LM3500_14 Datasheet, PDF (1/25 Pages) Texas Instruments – Synchronous Step-up DC/DC Converter for White LED Applications

LM3500
www.ti.com
SNVS231F – MAY 2004 – REVISED APRIL 2007
LM3500 Synchronous Step-up DC/DC Converter for White LED Applications
Check for Samples: LM3500
FEATURES
1
•2 Synchronous rectification, high efficiency and
no external schottky diode required
• Uses small surface mount components
• Can drive 2-5 white LEDs in series
– (may function with more low-V_F LEDs)
• 2.7V to 7V input range
• Internal output over-voltage protection (OVP)
circuitry, with no external zener diode required
– LM3500-16: 15.5V OVP; LM3500-21: 20.5V
OVP.
• True shutdown isolation
• Input undervoltage lockout
• Requires only small ceramic capacitors at the
input and output
• Thermal Shutdown
• 0.1µA shutdown current
• Small 8-bump thin micro SMD package
APPLICATIONS
• LCD Bias Supplies
• White LED Backlighting
• Handheld Devices
• Digital Cameras
• Portable Applications
DESCRIPTION
The LM3500 is a fixed-frequency step-up DC/DC converter that is ideal for driving white LEDs for display
backlighting and other lighting functions. With fully intergrated synchronous switching (no external schottky diode
required) and a low feedback voltage (500mV), power efficiency of the LM3500 circuit has been optimized for
lighting applications in wireless phones and other portable products (single cell Li-Ion or 3-cell NiMH battery
supplies). The LM3500 operates with a fixed 1MHz switching frequency. When used with ceramic input and
output capacitors, the LM3500 provides a small, low-noise, low-cost solution.
Two LM3500 options are available with different output voltage capabilities. The LM3500-21 has a maximum
output voltage of 21V and is typically suited for driving 4 or 5 white LEDs in series. The LM3500-16 has a
maximum output voltage of 16V and is typically suited for driving 3 or 4 white LEDs in series (maximum number
of series LEDs dependent on LED forward voltage). If the primary white LED network should be disconnected,
the LM3500 uses internal protection circuitry on the output to prevent a destructive over-voltage event.
A single external resistor is used to set the maximum LED current in LED-drive applications. The LED current
can easily be adjusted using a pulse width modulated (PWM) signal on the shutdown pin. In shutdown, the
LM3500 completely disconnects the input from output, creating total isolation and preventing any leakage
currents from trickling into the LEDs.
1
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Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
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2
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2004–2007, Texas Instruments Incorporated