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PDF MAX8901A Data sheet ( Hoja de datos )
| Número de pieza | MAX8901A | |
| Descripción | Highest Efficiency Supply | |
| Fabricantes | Maxim Integrated Products | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de MAX8901A (archivo pdf) en la parte inferior de esta página. Total 15 Páginas | ||
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19-0865; Rev 0; 8/07
EVAALVUAAILTAIOBNLEKIT
Highest Efficiency Supply for 2 to 6
Series WLEDs in a 2mm x 2mm TDFN Package
www.datasheet4u.com
General Description
The MAX8901A/MAX8901B step-up converters drive from
two to six series-connected white LEDs (WLEDs) with
constant current to provide uniform WLED intensity for
LCD backlighting in cell phones, PDAs, and other hand-
held devices. The MAX8901_ operate at a fixed 750kHz
(typ) switching frequency, allowing for tiny external com-
ponents, and are optimized for the highest possible effi-
ciency over the full 1-cell Li+/Li-Poly battery range.
These converters use a single input (ON) to enable the
IC and to control WLED intensity. The MAX8901A
requires a direct PWM input to regulate WLED intensity
with the WLED current proportional to the PWM duty
cycle. The MAX8901B uses single-wire, serial-pulse
dimming that reduces the WLED intensity in 32 linear
steps. Full-scale WLED current for serial-pulse
dimming is 24.75mA (MAX8901B, 0.75mA/step).
The MAX8901_ features an internal soft-start to eliminate
inrush currents during startup, input overvoltage
protection, WLED overvoltage protection, and a shut-
down mode with 0.01µA (typ) shutdown current. No
WLED current is present in shutdown provided the
WLED forward voltage is greater than the input supply
voltage. Additional features include undervoltage lock-
out (UVLO) and thermal shutdown.
The MAX8901_ are available in tiny 8-pin, 2mm x 2mm
TDFN-EP packages (0.8mm max height).
Applications
Display Backlight (from 2 to 6 WLEDs)
Cellular Phones
PDAs and Smartphones
MP3 and Portable Media Players
Portable Navigation Devices
Digital Cameras
INPUT
2.6V TO 5.5V
PWM DIMMING
CONTROL
3
IN
LX 4
7 MAX8901A
COMP
1
OVP
6
GND
5
PGND
2 ON
8
EP CS
OUTPUT
UP TO 25V
Features
♦ High Efficiency, Up to 91%
♦ 2.6V to 5.5V Input Voltage Range
♦ Fixed-Frequency Operation
♦ Supplies from 2 to 6 WLEDs with 1% LED Current
Accuracy
♦ Flexible Dimming Control
Direct PWM Dimming (MAX8901A)
32-Step, 1-Wire Serial Dimming
(MAX8901B)
♦ Input Undervoltage Lockout
♦ Input Overvoltage Lockout
♦ WLED Overvoltage Protection (25V typ)
♦ 0.01µA (typ) Shutdown Current
♦ No WLED Current in Shutdown
♦ Internal Soft-Start and Thermal Shutdown
Ordering Information
PART
PIN-PACKAGE PKG
CODE
TOP
MARK
MAX8901AETA+T
8 TDFN-EP*
2mm x 2mm
T822-1 +ABA
MAX8901BETA+T
8 TDFN-EP*
2mm x 2mm
T822-1 +ABB
Note: All devices are specified over the -40°C to +85°C operating
temperature range.
+Denotes a lead-free package.
*EP = Exposed paddle.
T = Tape and reel.
Pin Configuration appears at end of data sheet.
Typical Operating Circuits
INPUT
2.6V TO 5.5V
SERIAL-PULSE
DIMMING
CONTROL
3
IN
LX 4
MAX8901B
7
COMP
1
OVP
6
GND
5
PGND
2 ON
EP CS 8
OUTPUT
UP TO 25V
________________________________________________________________ Maxim Integrated Products 1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim's website at www.maxim-ic.com.
1 page  
Highest Efficiency Supply for 2 to 6
Series WLEDs in a 2mm x 2mm TDFN Package
www.datasheet4u.com
Typical Operating Characteristics (continued)
(Circuit of Figure 5, ILED = 24.75mA, VIN = VON = 3.6V, C1 = 1µF, C2 = 1µF, TA = +25°C, unless otherwise noted.)
LED AND BOOST EFFICIENCY
vs. INPUT VOLTAGE
95
BOOST
90
LED
85
80
75
70
2
6WLEDs,
INDUCTOR: TOKO A915AY-220M,
DIODE: CENTRAL SEMI CMDSH05-4
345
INPUT VOLTAGE (V)
6
800
700
600
500
400
300
200
100
0
2
IN CURRENT (IIN)
vs. SUPPLY VOLTAGE
MAX8901B
MAX8901A
3456
SUPPLY VOLTAGE (V)
7
SWITCHING WAVEFORMS
MAX8901A/B toc9
VI
50mV/div
AC-COUPLED
VIN
VOUT
VLX 10V/div
0V
100mV/div
VOUT
AC-COUPLED
ILEDs
ILX 100mA/div
1μs/div
VLX
0mA
INPUT OVERVOLTAGE
PROTECTION RESPONSE
MAX8901A/B toc10
6.4V 1V/div
5.4V (AC-COUPLED)
20ms/div
10V/div
0V
20mA/div
0mA
20mA/div
0V
STARTUP AND SHUTDOWN
RESPONSE (MAX8901A)
MAX8901A/B toc11
C2 = 0.1μF 2V/div
VON 0V
STARTUP AND SHUTDOWN
RESPONSE (MAX8901B)
MAX8901A/B toc12
2V/div
VON 0V
VOUT
ISUPPLY
ILEDs
10ms/div
10V/div
0V
100mA/div
0mA
20mA/div
0mA
VOUT
ISUPPLY
ILEDs
10ms/div
10V/div
0V
100mA/div
0mA
20mA/div
0mA
_______________________________________________________________________________________ 5
5 Page 
Highest Efficiency Supply for 2 to 6
Series WLEDs in a 2mm x 2mm TDFN Package
www.datasheet4u.com
Schottky Diode Selection
The high switching frequency of the MAX8901_
demands a high-speed rectification diode for optimum
efficiency. A Schottky diode is recommended due to its
fast recovery time and low forward voltage drop.
Ensure that the diode’s average and peak current
rating exceeds the average output current and peak
inductor current. In addition, the diode’s reverse
breakdown voltage must exceed VOUT. The RMS diode
current can be approximated from the following
equation:
IDIODE (RMS) = ILED × IPEAK
Capacitor Selection
Ceramic capacitors with X5R, X7R, or better dielectric
are recommended for stable operation over the entire
operating temperature range. The exact values of input
(C1) and output (C2) capacitors are not critical (see
Figures 4 and 5). The typical value for the input
capacitor is 1µF, and the typical value for the output
capacitor is 0.1µF (MAX8901A) or 1µF (MAX8901B).
Higher value capacitors can reduce input and output
ripple, but at the expense of size and higher cost. The
compensation capacitor (C3) stabilizes the converter
and controls soft-start. The compensation capacitor is
typically chosen to be 0.022µF for most applications.
Current-Sense Resistor (MAX8901A Only)
The MAX8901A uses a sense resistor (RCS) connected
from CS to GND to program the maximum WLED cur-
rent for 100% PWM duty cycle. The MAX8901A regu-
lates VCS to 0.5V (typ) for 100% duty cycle. Calculate
RCS (in ohms) using the following equation:
RCS
=
500
ILED(MAX)
where ILED(MAX) is the maximum WLED current in
milliamps. Maximum WLED current is programmed to
25mA using a 20Ω resistor.
PCB Layout
Due to fast switching waveforms and high-current
paths, careful attention is required when the PCB layout
is designed. Minimize trace lengths between the IC and
the inductor, the diode, the input capacitor, and the
output capacitor. For the MAX8901A, minimize the
trace length between the IC and RCS. Keep traces
short, direct, and wide. Keep noisy traces, such as the
LX node trace, away from CS. The input bypass
capacitor (CIN) should be placed as close as possible
to the IC. The ground connections of CIN and COUT
should be as close together as possible. PGND and
GND should be connected together at the input
capacitor ground terminal. Refer to the MAX8901 EV Kit
for an example layout.
______________________________________________________________________________________ 11
11 Page | ||
| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet MAX8901A.PDF ] | |
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