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PDF ( 数据手册 , 数据表 ) ADD5201

零件编号 ADD5201
描述 White LED Driver
制造商 Analog Devices
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ADD5201 数据手册, 描述, 功能
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 pdf, 数据表
ADD5201
TYPICAL PERFORMANCE CHARACTERISTICS
94
ILED = 20mA
92 BRIGHTNESS = 100%
fSW = 600kHz
90
8 PARALLEL × 8 SERIES
88
86
8 PARALLEL × 10 SERIES
84
82
80
78
5 10 15 20
INPUT VOLTAGE (V)
Figure 4. Boost Converter Efficiency vs. Input Voltage
25
32
30
28
26
24
22
20
18
16
14
12
10
8
85 105 125 145 165 185 205 225 245 265
RSET (kΩ)
Figure 5. LED Current vs. RSET
20
15
10
5
0
0 10 20 30 40 50 60 70 80 90
PWMI DUTY CYCLE (%)
Figure 6. LED Current vs. PWM Input Duty Cycle
100
Data Sheet
25
20
15
10
5
0
5 10 15 20
INPUT VOLTAGE (V)
Figure 7. LED Current vs. Input Voltage (ILED = 20 mA)
32
30
28
26
24
22
20
18
16
14
12
10
8
0.45
0.55
0.65
0.75
0.85
0.95
VHR (kΩ)
Figure 8. LED Current vs. Headroom Voltage
BRIGHTNESS = 100%
VOUT
10V/DIV
0V VSW
20V/DIV
0V
IL
0A 1A/DIV
4ms/DIV
Figure 9. Start-Up Waveforms (Brightness = 100%)
Rev. A | Page 8 of 20
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ADD5201 equivalent, schematic
ADD5201
Data Sheet
EXTERNAL COMPONENT SELECTION GUIDE
Inductor Selection
The inductor is an integral part of the step-up converter. It stores
energy during the switch-on time and transfers that energy to
the output through the output diode during the switch-off time.
An inductor in the range of 4.7 μH to 22 μH is recommended.
In general, lower inductance values result in higher saturation
current and lower series resistance for a given physical size.
However, lower inductance results in higher peak current, which
can lead to reduced efficiency and greater input and/or output
ripple and noise. Peak-to-peak inductor ripple current at close
to 30% of the maximum dc input current typically yields an
optimal compromise.
For determining the inductor ripple current, the input (VIN) and
output (VOUT) voltages determine the switch duty cycle (D) by
the following equation:
D VOUT VIN
VOUT
(1)
Using the duty cycle and switching frequency (fSW) determines
the on time in the following equation:
t ON
D
f SW
(2)
The inductor ripple current (ΔIL) in steady state is
I L
VIN
t ON
L
Solving for the inductance value (L),
L VIN t ON
I L
Make sure that the peak inductor current (that is, the maximum
input current plus half of the inductor ripple current) is less
than the rated saturation current of the inductor. In addition,
ensure that the maximum rated rms current of the inductor is
greater than the maximum dc input current to the regulator.
For duty cycles greater than 50% that occur with input voltages
greater than half the output voltage, slope compensation is required
to maintain stability of the current mode regulator. For stable
current mode operation, ensure that the selected inductance is
equal to or greater than LMIN:
L L MIN
VOUT VIN
2.9 A f SW
Inductor manufacturers include Coilcraft, Inc.; Sumida
Corporation; and Toko.
Input and Output Capacitors Selection
The ADD5201 requires input and output bypass capacitors to
supply transient currents while maintaining a constant input
and output voltage. Use a low effective series resistance (ESR)
10 μF or greater capacitor for the input capacitor to prevent noise
at the ADD5201 input. Place the input and output capacitors
between VIN and AGND, as close as possible to the ADD5201.
Ceramic capacitors are preferred because of their low ESR
characteristics. Alternatively, use a high value, medium ESR
capacitor in parallel with a 0.1 μF low ESR capacitor as close as
possible to the ADD5201.
The output capacitor maintains the output voltage and supplies
current to the load while the ADD5201 switch is on. The value
and characteristics of the output capacitor greatly affect the output
voltage ripple and stability of the regulator. Use a low ESR output
capacitor; ceramic dielectric capacitors are preferred.
For very low ESR capacitors, such as ceramic capacitors, the
ripple current due to the capacitance is calculated as follows.
Because the capacitor discharges during the on time (tON), the
charge removed from the capacitor (QC) is the load current
multiplied by the on time. Therefore, the output voltage ripple
(ΔVOUT) is
VOUT
QC
C OUT
I L t ON
C OUT
where:
COUT is the output capacitance.
IL is the average inductor current.
Using the duty cycle and switching frequency (fSW), users can
determine the on time by using Equation 2. The input (VIN) and
output (VOUT) voltages determine the switch duty cycle (D) as
shown in Equation 1.
Choose the output capacitor based on the following equation:
C OUT
I L (VOUT VIN )
f SW VOUT  VOUT
Capacitor manufacturers include Murata Manufacturing Co.,
Ltd.; AVX; Sanyo; and Taiyo Yuden Co., Ltd.
Diode Selection
The output diode conducts the inductor current to the output
capacitor and load while the switch is off. For high efficiency,
minimize the forward voltage drop of the diode. Schottky
diodes are recommended. However, to maintain efficiency in
high voltage, high temperature applications use an ultrafast
junction diode to prevent significant reverse leakage current
caused by the Schottky diode.
The output diode for a boost regulator must be chosen depending
on the output voltage and the output current. The diode must
be rated for a reverse voltage equal to or greater than the output
voltage used. The average current rating must be greater than
the maximum load current expected, and the peak current
rating must be greater than the peak inductor current. Using
Schottky diodes with lower forward voltage drop decreases
power dissipation but increases efficiency. The diode must be
rated to handle the average output load current. Many diode
manufacturers derate the current capability of the diode as a
function of the duty cycle. Verify that the output diode is rated
Rev. A | Page 16 of 20
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