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PDF MAX17061A Data sheet ( Hoja de datos )
| Número de pieza | MAX17061A | |
| Descripción | 8-String White LED Driver | |
| Fabricantes | Maxim Integrated Products | |
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19-4485; Rev 0; 2/09
www.DataSheet4EUV.cAAoLVmUAAILTAIOBNLEKIT
8-String White LED Driver with
SMBus for LCD Panel Applications
General Description
The MAX17061A 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. An internal switch current-mode step-up
controller drives the LED array, which can be configured
for up to eight strings in parallel and 10 LEDs per string.
Each string is terminated with ballast that achieves ±1.5%
current-regulation accuracy between strings, ensuring
even LED brightness. The MAX17061A has a wide input-
voltage range from 7.5V to 26V, and provides a fixed
25mA or adjustable 15mA to 30mA full-scale LED current.
The MAX17061A internally generates a DPWM signal for
accurate WLED dimming control. The DPWM frequency
is resistor programmable, while DPWM duty cycle is con-
trolled directly from an external PWM signal or through a
control word through the MAX17061A’s SMBus™ inter-
face. This DPWM control provides a dimming range with
8-bit resolution and supports Intel display-power-saving
technology (DPST) to maximize battery life.
The MAX17061A has multiple features to protect the
controller from fault conditions. Separate feedback
loops limit the output voltage under any circumstance,
ensuring safe operation. Once an open string is detect-
ed, the string is disabled while other strings operate
normally. The MAX17061A also features short LED
detection. The shorted strings are also disabled after a
2ms fault blanking interval. The controller features
cycle-by-cycle current limit to provide stable operation
and soft-start capability. If the MAX17061A is in current-
limit condition, the step-up converter is latched off after
an internal timer expires. A thermal-shutdown circuit
provides another level of protection.
The MAX17061A’s step-up controller features an internal
150mΩ (typ), 45V (max) power MOSFET with local cur-
rent-sense amplifier for accurate cycle-by-cycle current
limit. This architecture greatly simplifies the external cir-
cuitry and saves PCB space. Low-feedback voltage at
each LED string 625mV (typ) at 25mA LED current helps
reduce power loss and improve efficiency. The
MAX17061A features selectable switching frequency
(500kHz, 750kHz, or 1MHz), which enables a wide vari-
ety of applications that can trade off component size for
operating frequency.
The MAX17061A is available in a thermally enhanced
28-pin, 4mm x 4mm Thin QFN package.
Applications
Notebook, Subnotebook,
and Tablet Computer
Displays
Automotive Systems
Handy Terminals
Features
o Accurate Dimming Control Using SMBus, PWM
Interface
o Dimming Range with 8-Bit Resolution
o Adjustable DPWM Frequency with 1.5% Accuracy
o Up to Eight Parallel Strings Multiple Series-
Connected LEDs
o ±1.5% Current Regulation Accuracy Between
Strings
o Low String Feedback Voltage: 625mV at 25mA
LED Current
o Full-Scale LED Current Adjustable from 15mA to
30mA, or Preset 25mA
o Open and Short LED Protections
o Output Overvoltage Protection
o 0.15Ω Internal HV Power MOSFET (45V max)
o Wide Input-Voltage Range from 4.5V to 26V
o 500kHz/750kHz/1MHz Selectable Switching
Frequency
o Small 28-Pin, 4mm x 4mm, Thin QFN package
Ordering Information
PART
TEMP RANGE
PIN-PACKAGE
MAX17061AETI+
-40oC to +85oC
28 Thin QFN
+Denotes a lead(Pb)-free/RoHS-compliant package.
Simplified Operating Circuit
L1 D1
VIN
VOUT
VCC
5V
VDD IN
VCC
LX1, 2
ISET
PGND1, 2
CCV OV
PWM
CLK
DATA
MAX17061A
PWMI
PWMO
FB1
GND
N.C. OSC
FB2
FB3
FB4
SCL FB5
FB6
SDA FB7
FSET FB8
EP
R1
R2
Pin Configuration appears at end of data sheet.
SMBus is a trademark of Intel Corp.
________________________________________________________________ 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  
www.DataSheet4U.com
8-String White LED Driver with
SMBus for LCD Panel Applications
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, VIN = 12V, CCCV = 0.022µF, RCCV = 5.1kΩ, VISET = VOSC = VDD = VCC, 5V = RFSET = 464kΩ, VPWMI = GND,
TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER
BOOST CONVERTER
LX On-Resistance
Operating Frequency
OSC High-Level Threshold
CONDITIONS
20mA from LX_ to PGND
VOSC = VCC
VOSC = open
VOSC = GND
MIN TYP MAX UNITS
0.89
675
450
VCC -
0.4
0.3
1.10 MHz
825
kHz
560
V
OSC Midlevel Threshold
OSC Low-Level Threshold
Maximum Duty Cycle
LX Current Limit
Duty cycle = 75% (Note 1)
CONTRL INPUT
SDA, SCL Logic Input-High Level
SDA, SCL Logic Input-Low Level
PWMI Logic Input-High Level
PWMI Logic Input-Low Level
INPUT LEAKAGE
SDA Output Low Sink Current
VSDA = 0.4V
LED CURRENT
Full-Scale FB_ Output Current
ISET = VCC
RISET = 133k
RISET = 200k
RISET = 266k
ISET High-Level Threshold
Default setting
ISET Output Voltage
1.5
94
1.6
2.1
2.1
4
24.5
28.6
19.0
14.4
VCC -
0.4
1.166
VCC -
2.0
0.4
97
V
V
%
A
0.8 V
V
0.8 V
mA
25.5
31.4
21.0
15.6
1.306
mA
V
V
Current Regulation
Between Strings
ISET = VCC
-1.5 1.5 %
Minimum FB_ Regulation Voltage
Maximum FB_ Ripple
FB_ On-Resistance
IFB_ = 25mA
IFB_ = 30mA
IFB_ = 20mA
IFB_ = 15mA
IFB_ = 20mA (COUT = 1μF, OSC = VCC) (Note1)
VFB_ = 50mV (includes 10 sense resistor)
425
575
380
285
910
1100
740
560
200
28.4
mV
mVP-P
_______________________________________________________________________________________ 5
5 Page 
www.DataSheet4U.com
8-String White LED Driver with
SMBus for LCD Panel Applications
Pin Description (continued)
PIN NAME
FUNCTION
22 VDD Boost Regulator MOSFET Gate Drive Supply. Bypass VDD to GND with a ceramic capacitor of 1μF or greater.
23
VCC
5V Control Supply Input. VCC provides power to the MAX17061A. Bypass VCC to GND with a ceramic
capacitor of 1μF or greater.
24
CCV
Step-Up Converter Compensation Pin. Connect a 0.022μF ceramic capacitor and 5.1k resistor from CCV
to GND. When the MAX17061A shuts down, CCV is discharged to 0V through an internal 20k resistor.
25
OV
Overvoltage Sense. Connect OV to the center tap of a resistive voltage-divider from VOUT to ground. The
detection threshold for voltage limiting at OV is 1.236V (typ).
Full-Scale LED Current Adjustment Pin. The resistance from ISET to GND controls the full-scale current in
each LED string:
26 ISET
ILEDMAX = 20mA x 200k/RISET
The acceptable resistance range is 133k < RISET < 266k, which corresponds to full-scale LED current
of 30mA > ILEDMAX > 15mA. Connect ISET to VCC for a default full-scale LED current of 25mA.
27 FB1 LED String 1 Cathode Connection. FB1 is the open-drain output of an internal regulator, which controls
current through FB1. FB1 can sink up to 30mA. If unused, connect FB1 to VCC.
28
FB2
LED String 2 Cathode Connection. FB2 is the open-drain output of an internal regulator, which controls
current through FB2. FB2 can sink up to 30mA. If unused, connect FB2 to VCC.
— EP Exposed Backside Pad. Solder to the circuit board ground plane with sufficient copper connection to
ensure low thermal resistance. See the PCB Layout Guidelines section.
Detailed Description
The MAX17061A is a high-efficiency driver for arrays of
white LEDs. It contains a fixed-frequency current- mode
PWM step-up controller, dimming control circuit, SMBus
interface, internal power MOSFET, and eight regulated
current sources (see Figure 2). When enabled, the step-
up controller boosts the output voltage to provide suffi-
cient headroom for the current sources to regulate their
respective string currents. The MAX17061A features
selectable switching frequency (500kHz, 750kHz, or
1MHz), which allows trade-offs between external com-
ponent size and operating efficiency.
WLED brightness is controlled by turning the WLEDs
on and off with a DPWM signal. The DPWM frequency
can be accurately adjusted with a resistor. The bright-
ness of the LEDs is proportional to the duty cycle of the
DPWM signal, which is controlled externally through
either a PWM or 2-wire SMBus-compatible interface, or
both. When both interfaces are used at the same time,
the product of the PWM duty cycle and SMBus com-
mand value is used for the dimming control. This
DPWM control scheme provides a full dimming range
with 8-bit resolution.
The MAX17061A has multiple features to protect the
controller from fault conditions. Separate feedback
loops limit the output voltage in all circumstances. The
MAX17061A checks each FB_ voltage during the opera-
tion. If one or more strings are open, the corresponding
FB_ voltages are pulled below 175mV (typ), and open-
circuit fault is detected. As a result, the respective cur-
rent sources are disabled. When one or more LEDs are
shorted and the FB_ voltage exceeds 1.1 x VCC, short
fault is detected and the respective current source is
disabled. In either LED open or short conditions, the
fault strings are disabled while other strings can still
operate normally. The controller features cycle-by-
cycle current limit to provide stable operation and soft-
start protection. In a current-limit condition, the
controller shuts down after a 128µs overcurrent fault
timer expires. A thermal-shutdown circuit provides
another level of protection.
The MAX17061A requires an external 5V supply to pro-
vide the internal bias and gate drive for the step-up
controller.
______________________________________________________________________________________ 11
11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet MAX17061A.PDF ] | |
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