Four-String White LED Driver
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
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.
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.
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.
Trademarks and registered trademarks are the property of their respective owners.
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.
09858-001
ADD5205
TABLE OF CONTENTS
Features .............................................................................................. 1
Applications....................................................................................... 1
Functional Block Diagram .............................................................. 1
General Description ......................................................................... 1
Revision History ............................................................................... 2
Functional Block Diagram .............................................................. 3
Specifications..................................................................................... 4
Absolute Maximum Ratings............................................................ 6
Thermal Resistance ...................................................................... 6
ESD Caution.................................................................................. 6
Pin Configuration and Function Descriptions............................. 7
Data Sheet
Typical Performance Characteristics ..............................................8
Theory of Operation ...................................................................... 10
Current Mode, Stepup Switching Regulator Operation........ 10
Current Source............................................................................ 10
PWM Dimming Mode .............................................................. 10
Safety Features ............................................................................ 10
External Component Selection Guide..................................... 11
Layout Guidelines....................................................................... 12
Typical Application Circuit ........................................................... 13
Outline Dimensions ....................................................................... 14
Ordering Guide .......................................................................... 14
REVISION HISTORY
8/11—Revision 0: Initial Version
Rev. 0 | Page 2 of 16
ADD5205
SPECIFICATIONS
V
IN
= 3.7 V, SHDN = high, T
A
= −25°C to +85°C, unless otherwise noted. Typical values are at T
A
= 25°C.
Table 1.
Parameter
SUPPLY
Input Voltage Range
Quiescent Current
Shutdown Supply Current
SWITCH
On Resistance
Switch Current Limit
Leakage Current
OSCILLATOR
Switching Frequency
Maximum Duty Cycle
SOFT START
Soft Start Time
1
CURRENT SOURCE
ISET Pin Voltage
C_FILTER Pin Voltage
Adjustable LED Current
1
Constant Current Sink of 20 mA
2
Headroom Voltage of 20 mA
2
Current Matching Between Strings
2
LED Current Accuracy of 20 mA
2
Current Source Leakage Current
SHUTDOWN CONTROL
SHDN Voltage High
SHDN Voltage Low
PWM Control
PWM Input Frequency Range
1
PWM Voltage High
PWM Voltage Low
1
2
Data Sheet
Symbol
V
IN
I
Q
I
SD
R
DS(ON)
I
CL
I
LKG
f
OSC
D
MAX
Test Conditions/Comments
Min
2.8
Typ
Max
18
Unit
V
mA
μA
Ω
A
μA
MHz
%
ms
V
V
mA
mA
V
%
%
μA
V
V
kHz
V
V
V
IN
= 2.8 V to 18 V, not switching
V
IN
= 2.8 V to 18 V, SHDN = 0 V
I
SW
= 100 mA
3.4
1
0.3
1.9
1
1
90
1.5
V
SET
V
C_FILTER
I
LED
I
LED20
V
HR20
Duty = 100%
R
SET
= 130 kΩ
R
SET
= 130 kΩ
I
LED
= 20 mA
I
LED
= 20 mA
19.6
−2
−3
1.26
0.22
20
0.66
25
20.6
+2
+3
1
6
0.6
0.1
1.5
0.6
V
SHDN_HIGH
V
SHDN_LOW
V
IN
= 2.8 V to 18 V
V
IN
= 2.8 V to 18 V
1.5
V
PWM_HIGH
V
PWM_LOW
V
IN
= 2.8 V to 18 V
V
IN
= 2.8 V to 18 V
Guaranteed by design.
Tested at T
A
= 25°C.
Rev. 0 | Page 4 of 16
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