of 1.5x is better suited for driving white LEDs in these applications. The CM9130 charge pump automatically switches between the two conversion gains, 1x and 1.5x, allow- ing high efficiency levels over a wide operating input voltage range. The 1x mode allows the voltage to pass directly through to the output when sufficient input volt- age is available. As the battery discharges to the point where any one current source no longer has sufficient voltage headroom to maintain a constant current regu- lation, the 1.5x charge pump is enabled. At nominal loads, the switching losses and quiescent current are negligible. If these losses are ignored for simplicity, the efficiency, η, for an ideal 1.5x charge pump can be expressed as the output power divided by the input power: For an ideal 1.5x charge pump, IIN 1.5 x IOUT, and the efficiency may be expressed as; Many charge pumps are fixed 2x designs. The ideal 2x charge pump efficiency can be similarly expressed; In 1x mode, when the input voltage is above the output voltage, the ideal efficiency is simply VOUT/VIN. Charge C1 and C2 to ½ VIN each VIN C1 C2 ½ VIN VOUT ½ VIN Transfer ½ VIN charge to top of VIN VIN C1 C2 ½ VIN ½ VIN C OUT VOUT COUT η P LED P IN ------------- = IN SINK _ CURRENT LED IN OUT OUT IN OUT OUT IN LED SINK _ CURRENT LED OUT V 5 . 1 V 9 . 3 , V 9 . 3 ) V V ( For V 5 . 1 V I 5 . 1 V I ) V ( P P ) V V ( V × ≈ η = + × = ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ × × × ≈ + = P OUT P IN ------------- 3.9V 2.0 V IN × ----------------------- ≈ Application Information (cont’d) |
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