19-2028; Rev 1; 9/02
White LED Step-Up Converter in SOT23
General Description
The MAX1848 drives white LEDs with a constant cur-
rent to provide backlight in cell phones, PDAs, and
other hand-held devices. The step-up converter topology
allows series connection of the white LEDs so that the
LED currents are identical for uniform brightness. This
configuration eliminates the need for ballast resistors
and expensive factory calibration. Other benefits
include greater simplicity, lower cost, higher efficiency,
and greater reliability.
This step-up PWM converter includes an internal, high-
voltage, low R
DSON
N-channel MOSFET switch for high
efficiency and maximum battery life. A single analog
voltage Dual Mode
鈩?/div>
input provides a simple means of
brightness adjustment and on/off control. Fast 1.2MHz
current-mode PWM control allows for small input and
output capacitors and a small inductor while minimizing
ripple on the input supply/battery. Programmable soft-
start eliminates inrush current during startup.
The MAX1848 is available in space-saving 8-pin thin
QFN (3mm
鉁?/div>
3mm) and 8-pin SOT23 packages.
Features
o
Constant Current Regulation for Uniform
Illumination
o
High 87% Efficiency
o
Analog or Logic Control of LED Intensity
o
0.8W Output Power with Internal High-Voltage
MOSFET Switch
o
Small, Low-Profile External Components
o
2.6V to 5.5V Input Range
o
13V Maximum Output with Overvoltage Protection
o
Optimized for Low Input Ripple
o
Programmable Soft-Start
o
0.3碌A(chǔ) Shutdown Current
o
Small 8-pin Thin QFN (3mm
鉁?/div>
3mm) and
8-Pin SOT23 Packages
MAX1848
Applications
Cell Phones and Smart Phones
PDAs, Palmtops, and Wireless Handhelds
e-Books and Subnotebooks
White LED Display Backlighting
PART
MAX1848EKA
MAX1848ETA
Ordering Information
TEMP RANGE
-40擄C to +85擄C
-40擄C to +85擄C
PIN-PACKAGE
8 SOT23
8 Thin QFN
(3mm
鉁?/div>
3mm)
TOP
MARK
AAIM
ACR
Note:
Hand soldering is not recommended for the MAX1848
SOT23 package.
Typical Application Circuit
L1
33碌H
TOP VIEW
Pin Configuration
2.6V to 5.5V
C
IN
3.3碌F
V+
D1
LX
OUT
MAX1848
C
OUT
1碌F
COMP
1
CTRL
2
8
7
V+
CS
GND
PGND
COMP
CTRL
OUT
LX
1
2
8
7
V+
CS
GND
PGND
MAX1848
OUT
3
6
5
3
4
LX
4
MAX1848
6
5
LOGIC
OR DAC
C
COMP
0.15碌F
CTRL
COMP
PGND
GND
CS
R
SENSE
5鈩?/div>
SOT23
THIN QFN
3mm x 3mm
Dual Mode is a trademark of Maxim Integrated Products, Inc.
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim鈥檚 website at www.maxim-ic.com.
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