BL8545
Max. 3MHz, Variable Frequency Step-up DC/DC Converter
DESCRIPTION
The BL8545 variable frequency step-up
Converter drives white LEDs with a constant
current to provide backlight in cell phones,
PDAs, and other hand-held devices. It
features allowing series connection of the
white LEDs so that the LED currents are
identical for uniform brightness. An enable
input can be pulsed repeatedly to adjust
LEDs brightness. The fast 3MHz operation
frequency allows for smaller capacitor and
inductor. Fault condition protection uses
cycle-by cycle current limiting to sense
maximum inductor current and over-voltage
protection. The 0.2V low reference voltage
minimized the power loss across the current
sense resistor.
The converter can operate from 2V to 6V,
and capable of delivering maximum 200mA
output current at 4-LEDs application with 3V
input voltage. Quiescent current drawn from
power source is as low as 120uA. All of these
features make BL8545 be suitable for the
portable devices, which are supplied by a
single battery.
BL8545 is available in SOT23-6 package that
is
PB free
.
FEATURES
Up to 24V Output Voltage
Wide Operation Range: 2V to 6V
Maximum 3MHz Operating Frequency
PWM Dimming Control
Shutdown Current <1uA
Current Limit Cycle-by-Cycle
Low Current Sense Threshold: 200mV
24V Over Output Voltage Protection
Compact SOT23-6 Package
APPLICATIONS
Compact Back Light Module
Power Source for LED
Constant Current Source
TYPICAL APPLICATION
L1
VIN
10uH
D1
SS14
LED1
LED17
LED2
Cin
4.7uF
LED18
Cout
4.7uF
VIN
LX
OVP
LED3
LED19
ON
OFF
LED4
LC3300
BL8545
CE
GND
FB
LED20
R1
R5
Figure1. BL8545 Typical Application Circuit
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