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PDF ADD5207 Data sheet ( Hoja de datos )
| Número de pieza | ADD5207 | |
| Descripción | White LED Driver | |
| Fabricantes | Analog Devices | |
| Logotipo |  |
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Data Sheet
FEATURES
White LED driver based on inductive boost converter
Integrated 40 V MOSFET with 1.5 A peak current limit
Input voltage range: 6 V to 21 V
Maximum output adjustable up to 36 V
600 kHz to 1 MHz adjustable operating frequency
Typical 39 V fixed overvoltage protection (OVP)
Built-in soft start for boost converter
Drives up to 4 LED current strings
LED current adjustable up to 25 mA for each channel
Headroom control to maximize efficiency
Fixed LED dimming frequency: 8 kHz
LED open fault protection
Brightness control with PWM input
Dimming controls
4-channel operation: 90 degree phase shift between
channels
3-channel operation: 120 degree phase shift between
channels
General
Thermal shutdown
Undervoltage lockout
14-lead, 4 mm × 3 mm LFCSP
APPLICATIONS
Notebook PCs, UMPCs, and monitor displays
Four-String, White LED Driver
for LCD Backlight Applications
ADD5207
GENERAL DESCRIPTION
The ADD5207 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, 1.5 A internal switch and a
pin-adjustable operating frequency between 600 kHz and 1 MHz.
The ADD5207 contains four regulated current sources for
uniform LED brightness. Each current source can drive up to
25 mA and the LED-driving current is pin adjustable by an
external resistor. The ADD5207 drives up to four parallel
strings of multiple series-connected LEDs with a ±1.5% current
matching between strings.
The ADD5207 provides phase shift PWM brightness control
methods. LED dimming control is achieved through the PWM
input. The device includes an 8 kHz LED-dimming oscillator
for driving each current source. The ADD5207 operates over an
input voltage range of 6 V to 21 V, but the device can function
with a voltage as low as 5.6 V.
The ADD5207 also has multiple safety protection features to
prevent damage during fault conditions. If any LED is open, the
device automatically disables the faulty current source. The
internal soft start circuit prevents a high inrush current during
http://www.DataSheet4U.net/ startup. Thermal shutdown protection prevents thermal damage.
The ADD5207 is available in a low profile, thermally enhanced,
4 mm × 3 mm × 0.75 mm, 14-lead, RoHS-compliant lead frame
chip scale package (LFCSP) and is specified over the industrial
temperature range of −25°C to +85°C.
VIN
+
–
CIN
10µF
CIN2
0.1µF
TYPICAL APPLICATION CIRCUIT
L1
10µH
1 VIN
D1 COUT
14 13 4µF
SW OVP
9 PWM
ADD5207
OFF ON
CBYPASS
1µF
RF
100kΩ
10 SHDN
8 VDD
2 FSLCT
ISET
3
COMP
11
RSET
180kΩ
RC
6.8kΩ
CC
2.2nF
FB1 4
FB2 5
FB3 6
FB4 7
GND
12
C2
OPEN
Figure 1.
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 ©2009–2012 Analog Devices, Inc. All rights reserved.
datasheet pdf - http://www.DataSheet4U.net/
1 page  
Data Sheet
ADD5207
LED CURRENT REGULATION SPECIFICATIONS
VIN = 12 V, SHDN = high, TA = −25°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.
Table 2.
Parameter
CURRENT SOURCE
ISET Pin Voltage
Adjustable LED Current1
Constant Current Sink of 20 mA2
Minimum Headroom Voltage2
Current Matching Between Strings2
LED Current Accuracy2
Current Source Leakage Current
FPWM GENERATOR
Dimming Frequency
LED FAULT DETECTION
Open Fault Delay1
Symbol
VSET
ILED
ILED20
VHR20
Test Conditions/Comments
6 V ≤ VIN ≤ 21 V
RSET = 180 kΩ
RSET = 180 kΩ
RSET = 180 kΩ
RSET = 180 kΩ
fPWM
tD_OPENFAULT
Min
1.14
0
19.4
−1.5
−3
6.8
1 This electrical specification is guaranteed by design.
2 Tested at TA = +25°C.
Typ
1.18
20
0.66
8.0
Max
1.22
25
20.6
0.9
+1.5
+3
1
9.2
6.5
Unit
V
mA
mA
V
%
%
µA
kHz
µs
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Rev. A | Page 5 of 16
datasheet pdf - http://www.DataSheet4U.net/
5 Page 
Data Sheet
ADD5207
THEORY OF OPERATION
CURRENT MODE, STEP-UP SWITCHING
REGULATOR OPERATION
The ADD5207 uses a current mode PWM boost regulator to
generate the minimum voltage needed to drive the LED string
at the programmed LED current. The current mode regulation
system allows a fast transient response while maintaining a
stable output voltage. By selecting the proper resistor-capacitor
network from COMP to GND, the regulator response is
optimized for a wide range of input voltages, output voltages,
and load conditions. The ADD5207 can provide a 36 V maxi-
mum output voltage and drive up to 10 LEDs (3.4 V/25 mA
type of LEDs) for each channel.
INTERNAL 3.3 V REGULATOR
The ADD5207 contains a 3.3 V linear regulator that
is used for biasing internal circuitry. The internal regulator
requires a 1 μF bypass capacitor. Place this bypass capacitor
between Pin VDD (Pin 8) and GND, as close as possible to
Pin VDD.
BOOST CONVERTER SWITCHING FREQUENCY
The ADD5207 boost converter switching frequency is user
adjustable, between 600 kHz to 1 MHz, by using an external
resistor, RF. A frequency of 600 kHz is recommended to optim-
ize the regulator for high efficiency, and a frequency of 1 MHz
is recommended to minimize the size of external components.
See Figure 14 for considerations when selecting a switching
frequency and an adjustment resistor (RF).
1000
900
800
700
600
500
400
300
80
100 120 140 160 180 200
RF (kΩ)
Figure 14. Switching Frequency vs. RF
220
DIMMING FREQUENCY (fPWM)
The ADD5207 contains an internal oscillator to generate the
PWM dimming signal for LED brightness control. The LED
dimming frequency (fPWM) is fixed at 8 kHz internally.
CURRENT SOURCE
The ADD5207 contains four current sources to provide accu-
rate current sinking for each LED string. String-to-string
tolerance is kept within ±1.5% at 20 mA. Each LED string
current is adjusted up to 25 mA using an external resistor.
The ADD5207 contains an LED open fault protection circuit
for each channel. If the headroom voltage of the current source
remains below 150 mV while the boost converter output reaches
the OVP level, the ADD5207 recognizes that the current source
has an open-load fault for the current source, and the current
source is disabled.
If an application requires three LED strings, each LED string
should be connected using FB1 to FB3. The unused FB4 pin
should be tied to GND.
The ADD5207 contains hysteresis to prevent the LED current
change that is caused by a ±0.195% jitter of the PWM input.
Programming the LED Current
As shown in the Figure 2, the ADD5207 has an LED current set
pin (ISET). A resistor (RSET) from this pin to ground adjusts the
LED current up to 25 mA. LED current level can be set with
following equation:
http://www.DataSheet4U.net/
ILED
=
3600
RSET
(A)
PWM DIMMING MODE
The ADD5207 supports 8-bit resolution to control brightness.
However, each current source has a minimum on time require-
ment for LED current regulation such that the dimming is in
the range of 1.5% to 100%. Accordingly, even when the PWM
input duty cycle is more than 0% and less than 1.5%, the LED
duty cycle is held at 1.5%.
Phase Shift PWM Dimming
There is a phase delay between each current source channel that is
programmed by the number of current sources in operation. If the
application requires four separate LED strings, each string has a
90 degree phase delay between channels. If three LED strings are
connected at the FB1 to FB3 pins (FB4 = GND), each string has a
120 degree phase delay.
SAFETY FEATURES
The ADD5207 contains several safety features to provide stable
and reliable operation.
Soft Start
The ADD5207 contains an internal soft start function to reduce
inrush current at startup. The soft start time is typically 1.1 ms.
Overvoltage Protection (OVP)
The ADD5207 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
Rev. A | Page 11 of 16
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11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet ADD5207.PDF ] | |
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