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PDF ISL97801 Data sheet ( Hoja de datos )
| Número de pieza | ISL97801 | |
| Descripción | High Power LED Driver | |
| Fabricantes | Intersil Corporation | |
| Logotipo |  |
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®
Data Sheet
April 2, 2007
ISL97801
FN6428.1
High Power LED Driver
The ISL97801 is a high-power LED backlight driver with an
integrated 36V FET designed to drive up to 8 high-power
LEDs in series. The PWM converter runs from an internally
generated 1MHz clock. With efficiencies over 90% the
regulator provides tight control of LED current and may be
configured in either boost or buck topologies, allowing from 3
to 8 series diodes to be driven from wide input voltages.
LED light level may be controlled either by:
1. LED DC bias current set via the LEVEL pin, or
2. External low frequency PWM control via the
ENABLE/PWM pin.
In both control modes optional over temperature thermal
protection of the LED reduces the LED DC bias current
above an adjustable set temperature, protecting the LED
from thermal damage. An optional fault monitor drives an
external FET between the input supply and inductor,
providing short circuit current protection for the LED and
inductor as well as load dump protection for automotive
applications. For low cost applications the pass transistor
may be omitted and the fault pin bypassed.
The ISL97801 is packaged in a 20 Ld 4mm x 4mm QFN
package and is specified for operation over the -40°C to
+105°C temperature range.
Ordering Information
PART
NUMBER
(Note)
TAPE &
PART REEL/
MARKING QTY
PACKAGE
(Pb-free)
PKG.
DWG. #
ISL97801ARZ 978 01ARZ - 20 Ld 4x4 QFN L20.4x4C
ISL97801ARZ-TK 978 01ARZ 13”/ 20 Ld 4x4 QFN L20.4x4C
1,000
ISL97801ARZ-T 978 01ARZ 13”/ 20 Ld 4x4 QFN L20.4x4C
6,000
NOTE: Intersil Pb-free plus anneal products employ special Pb-free
material sets; molding compounds/die attach materials and 100%
matte tin plate termination finish, which are 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
• Drives 3-8 high-power LEDs in series, up to 32V
• 2.7V to 16V input voltage range
• Boost or Buck configurable switch
• 3A integrated FET
• Automotive load dump protection
• Light output temperature compensation
• LED over-temperature protection
• LED disconnect
• PWM/analog light level control
• Small, 20 Ld 4mm x 4mm QFN package
• Pb-free plus anneal available (RoHS compliant)
Applications
• Display backlighting
- Automotive
- LCD monitor
- Notebook displays
• LED accent lighting
• Automotive lighting
Pinout
ISL97801
(20 LD 4X4 QFN)
TOP VIEW
VDC 1
VHI 2
OVP 3
SWD1 4
SWD2 5
THERMAL
PAD
15 ENL
14 MODE
13 EN/PWM
12 SWS1
11 SWS2
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. 2007. All Rights Reserved
All other trademarks mentioned are the property of their respective owners.
1 page  
ISL97801
Typical Performance Curves (Continued)
10
8
5 LEDs
ILEDpeak = 380mA
6
4
2 10% @ 100Hz
0
-2
-4
10% @ 10kHz
99% @ 10kHz
-6
-8 99% @ 100Hz
-10
4 6 8 10 12 14 16
VIN (V)
FIGURE 7. 5 LEDs CURRENT ACCURACY vs INPUT VOLTAGE
16
14
3 LEDs
ILEDpeak = 380mA
12
10
8
6
4 99% @ 10kHz
2
0 99% @ 100Hz
-2
-4
4 5 6 7 8 9 10
VIN (V)
FIGURE 8. 3 LEDs CURRENT ACCURACY vs INPUT VOLTAGE
400
395
8 LEDs
ILEDpeak = 380mA
390 DUTY CYCLE = 99%
385
380
375 PWM @ 1kHz
370
365
360 PWM @ 10kHz
355 PWM @ 100Hz
350
6
8 10 12 14 16 18
VIN (V)
FIGURE 9. 8 LEDs LINE REGULATION OF PWM DUTY
CYCLE OF 99%
410
405
3 LEDs
ILEDpeak = 380mA
400 DUTY CYCLE = 99%
395
390
385 PWM @ 100Hz
380
375
370
PWM @ 10kHz
365
360
4 5 67
8 9 10
VIN (V)
FIGURE 11. 3 LEDs LINE REGULATION OF PWM DUTY
CYCLE OF 99%
420
415 5 LEDs
410 ILEDpeak = 380mA
405 DUTY CYCLE = 99%
400
395
390
385
99% @ 10kHz
380
375
370
365
360
355
350
4
99% @ 100Hz
6 8 10
12 14 16
VIN (V)
FIGURE 10. 5 LEDs LINE REGULATION OF PWM DUTY
CYCLE OF 99%
40
39
8 LEDs
ILEDpeak = 380mA
38 DUTY CYCLE = 10%
37
PWM @ 100Hz
36
35 PWM @ 1kHz
34
PWM @ 10kHz
33
32
31
30
6 8 10 12 14 16 18
VIN (V)
FIGURE 12. 8 LEDs LINE REGULATION OF PWM DUTY
CYCLE OF 10%
5 FN6428.1
April 2, 2007
5 Page 
ISL97801
Theory of Operation
General Description
The ISL97801 is a flexible, highly integrated high-power LED
driver consisting of a PWM switching controller and
integrated 36V NDMOS power FET. The device can drive up
to 8 series high-power LED's at currents up to 1A at 16V
input or 5 LEDs at current up to 350mA at 2.7V input. The
control loop can be configured as either as a boost or buck
regulator with the configuration of the buck/boostn pin,
providing an output voltage above or below the input supply
voltage, depending on the number of stacked LED's. The
controller operates from 2.7V to 16V depending on the
numbers of LEDs and current required and can be powered
by a single lithium ion battery, 5V or 12V regulated supplies
or automotive electrical systems. LED current is sensed
through a low value resistor in series with the LED. A
thermistor can be used to implement a thermal protection
scheme to limit the maximum LED temperature to a preset
desirable level.
Switching Regulator
The ISL97801 employs a current mode PWM control
scheme with a nominal switching frequency of 1MHz. This
provides fast transient response and enables the use of low
profile inductors and compact multilayer ceramic capacitors.
Settling time is optimized by the use of a simple control loop
without an error amplifier, relying instead on intrinsic gain
within the direct summing path. Due to the lower loop gain,
offset must be accounted for when setting up initial LED bias
current. Refer to the applications section of the datasheet for
further information. Figure 28 shows a block diagram of the
system.
Application Configurations
Operating Modes
The ISL97801 can operate as either a buck or boost
regulator. Hardwire BUCK/BOOSTN to GND for boost mode
or to VDC for buck mode. In buck mode the power NDMOS
drive circuit is "floated" (boot-strapped) allowing the NDMOS
gate to be driven above VIN to fully enhance the power
NDMOS. An internal Schottky diode between VDC (5V) and
VHI reduces external component count. Use a ceramic
capacitor of at least 50nF between VHI and SWS1/2 to
bootstrap VHI.
LED Load Connection
ISL97801 includes an auto-sensing FB level shift circuit that
enables the LED load to be connected to either GND or VIN.
An internal sense circuit monitors the FB pin voltage. When
the level exceeds VDC/2, the feedback reference voltage is
switched from GND to VIN. Refer to the application section
of the datasheet for typical application schematics.
Voltage
Feedback
LEVEL
SHIFT
EL7801
VIN
FB
+
-
VDC /2
GND
FIGURE 29. FB REFERENCE AUTO SWITCH
Start-up
To maximize external PWM switching speed, the ISL97801
does not include an internal soft-start circuit. When VDC
exceeds the power on reset threshold, switching is delayed
for 1ms (TDELAY) allowing the output capacitor to charge
through the inductor. If soft-start control is required, a
suitable application circuit is shown in Figure 30.
VBAT
VBAT FAULT
ISL97801 VIN
SWD1
SWD2
FB
SWS1 SWS2
10µH
L1
C1
4.7nF
VOUT
COUT
20µF
R1
R2 100
2k
0.5
RSENSE
FIGURE 30. EXTERNAL SOFT-START CIRCUIT
Light Level Control
Two light control schemes are provided:
1. An external PWM signal via the EN/PWM pin, providing
low frequency PWM dimming.
2. Bias current level adjustment via the LEVEL input or fixed
internal bias.
PWM Dimming
LED color temperature varies with bias current. In
backlighting applications PWM dimming offers better control
of color temperature because current through the LED's is
kept constant. A 5V gate driver (ENL) synchronized to
EN/PWM can be used to control an external N-Ch FET and
disconnect the LED stack during the PWM off period. The
switch prevents discharge of the output capacitor by the LED
load, maintaining a constant bias independent of PWM duty
cycle. Operation at 1kHz PWM rate is shown in Figure 31
and Figure 32. The load disconnect switch improves PWM
dynamic range, linearity and color temperature control. To
11 FN6428.1
April 2, 2007
11 Page | ||
| Páginas | Total 19 Páginas | |
| PDF Descargar | [ Datasheet ISL97801.PDF ] | |
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