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: I
CC
< 1
µ
A
• LED Short Circuit Protection
• Minimal External Components Needed
• Available in an 8-lead MLP and a 12-lead MLP Package
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
each LED current string and automatically adjusts the gener-
ated output DC voltage to the lowest minimum value
required by the LED’s 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 lead to
exceeding 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.
Preliminary Data Sheet
Applications
•
•
•
•
•
Cell Phones
Handheld Computers
PDAs, DSCs, MP3 Players
Keyboard Backlights
LED Displays
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
Typical Application
Analog or Digital Brightness Control
2.7V to 5V
L = 4.7µH
2.7V to 5V
L = 4.7µH
FAN5608DHMPX
V
OUT
4.7µF
FAN5608HMPX
IND
V
IN
A1
B1
A2
B2
IND
V
OUT
GND
CH2
CH1
NN
NC
IND
V
IN
A1
B1
A2
B2
IND
NC
GND
CH2
CH1
NC
4.7µF
V
OUT
DAC Input For CH1
DAC Input For CH2
DAC Input For CH1
DAC Input For CH2
4X4mm MLP-12 Package
with internal Schottky diode
Order Code: FAN5608DHMPX
4X4mm MLP-12 Package
with external Schottky diode
Order Code: FAN5608HMPX
REV. 0.8.3 5/29/03
FAN5608
Preliminary Data Sheet
voltage. The output current can then be programmed to any
desired value within its specified range. The
FAN5608DMPX/FAN5608MPX version uses a single exter-
nal resistor to set the current, and to turn the device ON and
OFF. The FAN5608DMPX/FAN5608MPX is available in an
8-lead MLP package with or without an internal Schottky
diode. The FAN5608DHMPX is available in a 12-lead MLP
package with an internal Schottky diode.
Typical Application
(Continued)
Analog Brightness Control
FAN5608DMPX
2.7V TO 5V
L = 4.7µH
IND
IND
V
IN
R
R
V
OUT
FAN5608MPX
GND
CH2
CH1
4.7µF
2.7V TO 5V L = 4.7µH
V
EXTERNAL
V
EXTERNAL
IND
IND
V
IN
NC
GND
CH2
CH1
4.7µF
V
OUT
A1
A2
R
R
A1
A2
3X3mm MLP-8 Package
with internal Schottky diode
Order Code: FAN5608DMPX
3X3mm MLP-8 Package
with external Schottky diode
Order Code: FAN5608MPX
Definition of Terms
Output Current Accuracy:
reflects the difference between the measured value of the output current (LED) and
programmed value of this current.
(
I
OUT
measured – I
OUT
programmed
) ×
100
Output Current Accuracy (%) = -------------------------------------------------------------------------------------------------------------
-
I
OUT
programmed
Current Matching:
refers to the absolute value of difference in current between the two LED branches.
(
I
LED
branch 1 – I
LED
branch 2
) ×
100
Current Matching (%) = ------------------------------------------------------------------------------------------------
-
(
I
LED
branch 1 + I
LED
branch 2
) ⁄
2
Efficiency:
is expressed as a ratio between the electrical power into the LEDs and the total power consumed from the input
power supply.
(
V
LED
branch 1
×
I
LED
branch 1 + V
LED
branch 1
×
I
LED
branch 1
) ×
100
Efficiency (%) = ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
V
IN
×
I
IN
Although this definition leads to a lower value than the boost converter efficiency, it more accurately reflects better system per-
formance, from the user’s point-of-view.
2
REV. 0.8.3 5/29/03
Preliminary Data Sheet
FAN5608
Pin Assignments
TOP-VIEW
NC
V
IN
A2
CH2
IND
1
2
3
4
8
7
6
5
V
OUT
/NC
12
11
10
IND
NC
12
V
OUT
/NC
11
10
IND
A1
CH1
GND
V
OUT
/NC
V
IN
A2
CH2
IND
1
2
3
4
8
7
6
5
A1
CH1
GND
V
OUT
/NC
GND
CH1
B1
1
9
IND
CH2
B2
GND
CH1
B1
1
9
IND
CH2
B2
2
8
2
8
3
7
3
7
4
5
6
4
5
6
A1 V
IN
A2
A1 V
IN
A2
3x3mm 8-Lead MLP
(Internal Schottky Diode)
3x3mm 8-Lead MLP
(External Schottky Diode)
4x4mm 12-Lead MLP(QUAD)
(Internal Schottky Diode)
4x4mm 12-Lead MLP(QUAD)
(External Schottky Diode)
FAN5608DMPX/FAN5608MPX
FAN5608DHMPX/FAN5608HMPX
Pin Descriptions
Pin No.
1
2
3
4
5
GND
CH1
B1
A1
V
IN
Pin Name
FAN5608DHMPX FAN5608HMPX
GND
CH1
A2
B1
CH2
A1
IND
V
IN
V
OUT
NC
6
7
8
9
10
11
12
A2
B2
CH2
IND
IND
V
OUT
NC
NC
NC
A2
GND
B2
CH1
CH2
A1
IND
IND
A1
CH1
GND
IND
CH2
A2
FAN5608DMPX
GND
V
IN
FAN5608MPX
GND
V
IN
Ground
Input Voltage
1st LED Cathode
DAC A2
DAC B1
2nd LED Cathode
DAC A1
Inductor
Input Voltage
Output LEDs Anode
No Connection
DAC A2
Ground
DAC B2
1st LED Cathode
2nd LED Cathode
DAC A1
Inductor
Inductor
Output LEDs Anode
No Connection
No Connection
Pin Function Description
REV. 0.8.3 5/29/03
3
FAN5608
Preliminary Data Sheet
Absolute Maximum Ratings
Parameter
V
IN
, A, B Voltage to GND
V
OUT
, CH1, CH2 Voltage to GND
Any LED Short Circuit Duration (Anode to Cathode)
Lead Soldering Temperature (10 seconds)
Thermal Resistance
θ
jc
Operating Junction Temperature Range
Storage Temperature Range
Electrostatic Discharge (ESD) Protection (Note 1, 2)
HBM
CDM
-55
4
1
8
150
150
Min
-0.3
-0.3
Typ
Max
6
24
Indefinite
300
°C
°C/W
°C
°C
kV
Unit
V
V
DC Electrical Characteristics
(V
IN
=2.7V to 5V, T
A
= 25 °C, unless otherwise noted. Boldface values indicate specifications over the ambient
operating temperature.)
Parameter
Conditions
Min.
Typ.
Max.
Units
Output Current Accuracy
Channel to Channel Current Matching
Efficiency (AVG)
Switching Frequency
Multiplication Ratio
FAN5608DMPX/
FAN5608MPX
FAN5608DHMPX/
FAN5608HMPX
Supply Current in OFF mode
Input A1, A2 Threshold
Digital
Mode
Analog Mode
Input B Threshold
Digital Mode
A = HIGH,
B = HIGH
A = HIGH,
B = HIGH
V
IN
> 3.0V
0.9
×
I
NOM
I
NOM
= 20
1.1
×
I
NOM
mA
3
80
0.5
900
850
1000
1000
0.1
V
IN
-0.7
0
1.2
0.6
×
V
IN
0
V
IN
0.6
V
IN
0.3
×
V
IN
V
1100
1150
%
%
MHz
V
A
= V
B
= 0V
High
Low
High
Low
µ
A
V
Recommended Operating Conditions
Parameter
Input Voltage Range
Operating Ambient Temperature Range
Output Voltage Range
Min
2.7
-40
V
IN
25
Typ
Max
5
85
18
Unit
V
°C
V
Notes:
1. Using Mil Std. 883E, method 3015.7(Human Body Model) and EIA/JESD22C101-A (Charge Device Model).
2. Avoid positive polarity ESD stress at the cathode of the internal Schottky diode.
4
REV. 0.8.3 5/29/03
Preliminary Data Sheet
FAN5608
Block Diagram
V
IN
OSC
DBB
COIL DRIVER
IND
V
OUT
START-UP
B1
A1
LINEAR REGULATOR
CH1
DAC1
REF CH1
BG
REF
REF CH2
W_OR
B2
A2
DAC2
POWER GOOD
LINEAR REGULATOR
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 V
IN
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 V
IN
, 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 two. 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 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 (V
CC
) 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. 0.8.3 5/29/03
5
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