RT8075ZQW

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1. Description

The RT8075ZQW is a high efficiency Pulse-Width-Modulated (PWM) dual step-down DC/DC converter. Capable of delivering up to 1A output current over a wide input voltage range from 2.5V to 5.5V, the RT8075 is ideally suited for portable electronic devices that are powered from 1-cell Li-ion battery or from other power sources such as cellular phones, PDAs, PC WLAN card and hand-held devices. Three operating modes are available including : PWM mode, Low Dropout Mode and shut-down mode. The Internal synchronous rectifier with low RDS(ON) dramatically reduces conduction loss at PWM mode. No external Schottky diode is required in practical application. The RT8075 enters Low Dropout mode when normal PWM cannot provide regulated output voltage by continuously turning on the upper P-MOSFET. The RT8075 enters shutdown mode and consumes less than 0.1μA when the EN pin is pulled low. The switching ripple is easily smoothed-out by small package filtering elements due to the fixed operating frequency of 1.25MHz. The RT8075 is available in the WDFN-10L 3x3 package.

2. Features

    1. 2.5V to 5.5V Input Range

    2. 1A Output Current

    3. 1.25MHz Fixed Frequency PWM Operation

    4. 95% Efficiency

    5. No Schottky Diode Required

    6. 0.6V Reference Allows Low Output Voltage

    7. Low Dropout Operation : 100% Duty Cycle

    8. Small 10-Lead WDFN Package

    9. RoHS Compliant and Halogen Free

3. Applications

    1. Portable Instruments

    2. Microprocessors and DSP Core Supplies

    3. Cellular Phones

    4. Wireless and DSL Modems

    5. PC Cards

4. Pin Configurations

5. Pin Functional

6. Electricalar Chacteristics

7. Inductor Core Selection

Once the value for L is known, the type of inductor must be selected. High efficiency converters generally cannot afford the core loss found in low cost powdered iron cores, forcing the use of more expensive ferrite or mollypermalloy cores. Actual core loss is independent of core size for a fixed inductor value but it is very dependent on the inductance selected. As the inductance increases, core losses decrease. Unfortunately, increased inductance requires more turns of wire and therefore copper losses will increase. Ferrite designs have very low core losses and are preferred at high switching frequencies, so design goals can concentrate on copper loss and preventing saturation. Ferrite core material saturates “hard”, which means that inductance collapses abruptly when the peak design current is exceeded. This results in an abrupt increase in inductor ripple current and consequent output voltage ripple. Do not allow the core to saturate! Different core materials and shapes will change the size/ current and price/current relationship of an inductor. Toroid or shielded pot cores in ferrite or permalloy materials are small and don't radiate energy but generally cost more than powdered iron core inductors with similar characteristics. The choice of which style inductor to use mainly depends on the price vs size requirements and any radiated field/EMI requirements.