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Preliminary ML0308
ML0308 Backlight LED Boost Converter
The ML0308 is a step-up DC-DC converter specifically designed to drive up to four white LEDs in series from a single lithium-ion cell. The device provides regulated and inherently matched current to the LEDs with additional functions: automatic soft-start, output overvoltage protection, ON/OFF and dimming control. The ML0308 switches at 1.0 MHz, featuring the use of tiny external components.
PACKAGE INFORMATION
Features
Inherently-matched LED current Drives up to four white LEDs from 3.6V supply Automatic soft-start Output overvoltage protection High efficiency
Applications
LED backlighting with dimming control High efficiency step-up converter
MARKING DIAGRAM
Figure 1: Typical application circuit
Preliminary ML0308 ABSOLUTE MAXIMUM RATINGS Rating Input voltage Output voltage Operating temperature Storage temperature ELECTICAL CHARACTISTICS
PARAMETER Minimum Operating Voltage Maximum Operating Voltage Feedback Voltage Supply Current Switching EN Pin = 0V EN Pin HIGH Threshold EN Pin LOW Threshold Switch Frequency Duty Ratio MOSFET Current Limit MOSFET ON Resistance MOSFET Leakage Current Overvoltage Limit Soft-start Time VIN =3.0V, IDS = 100mA VIN =5.5V 16.7 200 1.0 17.5 0.5 0.7 73 180 1.0 75 250 1.53 77 0C to 85C 185 200
Pin VIN SW EN FB
Value 6.0 18 10 VIN+0.3 -30 to 80 -40 to 125
Unit V V V V C C
All specifications apply under the condition VIN = 3.0V and TA = 25C unless specified. The donates the specifications which apply over the full operating temperature range
CONDITIONS
MIN 3.0
TYP
MAX
UNITS V
5.5 215
V mV
100
150 0.1 1.2
uA uA V V MHz % mA

uA V us
Preliminary ML0308 PIN FUNCTION DESCRIPTION Pin SW (Pin 1) Description
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. 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. This pin provides the output current range adjustment by means of a sense resistor connected to the internal analog control circuitry. 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. 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.
GND (Pin 2)
FB (Pin 3) EN (Pin 4) VIN (Pin 5)
INTERNAL BLOCK DIAGRAM
Figure 2: Internal block diagram
Preliminary ML0308 THEORY OF OPERATION 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 DESCRIPTION PRE0 Preliminary Release PRE1 Preliminary Release1
DATE 12/03/2004 18/08/2004
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.

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