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| PRELIMINARY GM7620 FIXED FREQUENCY STEP-UP DC/DC CONVERTER www..com 1.2MHz Fixed Frequency Switching Inherently Matched LED Current Adjustable Control of LED Current Drives Five White LEDs from 2V Drives Six White LEDs from 2.7V Drives Eight White LEDs from 3V Disconnects LEDs In Shutdown Uses Tiny Ceramic Capacitors Uses Tiny 1mm-Tall Inductors Regulates Current Even When VIN > VOUT Operates with VIN as Low as 1V Up to 80% Efficiency The GM7620 is a fixed frequency step-up DC/DC converter designed to operate as a constant-current source. Because it directly regulates output current, the GM7620 is ideal for driving light emitting diodes (LEDs) whose light intensity is proportional to the current passing through them, not the voltage across their terminals. With an input voltage range of 1V to 10V, the device works from a variety of input sources. The GM7620 accurately regulates LED current even when the input voltage is higher than the LED voltage, greatly simplifying batterypowered designs. A single external resistor sets LED current between 5mA and 40mA, which can then be easily adjusted using either a DC voltage or a pulse width modulated (PWM) signal. When the GM7620 is placed in shutdown, the LEDs are disconnected from the output, ensuring a quiescent current of under 1mA for the entire circuit. The device's 1.2MHz switching frequency permits the use of tiny, low profile chip inductors and capacitors to minimize footprint and cost in space-conscious portable applications. The GM7620 is available in 6-lead plastic SOT-23 package. Applications: Handheld Computers Cellular Telephones Digital Cameras Portable MP3 Players TYPICAL APPLICATION (Li-ION Driver for 4 White LEDs) L1 6.8H VIN 2.7V to 4.2V 6 VIN C1 4.7F GM7620 PWM DIMMING CONTROL 5 SHDN RSET 4 RSET 1.5k LED 3 GND 2 15mA 1 SW C2 1F D1 Revision 1, December 2002 1 www.gammamicro.com PRELIMINARY GM7620 FIXED FREQUENCY STEP-UP DC/DC CONVERTER PIN CONNECTIONS AND FUNCTIONS PIN CONNECTIONS (Top View) SW 1 www..com 6 VIN 5 SHDN 4 RSET GND 2 LED 3 6-lead SOT-23 PIN 1 2 3 4 5 6 PARAMETER SW GND LE D RSET SHDN VIN DESCRIPTION Switch Pin. This is the collector of the internal NPN power switch. Minimize the metal trace area connected to this pin to minimize EMI. Ground Pin. Tie this pin directly to local ground plane. LED Pin. This is the collector of the internal NPN LED switch. Connect the cathode of the bottom LED to this pin. A resistor between this pin and ground programs the LED current (that flows into the LED pin). This pin is also used to provide LED dimming. Shutdown Pin. Tie this pin higher than 0.85V to turn on the GM7620; tie below 0.25V to turn it off. Input Supply Pin. Bypass this pin with a capacitor to ground as close to the de vice as possible. ORDERING INFORMATION . GM7620 PACKAGE SOT23-6 PART No. GM7620ST26 Revision 1, December 2002 2 www.gammamicro.com PRELIMINARY GM7620 FIXED FREQUENCY STEP-UP DC/DC CONVERTER ELECTRICAL CHARACTERISTICS (VIN = 1.2V, VSHDN = 1.2V, unless otherwise specified) PARAMETER Minimum Input Voltage Qu www..com i escent C urrent RSET Pin Voltage LED Pin Voltage VRSET = 0.2V VSHDN = 0V RSET = 1.50k RSET = 1.50k, VIN < VOUT RSET = 562 , VIN= 1.5V LED Pin Current RSET = 750 , VIN = 1.2V RSET = 1.50k, VIN = 1.2V RSET = 4.53k, VIN = 1.2V LED Pin Current Temperature Coefficient Switching Frequency Maximum Switch Duty Cycle Switch Current Limit Switch VCESAT SHDN Pin Current Start-Up Threshold (SHDN Pin) Shutdown Threshold (SHDN Pin) Switch Leakage Current Switch Off, VSW = 5V 0.01 ISW = 300mA VSHDN = 0V VSHDN = 2V 0.85 0.25 5 ILED = 15mA VIN = 1V * 0.8 90 400 33 25 12.5 1.2 0.1 100 120 38 30 15 5 -0.02 1.2 95 550 150 0 15 780 200 0.1 30 1.6 mA/C MHz % mA mV A 180 45 36 17.5 mA CONDITIONS MIN TYP MAX 1 1.6 1.0 UNIT V mA A mV mV V A * specification that apply over the full operating temperature range (The GM7620 is guaranteed to meet specifications from 0C to 70C. Specifications over the - 40C to 85C operating temperature range are assured by design, characterization and correlation with statistical process controls), otherwise specifications are T = 25C. A Revision 1, December 2002 3 www.gammamicro.com PRELIMINARY GM7620 FIXED FREQUENCY STEP-UP DC/DC CONVERTER ABSOLUTE MAXIMUM RATINGS RATING VIN Voltage SHDN Voltage Range SW Voltage LED Voltage (VPin 1 = 40 V) S www..com ET VALUE 10 10 36 36 1 +125 0 to +70 -65 to +150 +300 UNIT V V V V V C C C C R Voltage Junction Temperature Operating Temperature Range Storage Temperature Range Lead Temperature (soldering, 10 sec.) BLOCK DIAGRAM L1 VIN SHDN C1 5 6 DRIVER VIN 1 Q1 SW C2 + x5 0.04 + + S Q R A2 A1 + 1.2MHz Oscillator + DRIVER Q2 3 LED ILED D1 VOUT LED CURRENT REFERENCE 2 4 RSET GND RSET ISET Revision 1, December 2002 4 www.gammamicro.com PRELIMINARY GM7620 FIXED FREQUENCY STEP-UP DC/DC CONVERTER SOT-23-6 PACKAGE OUTLINE DIMENSIONS www..com NOTES: 1. PACKAGE BODY SIZES EXCLUDE MOLD FLASH AND GATE BURRS 2. DIMENSION L IS MEASURED IN GAGE PLANE 3. TOLERANCE 0.10 mm UNLESS OTHERWISE SPECIFIED 4. COPLANARITY: 0.10 mm SYMBOL A A1 A2 b C D E e H L e1 1 Dimensions In Millimeters MIN 1.00 0 0.70 0.35 0.10 2.70 1.40 2.60 0.37 1 NOM 1.10 0.80 0.40 0.15 2.90 1.60 1.90 TYP. 2.80 0.95 TYP. 5 9 3.00 MAX 1.30 0.10 0.90 0.50 0.25 3.10 1.80 Revision 1, December 2002 5 www.gammamicro.com |
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