Electronic Components Datasheet Search
  English  ▼
ALLDATASHEET.NET

X  

AD8240 Datasheet(PDF) 8 Page - Analog Devices

Part # AD8240
Description  LED Driver/Monitor
Download  12 Pages
Scroll/Zoom Zoom In 100%  Zoom Out
Manufacturer  AD [Analog Devices]
Direct Link  http://www.analog.com
Logo AD - Analog Devices

AD8240 Datasheet(HTML) 8 Page - Analog Devices

Back Button AD8240_15 Datasheet HTML 4Page - Analog Devices AD8240_15 Datasheet HTML 5Page - Analog Devices AD8240_15 Datasheet HTML 6Page - Analog Devices AD8240_15 Datasheet HTML 7Page - Analog Devices AD8240_15 Datasheet HTML 8Page - Analog Devices AD8240_15 Datasheet HTML 9Page - Analog Devices AD8240_15 Datasheet HTML 10Page - Analog Devices AD8240_15 Datasheet HTML 11Page - Analog Devices AD8240_15 Datasheet HTML 12Page - Analog Devices  
Zoom Inzoom in Zoom Outzoom out
 8 / 12 page
background image
AD8240
Rev. 0 | Page 8 of 12
ADVANTAGES OF DRIVING LED LAMPS WITH CONSTANT VOLTAGE
The advantages of driving LED lamps with constant voltage are
Low system cost
Accurate monitoring
Proven strategy
BACKGROUND
A great variety of LED lamps are being used in automotive
applications. The most popular application is center brake
lamps. Currently, many manufacturers are developing
technology to use LEDs for left/right brake lamps, running
lamps, and turn signals. There are also plans to use high power
LEDs for forward lighting fog lamps and low beams.
There are two fundamental types of LEDs used in these applica-
tions. The first is the low power bright LED. The second type is
the high power, extremely bright LED in the 1 W to 10 W range.
While the following information can be applied to applications
using the high power LED, or incandescent lamps, the constant
voltage method is designed for applications typically using the
low power bright LEDs. This type of LED is used in arrays that
form LED lamps.
MONITORING THE LEDS
In addition to driving the LED lamp, the electronics in the
control module must include a method for monitoring partial
LED failure in the lamp. Certain factors, such as overdriving
and mechanical stress, can cause LED failures.
Auto manufacturers are using LED lamps as a way to differen-
tiate themselves and give a car a unique appearance. Several
failed LEDs in the lamp would ruin the aesthetics of the lamp.
As a result, manufacturers are demanding the ability to monitor
the LED lamps for partial failure.
In addition to monitoring the LEDs for aesthetic reasons,
monitoring must also be included as a result of automotive
regulations. These regulations specify the minimum light
output of external lamps. For example, if half of the LEDs in
a particular lamp failed, the lamp would still operate, but the
light output would be insufficient to meet automotive
regulations for brightness. This concern is not an issue for
incandescent bulbs, because they are either completely on or
completely off. The ability of the LED lamp to provide some
light output in the case of partial outage, however, allows for an
extra degree of safety over incandescent lamps. Additionally,
there are automotive regulations requiring the monitoring of
the turn signals regardless of the type of light source.
DRIVING AUTOMOTIVE LEDS
There are two different architectures for driving LEDs in
left/right/center brake lamps, running lamps, and turn signals.
Constant Current
The most common method for driving LEDs is with a constant
current. This current can be supplied from a constant current
source or from a constant voltage source in series with a ballast
resistor. Driving LEDs without some form of ballast carries
some risk of premature LED failure due to thermal runaway in
high temperature ambient conditions.
For example, in the simplest application, the center brake lamp
is driven from a relatively constant voltage with brightness
controlled by a series ballast resistor. This simple driving
method has been used in a wide variety of automotive platforms
for some time. With this method, the LEDs and ballast resistors
are preselected for brightness as part of the manufacturing
strategy.
When driving with a constant current source, LED driving
and monitoring cannot be done using two or fewer wires
(shared ground). Since the current is constant, it does not
change with partial LED failure. Instead, the current is divided
among the remaining functional LEDs, causing them to fail
prematurely at an unpredictable rate. Additionally, it is not
possible to detect partial failure by measuring the voltage
change. The voltage does not change by a detectable amount
because of the steep V/I curve exhibited by bright LEDs. When
using a constant current scheme, at least one additional wire
per lamp must be added to the harness to monitor partial or
total LED failure. Additionally, electronic modules must be
added to each lamp.
Constant Voltage
Driving LEDs with a constant voltage allows for easy, low cost
detection of partial failure, an advantage not available with a
constant-current architecture. This is because the current from
the voltage source changes in direct proportion to the number
of LEDs that have failed. This current can be measured with a
low cost shunt and an amplifier back at the body control
module. This detection scheme is implemented in the AD8240
LED driver/monitor through the use of a high-side, current-
sensing amplifier. The current is measured on the high side in
order to separate the current from those combined in the
chassis ground return or shared-wire ground return.


Similar Part No. - AD8240_15

ManufacturerPart #DatasheetDescription
logo
Analog Devices
AD8240YRM AD-AD8240YRM Datasheet
223Kb / 12P
   LED Driver/Monitor
REV. 0
AD8240YRM-REEL AD-AD8240YRM-REEL Datasheet
223Kb / 12P
   LED Driver/Monitor
REV. 0
AD8240YRM-REEL7 AD-AD8240YRM-REEL7 Datasheet
223Kb / 12P
   LED Driver/Monitor
REV. 0
More results

Similar Description - AD8240_15

ManufacturerPart #DatasheetDescription
logo
Analog Devices
AD8240 AD-AD8240 Datasheet
223Kb / 12P
   LED Driver/Monitor
REV. 0
logo
Texas Instruments
TLC5960 TI-TLC5960 Datasheet
682Kb / 33P
[Old version datasheet]   Eight-Channel LED Driver with Intelligent Headroom Voltage Monitor (iHVM)
TLS2205 TI-TLS2205 Datasheet
775Kb / 31P
[Old version datasheet]   VOICE - COIL MOTOR DRIVER, SPINDLE - MOTOR DRIVER, AND VOLTAGE MONITOR
logo
Linear Technology
LT3796 LINER-LT3796 Datasheet
331Kb / 8P
   100V LED Controller with Current Monitor
logo
Rohm
BA618 ROHM-BA618 Datasheet
74Kb / 4P
   LED driver
logo
Texas Instruments
TLC5923 TI-TLC5923 Datasheet
246Kb / 15P
[Old version datasheet]   LED DRIVER
TLC5904 TI-TLC5904 Datasheet
414Kb / 27P
[Old version datasheet]   LED DRIVER
TLC5911 TI-TLC5911 Datasheet
474Kb / 30P
[Old version datasheet]   LED DRIVER
TLC5922 TI1-TLC5922_14 Datasheet
378Kb / 19P
[Old version datasheet]   LED DRIVER
logo
Dialog Semiconductor
SLG7NT4082 DIALOG-SLG7NT4082 Datasheet
372Kb / 9P
   LED DRIVER
More results


Html Pages

1 2 3 4 5 6 7 8 9 10 11 12


Datasheet Download

Go To PDF Page


Link URL




Privacy Policy
ALLDATASHEET.NET
Does ALLDATASHEET help your business so far?  [ DONATE ] 

About Alldatasheet   |   Advertisement   |   Contact us   |   Privacy Policy   |   Link Exchange   |   Manufacturer List
All Rights Reserved©Alldatasheet.com


Mirror Sites
English : Alldatasheet.com  |   English : Alldatasheet.net  |   Chinese : Alldatasheetcn.com  |   German : Alldatasheetde.com  |   Japanese : Alldatasheet.jp
Russian : Alldatasheetru.com  |   Korean : Alldatasheet.co.kr  |   Spanish : Alldatasheet.es  |   French : Alldatasheet.fr  |   Italian : Alldatasheetit.com
Portuguese : Alldatasheetpt.com  |   Polish : Alldatasheet.pl  |   Vietnamese : Alldatasheet.vn
Indian : Alldatasheet.in  |   Mexican : Alldatasheet.com.mx  |   British : Alldatasheet.co.uk  |   New Zealand : Alldatasheet.co.nz
Family Site : ic2ic.com  |   icmetro.com