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PDF MAX8790 Data sheet ( Hoja de datos )

Número de pieza MAX8790
Descripción Six-String White LED Driver
Fabricantes Maxim Integrated Products 
Logotipo Maxim Integrated Products Logotipo



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No Preview Available ! MAX8790 Hoja de datos, Descripción, Manual

19-0658; Rev 0; 11/06
EVAALVUAAILTAIOBNLEKIT
Six-String White LED Driver with Active
Current Balancing for LCD Panel Applications
General Description
The MAX8790 is a high-efficiency driver for white light-
emitting diodes (LEDs). It is designed for large liquid-
crystal displays (LCDs) that employ an array of LEDs as
the light source. A current-mode step-up controller drives
up to six parallel strings of multiple series-connected
LEDs. Each string is terminated with ballast that achieves
±1.5% current regulation accuracy, ensuring even bright-
ness for all LEDs. The MAX8790 has a wide input-voltage
range from 4.5V to 26V, and provides a fixed 20mA or
adjustable 15mA to 25mA full-scale LED current.
The MAX8790 has two dimming control modes to
enable a wide variety of applications. In direct DPWM
mode, the LED current is directly turned on and off by a
PWM signal. In analog dimming mode, an internal
phase-locked loop (PLL) circuit translates the PWM sig-
nal into an analog signal and linearly controls the LED
current down to 12.5%. Below 12.5%, digital dimming is
added to allow lower average LED current down to 1%.
Both control methods provide 100:1 dimming range.
The MAX8790 has multiple features to protect the con-
troller from fault conditions. Separate feedback loops limit
the output voltage if one or more LEDs fail open or short.
The controller features cycle-by-cycle current limit to pro-
vide consistent operation and soft-start capability. A ther-
mal-shutdown circuit provides another level of protection.
The step-up controller uses an external MOSFET, which
provides good efficiency and allows for scalable output
power and maximum operating voltage. Low feedback
voltage at each LED string (450mV) helps reduce
www.DaptaoSwheeretl4oUs.sc.oTmhe MAX8790 features selectable switching
frequency (500kHz, 750kHz, or 1MHz), which allows
trade-offs between external component size and ope-
rating efficiency.
The MAX8790 is available in a thermally enhanced,
lead-free, 20-pin, 4mm x 4mm, Thin QFN package.
Applications
Notebook, Subnotebook, and Tablet Computer
Displays
Automotive Systems
Handy Terminals
Ordering Information
PART
TEMP RANGE PIN-PACKAGE PKG
CODE
MAX8790ETP+ -40°C to +85°C 20 Thin QFN
T2044-3
(4mm x 4mm)
+Denotes a lead-free package.
Features
o Drives Six Parallel Strings with Multiple Series-
Connected LEDs per String
o ±1.5% Current Regulation Accuracy Between
Strings
o Low 450mV Feedback Voltage at Full Current
Improves Efficiency
o Step-Up Controller Regulates the Output Just
Above the Highest LED String Voltage
o Full-Scale LED Current Adjustable from 15mA to
25mA, or Preset 20mA
o Wide 100:1 Dimming Range
o Programmable Dimming Control: Direct DPWM or
Analog Dimming
o Built-In PLL for Synchronized Dimming Control
o Open and Short LED Protections
o Output Overvoltage Protection
o Wide Input Voltage Range from 4.5V to 26V
o External MOSFET Allows a Large Number of LEDs
per String
o 500kHz/750kHz/1MHz Switching Frequency
o Small, 20-Pin, 4mm x 4mm Thin QFN Package
Simplified Operating Circuit
VIN
CIN
0.1μF
L1 D1 VOUT
SHDN IN
VCC
FSET
ISET
EXT
CS
MAX8790
GND
BRT
N.C. OSC
OV
N.C. CPLL
CCV
FB1
FB2
ENA FB3
FB4
EP FB5
FB6
N1
Rs
R1
R2
Pin Configuration appears at end of data sheet.
________________________________________________________________ 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




MAX8790 pdf
Six-String White LED Driver with Active
Current Balancing for LCD Panel Applications
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1. VIN = 12V, VSHDN = VIN, CCV = 0.1µF, TA = -40°C to +85°C, unless otherwise noted.) (Note 2)
PARAMETER
LED CURRENT
Full-Scale FB_ Output Current
CONDITIONS
ISET = VCC, BRT = 100%
RISET = 80kΩ to GND, BRT = 100%
RISET = 133kΩ to GND, BRT = 100%
ISET High-Level Threshold
Default setting for 20mA full-scale LED current
ISET Voltage
20% Output Current
Current Regulation Between
Strings
Minimum FB_ Regulation Voltage
Maximum FB_ Ripple
FB_ On-Resistance
FB_ Leakage Current
BRT Input Frequency
FAULT PROTECTION
OV Threshold Voltage
ISET = VCC, BRT = 20%
ISET = VCC, BRT = 100%
ISET = VCC, BRT = 20%
RISET = 80kΩ to GND, BRT = 100%
ISET= VCC, BRT = 100%
ISET = VCC, BRT = 12.5%
ISET= VCC, COUT = 1µF, OSC = VCC (Note 1)
VFB_ = 50mV
SHDN = GND, VFB_ = 26V
SHDN = VIN, BRT = GND, VFB_ = 15V
MIN TYP MAX
19.2
24.0
14.4
VCC -
0.4
1.12
3.8
-2
-3
280
250
140
100
20.8
26.0
15.6
1.26
4.2
+2
+3
840
760
530
200
20
1
28
500
1.16 1.30
FB_ Overvoltage Threshold
www.DatFaASUheLeTt4SUh.uctodmown Timer
PHASE-LOCKED LOOP
VFB_ > 5.6V (typ)
VCC +
0.2
50
VCC +
1.45
80
FSET High-Level Threshold
PLL disabled
BRT Frequency Capture Range
RFSET = 500kΩ
RFSET = 250kΩ
Note 1: Specifications are guaranteed by design, not production tested.
Note 2: Specifications to -40°C are guaranteed by design, not production tested.
VCC -
0.4
150
300
250
500
UNITS
mA
V
V
mA
%
mV
mVP-P
Ω
µA
Hz
V
V
ms
V
Hz
Hz
_______________________________________________________________________________________ 5

5 Page





MAX8790 arduino
Six-String White LED Driver with Active
Current Balancing for LCD Panel Applications
IN 5V LINEAR
REGULATOR
ERROR
COMPARATOR
OUTPUT OVERVOLTAGE
COMPARATOR
1.25V
OV
VCC
VCC
OSCILLATOR
OSC
SHDN
TRI-LEVEL
COMPARATOR
CCV
ISET REF ADJ
FSET OSC CLK
256 x fBRT
www.DataSheet4U.com VCC - 0.4V
CLOCK
SLOPE
COMPENSATION
65ms TIMER
SHUTDOWN
LATCH
ERROR
AMPLIFIER
gm
FB OVERVOLTAGE
COMPARATOR
VCC + 0.6V
HVC
LVC
REF SAT
8-BIT DAC
8
DIGITAL CONTROL
CPLL PLL
BRT
ENA
8-BIT
COUNTER
8
8
8-BIT
LATCH
5 MSBs
5 LSBs
DIGITAL
COMPARATOR
CONTROL AND
DRIVER LOGIC
CURRENT SENSE
FB6
FB5
FB4
FB3
FB2
EN N
10Ω
CURRENT SOURCE
CURRENT SOURCE
CURRENT SOURCE
CURRENT SOURCE
CURRENT SOURCE
CURRENT SOURCE
EXT
CS
FB1
GND
FB2
FB3
FB4
FB5
FB6
Figure 2. Control Circuit Block Diagram
______________________________________________________________________________________ 11

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