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EL7586ILZ-T7 Datasheet(PDF) 9 Page - Intersil Corporation |
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EL7586ILZ-T7 Datasheet(HTML) 9 Page - Intersil Corporation |
9 / 21 page 9 FN9210.2 January 17, 2006 Applications Information The EL7586 and EL7586A provide a high integrated multiple output power solution for TFT-LCD applications. The system consists of one high efficiency boost converter and three linear-regulator controllers (VON, VOFF, and VLOGIC) with multiple protection functions. A block diagram is shown in Figure 25. Table 1 lists the recommended components. The EL7586, and EL7586A integrate an N-channel MOSFET boost converter to minimize external component count and cost. The AVDD, VON, VOFF, and VLOGIC output voltages are independently set using external resistors. VON, VOFF voltages require external charge pumps which are post regulated using the integrated LDO controllers. Boost Converter The main boost converter is a current mode PWM converter at a fixed frequency of 1MHz which enables the use of low profile inductors and multiplayer ceramic capacitors. This results in a compact, low cost power system for LCD panel design. The EL7586 and EL7586A are designed for continuous current mode, but they can also operate in discontinuous current mode at light load. In continuous current mode, current flows continuously in the inductor during the entire switching cycle in steady state operation. The voltage conversion ratio in continuous current mode is given by: Where D is the duty cycle of the switching MOSFET. Figure 26 shows the block diagram of the boost regulator. It uses a summing amplifier architecture consisting of GM stages for voltage feedback, current feedback and slope compensation. A comparator looks at the peak inductor current cycle by cycle and terminates the PWM cycle if the current limit is reached. An external resistor divider is required to divide the output voltage down to the nominal reference voltage. Current drawn by the resistor network should be limited to maintain the overall converter efficiency. The maximum value of the resistor network is limited by the feedback input bias current and the potential for noise being coupled into the feedback pin. A resistor network in the order of 60k is recommended. The boost converter output voltage is determined by the following equation: The current through the MOSFET is limited to 2A peak for the EL7586. This restricts the maximum output current based on the following equation: Where IL is peak to peak inductor ripple current, and is set by: where fS is the switching frequency. TABLE 1. RECOMMENDED COMPONENTS DESIGNATION DESCRIPTION C1, C2, C3 10µF, 16V X7R ceramic capacitor (1206) TDK C3216X7RIC106M C20, C31 4.7µF, 25V X5R ceramic capacitor (1206) TDK C3216X5R1A475K D1 1A 20V low leakage Schottky rectifier (CASE 457-04) ON SEMI MBRM120ET3 D11, D12, D21 200mA 30V Schottky barrier diode (SOT-23) Fairchild BAT54S L1 6.8µH 1.3A Inductor TDK SLF6025T-6R8M1R3-PF Q1 -2.4 -20V P-channel 1.8V specified PowerTrench MOSFET (SuperSOT-3) Fairchild FDN304P Q4 -2A -30V single P-channel logic level PowerTrench MOSFET (SuperSOT-3) Fairchild FDN360P Q3 200mA 40V PNP amplifier (SOT-23) Fairchild MMBT3906 Q2 200mA 40V NPN amplifier (SOT-23) Fairchild MMBT3904 Q5 1A 30V PNP low saturation amplifier (SOT-23) Fairchild FMMT549 A VDD V IN ---------------- 1 1D – ------------- = A VDD R 1 R 2 + R 1 --------------------- V REF = I OMAX I LMT I L 2 -------- – VIN V O --------- = I L V IN L --------- D f S ----- = EL7586, EL7586A |
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