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ML1565QFNG Folha de dados(PDF) 10 Page - Minilogic Device Corporation Limited |
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ML1565QFNG Folha de dados(HTML) 10 Page - Minilogic Device Corporation Limited |
10 / 21 page P10/21 Rev. C, Sep 2005 ML1565 Detailed Description (1) The ML1565 is a complete digital still camera power con- version IC. It can accept input from a variety of sources including single-cell Li+ batteries, 2-cell alkaline or NiMH batteries, as well as systems designed to accept both battery types. The ML1565 includes five DC-to-DC con- verter channels to generate all required voltages. 1) Synchronous rectified step-up DC-to-DC converter with on-chip MOSFETs--This typically supplies 3.3V for main system power. 2) Synchronous rectified step-down DC-to-DC converter with on-chip MOSFETs ---Powering the stepdown from the step-up output provides efficient (up to 90%) buck-boost functionality that supplies a regulated output when the battery voltage is above or below the output voltage. The step-down can also be powered from the battery. 3) Auxiliary DC-to-DC Controller 1 -- Typically used for 5V output for motor, strobe, or other functions as required. 4) Auxiliary DC-to-DC Controller 2--Typically supplies LCD bias voltages with either a multi-output flyback transformer, or boost converter with charge pump inverter. Alternately may power white LEDs for LCD backlighting. 5) Auxiliary DC-to-DC Controller 3 Typically supplies CCD bias voltages with either a multi-output flyback transformer, or boost converter with charge pump inverter. All ML1565 DC-to-DC converter channels employ fixed frequency PWM operation. In addition to multiple DC-to-DC channels, the ML1565 also includes overload protection, soft-start circuitry, adjustable PWM operating frequency, and a power-OK(POK) output to signal when the step-down converter output voltage (for CPU core) is in regulation. Step-up DC-to-DC Converter The step-up DC-to-DC converter channel generates a 2.7V to 5.5V output voltage range from a 0.9V to 5.5V battery input voltage. An internal switch and synchronous rectifier allow conversion efficiencies as high as 95% while reducing both circuit size and the number of external com ponents. Under m oderate to heavy loading, The converter operates in a low-noise PWM mode with constant frequency. Switching harmonics generated by fixed-frequency operation are consistent and easily filtered. The step-up is a current-mode PWM. An error signal (at COMPSU) represents the difference between the feedback voltage and the reference. The error signal programs the inductor current to regulate the output voltage. At light loads (under 75mA when boosting from 2V to 3.3V), efficiency is enhanced by burst mode in which switching occurs only as needed to service the load. In this mode, the inductor current peak is limited to typically 200mA for each pulse. Step-Down DC-to-DC Converter The step-down DC-to-DC converter channel is optimized for generating output voltages down to 1.25V. Lower output voltages can be set by adding an additional resistor (see the Applications Information section). An internal switch and synchronous rectifier allow conversion efficiencies as high as 95% while reducing both circuit size and the number of external components. Under moderate to heavy loading, the converter operates in a low-noise PWM mode with constant frequency. Switching harmonics generated by fixed-frequency, operation are consistent and easily filtered. The step-down is a current-mode PWM. An error signal (at COMPSD) represents the difference between the feedback voltage and the reference. The error signal programs the inductor current to regulate the output voltage. At light loads (under 120 mA), efficiency is enhanced by burst mode in which switching occurs only as needed to service the load. In this mode, the inductor current peak is limited to 150mA (typ) for each pulse. The step-down remains inactive until the step-up DC-to-DC is in regulation. This means that the step-down DC-to-DC on/off pin (ONSD) is overridden by ONSU. The soft-start sequence for the step-down begins 1024 OSC cycles after the step-up output is in regulation. If the step-up, step-down, or any of the auxiliary controllers remains faulted for 200ms, all channels turn off. The step-down also features and open-drain SDOK output that goes low when the output is in regulation. |
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