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Analog Devices Semiconductor Electronic Components Datasheet

AD8240 Datasheet

LED Driver/Monitor

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AD8240 pdf
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FEATURES
PWM input for LED brightness control
Open LED detection
Latch-off overcurrent protection
Constant voltage regulated output
Supply range: 9 V to 27 V
Regulated voltage range: 12.5 V to 27 V
Operating current: 300 µA
Shutdown current: 10 µA
Temperature range −40°C to +125°C
8-lead MSOP package
GENERAL DESCRIPTION
The AD8240 LED driver/monitor, in combination with an
external transistor, supplies a constant 12 V to drive LED
lamps. This allows cost-effective LED lamp monitoring and
short-circuit protection. The output is regulated at 12 V when
the supply voltage is between 12.5 V and 27 V.
A CMOS compatible, level-dependent, digital input can be used
for PWM control of the LED brightness. VO is turned on when
the PWM input is high and turned off when the input is low.
The AD8240 is designed to work with a PWM frequency up
to 500 Hz, and a typical PWM range from 5% to 95%.
Open LED detection is accomplished by measuring the change
in LED lamp current caused by an open LED(s) through the use
of an internal high-side current-sense amplifier that amplifies
the voltage across an external current shunt. The voltage across
the shunt resistor is amplified to a level that can be measured by
a microcontroller A/D converter or a comparator. The ability to
measure the change in LED lamp current is the key benefit of
constant-voltage LED lamp driving.
The output is current-limited by latching off the output voltage
when the current reaches a preset level. The current limit is set
by selecting the value of the external current shunt that causes
the output of the sense amplifier to slightly exceed the 5 V
reference level when the current exceeds a maximum level.
When the sense amplifier output exceeds 5 V, it trips an internal
comparator that causes the driver to latch off the output voltage.
The latch is reset during the next PWM cycle. The overcurrent
condition can also be detected by a microcontroller or external
comparator by measuring the sense amplifier output.
Rev. 0
Information furnished by Analog Devices is believed to be accurate and reliable.
However, no responsibility is assumed by Analog Devices for its use, nor for any
infringements of patents or other rights of third parties that may result from its use.
Specifications subject to change without notice. No license is granted by implication
or otherwise under any patent or patent rights of Analog Devices. Trademarks and
registered trademarks are the property of their respective owners.
LED Driver/Monitor
AD8240
FUNCTIONAL BLOCK DIAGRAM
VPLUS SHUNT BASE
56
7
VO
8
VSENSE 1
RSENSE
10k
5V
REFERENCE 2
PWM 3
AD8240
LATCH-OFF
DRIVER
R1
350k
R2
250k
4
GND
Figure 1.
PRODUCT HIGHLIGHTS
1. Partial LED lamp failure detection.
Allows for compliance with automotive regulations
for turn signal functionality detection and minimum
brightness, as well as running/brake light minimum
brightness compliance.
2. Current limiting/latch-off protection.
Limiting and latching off the LED current protects vehicle
wiring and prevents lamp damage
3. PWM input.
Provides brightness control.
4. Constant voltage output.
Saves cost by minimizing wiring and system design
complexity.
5. Drives an external transistor for low power operation.
Providing for an external power transistor allows the
AD8240 to be a low cost solution in a small package. A
more efficient design is made possible when the system
designer can select a power device with specifications
that match the application requirements.
6. Linear regulation.
Minimizes EMI, which allows faster system integration,
qualification, and time to market. Additionally, costs are
reduced by eliminating the inductor required for a
switching design. Because of the power-saving nature of
LED lamps as compared to incandescent lamps, a
switching driver is typically not required.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.326.8703 © 2004 Analog Devices, Inc. All rights reserved.


Analog Devices Semiconductor Electronic Components Datasheet

AD8240 Datasheet

LED Driver/Monitor

No Preview Available !

AD8240 pdf
AD8240
TABLE OF CONTENTS
Specifications..................................................................................... 3
Absolute Maximum Ratings............................................................ 4
Product Description......................................................................... 5
Linear Regulator (Block A) ......................................................... 5
High-Side Current-Sense Amplifier with Open LED
Detection (Block B)...................................................................... 5
Comparator with Latch-off OverCurrent Protection
(Block C)........................................................................................ 5
Intelligent Driver (Block D) ........................................................ 5
REVISION HISTORY
4/04—Revision 0: Initial Version
Using/Evaluating the AD8240 LED Driver Monitor ....................6
Setup................................................................................................6
Controlling the LED lamp............................................................7
Using/Evaluating the VSense Output .............................................7
Advantages of Driving LED Lamps with Constant Voltage ........8
Background ....................................................................................8
Monitoring the LEDs ....................................................................8
Driving Automotive LEDs............................................................8
Outline Dimensions ....................................................................... 10
Ordering Guide .......................................................................... 11
Rev. 0 | Page 2 of 12


Part Number AD8240
Description LED Driver/Monitor
Maker Analog Devices
Total Page 12 Pages
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