www.fairchildsemi.com
FAN5609
LED Driver with Adaptive Charge Pump DC/DC
Converter
Features
•
•
•
•
•
Parallel LED Driver Supports All Forward Voltages
Adaptive V
OUT
Adjustment to the Highest Diode Voltage
Internally Matched LED Current Sources
No External Components Needed to Set LED Current
Built-in Charge Pump has Three Modes of Operation:
– Linear Regulation V
IN
> 4.2V
– 3/2 DC-DC Converter and Regulation 3.6V<V
IN
<4.2V
– 2/1 DC-DC Converter and Regulation 2.7V<V
IN
<3.6V
Up to 86% Efficiency
Low EMI, Low Ripple
Up to 80mA Output Current (4
×
20mA)
Built-in DAC for Digital or PWM Brightness Control
Can be Duty Cycle Modulated between 0 to 18mA
2.7V to 5.5V Input Voltage Range
I
CC
< 2µA in Shutdown Mode
1MHz Operating Frequency
Shutdown Isolates Output from Input
Soft-Start Limits Inrush Current
Short Circuit Protection
Minimal External Components Needed
Available in a 14-lead TSSOP Package
Available in a 16-lead MLP Package
Applications
•
•
•
•
•
Cell Phones
Handheld Computers
PDA, DSC, MP3 Players
Keyboard Backlight
LED Displays
Description
The FAN5609 generates regulated output current from a
battery with input voltage varying between 2.7V to 5.5V.
Switch reconfiguration and fractional switching techniques
are utilized to achieve high efficiency over the entire input
voltage range. A proprietary internal circuitry continuously
monitors each LED current loop and automatically adjusts
the generated output DC voltage to the lowest minimum
value required by the LED having the highest forward
voltage. This adaptive nature of the FAN5609 eliminates the
need for LED pre-selection (matching) and ensures opera-
tion at high efficiency. When the input voltage is sufficiently
high to sustain the programmed current level in the LEDs,
the FAN5609 re-configures itself to operate as a linear
regulator, and the DC-DC converter is turned off. An internal
two-bit digital to analog converter provides programmability
of the output currents. Only two 0.1µF bucket capacitors and
two 4.7µF input/output capacitors are needed for proper
operation.
Soft-start circuitry prevents excessive current draw during
power on. The device has built-in short circuit protection.
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Typical Application
V
OUT
C
OUT
V
IN
C
IN
V
OUT
V
IN
IN A
LED-
LED-
LED-
LED-
CAP-
CAP2
CAP+
CAP+
CAP1
D
A
C
FAN5609
GND
IN B
CAP-
REV. 1.0.2 5/30/03
FAN5609
PRODUCT SPECIFICATION
Pin Assignments
NC
CAP2+
13
12
11
10
9
5
6
7
8
Top-View
V
IN
V
OUT
GND
B
A
LED-
LED-
CAP2-
CAP2+
CAP1+
CAP1-
NC
LED-
LED-
CAP2-
14
16
15
FAN5609
V
IN
V
OUT
GND
B
NC
1
2
3
4
CAP1+
CAP1-
NC
LED-
LED-
LED-
FAN5609
14-Lead TSSOP
FAN5609
4x4mm 16-Lead MLP
Pin Descriptions
FAN5609
Pin No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
14L-TSSOP
V
IN
V
OUT
GND
B
A
LED -
LED -
LED -
LED -
NC
CAP1-
CAP1+
CAP2+
CAP2-
4mmX4mm 16L-MLP
V
IN
V
OUT
GND
B
A
LED -
LED -
LED -
LED -
NC
CAP1-
CAP1+
CAP2+
CAP2-
NC
NC
Input
Output to LEDs Anode
Ground
DAC B
DAC A
4th LED Cathode
3rd LED Cathode
2nd LED Cathode
1st LED Cathode
No Connection
Bucket capacitor negative terminal
Bucket capacitor positive connection
Bucket capacitor positive terminal
Bucket capacitor negative connection
No Connection
No Connection
Pin Function Description
Test Circuit
CAP2
NC NC
V
IN
= 2.7V to 5.5V
1
C
IN
V
OUT
C
OUT
4.7µF
V
L
4
V
H
5
8
9
4.7µF
FAN5609
NC
16
0.1µF
13
12
CAP1
0.1µF
V
H
V
L
4 White LEDs
Fairchild QTLP670C-IW
Super Bright LED
All capacitors are Ceramic chip capacitor
2
LED-
A
REV. 1.0.2 5/30/03
PRODUCT SPECIFICATION
FAN5609
Absolute Maximum Ratings
Parameter
V
IN
, V
OUT
, A, B Voltage to GND
CAP+, CAP-, to GND
V
OUT
Short Circuit Duration
Lead Soldering Temperature (10 seconds)
Operating Junction Temperature Range
Storage Temperature
Electrostatic Discharge Protection Level (Note 1)
HBM
CDM
-55
4
2
Min
-0.3
-0.3
Max
6.0
V
IN
+ 0.3
INDEFINITE
300
150
150
°C
°C
°C
kV
Unit
V
V
Recommended Operating Conditions
Parameter
Input Voltage Range, V
IN
Operating Ambient Temperature Range
Min
2.7
-40
25
Typ
Max
5.5
85
Unit
V
°C
DC Electrical Characteristics
Unless otherwise noted, V
IN
=3V to 5.5V, T
A
= 25°C. Refer to “Test Circuit”.
Boldface
values indicate specifications
over the ambient operating temperature range.
Parameter
Conditions
Min.
Typ.
Max.
Units
Quiescent Current
Output Current Accuracy
I
NOM
= 20mA
LED to LED Current Matching
Efficiency
Input A, B Threshold
V
IN
at Configuration
Change
Oscillator Frequency
Supply Current, "OFF Mode"
V
OUT
= 5.5V,
No Load
A = High
B = High
V
IN
= 5.5V
A = B = High
V
IN
= 4.5V
V
IN
= 3V
Low
High
From 1:1 to 3:2
From 3:2 to 2:1
0.80
0
0.6
×
V
IN
17
-5
1.5
20
4
23
+5
mA
mA
%
%
85 to75
65 to 55
0.3
×
V
IN
V
IN
4.2
3.6
1
1.2
2
V
V
MHz
µ
A
Note:
1. Using Mil Std. 883E, method 3015.7(Human Body Model) and EIA/JESD22C101-A (Charge Device Model)
REV. 1.0.2 5/30/03
3
FAN5609
PRODUCT SPECIFICATION
Block Diagram
1µF
V
IN
Linear
Regulator
V
OUT
Voltage
Selector
A
DAC
B
D
R
I
V
E
R
S
Power
Good
P
U
M
P
On Off
And
Current Range
Oscillator
Bandgap
Reference
Range Selection
Reference
Analog
Detector
5µF
I. LIM.
I. LIM.
Ref2
Ref1
Regulator
Ref3
Mode Change
V
IN
Ref4 (BG)
GND
1µF
Circuit Description
The FAN5609’s switched capacitor DC/DC converter auto-
matically configures its internal switches to achieve high effi-
ciency and to provide tightly regulated output currents for
the LEDs. An analog detector determines which diode
requires the highest voltage in order to sustain the pre-set
current levels, and adjusts the pump regulator accordingly.
Every diode has its own linear current regulator. In addition,
a voltage regulator controls the output voltage when the bat-
tery voltage is within a range where linear regulation can
provide maximum possible efficiency. If the battery voltage
is too low to sustain the diode current in the linear mode,
a fractional 3:2 charge pump is enabled. When the battery
voltage drops further and this mode is no longer sufficient to
sustain proper operation, the pump is automatically reconfig-
ured to operate in 2:1 mode. As the battery discharges and
the voltage decays, the FAN5609 switches between modes to
maintain a constant current through LED throughout the bat-
tery life. The transition has hysteresis to prevent toggling.
Supply Voltage
The internal supply voltage for the device is automatically
selected from V
IN
or V
OUT
pins, whichever is higher.
Soft Start
The soft-start circuit limits inrush current when the device is
initially powered up and enabled. The reference voltage con-
trols the rate of the output voltage ramp-up to its final value.
Typical start-up time is 1ms. The rate of the output voltage
ramp-up is controlled by an internally generated slow ramp,
and an internal variable resistor limits the input current.
4
REV. 1.0.2 5/30/03
I. LIM.
I. LIM.
Low Battery Ref.
PRODUCT SPECIFICATION
FAN5609
Switch Configuration
V
IN
V
IN
V
OUT
+
CAP1
-
V
OUT
=
2 X V
IN
+
CAP2
GND
-
C
OUT
Figure 1
Step-up, 2:1 configuration.
Switch positions shown in charge phase.
Reverse all switches for pump phase.
GND
Figure 2
Step-up
3:2 configuration
Switch positions shown in charge phase.
Reverse all switches for pump phase.
Shutdown and Short Circuit Current Limit
Set both DAC inputs low to shut down the device. Built-in
short circuit protection limits the supply current to a maxi-
mum of 50mA.
Digital Control
A digital-to-analog converter (DAC) allows selection of the
following modes: OFF, 7mA, 14mA, 20mA, per diode.
By turning the IN B pin ON and OFF, the current can be
modulated between 7 to 20mA to achieve any I
Average
value
(PWM). In PWM mode, the modulating frequency has to be
set sufficiently high in order to avoid a flickering effect
(100Hz to 1kHz).
A
B
I
LED
0
0
OFF
1
0
7mA
0
1
14mA
1
1
20mA
Digital Control with PWM
Any input can be modulated by a pulse train of variable duty
cycle (
δ
). By turning ON and OFF DAC inputs A or B, the
current can be continuously modulated to any average value
between 1 to 19mA. For a maximum range of LED current,
both A&B can be modulated at the same time.
REV. 1.0.2 5/30/03
5
PCB设计
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