CAT32TDI-T3 Datasheet, PDF (1/13 Pages) ON Semiconductor – CMOS White LED Driver

CAT37
CMOS White LED Driver Boost Converter
FEATURES
„ Low quiescent ground current (0.5mA typical)
„ Power efficiency over 80%
„ Compatible pinout with LT1937
„ Adjustable output current (up to 40mA)
„ High frequency 1.2MHz operation
„ Input voltage operation down to 2.5V
„ Low resistance (0.5Ω) power switch
„ Drives up to 4 White LEDs in series
„ Shutdown current less than 1µA
„ Load fault protection against open-circuits
„ Low value external components
„ Low profile (1mm) TSOT-23 5-lead package
APPLICATION
„ Color LCD and keypad backlighting
„ Cellular phones
„ Handheld terminals
„ Digital cameras
„ PDAs/Games
„ Portable MP3 players
For Ordering Information details, see page 11.
DESCRIPTION
The CAT37 is a DC/DC step up converter that delivers
a regulated output current. Operation at a constant
switching frequency of 1.2MHz allows the device to be
used with very small value external inductor and
ceramic capacitors.
The CAT37 is targeted to drive multiple white light-
emitting diodes (LEDs) connected in series and
provides the necessary regulated current to control
the brightness and the color purity. An external
resistor R1 controls the output current level. LED
currents of up to 40mA can be supported over a wide
range of input supply voltages from 2.5V to 7V,
making the device ideal for battery-powered
applications.
A high voltage output stage allows up to 4 White LEDs
to be driven in series. Series drive provides inherent
current matching.
LED dimming can be done by using a DC voltage, a
logic signal, or a pulse width modulation (PWM)
signal. The shutdown input pin allows the device to be
placed in power-down mode with “near zero”
quiescent current.
In addition to overcurrent limiting protection, the
device also includes detection circuitry to ensure
protection against open-circuit load fault conditions.
The device is available in a low profile (1mm max
height) 5-lead TSOT-23 package.
TYPICAL APPLICATION CIRCUIT
VIN
3V to 5V
L1
6.8µH
D1
C1
1µF
5
1
VIN
SW
ON OFF
CAT37
4
SHDN
GND
2
FB ³
C2
1µF
15mA
R1
6.34Ω
C1: Taiyo Yuden JMK212BJ475
C2: Taiyo Yuden EMK212BJ105
L1: Panasonic ELJEA6R8 or equivalent
Figure 1. Driver for Four High-Brightness White LEDs
© 2009 SCILLC. All rights reserved.
1
Characteristics subject to change without notice
Doc. No. MD-5005 Rev. V