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MP1530DQ Datasheet(PDF) 10 Page - Monolithic Power Systems |
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MP1530DQ Datasheet(HTML) 10 Page - Monolithic Power Systems |
10 / 15 page MP1530 – TRIPLE OUTPUT STEP-UP PLUS LINEAR REGULATORS FOR TFT BIAS MP1530 Rev. 1.4 www.MonolithicPower.com 10 5/19/2006 MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. APPLICATION INFORMATION COMPONENT SELECTION Setting the Output Voltages Set the output voltage on each output by selecting the resistive voltage divider ratio. The voltage divider drops the output voltage to the feedback threshold voltage. Use 10kΩ to 50kΩ for the low-side resistor RL of the voltage divider. For the step-up converter, determine the high- side resistor RH by the equation: ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ − = L 1 FB 1 FB MAIN H R V V V R Where VMAIN is the output voltage of the step-up converter. For the positive charge-pump, determine the high-side resistor RH by the equation: ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ − = L 3 FB 3 FB GH H R V V V R For the negative charge-pump, determine the high-side resistor RH by the equation: ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ − = L REF GL H R V V R Selecting the Inductor The inductor is required to force the higher output voltage while being driven by the input voltage. A larger value inductor results in less ripple current that results in lower peak inductor current, reducing stress on the internal N-Channel.switch. However, the larger value inductor has a larger physical size, higher series resistance, and/or lower saturation current. A 4.7µH inductor is recommended for most applications. A good rule of thumb is to allow the peak-to-peak ripple current to be approximately 30-50% of the maximum input current. Make sure that the peak inductor current is below 75% of the current limit to prevent loss of regulation due to the current limit. Also make sure that the inductor does not saturate under the worst-case load transient and startup conditions. Calculate the required inductance value by the equation: I f V ) V - (V V L SW OUT IN OUT IN ∆ × × = × η × × = IN ) MAX ( LOAD OUT ) MAX ( IN V I V I ( ) ) MAX ( IN I % 50 % 30 I − = ∆ Where ILOAD(MAX) is the maximum load current, ∆I is the peak-to-peak inductor ripple current, and η is efficiency. Selecting the Input Capacitor An input capacitor is required to supply the AC ripple current to the inductor, while limiting noise at the input source. A low ESR capacitor is required to keep the noise at the IC to a minimum. Since it absorbs the input switching current it requires an adequate ripple current rating. Use a capacitor with RMS current rating greater than the inductor ripple current (see Selecting The Inductor to determine the inductor ripple current). One 10µF ceramic capacitor is used in the application circuit of Figure 3 because of the high source impedance seen in typical lab setups. Actual applications usually have much lower source impedance since the step-up converter typically runs directly from the output of another regulated supply. Typically, the input capacitance can be reduced below the value used in the typical application circuit. To insure stable operation place the input capacitor as close to the IC as possible. Alternately a smaller high quality 0.1µF ceramic capacitor may be placed closer to the IC if the larger capacitor is placed further away. |
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