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ACT8849 データシート(PDF) 31 Page - Active-Semi, Inc |
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ACT8849 データシート(HTML) 31 Page - Active-Semi, Inc |
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31 / 35 page  ACT8849 Rev PrB, 12-Jun-14 Innovative PowerTM - 31 - www.active-semi.com Copyright © 2014 Active-Semi, Inc. Active-Semi Confidential―Do Not Copy or Distribute ActivePMU TM is a trademark of Active-Semi. I2CTM is a trademark of NXP. General Description REG1, REG2, REG3, and REG4 are fixed-frequency, current-mode, synchronous PWM step-down converters that achieves peak efficiencies of up to 97%. These regulators operate with a fixed frequency of 2.25MHz, minimizing noise in sensitive applications and allowing the use of small external components. Additionally, REG1, REG2, REG3, and REG4 are available with a variety of standard and custom output voltages, and may be software- controlled via the I2C interface for systems that require advanced power management functions. 100% Duty Cycle Operation REG1, REG2, REG3, and REG4 are capable of operating at up to 100% duty cycle. During 100% duty cycle operation, the high-side power MOSFETs are 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. Operating Mode By default, REG1, REG2, REG3, and REG4 operate in fixed-frequency PWM mode at medium to heavy loads, then transition to a proprietary power-saving mode at light loads in order to save power. Synchronous Rectification REG1, REG2, REG3, and REG4 each feature integrated synchronous rectifiers, maximizing efficiency and minimizing the total solution size and cost by eliminating the need for external rectifiers. Soft-Start REG1, REG2, REG3, and REG4 include internal 400 us soft-start ramps which limit the rate of change of the output voltage, minimizing input inrush current and ensuring that the output powers up in a monotonic manner that is independent of loading on the outputs. This circuitry is effective any time the regulator is enabled, as well as after responding to a short-circuit or other fault condition. Compensation REG1, REG2, REG3, and REG4 utilize current-mode control and a proprietary internal compensation scheme to simultaneously simplify external component selection and optimize transient performance over their full operating range. No compensation design is required; simply follow a few simple guide lines described below when choosing external components. Input Capacitor Selection The input capacitor reduces peak currents and noise induced upon the voltage source. A 10μF ceramic capacitor is recommended for each regulator in most applications. Output Capacitor Selection REG1, REG2, REG3, and REG4 were designed to take advantage of the benefits of ceramic capacitors, namely small size and very-low ESR. REG1, REG2, REG3 and REG4 are designed to operate with 33uF or 44uF output capacitor over most of their output voltage ranges, although more capacitance may be desired depending on the duty cycle and load step requirements. Two of the most common dielectrics are Y5V and X5R. Whereas Y5V dielectrics are inexpensive and can provide high capacitance in small packages, their capacitance varies greatly over their voltage and temperature ranges and are not recommended for DC/DC applications. X5R and X7R dielectrics are more suitable for output capacitor applications, as their characteristics are more stable over their operating ranges, and are highly recommended. Inductor Selection REG1, REG2, REG3, and REG4 utilize current-mode control and a proprietary internal compensation scheme to simultaneously simplify external component selection and optimize transient performance over their full operating range. These devices were optimized for operation with 2.2μH or 1μH inductors. Choose an inductor with a low DC- resistance, and avoid inductor saturation by choosing inductors with DC ratings that exceed the maximum output current by at least 30%. Configuration Options Output Voltage Programming By default, each regulator powers up and regulates to its default output voltage. For REG2, REG3 and REG4, the output voltage is selectable by setting corresponding VSEL pin that when VSEL is low, output voltage is programmed by VSET0[-] bits, and when VSEL is high, output voltage is programmed by VSET1[-] bits. Also, once the system is enabled, each regulator's output voltage may be independently programmed to a different value. Program the output voltages via the I2C serial interface by writing to the regulator's VSET0[-] register if VSEL is low or VSET1[-] register if VSEL is high as shown in Table 3. STEP-DOWN DC/DC REGULATORS |
同様の部品番号 - ACT8849 |
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同様の説明 - ACT8849 |
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