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PDF ISL97636 Data sheet ( Hoja de datos )

Número de pieza ISL97636
Descripción 8-Channel LED Driver
Fabricantes Intersil Corporation 
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®
Data Sheet
May 9, 2008
ISL97636
FN6570.0
8-Channel LED Driver
The ISL97636 is an integrated power LED driver that
controls 8 channels of LED current for LCD backlight
applications. The ISL97636 is capable of driving typically 72
(8x9) pieces of 3.5V/30mA or 80 (8x10) pieces of
3.2V/20mA LEDs. The ISL97636’s contains 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 ISL97636 features a dynamic
headroom control that monitors the highest LED forward
voltage string and uses its feedback signal for output
regulation.
The LED brightness can be pulse width modulated with an
applied PWM signal from DC to audio noise free 20kHz.
The ISL97636 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.
Available in the 24 Ld 4mmx4mm QFN, the ISL97636
operates from -40°C to +85°C with input voltage ranges from
6V to 24V for high LEDs count applications.
Ordering Information
PART
NUMBER
(Note)
PART
MARKING
PACKAGE
(Pb-Free)
PKG.
DWG. #
ISL97636IRZ* 976 36IRZ 24 Ld 4x4 QFN 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.
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
• PWM Signal up to 20kHz Dimming
• Protections
- String Open Circuit Detection
- String Short Circuit Detection with Selectable Thresholds
- Over-Temperature Protection
- Overvoltage Protection
- Optional Input Overcurrent Protection w/Disconnect SW
• 1.2MHz Switching Frequency
• 24 Ld 4mmx4mm QFN Package
• Pb-Free (RoHS compliant)
Applications
• Notebook Displays LED Backlighting
• LCD Monitor LED Backlighting
• Automotive Displays LED Backlighting
• Automotive or Traffic Lighting
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.

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ISL97636 pdf
ISL97636
Electrical Specifications
All specifications below are tested at TA = -40°C to +85°C; VIN = 12V, EN = 5V, RSET = 36.6kΩ; 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
Line Regulation
Boost Maximum Duty Cycle
VIN = 18V, 72 LEDs,
20mA each, L = 8.2µH
with DCR 106mΩ,
TA = +25°C
VIN = 12V, 72 LEDs,
20mA each, L = 8.2µH
with DCR 106mΩ,
TA = +25°C
VIN = 6V, 72 LEDs,
20mA each, L = 8.2µH
with DCR 106mΩ,
TA = +25°C
82
91
90
86
0.1
%
%
%
%
%
Dmin
Boost Minimum Duty Cycle
7%
fS
ILX_leakage
Switching Frequency
LX Leakage Current
VLX = 36V, EN = 0
1.0 1.2 1.3 MHz
10 µA
REFERENCE
Imatch
Channel-to-Channel Current Matching
IACC
Current Accuracy
FAULT DETECTION
IOUT = 30mA
-3.5 ±1 +3.5 %
±3 %
VSC
Short Circuit Threshold
PWM Dimming = 100%
7.8
8
8.8
V
Vtemp_acc
Over-Temperature Threshold Accuracy
5 °C
VOVPlo
Overvoltage Limit on OVP Pin
1.17 1.2 1.23
V
OVPhys
OVP Hysteresis
20 mV
OVPfault
OVP Short Detection Fault Level
300 mV
CURRENT SOURCES
Vheadroom
VRSET
ILEDmax
FAULT PIN
Dominant Channel Current Source
Headroom at IIN Pin
Voltage at RSET Pin
Maximum LED Current Per Channel
ILED = 20mA
TA = +25°C
RSET = 36.6kΩ
RSET = 20.9kΩ
100 mV
680 700 720 mV
35 mA
Ifault
Fault Pull-down Current
VIN = 12V
10 18 30 µA
Vfault
FAULT Clamp Voltage with Respect to VIN VIN = 12, VIN - Vfault
7.5
V
IlxStartup
LX Start-up Current
VDC = 5.2V
1 2.7 7 mA
5 FN6570.0
May 9, 2008

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ISL97636 arduino
ISL97636
For example, if the maximum required LED current
(ILED(max)) is 20mA, rearranging Equation 1
yields Equation 3:
RSET = 733 0.02 = 36.6kΩ
(EQ. 2)
PWM CURRENT CONTROL
The average LED current of each channel can be controlled by
an external PWMI signal, as shown in Equation 3:
ILED(ave) = ILED × PWMI
(EQ. 3)
The PWM dimming frequency can be, for example, 20kHz,
but there are minimum on and off time requirements such
that the dimming will be in the range of 10% to 99.5%. If the
dimming frequency is below 5kHz, the dimming range can
be 1% to 99.5%.
The PWM dimming off time cannot be longer than 28ms or
else the driver will enter shutdown.
5V Low Dropout Regulator
A 5.2V LDO regulator is present at the VDC pin to develop
the necessary low voltage supply which is used by the chips
internal control circuitry. Because VDC is an LDO pin, it
requires a bypass capacitor of 1µF or more for the
regulation. For applications with an input voltage 5.5V, the
VIN and VDC pins can be connected together. The VDC pin
can be used as a coarse reference with few mA sourcing
capability.
Inrush Control and Soft-start
The ISL97636 has separately built-in independent inrush
control and soft-start functions. The inrush control function is
built around the short circuit protection FET, and is only
available in applications which include this device. At
start-up, the fault protection FET is turned on slowly due to a
30µA pull-down current output from the FAULT pin. This
discharges the fault FET's gate-source capacitance, turning
on the FET in a controlled fashion. As this happens, the
output capacitor is charged slowly through the weakly turned
on FET before it becomes fully enhanced. This results in a
low inrush current. This current can be further reduced by
adding a capacitor (in the 1nF to 5nF range) across the gate
source terminals of the FET.
Once the chip detects that the fault protection FET is turned
on hard, it is assumed that inrush is complete. At this point,
the boost regulator will begin to switch and the current in the
inductor will ramp-up. The current in the boost power switch
is monitored and the switching terminated in any cycle
where the current exceeds the current limit. The ISL97636
includes a soft-start feature where this current limit starts at a
low value (375mA). This is stepped up to the final 3A current
limit in seven further steps of 375mA. These steps will
happen over a 1ms total time, such that after 1ms the final
limit will be reached. This allows the output capacitor to be
charged to the required value at a low current limit and
prevents high input current for systems that have only a low
to medium output current requirement.
For systems with no master fault protection FET, the inrush
current will flow towards COUT when VIN is applied and it is
determined by the ramp rate of VIN and the values of COUT
and L.
Fault Protection and Monitoring
The ISL97636 features extensive protection functions to
cover all the perceivable failure conditions. The failure mode
of a LED can be either open circuit or as a short. The
behavior of an open circuited LED can additionally take the
form of either infinite resistance or, for some LEDs, a zener
diode, which is integrated into the device in parallel with the
now opened LED.
For basic LEDs (which do not have built-in zener diodes), an
open circuit failure of an LED will only result in the loss of
one channel of LEDs without affecting other channels.
Similarly, a short circuit condition on a channel that results in
that channel being turned off does not affect other channels
unless a similar fault is occurring.
Due to the lag in boost response to any load change at its
output, certain transient events (such as LED current steps
or significant step changes in LED duty cycle) can transiently
look like LED fault modes. The ISL97636 uses feedback
from the LEDs to determine when it is in a stable operating
region and prevents apparent faults during these transient
events from allowing any of the LED stacks to fault out. See
Table 1 for more details.
A fault condition that results in an input current that exceeds
the devices electrical limits will result in a shutdown of all
output channels.
Short Circuit Protection (SCP)
The short circuit detection circuit monitors the voltage on
each channel and disables faulty channels which are
detected above 8V (the action taken is described in Table 1.)
Open Circuit Protection (OCP)
When one of the LEDs becomes open circuit, it can behave
as either an infinite resistance or a gradually increasing finite
resistance. The ISL97636 monitors the current in each
channel such that any string which reaches at least 75% of
the intended output current is considered “good”. Should the
current subsequently fall below 50% of the target, the channel
will be considered an “open circuit”. Furthermore, should the
boost output of the ISL97636 reach the OVP limit or should
the lower over-temperature threshold be reached, all
channels which are not “good” will immediately be considered
as “open circuit”. Detection of an “open circuit” channel will
result in a time-out before disabling of the affected channel.
This time-out is sped up when the device is above the lower
over-temperature threshold in an attempt to prevent the upper
over-temperature trip point from being reached.
11 FN6570.0
May 9, 2008

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