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PDF ISL97635 Data sheet ( Hoja de datos )
| Número de pieza | ISL97635 | |
| Descripción | SMBus 8-Channel LED Driver | |
| Fabricantes | Intersil Corporation | |
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Data Sheet
December 22, 2008
ISL97635
FN6434.2
SMBus 8-Channel LED Driver
The ISL97635 is a digitally controlled LED driver that
controls 8 channels of LED current for LCD backlight
applications. The ISL97635 is capable of driving typically 72
(8x9) pieces of 3.5V/30mA or 80 (8x10) pieces of
3.2V/20mA LEDs. The ISL97635’s 8 channels of voltage
controlled current sources with typical currents matching of
±1%, which compensate for the non-uniformity effect of
forward voltages variance in the LED stacks. To minimize the
voltage headroom and power loss in the typical multi-strings
operation, the ISL97635 features a dynamic headroom
control that monitors the highest LED forward voltage string
and uses its feedback signal for output regulation.
The LED dimming control can be achieved through a
SMBus, an external PWM, or a variable DC (analog light
sensor) input. SMBus controlled dimming allows 256 levels
each of PWM and DC current adjustments. The SMBus
PWM dimming frequency can be adjusted from 100Hz to
5kHz by an external capacitor. External PWM input allows up
to 20kHz audio noise free PWM dimming. The SMBus PWM
setting and an external PWMI signal can also be combined
to provide a dynamic PWM dimming that complies with
Intel’s DPST (Display Power Saving Technology)
requirement.
One or more channels can be selected sequentially in any
order, allowing scrolling in RGB LED backlighting
applications.
The ISL97635 features extensive protection functions that
include string open and short circuit detections, OVP, OTP,
thermal shutdown and an optional input overcurrent
protection with master fault disconnect switch. The fault
conditions will be recorded in the Fault/Status register. There
are selectable short-circuit thresholds and the switching
frequency can be programmed between 600kHz and
1.2MHz.
Available in the 24 Ld 4mmx4mm QFN, the ISL97635
operates from -40°C to +85°C with input voltage ranging
from 6V to 24V.
Features
• 8 Channels
• 6V to 24V Input
• 34.5V Output Max
• Drive Maximally 72 (3.5V/30mA each) or 80 (3.2V/20mA
each) LEDs
• Current Matching ±1% Typ
• Dynamic Headroom Control
• Dimming Controls
- SMBus 8-Bit PWM Current Control
- SMBus 8-Bit DC Current Control
- External PWM Input up to 20kHz Dimming
- SMBus and External PWM DPST Dimming Control
- DC-to-PWM Dimming Control
• Protections
- String Open Circuit Detection
- String Short Circuit Detection with Selectable Thresholds
- Over-Temperature Protection
- Overvoltage Protection
- Input Overcurrent Protection with Disconnect Switch
• 600kHz/1.2MHz Selectable fSW
• Selectable Channels Allows Scrolling Backlight
• 24 Ld (4mmx4mm) QFN Package
• Pb-Free (RoHS compliant)
Applications
• Notebook Displays WLED or RGB LED Backlighting
• LCD Monitor LED Backlighting
• Automotive Displays LED Backlighting
• Automotive or Traffic Lighting
Ordering Information
PART NUMBER
PART
(Note)
MARKING
ISL97635IRZ* 976 35IRZ
PACKAGE
(Pb-free)
24 Ld 4x4 QFN
PKG.
DWG. #
L24.4x4D
*Add “-T” or “-TK” suffix for tape and reel. Please refer to TB347 for
details on reel specifications.
NOTE: These Intersil Pb-free plastic packaged products employ
special Pb-free material sets, molding compounds/die attach
materials, and 100% matte tin plate plus anneal (e3 termination
finish, which is RoHS compliant and compatible with both SnPb and
Pb-free soldering operations). Intersil Pb-free products are MSL
classified at Pb-free peak reflow temperatures that meet or exceed
the Pb-free requirements of IPC/JEDEC J STD-020.
1 CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-888-INTERSIL or 1-888-468-3774 | Intersil (and design) is a registered trademark of Intersil Americas Inc.
Copyright Intersil Americas Inc. 2008. All Rights Reserved
All other trademarks mentioned are the property of their respective owners.
1 page  
ISL97635
Electrical Specifications
All specifications below are tested at TA = -40°C to +85°C; VIN = 12V, EN = 5V, RSET = 36.6kΩ,
unless otherwise noted. Parameters with MIN and/or MAX limits are 100% tested at +25°C, unless otherwise
specified. Temperature limits established by characterization and are not production tested. (Continued)
PARAMETER
DESCRIPTION
CONDITION
MIN TYP MAX UNIT
Eff_peak
Peak Efficiency
ΔIOUT/ΔVIN
DMAX
DMIN
fOSC_hi
fOSC_lo
ILX_leakage
Line Regulation
Boost Maximum Duty Cycle
Boost Minimum Duty Cycle
Lx Frequency
Lx Frequency
Lx Leakage Current
VIN = 18V, 54 LEDs, 20mA
each, L = 8.2µH with DCR
106mΩ, TA = +25°C
VIN = 12V, 54 LEDs, 20mA
each, L = 8.2µH with DCR
106mΩ, TA = +25°C
VIN = 6V, 54 LEDs, 20mA
each, L = 8.2µH with DCR
106mΩ, TA = +25°C
Register 0x08, fSW = 1
Register 0x08, fSW = 0
VLX = 36V, EN = 0
91 %
88 %
86 %
0.1 %
82 %
7%
1.0 1.2 1.3 MHz
550 600 650 kHz
10 µA
REFERENCE
IMATCH
Channel-to-Channel Current Matching
IACC
Current Accuracy
FAULT DETECTION
IOUT = 30mA, BRT = 255
-3.5 ±1 +3.5
±3
%
%
VSC Short Circuit Threshold Accuracy
Reg0x08 = 0x0F or 0x0B
Reg0x00 = 0xFF
7.8 8 8.8
V
Reg0x08 = 0x0E or 0x0A
Reg0x00 = 0xFF
2.8 3.1 3.8
V
Vtemp_acc
Over-Temperature Threshold Accuracy
VOVPlo
Overvoltage Limit on OVP Pin
OVPhys
OVP Hysteresis
OVPfault
OVP Short Detection Fault Level
SMBus INTERFACE
5
1.17 1.2 1.23
20
300
°C
V
mV
mV
VIL Guaranteed Range for Data, Clock Input Low Voltage
0.8 V
VIH Guaranteed Range for Data, Clock Input High Voltage
2.1 VDD V
VOL
SMBus Data Line Logic Low Voltage with 1.1kΩ series
resistor from data bus to SMBDAT pin
IPULLUP = 350µA
0.4 V
SMBus Data Line Logic Low Voltage without series resistor IPULLUP = 4mA
from data bus to SMBDAT pin
0.17 V
ILEAK
Input Leakage On SMBData/SMBClk
VDD Nominal Bus Voltage
SMBus TIMING SPECIFICATIONS (Note 4)
3V to 5V ±10%
-1 1 µA
2.7 5.5 V
fSMB
tBUF
tHD:STA
SMBus Clock Frequency
Bus Free Time Between Stop and Start Condition
Hold Time After (Repeated) START Condition. After this
Period, the First Clock is Generated
10 100 kHz
4.7 µs
4.0 µs
tSU:STA
tSU:STO
Repeated Start Condition Setup Time
Stop Condition Setup Time
4.7 µs
4.0 µs
5 FN6434.2
December 22, 2008
5 Page 
ISL97635
Pin Descriptions (I = Input, O = Output, S = Supply) (Continued)
PIN
NAME
TYPE
DESCRIPTION
22 COMP
O Boost compensation pin
23 VIN
S Input voltage for the device and LED power
24 VDC
S De-couple capacitor for internally generated supply rail. If 2.7V < VBL+ < 5.5V, apply VDC directly with
a supply voltage of 2.7V to 5.5V
Theory of Operation
PWM Boost Converter
The current mode PWM boost converter produces the
minimal voltage needed to enable the LED stack with the
highest forward voltage drop to run at the programmed
current. The ISL97635 employs current mode control boost
architecture that has a fast current sense loop and a slow
voltage feedback loop. Such architecture achieves a fast
transient response that is essential for the notebook
backlight application where the power can be a series of
drained batteries or instantly change to an AC/DC adapter
without rendering a noticable visual nuisance. The number
of LEDs that can be driven by ISL97635 depends on the
type of LED chosen in the application. The ISL97635 is
capable of boosting up to 34.5V and typically driving 9 LEDs
in series for each of the 8 channels, enabling a total of 72
pieces of the 3.5V/30mA type of LEDs.
Enable and PWMI
The EN/PWMI pin serves dual purposes; it is used as an
Enable signal and can be used as a PWM input signal for
dimming. If a PWM signal is applied to this pin, the first pulse of
minimum 40µs will be used as an Enable signal. If there is no
signal for longer than 28ms, the device will enter shutdown. The
EN/PWMI pin cannot be floating thus a 10kΩ pull-down resistor
may need to be added.
Current Matching and Current Accuracy
Each channel of the LED current is regulated by the current
source circuit, as shown in Figure 17.
The LED peak current is set by translating the RSET current
to the output with a scaling factor of 733/RSET. The source
terminals of the current source MOSFETs are designed as
100mV to minimize the power loss. The sources of errors of
the channel-to-channel current matching come from the
op amp’s offset, internal layout, reference, and current
source resistors. These parameters are optimized for current
matching and absolute current accuracy. On the other hand,
the absolute accuracy is additionally determined by the
external RSET, and therefore, additional tolerance will be
contributed by the current setting resistor. A 1% tolerance
resistor is therefore recommended.
+- REF
RSET
+
-
PWM DIMMING
DC DIMMING
+
-
FIGURE 17. SIMPLIFIED CURRENT SOURCE CIRCUIT
Dynamic Headroom Control
The ISL97635 features a proprietary Dynamic Headroom
Control circuit that detects the highest forward voltage string
or effectively the lowest voltage from any of the IIN pins.
When this lowest IIN voltage is lower than the short circuit
threshold, VSC, such voltage will be used as the feedback
signal for the boost regulator. The boost makes the output to
the correct level such that the lowest IIN pin is at the target
headroom voltage. Since all LED stacks are connected to
the same output voltage, the other IIN pins will have a higher
voltage, but the regulated current source circuit on each
channel will ensure that each channel has the same
programmed current. The output voltage will regulate
cycle-by-cycle and is always referenced to the highest
forward voltage string in the architecture.
Dimming Controls
The ISL97635 allows two ways of controlling the LED
current, and therefore, the brightness. They are:
1. DC current adjustment
2. PWM chopping of the LED current defined in Step 1.
There are various ways to achieve DC or PWM current
control, which will be described in the following.
11 FN6434.2
December 22, 2008
11 Page | ||
| Páginas | Total 28 Páginas | |
| PDF Descargar | [ Datasheet ISL97635.PDF ] | |
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