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ADD5205 Schematic ( PDF Datasheet ) - Analog Devices

Teilenummer ADD5205
Beschreibung Four-String White LED Driver
Hersteller Analog Devices
Logo Analog Devices Logo 




Gesamt 16 Seiten
ADD5205 Datasheet, Funktion
www.DataSheet.co.kr
Data Sheet
FEATURES
White LED driver based on inductive boost converter
Input voltage range: 2.8 V to 18 V
Internal compensation
1 MHz fixed operating frequency
28 V fixed overvoltage protection
Built-in soft start for boost converter
Drives up to 4 LED current sources
LED current adjustable up to 25 mA for each channel
DC current level brightness control with PWM input
LED open fault protection
General
Thermal shutdown
Undervoltage lockout
12-lead, 3 mm × 3 mm × 0.75 mm LFCSP package
APPLICATIONS
Smart PCs, PMPs, tablet PCs, UMPCs, and notebooks
GENERAL DESCRIPTION
The ADD5205 is a white LED driver for backlight applications
based on high efficiency, current mode, step-up converter
technology. It is designed with a 0.3 Ω internal switch and 1 MHz
fixed operating frequency. The ADD5205 contains four regulated
constant current sources for uniform brightness intensity. Each
current source is capable of driving up to 25 mA.
The ADD5205 has four parallel strings of multiple series connected
LEDs with ±2% current matching. The device provides adjustable
current sources that drive up to 25 mA using an external resistor.
The LED current can be controlled by a PWM signal input on
the PWM pin. An internal circuit translates the PWM signal to
an analog signal with an external capacitor and linearly controls
the LED current.
Four-String White LED Driver
ADD5205
FUNCTIONAL BLOCK DIAGRAM
STEP-UP SWITCHING REGULATOR
4-CHANNEL CURRENT SOURCES
BRIGHTNESS CONTROL LOGIC
UNDERVOLTAGE LOCKOUT
SOFT START
THERMAL PROTECTION
OVERVOLTAGE PROTECTION
AUTODISABLE FOR LED OPEN
Figure 1.
The ADD5205 has multiple safety protection features to prevent
any damage during fault conditions. If one or more LEDs are open,
the device disables the faulty current regulator automatically.
The internal soft start prevents inrush current during startup. A
thermal shutdown protection feature prevents thermal damage.
The ADD5205 is available in a low profile, thermally enhanced
3 mm × 3 mm × 0.75 mm, 12-lead lead frame chip scale package
(LFCSP) and is specified over the temperature range of −25°C
to +85°C.
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.
Trademarksandregisteredtrademarksarethepropertyoftheirrespectiveowners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.461.3113
©2011 Analog Devices, Inc. All rights reserved.
Datasheet pdf - http://www.DataSheet4U.net/






ADD5205 Datasheet, Funktion
www.DataSheet.co.kr
ADD5205
ABSOLUTE MAXIMUM RATINGS
TA = 25°C, unless otherwise noted.
Table 3.
Parameter
VIN
SW
SHDN,
ISET, C_FILTER
PWM
FB1, FB2, FB3, FB4
OVP
Maximum Junction Temperature (TJ max)
Operating Temperature Range (TA)
Storage Temperature Range (TS)
Reflow Peak Temperature (20 sec to 40 sec)
Rating
−0.3 V to +20 V
−0.3 V to +32 V
−0.3 V to +7 V
−0.3 V to +3.6 V
−0.3 V to +7 V
−0.3 V to +32 V
−0.3 V to +32 V
150°C
−25°C to +85°C
−65°C to +150°C
260°C
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
Data Sheet
THERMAL RESISTANCE
θJA is specified for the worst-case conditions, that is, a device
soldered in a circuit board for surface-mount packages.
Table 4. Thermal Resistance
Package Type
θJA θJC Unit
12-Lead LFCSP
41.6 7.65 °C/W
ESD CAUTION
Rev. 0 | Page 6 of 16
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6 Page









ADD5205 pdf, datenblatt
www.DataSheet.co.kr
ADD5205
LAYOUT GUIDELINES
When designing a high frequency, switching, regulated power
supply, layout is very important. Using a good layout can solve
many problems associated with these types of supplies. The main
problems are loss of regulation at high output current and/or
large input-to-output voltage differentials, excessive noise on
the output and switch waveforms, and instability. Using the
following guidelines can help minimize these problems.
Make all power (high current) traces as short, direct, and thick
as possible. It is good practice on a standard printed circuit
board (PCB) to make the traces an absolute minimum of 15 mil
(0.381 mm) per ampere. Place the inductor, output capacitors,
and output diode as close to each other as possible. This helps
reduce the EMI radiated by the power traces that is due to the
high switching currents through them. This also reduces lead
inductance and resistance, which in turn reduces noise spikes,
ringing, and resistive losses that produce voltage errors.
The grounds of the IC, input capacitors, output capacitors, and
output diode (if applicable), should be connected close together,
directly to a ground plane. It is also a good idea to have a ground
plane on both sides of the PCB. This reduces noise by reducing
ground loop errors and by absorbing more of the EMI radiated
by the inductor.
Due to how switching regulators operate, there are two power
states: on and off. During each state, there is a current loop made
by the power components currently conducting. Place the power
components so that the current loop is conducting in the same
direction during each of the two states. This prevents magnetic
field reversal caused by the traces between the two half cycles
and reduces radiated EMI.
Data Sheet
Layout Procedure
Use the following general guidelines when designing PCBs:
Keep CIN close to the VIN and GND leads of the ADD5205.
Keep the high current path from CIN (through L1) to the
SW and GND leads as short as possible.
Keep the high current path from CIN (through L1), D1, and
COUT as short as possible.
Keep high current traces as short and wide as possible.
Place the COVP as close as possible to the OVP pin.
Place the LED current setting resistors as close as possible
to each pin to prevent noise pickup.
Avoid routing noise sensitive traces near high current
traces and components, especially the LED current setting
node (ISET).
Use a thermal pad size that is the same dimension as the
exposed pad on the bottom of the package.
Heat Sinking
When using a surface-mount power IC or external power
switches, the PCB can often be used as the heat sink. This is
done by using the copper area of the PCB to transfer heat from
the device. Users should maximize this area to optimize thermal
performance.
Rev. 0 | Page 12 of 16
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