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LM3501
Synchronous Step-up DC/DC Converter for White LED
Applications
General Description
The LM3501 is a fixed frequency synchronous step-up
DC/DC converter in a small 8-bump thin micro SMD pack-
age. The LM3501 is ideal for white LED applications for
cellular phone back-lighting requiring low current and high
efficiency. Its fixed 1MHz operating frequency allows the use
of small, low ESR capacitors as well as a more predictable
frequency spectrum, which is important in cellular phone
applications. The LM3501 can drive 2 to 4 white LEDs in
series from a single Li-Ion battery or 3 cell NiMH with no
external rectification diode. For white LED applications, a
single external resistor is used to set the maximum LED
current. The white LED current can easily be adjusted using
an external voltage signal from a DAC or micro-controller.
The LM3501 uses special protection circuitry on the output
to prevent an overvoltage event if the primary white LED
network should be disconnected eliminating the need of an
extra protection Zener diode. In shutdown, the LM3501 dis-
connects the input and output creating a true isolation pre-
venting any LED light from emitting over the full input oper-
ating voltage range and temperature.
Features
n Synchronous rectification, high efficiency and no
external schottky diode required
n Uses small surface mount components
n Can drive up to 3 (or 4 low V
F
) white LEDs in series
n 2.7V to 7V input range
n True shutdown isolation, no LED leakage current
n DC voltage LED current control
n Input undervoltage lockout
n Output overvoltage protection, no external zener diode
required
n Requires only a small 16V ceramic capacitor at the
output
n Thermal Shutdown
n 0.1µA shutdown current
n Small 8-bump thin micro SMD package
Applications
n LCD Bias Supplies
n White LED Back-Lighting
n Handheld Devices
n Digital Cameras
n Portable Applications
Typical Application Circuit
20065301
FIGURE 1. Typical 3 LED Application
December 2003
Synchronous Step-up DC/DC Converter for White LED Applications
© 2003 National Semiconductor Corporation DS200653 www.national.com
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