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LM27964 White LED Driver System with I2C Compatible Brightness Control
August 2007
LM27964 White LED Driver System with I2C Compatible Brightness Control
General Description
The LM27964 is a charge-pump-based white-LED driver that is ideal for mobile phone display backlighting. The LM27964 can drive up to 6 LEDs in parallel along with multiple keypad LEDs, with a total output current up to 180mA. Regulated internal current sources deliver excellent current matching in all www.DataSheet4U.com LEDs. The LED driver current sources are split into two independently controlled groups. The primary group (4 LEDs) can be used to backlight the main phone display and the second group (2 LEDs) can be used to backlight a secondary display. A single Keypad LED driver can power up to 16 keypad LEDs with a current of 5mA each. The LM27964 has an I2C compatible interface that allows the user to independently control the brightness on each bank of LEDs. The LM27964 works off an extended Li-Ion input voltage range (2.7V to 5.5V). The device provides excellent efficiency without the use of an inductor by operating the charge pump in a gain of 3/2, or in Pass-Mode. The proper gain for maintaining current regulation is chosen, based on LED forward voltage, so that efficiency is maximized over the input voltage range. The LM27964 is available in National's small 24-pin Leadless Leadframe Package (LLP-24).
Features
■ 87% Peak LED Drive Efficiency ■ 0.2% Current Matching between Current Sinks ■ Drives 6 LEDs with up to 30mA per LED in two distinct ■ ■ ■ ■ ■ ■ ■
groups, for backlighting two displays (main LCD and sub LCD) Dedicated Keypad LED Driver with up to 80mA of drive current Independent Resistor-Programmable Current Settings I2C Compatible Brightness Control Interface Adaptive 1×- 3/2× Charge Pump Extended Li-Ion Input: 2.7V to 5.5V Small low profile industry standard leadless package, LLP 24 : (4mm x 4mm x 0.8mm) LM27964SQ-I LED PWM frequency = 10kHz, LM27964SQ-C LED PWM frequency = 23kHz
Applications
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Mobile Phone Display Lighting Mobile Phone Keypad Lighting PDAs Backlighting General LED Lighting
Typical Application Circuit
20138101
© 2007 National Semiconductor Corporation
201381
www.national.com
LM27964
Connection Diagram
24 Pin Quad LLP Package NS Package Number SQA24A
www.DataSheet4U.com
20138102
Pin Descriptions
Pin #s 24 23 19, 22 (C1) 20, 21 (C2) 13, 14, 15, 16 4, 5 6 17 3 12 1 2 7 9, 10, 18, DAP 8, 11 Pin Names VIN POUT C1, C2 Charge Pump Output Voltage Flying Capacitor Connections Pin Descriptions Input voltage. Input range: 2.7V to 5.5V.
D4A, D3A, D2A, D1A LED Drivers - GroupA D1B, D2B DKEY ISETA ISETB ISETK SCL SDIO VIO GND NC LED Drivers - GroupB LED Driver - KEYPAD Placing a resistor (RSETA) between this pin and GND sets the full-scale LED current for Group A LEDs. LED Current = 200 × (1.25V ÷ RSETA) Placing a resistor (RSETB) between this pin and GND sets the full-scale LED current for Group B LEDs. LED Current = 200 × (1.25V.