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ACT8309NHADJ-T Datasheet(PDF) 6 Page - Active-Semi, Inc |
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ACT8309NHADJ-T Datasheet(HTML) 6 Page - Active-Semi, Inc |
6 / 10 page ACT8309/8310/8311 Rev 0, 15-Jun-10 Active-Semi Innovative Power TM - 6 - www.active-semi.com Copyright © 2010 Active-Semi, Inc. ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ − = 1 V V R R FB OUT 2 FB 1 FB FUNCTIONAL DESCRIPTION The patent-pending ACT8309/ACT8310/ACT8311 are current-mode, fixed-frequency PWM, synchro- nous step-down DC/DC converters that are capable of delivering up to 1.5A (ACT8311) with efficiency of up to 95%. These devices feature very low- resistance power MOSFETs and 100% duty cycle operation, making them ideal choices for portable applications requiring a 3.0V or 3.3V rail to be gen- erated form a Li+ battery. These device operate with a fixed frequency of 1.35MHz, minimizing noise in sensitive equipment as well as optimizing both efficiency and component size and cost. 100% Duty Cycle Operation These devices are capable of operating at up to 100% duty cycle operation. During 100% duty cycle operation, the high-side power MOSFET is held on continuously, providing a direct connection from the input to the output (through the inductor), ensuring the lowest possible dropout voltage in battery- powered applications. Synchronous Rectification The ACT8309/ACT8310/ACT8311 each feature integrated n-channel synchronous rectifiers, maxi- mizing efficiency and minimizing the total solution size and cost by eliminating the need for external rectifiers. Soft-Start The ACT8309/ACT8310/ACT8311 each include integrated soft-start circuitry. When enabled, the output voltage track an internal 200µs soft-start ramp so that the output power up in a controlled, monotonic manner that is independent of loading. Compensation The ACT8309/ACT8310/ACT8311 each utilize cur- rent-mode control and a proprietary internal compen- sation scheme to simultaneously simplify external component selection and optimize transient perform- ance over their full operating range. No compensation design is required, simply follow a few simple guide- lines described below when choosing external com- ponents. Capacitor Selection The input capacitor reduces peak currents and noise induced upon the voltage source. A 10µF ceramic capacitor is recommended for most appli- cations. For most applications, a 22µF ceramic output ca- pacitor is recommended. Although the these regula- tors were designed to take advantage of the bene- fits of ceramic capacitors, namely small size and very-low ESR, low-ESR tantalum capacitors can provide acceptable results as well. Inductor Selection These devices were optimized for operation with 3.3µH inductors, although inductors in the 1.5µH to 4.7µH range may be used. Choose an inductors with a low DC-resistance, and avoid inductor satu- ration by choosing inductors with DC ratings that exceed the maximum output current of the applica- tion by at least 30%. Output Voltage Setting Figure 3 shows the feedback network necessary to set the output voltage when using adjustable output voltage options. output voltage options. Select com- ponents as follows: Set RFB2 = 200kΩ, calculate RFB1 using the following equation: Where VFB is 0.8V. Figure 3: Output Voltage Setting Enable/Disable Control These devices may be enabled and disabled using the EN input. Drive EN to a logic-high to enable the regulator, drive EN to a logic-low to disable the regulator. When disabled, each regulator’s quies- cent supply current drops to less than 1µA. Power-OK Output (POK) These devices feature an open-drain “Power-OK” indicator output. This output sinks current whenever the output voltage is (typically) 5% below the regu- lation voltage, and goes high-impedance when the output voltage is above this threshold. To generate FB ACT8309/ ACT8310/ ACT8311 VOUT RFB1 RFB2 |
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