FAN5608DHMPX [ONSEMI]
LED Driver;
ONSEMI 
www.fairchildsemi.com
FAN5608
Serial/Parallel LED Driver with Current-Regulated,
Step-Up DC/DC Converter
Features
Description
• 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
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.
• Low Shutdown Current: I < 1µA
CC
• LED Short Circuit Protection
• Minimal External Components Needed
• Available in an 8-lead MLP and a 12-lead MLP Package
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
L = 4.7µH
2.7V to 5V
L = 4.7µH
2.7V to 5V
IND
NC
IND
V
IND
OUT
IND
V
OUT
V
IN
V
V
IN
4.7µF
OUT
4.7µF
A1
B1
GND
CH2
CH1
A1
B1
GND
CH2
CH1
DAC Input For CH1
DAC Input For CH2
DAC Input For CH1
DAC Input For CH2
A2
B2
A2
B2
NC
NC
4X4mm MLP-12 Package
4X4mm MLP-12 Package
with external Schottky diode
Order Code: FAN5608HMPX
with internal Schottky diode
Order Code: FAN5608DHMPX
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
L = 4.7µH
2.7V TO 5V
VOUT
GND
IND
4.7µF
V
OUT
L = 4.7µH
2.7V TO 5V
V
IN
NC
IND
V
EXTERNAL
R
R
4.7µF
V
IN
GND
A1
A2
CH2
CH1
V
EXTERNAL
R
R
A1
A2
CH2
CH1
3X3mm MLP-8 Package
3X3mm MLP-8 Package
with internal Schottky diode
Order Code: FAN5608DMPX
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
measured – I
programmed) × 100
OUT
OUT
Output Current Accuracy (%) = -------------------------------------------------------------------------------------------------------------
programmed
I
OUT
Current Matching: refers to the absolute value of difference in current between the two LED branches.
(I branch 1 – I branch 2) × 100
LED
LED
Current Matching (%) =
------------------------------------------------------------------------------------------------
(I branch 1 + I branch 2) ⁄ 2
LED
LED
Efficiency: is expressed as a ratio between the electrical power into the LEDs and the total power consumed from the input
power supply.
(V
branch 1 × I
branch 1 + V
branch 1 × I
branch 1) × 100
LED
LED
LED
LED
Efficiency (%) = ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
× I
V
IN
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
VOUT/NC
VOUT/NC
NC
IND
NC
IND
12
11
10
12
11
10
A1
1
2
3
4
8
7
6
5
A1
V
IN
V
1
2
3
4
8
7
6
5
IN
CH1
GND
CH1
GND
1
2
3
9
A2
GND
IND
CH2
B2
A2
1
2
3
9
8
7
GND
IND
CH2
B2
CH2
CH2
8
7
CH1
B1
CH1
B1
VOUT/NC
VOUT/NC
IND
IND
4
5
6
4
5
6
A1
V
A2
A1
V
A2
IN
IN
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.
Pin Name
Pin Function Description
FAN5608DHMPX FAN5608HMPX FAN5608DMPX FAN5608MPX
1
2
3
4
5
GND
CH1
B1
GND
CH1
B1
GND
GND
Ground
V
V
Input Voltage
1st LED Cathode
DAC A2
IN
IN
A2
A2
DAC B1
CH2
IND
CH2
IND
2nd LED Cathode
DAC A1
A1
A1
Inductor
V
V
Input Voltage
Output LEDs Anode
No Connection
DAC A2
IN
IN
V
OUT
NC
GND
CH1
A1
6
7
8
A2
B2
A2
B2
GND
CH1
A1
Ground
DAC B2
1st LED Cathode
2nd LED Cathode
DAC A1
CH2
CH2
9
IND
IND
IND
IND
Inductor
10
11
Inductor
V
Output LEDs Anode
No Connection
No Connection
OUT
NC
NC
12
NC
REV. 0.8.3 5/29/03
3
FAN5608
Preliminary Data Sheet
Absolute Maximum Ratings
Parameter
Min
-0.3
-0.3
Typ
Max
6
Unit
V
V , A, B Voltage to GND
IN
V
, CH1, CH2 Voltage to GND
24
V
OUT
Any LED Short Circuit Duration (Anode to Cathode)
Lead Soldering Temperature (10 seconds)
Indefinite
300
°C
°C/W
°C
Thermal Resistance θ
8
jc
Operating Junction Temperature Range
Storage Temperature Range
150
150
-55
4
°C
Electrostatic Discharge (ESD) Protection (Note 1, 2)
HBM
CDM
kV
1
DC Electrical Characteristics
(V =2.7V to 5V, T = 25 °C, unless otherwise noted. Boldface values indicate specifications over the ambient
IN
A
operating temperature.)
Parameter
Conditions
Min.
Typ.
Max.
Units
Output Current Accuracy
Channel to Channel Current Matching
Efficiency (AVG)
A = HIGH,
B = HIGH
0.9 × I
I
= 20 1.1 × I
mA
NOM
NOM
NOM
A = HIGH,
B = HIGH
3
%
%
V
> 3.0V
80
IN
Switching Frequency
0.5
MHz
Multiplication Ratio
FAN5608DMPX/
900
850
1000
1100
1150
FAN5608MPX
FAN5608DHMPX/
FAN5608HMPX
1000
0.1
Supply Current in OFF mode
Input A1, A2 Threshold
V = V = 0V
µA
A
B
Digital
Mode
High
V -0.7
V
IN
IN
Low
0
0.6
V
Analog Mode
Digital Mode
1.2
Input B Threshold
High
Low
0.6 × V
V
IN
IN
V
0
0.3 × V
IN
Recommended Operating Conditions
Parameter
Min
2.7
-40
Typ
Max
5
Unit
V
Input Voltage Range
Operating Ambient Temperature Range
25
85
18
°C
V
Output Voltage Range
V
IN
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
IND
V
OSC
DBB
COIL DRIVER
OUT
CH1
LINEAR REGULATOR
W_OR
START-UP
REF
B1
A1
DAC1
DAC2
REF CH1
REF CH2
BG
B2
A2
LINEAR REGULATOR
CH2
POWER GOOD
GND
Note: In the 8-pin version (analog version only), pins B1 and B2 are omitted.
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.
Circuit Description
When the input voltage is connected to V 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
IN
not selected, its output will go high to about V , and the
diodes are turned off.
IN
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)
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.
and HIGH (V ) control signals. In analog mode, A1 and
CC
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
Preliminary Data Sheet
FAN5608
Digital Control
No Load Protection
The FAN5608’s digital decoder allows selection of the fol-
lowing modes of operation: OFF, 5mA, 10mA, 20mA per
branch.
A built-in over voltage protection circuit prevents the device
from being damaged when it is powered up with no load.
This circuit reduces the boost converter duty cycle, to a min-
imum thus limiting the output voltage to a safe value when
no load condition is detected. If one of the two enable
branches is accidentally disconnected, the converter contin-
ues the operation, however, the current in the remaining
branch is no longer regulated and the actual branch current
will be determined by the input voltage, the inductor value
and the switching frequency.
A
B
0
0
1
0
0
1
1
1
I
OFF
5mA 10mA 20mA
LED
Analog Control with PWM
Inputs A1 and A2 are used to control the LED currents.
Inputs B1 and B2 should be connected to GND (logic level
"0"). An external resistor (R) is connected from A1 and/or
However, the FAN5608 can be damaged when a full load
(more than six LEDs, driven by 20mA) is suddenly discon-
A2 to a stable voltage source (V
) to control the
nected from V
. To protect the FAN5608 against this
EXTERNAL
OUT
LED current, I
follows:
. The formula used to calculate I
is as
unlikely event, an external 20V Zener diode can be con-
nected between V and GND.
LED
LED
OUT
V
– V
Ref
External
-----------------------------------------
× 1000
I
=
Shutdown Mode
LED
R
Each branch can be independently disabled by applying
LOW logic level voltage to the A and B inputs. When both
branches are disabled, the FAN5608 enters Shutdown mode
and the supply current is reduced to less than 1µA.
Where V
= 1.22V
Ref
Pulse-Width-Modulation (PWM) Control
A variable duty cycle(δ) can modulate any DAC input. Care
should be taken to not use a too low frequency, otherwise a
flickering effect may occur. The minimum range is 100Hz to
1KHz. For a maximum range of LED current, both A and B
inputs can be modulated at the same time.
PWM Control
1. A is PWM Controlled, B is Low. I
(Average) = δ x 5mA, where δ is Duty Cycle. (Note 3)
LED
A Input (PWM)
30%
Duty Cycle
70%
Duty Cycle
1KHz
1KHz
B Input (0)
ILED (Average) = 0.7 x 5mA = 3.5mA
ILED (Average) = 0.3 x 5mA = 1.5mA
I
0mA
OFF
LED
Note:
3. Proportionally select the duty cycle to achieve a typical LED current between 1mA to 4mA.
REV. 0.8.3 5/29/03
6
Preliminary Data Sheet
FAN5608
PWM Control (Continued)
2. A is High and B is PWM. I
(Average) = 5mA + δ x 15mA, where δ is Duty Cycle.(Note 4, 5)
LED
A Input
B Input (PWM)
30%
Duty Cycle
70%
Duty Cycle
1KHz
1KHz
ILED (Average) = 0.7 x 20mA + 0.3 x 5mA = 15.5mA
ILED (Average) = 0.3 x 20mA + 0.7 x 5mA = 9.5mA
I
OFF
0mA
LED
3. A and B are PWM. I
(Average) = δ x 20mA, where δ is Duty Cycle.(Note 4)
LED
A Input (PWM)
30%
Duty Cycle
70%
Duty Cycle
1KHz
1KHz
B Input (PWM)
30%
Duty Cycle
70%
Duty Cycle
1KHz
1KHz
ILED (Average) = 0.7 x 20mA = 14mA
ILED (Average) = 0.3 x 20mA = 6mA
LED CURRENT
0mA
OFF
Notes:
4. Maximum PWM frequency can be up to 30KHz.
5. Proportionally select the duty cycle to achieve a typical LED current between 1mA and 19mA.
REV. 0.8.3 5/29/03
7
FAN5608
Preliminary Data Sheet
A larger value input capacitor placed as close as possible to
FAN5608 may be needed to reduce the input voltage ripple
in noise sensitive applications. An additional LC filter
between the battery and the FAN5608 input can help to fur-
ther reduces the battery ripple to the level required by a par-
ticular application.
Applications Information
Inductor Selection
The inductor is one of the main components required by the
boost converter to store energy. The amount of energy stored
in the inductor and transferred to the load is controlled by the
regulator using PWM and pulse skipping techniques.
FAN5608 operates the inductor in discontinuous conduction
mode in most cases.
PCB Layout Consideration
The FAN5608 is available in both a single Die Attach Pad
(DAP) and a dual DAP package. In the single DAP package,
DAP is connected to GND. In the dual DAP package, one
To ensure proper operation of the current regulator over the
entire range of conditions, the inductor should be selected
DAP is connected to GND and another to V
, therefore it
OUT
is not necessary to provide any external connection to the
DAPs. Since the internal power dissipation is low, both the
3x3mm and 4x4mm MLP packages are capable of dissipat-
ing maximum power, without providing any PCB land pat-
tern. When viewing the bottom of the package of a single
DAP device, a single exposed metal island can be seen; when
viewing the bottom of the package of a dual DAP device, two
electrically isolated exposed metal islands can be seen.
based on the maximum required power (P
) and the mini-
OUT
mum input voltage (V ).
IN
2
(V ) × F
IN
---------------------------
L <
P
OUT
where units of L, V , and P
are in µH, Volt, and Watt,
OUT
IN
respectively F = 0.4 is a factor depending upon the FAN5608
architecture.
The above relation is applicable up to P
= 0.6W and
OUT
L = 4.3µΗ, or greater. At lower inductor value the efficiency
decreases due to the resistive loss in the switching Power
FET. Using L = 4.3µΗ and increasing the load to 12 LED x
20mA (P
= 800mW) requires V > 3.5V to maintain a
OUT
IN
constant 20mA current through LEDs. The inductor L =
4.3µH ensures proper operation for 2 x 4 white LEDs with
20mA at 3.5V for V > 2.8V.
IN
For any lighter load or higher V , the inductance can be
IN
increased to improve the system efficiency. Application
examples are given in Figure 1 through Figure 4.
The peak current in the inductor is:
T
× V
IN_Max
ON_Max
I= ---------------------------------------------------
L
which gives the maximum rated current for the inductor. For
L = 4.3µH, T
= 1.25µS and V
= 4.2V, the
ON_Max
IN_Max
inductor saturation current should be at least 1A.
Capacitor Selection
Low ESR capacitors should be used to minimize the input
and output ripple voltage. Use of C = 4.7µF/6.3V and
IN
C
= 4.7µF/25V type X5R/X7R multi layer ceramic
OUT
capacitor is recommended.
8
REV. 0.8.3 5/29/03
Preliminary Data Sheet
FAN5608
Application Examples
1. Driver For Four White LEDs
Efficiency vs Input Voltage
Four LEDs
0.85
0.80
0.75
0.70
ILED =20mA
L = 6.8µH
2.7V to 5V
IND
IND
V
OUT
V
V
IN
OUT
4.7µF
A1
B1
GND
CH2
CH1
DAC Input For CH1
DAC Input For CH2
A2
B2
NC
ILED =10mA
2.5
3.0
3.5
4.0
4.5
5.0
5.5
Input Voltage (V)
Figure 1
2. Driver For Six White LEDs
Efficiency vs Input Voltage
Six LEDs
0.90
0.85
0.80
0.75
0.70
0.65
0.60
ILED =20mA
L = 6.8µH
2.7V to 5V
IND
IND
V
OUT
V
V
IN
OUT
4.7µF
A1
B1
GND
CH2
CH1
DAC Input For CH1
DAC Input For CH2
A2
B2
NC
ILED =10mA
2.5
3.0
3.5
4.0
4.5
5.0
5.5
Input Voltage (V)
Figure 2
3. Driver For Eight White LEDs
Efficiency vs Input Voltage
Eight LEDs
0.90
0.85
0.80
0.75
0.70
0.65
0.60
L =4.7µH
ILED =20mA
2.7V to 5V
IND
IND
V
OUT
V
V
IN
OUT
4.7µF
A1
B1
GND
CH2
CH1
DAC Input For CH1
DAC Input For CH2
A2
B2
NC
ILED =10mA
2.5
3.0
3.5
4.0
4.5
5.0
5.5
Input Voltage (V)
Figure 3
REV. 0.8.3 5/29/03
9
FAN5608
Preliminary Data Sheet
4. Driver For Twelve White LEDs
Efficiency vs Input Voltage
Twelve LEDs
0.80
0.75
0.70
0.65
0.60
0.55
0.50
ILED =10mA
L = 4.7µH
2.7V to 5V
IND
IND
V
OUT
V
V
IN
OUT
4.7µF
A1
B1
GND
CH2
CH1
DAC Input For CH1
DAC Input For CH2
A2
B2
NC
ILED =20mA
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 higher load current compliance rating is required
10
REV. 0.8.3 5/29/03
Preliminary Data Sheet
FAN5608
Mechanical Dimensions
4x4mm 12-Lead MLP (Internal Schottky Diode)
GND
VOUT
REV. 0.8.3 5/29/03
11
FAN5608
Preliminary Data Sheet
Mechanical Dimensions
4x4mm 12-Lead MLP (External Schottky Diode)
12
REV. 0.8.3 5/29/03
Preliminary Data Sheet
FAN5608
Mechanical Dimensions
3x3mm 8-Lead MLP (Internal Schottky Diode)
VOUT
GND
REV. 0.8.3 5/29/03
13
FAN5608
Preliminary Data Sheet
Mechanical Dimensions
3x3mm 8-Lead MLP (External Schottky Diode)
14
REV. 0.8.3 5/29/03
Preliminary Data Sheet
FAN5608
Ordering Information
Product Number
Package Type
Schottky Diode
Internal
Order Code
FAN5608
12-Lead MLP(4x4mm)
8-Lead MLP(3x3mm)
FAN5608DHMPX
FAN5608HMPX
FAN5608DMPX
FAN5608MPX
External
Internal
External
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FAIRCHILD SEMICONDUCTOR RESERVES THE RIGHT TO MAKE CHANGES WITHOUT FURTHER NOTICE TO
ANY PRODUCTS HEREIN TO IMPROVE RELIABILITY, FUNCTION OR DESIGN. FAIRCHILD DOES NOT ASSUME
ANY LIABILITY ARISING OUT OF THE APPLICATION OR USE OF ANY PRODUCT OR CIRCUIT DESCRIBED HEREIN;
NEITHER DOES IT CONVEY ANY LICENSE UNDER ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS.
PRELIMINARY INFORMATION DESCRIBES PRODUCTS THAT ARE NOT IN FULL PRODUCTION AT THE TIME OF
PRINTING. SPECIFICATIONS ARE BASED ON SIMULATION AND LIMITED CHARACTERIZATION. THEY MAY CHANGE
WITHOUT NOTICE. CONTACT FAIRCHILD SEMICONDUCTOR FOR CURRENT INFORMATION.
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FAIRCHILD’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES
OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD SEMICONDUCTOR
CORPORATION. As used herein:
1. Life support devices or systems are devices or systems
which, (a) are intended for surgical implant into the body,
or (b) support or sustain life, and (c) whose failure to
perform when properly used in accordance with
instructions for use provided in the labeling, can be
reasonably expected to result in a significant injury of the
user.
2. A critical component in any component of a life support
device or system whose failure to perform can be
reasonably expected to cause the failure of the life support
device or system, or to affect its safety or effectiveness.
www.fairchildsemi.com
REV. 0.8.3 5/29/03
2003 Fairchild Semiconductor Corporation
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