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PDF FAN5608DHMPX Data sheet ( Hoja de datos )
| Número de pieza | FAN5608DHMPX | |
| Descripción | Serial/Parallel LED Driver with Current-Regulated/ Step-Up DC/DC Converter | |
| Fabricantes | Fairchild Semiconductor | |
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www.fairchildsemi.com
FAN5608
Serial/Parallel LED Driver with Current-Regulated,
Step-Up DC/DC Converter
Features
• Two Independent Channels Drive up to Six LEDs per
Channel
• Adaptive Output Voltage Drive to Maximize Efficiency
• PWM/PFM Mode of Operation of the Boost Circuit
• Up to 85% Efficiency
• Up to 2 × 20mA Output
• Two Built-in DACs for Independent (Digital) Brightness
Control for Both Channels
• LED’s Current Can be Duty-Cycle-Modulated between
0 to 20mA
• Digital, Analog, and PWM Brightness Control
• 2.7V to 5V Input Voltage Range
• 0.5MHz Operating Frequency (8MHz internal clock)
• Soft Start
• Low Shutdown Current: ICC < 1µA
• LED Short Circuit Protection
• Minimal External Components Needed
• Available in space saving 8-lead and 12-lead MLP
Packages.
Applications
• Cell Phones
• Handheld Computers
• PDAs, DSCs, MP3 Players
• Keyboard Backlights
• LED Displays
Description
The FAN5608 LED driver generates regulated output cur-
rents from a battery with input voltage varying between 2.7V
to 5V. An internal NMOS switch drives an external inductor,
and a Schottky diode delivers the inductor’s stored energy to
the load. Proprietary internal circuitry continuously monitors
the currrent on both strings and automatically adjusts the
generated output DC voltage to the lowest minimum value
required by the LEDs string with the highest summarized
forward voltage. This adaptive nature of the FAN5608
ensures operation at the highest possible efficiency. Soft start
circuitry prevents excessive current drawn from the supply
during power on. Any number of LEDs can be connected in
series as long as the summed forward voltages do not exceed
the specified operating output voltage range. Although it is
not required to have an equal number of LEDs connected in
series within each branch, the highest efficiency and best
current regulation is always achieved when an equal number
of LEDs are serially connected.
In the FAN5608 device, two internal two-bit D/A converters
provide independent programmability of each output channel
current. Analog programming of the output current is
also possible in the FAN5608. To do this, ground the "B"
pins and connect a resistor between the "A" pins and a
fixed supply voltage. The output current can then be
programmed to any desired value within its specified range.
The FAN5608DMPX/FAN5608MPX version uses a single
Typical Application
Digital Brightness Control
CIN
2.7V to 5V
L = 4.7µH
DAC Input For CH1
DAC Input For CH2
IND
VIN
A1
B1
A2
B2
IND
VOUT
GND
CH2
CH1
NNCN
4.7µF
VOUT
CIN
2.7V to 5V
L = 4.7µH
DAC Input For CH1
DAC Input For CH2
IND
VIN
A1
B1
A2
B2
IND
NC
GND
CH2
CH1
NC
4.7µF
VOUT
4X4mm MLP-12 Package
with internal Schottky diode
Order Code: FAN5608DHMPX
4X4mm MLP-12 Package
with external Schottky diode
Order Code: FAN5608HMPX
REV. 1.0.3 6/28/04
1 page  
FAN5608
Block Diagram
VIN
B1
A1 DAC1
B2
A2 DAC2
PRODUCT SPECIFICATION
OSC
DBB
COIL DRIVER
START-UP
REF CH1
BG REF
REF CH2
POWER GOOD
LINEAR REGULATOR
W_OR
LINEAR REGULATOR
IND
VOUT
IND
CH1
CH2
GND
Note: In the 8-pin version (analog version only), pins B1 and B2 are omitted.
Circuit Description
When the input voltage is connected to VIN pin, the system is
turned on, the bandgap reference acquires its nominal volt-
age and the soft-start cycle begins. Once “power good” is
achieved (0.5mA in the diodes), the soft-start cycle stops and
the boost voltage increases to generate the desired current
selected by the input control pins. If the second channel is
not selected, its output will go high to about VIN, and the
diodes are turned off.
The FAN5608 DC/DC converter automatically adjusts its
internal duty cycle to achieve high efficiency. It provides
tightly regulated output currents for the LEDs. An internal
circuit determines which LED string requires the highest
voltage in order to sustain the pre-set current levels, and
adjusts the boost regulator accordingly.
To maintain the regulated current at the selected value, the
difference in the number of LEDs between branches should
not exceed one. If only one branch is used, another branch
should be disabled, connecting the corresponding DAC
inputs to low. If the output external capacitor is shorted, the
Schottky diode can be damaged, therefore such a condition
should be avoided.
LED Brightness Control
The control inputs are A1, B1 for CH1 and A2, B2 for CH2.
B1 and B2 are digital inputs, thus they require LOW (GND)
and HIGH (VCC) control signals. In analog mode, A1 and A2
are connected to an external stable voltage source via an
external resistor, and B1 and B2 inputs are connected to
ground. The current flowing through the resistor is scaled by
a factor of approximately 1000.
REV. 1.0.3 6/28/04
5
5 Page 
FAN5608
PRODUCT SPECIFICATION
4. Driver For 12 White LEDs
2.7V to 5V L = 4.7µH
DAC Input For CH1
DAC Input For CH2
IND
VIN
A1
B1
A2
B2
IND
VOUT
GND
CH2
CH1
NNCN
4.7µF
VOUT
Efficiency vs Input Voltage
Twelve LEDs
0.80
ILED = 10mA
0.75
0.70
0.65
0.60
ILED = 20mA
0.55
0.50
2.5 3.0 3.5 4.0 4.5 5.0 5.5
Input Voltage (V)
Figure 4
Note:
Refer to the Application Information, if a higher load current compliance rating is required
Typical Performance Characteristics
TA = 25°C, CIN = COUT = 4.7µF, L = 4.7µH, unless otherwise noted.
0.065
Shutdown Current vs Input Voltage
0.060
0.055
0.050
0.045
0.040
0.035
2.5 3.0 3.5 4.0 4.5 5.0 5.5
Input Voltage (V)
REV. 1.0.3 6/28/04
11
11 Page | ||
| Páginas | Total 17 Páginas | |
| PDF Descargar | [ Datasheet FAN5608DHMPX.PDF ] | |
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