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PDF MAX1848 Data sheet ( Hoja de datos )
| Número de pieza | MAX1848 | |
| Descripción | White LED Step-Up Converter in SOT23 | |
| Fabricantes | Maxim Integrated | |
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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 RDSON N-channel MOSFET switch for high
efficiency and maximum battery life. A single analog
voltage Dual Mode™ 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 ✕ 3mm) and 8-pin SOT23 packages.
Applications
Cell Phones and Smart Phones
PDAs, Palmtops, and Wireless Handhelds
e-Books and Subnotebooks
White LED Display Backlighting
Typical Application Circuit
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 0.3µA Shutdown Current
o Small 8-pin Thin QFN (3mm ✕ 3mm) and
8-Pin SOT23 Packages
Ordering Information
PART
TEMP RANGE PIN-PACKAGE
TOP
MARK
MAX1848EKA
MAX1848ETA
-40°C to +85°C
-40°C to +85°C
8 SOT23
8 Thin QFN
(3mm ✕ 3mm)
AAIM
ACR
Note: Hand soldering is not recommended for the MAX1848
SOT23 package.
Pin Configuration
2.6V to 5.5V
CIN
3.3µF
LOGIC
OR DAC
CCOMP
0.15µF
L1
33µH
LX
V+ OUT
MAX1848
PGND
CTRL
GND
D1
COUT
1µF
COMP
CS
RSENSE
5Ω
TOP VIEW
COMP 1
CTRL 2
OUT 3
LX 4
MAX1848
8 V+
COMP 1
7 CS
CTRL 2
6 GND
OUT 3
5 PGND
LX 4
MAX1848
8 V+
7 CS
6 GND
5 PGND
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’s website at www.maxim-ic.com.
1 page  
White LED Step-Up Converter in SOT23
Typical Operating Characteristics (continued)
(See Typical Application Circuit, V+ = 3V, ILED = 15mA, L = 33µH, COUT = 1µF, CCOMP = 0.15µF, RSENSE = 5Ω, CTRL = 1V, 2 LEDs,
TA = +25°C, unless otherwise noted.)
VCTRL
VCTRL TRANSIENT RESPONSE
MAX1848 toc10
2.0V
1.0V
6.7V
VOUT 6.3V
30mA
ILED
CCOMP = 1µF
15mA
20ms/div
VLX
IL
VIN_RIPPLE
VOUT_RIPPLE
SWITCHING WAVEFORMS
MAX1848 toc11
6.5V
0
61mA
17mA
10mV/div
200ns/div
10mV/div
Pin Description
PIN NAME
FUNCTION
Compensation Pin for Error Amplifier. Connect capacitor from COMP to GND. Startup time is set
1
COMP
by the capacitance connected to this pin (0.833ms for each 0.01µF). VCOMP passively
discharges to GND when in shutdown.
Brightness/Shutdown Dual Mode Control Input. LED brightness and IC shutdown are controlled
2
CTRL
by the voltage on CTRL. Voltages between 250mV and 5.5V or (V+ + 2V), whichever is less,
adjust the brightness from dim to bright, respectively. To put the IC into shutdown, drive below
100mV or connect to GND.
Overvoltage Sense. When VOUT is greater than 13.25V, the internal N-channel MOSFET is turned
3
OUT
off and VCOMP decays to GND. When VOUT drops below 12.25V, the IC will re-enter soft-start.
Connect a 1µF capacitor from OUT to GND.
4 LX Inductor Connection. Drain of the internal high-voltage N-channel MOSFET.
5
PGND
Power Ground. Source of the internal high-voltage N-channel MOSFET.
6
GND
Ground
Current-Sense Feedback Input. Connect a resistor from this pin to GND to set the LED bias
7 CS
current. This pin regulates to 7.5% of VCTRL.
8
V+
Supply Voltage Input. The IC is powered from this pin. Input range is 2.6V to 5.5V. Bypass with a
ceramic capacitor to GND.
_______________________________________________________________________________________ 5
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| Páginas | Total 9 Páginas | |
| PDF Descargar | [ Datasheet MAX1848.PDF ] | |
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