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ZLED7012ZI1R Datasheet(PDF) 11 Page - Integrated Device Technology |
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ZLED7012ZI1R Datasheet(HTML) 11 Page - Integrated Device Technology |
11 / 14 page ZLED7012 Datasheet © 2016 Integrated Device Technology, Inc. 11 April 20, 2016 Cin VCC EN/SET GND C+ C- Cout 2.8 V to 5.5V Vout D0 D1 D2 D3 1 2 n<=14 1 μF 2.2 μF 2.2 μF NC NC ZLED7012 Cpump 4 Application Circuit Design 4.1. Applications The ZLED7012 is designed for white or other color LED applications requiring a controlled LED current that is generated from a varying input voltage. Typical applications include main/sub LCD display backlighting, cell phones (including smartphones), personal digital assistants (PDAs), MP3/MP4 devices, portable media players (PMPs), and general purpose low-voltage industrial applications. See section 4.2.3 for details and requirements for the LEDs. Figure 4.1 Basic Application Circuit using D2:D0 4.2. External Components 4.2.1. External Capacitors Cout and Cin The values and type of capacitors used for Cin and Cout can affect several circuit parameters including transient performance, turn-on time, and output ripple. Use low equivalent series resistance (ESR) ceramic capacitors (internal resistance < 100mΩ) for best performance, lower costs, and component size reduction. Low ESR capacitors can enable applications at the highest LED forward voltage with the lowest supply voltage. Tantalum and aluminum electrolytic are not generally recommended because the ESR is typically in the range of several ohms. Note: The recommended starting value when determining the optimal value for Cout is 2.2μF. There is often a design trade-off between low ESR ratings and smaller size because physically larger ceramic capacitors usually have a relatively lower ESR, which can improve the operating range of the circuit. Cin is a bypass capacitor ( ≥ 2.2μF) essential to proper operation because it must deliver the dynamic current for the charge pump. 4.2.2. External Pump Capacitor The external pump capacitor Cpump connected between the C+ and C- pins is an essential part of the ZLED7012’s internal charge pump circuit. Because the ZLED7012 operates at a constant charge-pump frequency of 1MHz (typical), it is important that the pump capacitance is greater than 0.47 μF so it can transfer enough charge each cycle to supply sufficient load current. To reduce voltage fluctuations on the supply line, do not use a value for the pump capacitor that is greater than the bypass capacitor, Cin. |
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