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ADD5201 Schematic ( PDF Datasheet ) - Analog Devices

Teilenummer ADD5201
Beschreibung White LED Driver
Hersteller Analog Devices
Logo Analog Devices Logo 




Gesamt 20 Seiten
ADD5201 Datasheet, Funktion
Data Sheet
High Efficiency, Eight-String, White LED
Driver for LCD Backlight Applications
ADD5201
FEATURES
White LED driver based on inductive boost converter
Integrated 50 V MOSFET with 2.9 A peak current limit
Input voltage range: 6 V to 21 V
Maximum output adjustable up to 45 V
350 kHz to 1 MHz adjustable operating frequency
Built-in soft start for boost converter
Drives up to eight LED current sources
LED current adjustable up to 30 mA for each channel
Headroom control to maximize efficiency
Adjustable output dimming frequency: 200 Hz to 10 kHz
LED open/short fault protection
Selectable brightness control interface modes
PWM input
SMBus serial interface
Selectable dimming controls
Fixed delay PWM dimming control with 8-bit resolution
No delay PWM dimming control with 8-bit resolution
Phase shift PWM dimming control with 8-bit resolution
Direct PWM dimming control
DC current dimming mode with 8-bit resolution
General
Thermal shutdown
Undervoltage lockout
28-lead, 4 mm × 4 mm LFCSP
APPLICATIONS
Notebook PCs, UMPCs, and monitor displays
GENERAL DESCRIPTION
The ADD5201 is a white LED driver for backlight applications
based on high efficiency, current mode, step-up converter tech-
nology. It is designed with a 0.15 Ω, 2.9 A internal switch and a
pin adjustable operating frequency between 350 kHz and 1 MHz.
The ADD5201 contains eight regulated current sources for
uniform brightness intensity. Each current source can be
driven up to 30 mA.
The ADD5201 drives up to eight parallel strings of multiple
series connected LEDs with a ±1.5% current regulation accuracy.
The device provides an adjustable LED driving current up to
30 mA for each channel by an external resistor. The ADD5201
provides various brightness control methods. The LED dimming
control can be achieved through SMBus and/or pulse-width
modulation (PWM) input. Each dimming mode is selectable
BLOCK DIAGRAM
STEP-UP SWITCHING REGULATOR
EIGHT CURRENT SOURCES
INTERFACE
8-BIT DIMMING CONTROL LOGIC
UNDERVOLTAGE LOCKOUT
SOFT START
THERMAL PROTECTION
OVERVOLTAGE PROTECTION
AUTODISABLE FOR LED OPEN/SHORT
Figure 1.
with two external dimming mode selection pins. The device pro-
vides a pin adjustable output dimming frequency range from
200 Hz to 10 kHz.
The ADD5201 operates over an input voltage range of 6 V to
21 V, but the device can function with a voltage as low as 5.4 V.
The ADD5201 has multiple safety protection features to prevent
damage during fault conditions. If any LED is open or short, the
device automatically disables the faulty current regulator. The
internal soft start prevents inrush current during startup. A
thermal shutdown protection prevents thermal damage.
The ADD5201 is available in a low profile, thermally enhanced,
4 mm × 4 mm × 0.75 mm, 28-lead, RoHS compliant lead frame
chip scale package (LFCSP) and is specified over the industrial
temperature range of −25°C to +85°C.
Rev. A
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibilityisassumedbyAnalogDevices for itsuse,nor foranyinfringementsofpatentsor 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
©2012 Analog Devices, Inc. All rights reserved.
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ADD5201 Datasheet, Funktion
ADD5201
ABSOLUTE MAXIMUM RATINGS
TA = 25°C, unless otherwise noted.
Table 5.
Parameter
VIN
SW
SHDN
ISET, FSLCT, COMP, R_FPWM, C_FPWM
SDA, SCL, PWMI
FB1, FB2, FB3, FB4, FB5, FB6, FB7, FB8
OVP
VDDIO
SEL1, SEL2
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 +23 V
−0.3 V to +50 V
−0.3 V to +6 V
−0.3 V to +3.5 V
−0.3 V to +6 V
−0.3 V to +50 V
−0.3 V to +3 V
−0.3 V to +3.7 V
−0.3 V to +6 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 6. Thermal Resistance
Package Type
28-Lead LFCSP
θJA
32.6
θJC
1.4
Unit
°C/W
ESD CAUTION
Rev. A | Page 6 of 20
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ADD5201 pdf, datenblatt
ADD5201
Data Sheet
DUTY = 60%
PWMI
DUTY = 60%
fPWM
ILED1
tON tOFF
ILED2
ILED8
Figure 19. No Delay PWM Dimming Timing
Direct PWM
The direct PWM mode is selected when SEL1 = low and SEL2 =
low. In the direct PWM mode, the PWM input controls the LED
dimming logic of the ADD5201. It turns the current sources on
and off without any modulation of the PWM input. In addition,
each current source has no phase delay in this mode. The LED
brightness is changed by the PWM input duty ratio.
PWMI
DUTY = 60%
ILED1
DUTY = 60%
ILED2
ILED3
ILED8
Figure 20. Direct PWM Dimming Timing
DC CURRENT DIMMING MODE
DC current mode is selected when SEL1 = low and SEL2 = open
for a PWMI application, or when SEL1 = low and SEL2 = high for
an SMBus application. In the dc current dimming mode, the
maximum LED current is set by the value of RSET. The PWM
input or the SMBus can change the LED current in 256 steps
between 0 mA and the maximum LED current.
PWMI
DUTY = 80%
DUTY = 60%
DUTY = 40%
DUTY = 20%
ILED MAX
ILED
0.8 × ILED MAX
0.6 × ILED MAX
0.4 × ILED MAX
0A
Figure 21. DC Current Dimming
0.2 × ILED MAX
SAFETY FEATURES
The ADD5201 contains many safety features to provide stable
operation: soft start, overvoltage protection, open load protection,
short-circuit protection, undervoltage lockout, and thermal
protection.
Soft Start
The ADD5201 contains an internal soft start function to prevent
inrush current at startup. The soft start time is typically 1.5 ms.
Overvoltage Protection (OVP)
The ADD5201 contains OVP circuits to prevent boost converter
damage if the output voltage becomes excessive for any reason.
To keep a safe output level, the integrated OVP circuit monitors
the output voltage. When the OVP pin voltage is reached by the
OVP rising threshold, the boost converter stops switching, causing
the output voltage to drop. When the OVP pin voltage becomes
lower than the OVP falling threshold, the boost converter resumes
switching, causing the output to rise. There is about 7.5% hysteresis
between the rising and falling thresholds.
The OVP level can be calculated using the following equation:
VOVP
=
1.2 V
R1
×
(R1
+
R2)
VOVP
DRIVER
OVP
COMP
22
R2
R1 C1
REF
Figure 22. Overvoltage Protection Circuit
In general, the suitable OVP level is 5 V higher than the nominal
boost switching regulator output. Large resistors, up to 1 MΩ,
can be used for Resistor R2 to minimize power loss. In addition,
some applications require C1 to prevent noise interference at
the OVP pin in the range of 10 pF to 30 pF.
Open Load Protection (OLP)
The ADD5201 contains a dynamic headroom control circuit to
minimize power loss at each current source. Therefore, the min-
imum feedback voltage is the reference for regulating the output
voltage of the ADD5201 boost converter. If one or more LED
strings is opened during normal operation, the current source
headroom voltage (VHR) is pulled to AGND. In this condition,
OLP is active if VHR is less than 200 mV until the boost converter
output voltage rises to equal the OVP level.
Short-Circuit Protection (SCP)
The ADD5201 contains a short-circuit protection (SCP) circuit.
If several LEDs are shorted in an LED string, a mismatched
voltage is developed across the string. When the VHR is higher
than 7.3 V, the SCP circuit is activated and the current source is
disabled. This protection starts to monitor each current source
after the startup of the boost converter.
Rev. A | Page 12 of 20
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