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PDF ADD5205 Data sheet ( Hoja de datos )
| Número de pieza | ADD5205 | |
| Descripción | Four-String White LED Driver | |
| Fabricantes | Analog Devices | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de ADD5205 (archivo pdf) en la parte inferior de esta página. Total 16 Páginas | ||
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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/
1 page  
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Data Sheet
ADD5205
VIN = 3.7 V, SHDN = high, TA = −25°C to +85°C, unless otherwise noted. Typical values are at TA = 25°C.
Table 2.
Parameter
THERMAL PROTECTION
Thermal Shutdown Threshold1
Thermal Shutdown Hysteresis1
UVLO
UVLO Rising Threshold
UVLO Falling Threshold
OVERVOLTAGE PROTECTION
Overvoltage Threshold on OVP Pin
Symbol
TSD
TSDHYST
VUVLOR
VUVLOF
VOVP
Test Conditions/Comments
VIN rising
VIN falling
Min Typ Max Unit
160 °C
30 °C
2.5 V
2V
28 V
1 Guaranteed by design.
Rev. 0 | Page 5 of 16
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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 3.3 μH to 6.8 μH range is recommended. In
general, lower inductance values result in higher saturation
current and lower series resistance for a given physical size.
The input (VIN) and output (VOUT) voltages determine the switch
duty cycle (D), which in turn can be used to determine the
inductor ripple current.
D = VOUT − VIN
VOUT
Use the duty cycle and switching frequency (fSW) to determine
the on time (tON).
t ON
=
D
f SW
The inductor ripple current (ΔIL) in a steady state is
ΔI L
=
VIN
× tON
L
Solve for the inductance value (L).
L = VIN ×tON
ΔI L
Ensure 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.
I LPK
= I LAVG
+
1
2
ΔI
L
,
I LAVG
=
IOUT ×VOUT
η ×VIN
ΔI L
=
1
L
VIN
VOUT − VIN
fSW ×VOUT
where:
ILPK is the peak inductor current.
ILAVG is the input average current.
ADD5205
Table 6 shows a list of recommend inductors.
Table 6. Recommended Inductors
Coilcraft Part No. L (μH) ISAT (A)
XFL4020-332ML 3.3
2.7
LPS4012-472ML
4.7
1.6
LPS4018-472ML
4.7
1.8
LPS4018-682ML
6.8
1.2
Size (mm)
4×4×2
3.9 × 3.9 × 1.1
3.9 × 3.9 × 1.7
3.9 × 3.9 × 1.7
Input and Output Capacitors Selection
The ADD5205 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)
4.7 μF or greater capacitor for the input capacitor to prevent noise
at the ADD5205 input. Place the input between VIN and GND,
as close as possible to the ADD5205.
The output capacitor maintains the output voltage and supplies
current to the load while the ADD5205 switch is on. The value
and characteristics of the output capacitor greatly affect the
output voltage ripple and stability of the regulator. Use a ceramic
X5R or X7R dielectric capacitor, and for the output capacitor, a
4.7 μF or greater capacitor is preferred.
Place a 100 nF or greater capacitor as close as possible to the
OVP pin of ADD5205.
Diode Selection
The output diode conducts the inductor current to the output
capacitor and loads while the switch is off. For high efficiency,
minimize the forward voltage drop of the diode. Schottky diodes
are recommended.
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 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.
Rev. 0 | Page 11 of 16
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| PDF Descargar | [ Datasheet ADD5205.PDF ] | |
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