ML0308 MINILOGIC | Alldatasheet
Document overview
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Technical content
Features
z Drives up to four white LEDs from 3.6V supply z Automatic soft-start z Output overvoltage protection z High efficiency
Applications
z LED backlighting with dimming control z High efficiency step-up converter MARKING DIAGRAM Figure 1: Typical application circuit
6.0 V Output voltage SW V EN V FB VIN+0.3 V Operating temperature -30 to 80 Storage temperature -40 to 125 ELECTICAL CHARACTISTICS All specifications apply under the condition VIN = 3.0V and TA = 25°C unless specified. The ˙ donates the specifications which apply over the full operating temperature range PARAMETER CONDITIONS MIN TYP MAX UNITS Minimum Operating Voltage 3.0 V Maximum Operating Voltage 5.5 V Feedback Voltage 0°C to 85°C 185 200 215 mV Supply Current Switching EN Pin = 0V 100 150 0.1 uA uA EN Pin HIGH Threshold 1.2 V EN Pin LOW Threshold 0.5 V Switch Frequency 0.7 1.0 1.53 MHz Duty Ratio MOSFET Current Limit 180 250 mA MOSFET ON Resistance VIN =3.0V, IDS = 100mA Ω MOSFET Leakage Current VIN =5.5V 1.0 uA Overvoltage Limit 16.7 17.5 V Soft-start Time 200 us
Description
SW (Pin 1) This pin is the power side of the external inductor and must be connected to the external Schottky diode. It provides the output current to the load. Since the boost converter operates in a current loop mode, the output voltage can range up to 16V but shall not exceed this limit. GND (Pin 2) This pin is the system ground for the ML0308 and carries both the power and the analog signals. High quality ground must be provided to avoid spikes and/or uncontrolled operation. Care must be observed to avoid high−density current flow in a limited PCB copper track so arobust ground plane connection is recommended. FB (Pin 3) This pin provides the output current range adjustment by means of a sense resistor connected to the internal analog control circuitry. EN (Pin 4) This pin is the chip-enable Pin. Ground this pin to shutdown the chip. Apply a clock with different duty ratio to control brightness of the LEDs. VIN (Pin 5) The external voltage supply is connected to this pin. A high quality reservoir capacitor must be connected across pin 5 and Ground to achieve the specified output voltage parameters. A 4.7uF/6.3 V, low ESR capacitor must be connected as close as possible across pin 5 and ground pin 2. INTERNAL BLOCK DIAGRAM Figure 2: Internal block diagram
The ML0308 uses a PFM, current mode control scheme to provide excellent line and load regulation. Its operation can be best explained with reference to figure 2 and figure 1. The oscillator generates a clock of 1.0MHz with 75% duty ratio for the main control logic. When EN pin goes HIGH, the power MOSFET switches at 1.0 MHz to drive the LED current up to the target level. When the inductor current reaches the limit, comparator A3 will toggle and the MOSFET will stop charging the inductor until the inductor current falls below the limit. Therefore, soft-start is achieved and potential hazards from explosive startup are avoided. When LED current reaches and rises over the regulation point, feedback voltage at FB pin will raise over 200mV and comparator A2 toggles. The chip will then stop switching the MOSFET until LED current falls below the threshold. Therefore, LED current is regulated and the threshold. HISTORY OF REVISION REV DISCLAIMER: The information presented in this document does not form part of any quotation or contract, is believed to be accurate and reliable and may be changed without notice. No liability will be accepted by the publisher for any consequence of its use.