CAT37
CMOS White LED Driver Boost Converter
FEATURES
s
Low quiescent ground current (0.5mA typical)
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Power efficiency over 80%
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Compatible pinout with LT1937
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Adjustable output current (up to 40mA)
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High frequency 1.2MHz operation
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Input voltage operation down to 2.5V
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Low resistance (0.5Ω) power switch
Ω
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Drives up to 4 White LEDs in series
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Shutdown current less than 1µA
H
GEN
FR
ALO
EE
LE
A
D
F
R
E
E
TM
s
Load fault protection against open-circuits
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Low value external components
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Low profile 5-lead SOT23 (1mm max) and
TDFN (0.8mm) package
APPLICATIONS
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Color LCD and keypad backlighting
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Cellular phones
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Handheld terminals
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Digital cameras
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PDAs/Games
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Portable MP3 players
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 thin SOT23 package and in a TDFN (0.8mm max
height) package.
D1
TYPICAL APPLICATION
VIN
3 V to 5 V
5
VIN
1
SW
CAT37
OFF ON
4
SHDN
FB
GND
2
SOT23 Pin Numbers
15mA
3
C1: Taiyo Yuden JMK212BJ475
C2: Taiyo Yuden EMK212BJ105
D1: Zetez ZHCS400
L1: Panasonic ELJEA6R8 or equivalent
Figure 1. Driver for Four High-Brightness White LEDs
© 2004 by Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
1
Doc No. 5005, Rev. R
CATALYST [ CATALYST SEMICONDUCTOR ]
