FAN5607 LED Driver with Adaptive Charge Pump DC/DC Converter

FAN5607 LED Driver with Adaptive Charge Pump DC/DC Converter
www.fairchildsemi.com
FAN5607
LED Driver with Adaptive Charge Pump DC/DC
Converter
Features
Description
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The FAN5607 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 FAN5607 eliminates the
need for LED pre-selection (matching) and ensures operation at high efficiency. When the input voltage is sufficiently
high to sustain the programmed current level in the LEDs,
the FAN5607 re-configures itself to operate as a linear regulator, and the DC-DC converter is turned off. Only two 0.1µF
to 1µF bucket capacitors and two 4.7µF input/output capacitors are needed for proper operation. LED current can be
programmed using an external resistor. The resistor sets the
maximum LED current and a PWM signal applied to the
enable pin can modulate that current level between 0mA
(off) and the maximum level.
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Parallel LED Driver Supports all Forward Voltages
Adaptive VOUT Adjustment to the Highest Diode Voltage
Internally Matched LED Current Sources
Built-in Charge Pump has Three Modes of Operation:
– 1X, 1.5X, and 2X Mode
Up to 93% Efficiency
Low EMI, Low Ripple
Up to 120mA Output Current ( 4 × 30 mA )
External Resistor to Set Maximum (100%) LED Current
Enable Input Can be Duty-Cycle-Modulated to Control
LED Current Level Between 0 and 100%
2.4V to 5.5V Input Voltage Range
ICC < 1µA 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 4x4mm 16-lead MLP Package
Applications
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Soft-start circuitry prevents excessive current draw during
power on. The device has built-in short circuit protection.
Cell Phones
Handheld Computers
PDA, DSC, MP3 Players
Keyboard Backlight
LED Displays
The device is available in 4x4mm 16-lead MLP package.
Typical Application
VOUT
COUT
VIN
VOUT
VIN
LED-
LED-
EN
LED-
LEDCAP-
CIN
FAN5607
CAP2
CAP+
CAP+
RSET
RSET
CAP1
GND
CAP-
REV. 1.0.1 12/2/04
FAN5607
PRODUCT SPECIFICATION
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 – IOUT 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 – ILED branch 2 ) × 100
Current Matching (%) = ---------------------------------------------------------------------------------------------------( I LED branch 1 + ILED branch 2 )
Efficiency: is expressed as a ratio between the electrical power into the LEDs and the total power consumed from the input
power supply.
4
∑ VLEDi × ILEDi
i=1
Efficiency = -------------------------------------------V IN × I IN
Note:
1. Some competitors calculate the power efficiency as a function of VOUT instead of VLED. This method neglects the power lost
due to the cathode voltage ≠ 0 and provides an efficiency “improved” up to 5%.
2
REV. 1.0.1 12/2/04
PRODUCT SPECIFICATION
FAN5607
Pin Assignments
LED-
LED-
LED-
LED-
Top-View
16
15
14
13
CAP2+
NC
3
10
CAP2-
NC
4
9
CAP1-
6
OUT
5
7
8
CAP1+
GND
11
VIN
12
2
RSET
1
V
EN
NC
FAN5607
4x4mm 16-Lead MLP
Pin Descriptions
Pin No.
Pin Name
Pin Function Description
1
EN
Enable Pin
2
NC
No Connection
3
NC
No Connection
4
NC
No Connection
5
RSET
External resistor to set LED current
6
VOUT
Output to LEDs Anode
7
VIN
8
CAP1+
Bucket capacitor positive connection
9
CAP1-
Bucket capacitor negative terminal
10
CAP2-
Bucket capacitor negative connection
11
CAP2+
Bucket capacitor positive terminal
12
GND
Ground
13
LED-
4th LED Cathode
14
LED-
3rd LED Cathode
15
LED-
2nd LED Cathode
16
LED-
1st LED Cathode
Input
Test Circuit
To VOUT Pin
16
EN
1
NC
13
12
CAP2
FAN5607
1µF
NC
NC
4
5
8
9
1µF
RSET
4.7µF
4 White LEDs
Fairchild QTLP670C-IW
Super Bright LED
VOUT
VIN = 2.7V to 5.5V
CIN
CAP1
4.7µF
COUT
All capacitors are Ceramic chip capacitors
Figure 1. Test Circuit
REV. 1.0.1 12/2/04
3
FAN5607
PRODUCT SPECIFICATION
Absolute Maximum Ratings (Note 2)
Parameter
Min
Max
Unit
VIN, VOUT Voltage to GND
-0.3
6.0
V
Any other Pin Voltage to GND
-0.3
VIN + 0.3
V
Power Dissipation
Internally
Limited
Lead Soldering Temperature (10 seconds)
300
°C
Operating Junction Temperature Range
150
°C
150
°C
Storage Temperature
Electrostatic Discharge Protection Level (Note 3)
-55
HBM
4
CDM
2
Parameter
Min
Typ
Input Voltage Range, VIN
2.4
Operating Ambient Temperature Range
-40
kV
Recommended Operating Conditions
25
LED Forward Voltage
Current through each LED
2
Max
Unit
5.5
V
85
°C
4
V
30
mA
Note:
2. Operation beyond the absolute maximum ratings may cause damage to device.
3. Using Mil Std. 883E, method 3015.7(Human Body Model) and EIA/JESD22C101-A (Charge Device Model)
4
REV. 1.0.1 12/2/04
PRODUCT SPECIFICATION
FAN5607
Electrical Characteristics
VIN = 2.7V to 5.5V, TA = -40ºC to +85ºC, Test Circuit Figure 1, Unless otherwise noted.
Typical values are at TA = 25˚C
Parameter
Conditions
Input Undervoltage Lockout
Min.
Typ.
Max.
1.7
1.8
2.3
Units
V
ILED Accuracy
I LED ≤ 20mA
5
%
Current Matching
I LED ≤ 20mA
3
%
LED Vf = 3.5V
3.62
VIN = 5.5V,
IOUT = 0mA
130
Output Voltage (VOUT = Vf + VCathode)
Quiescent Current, IQ
Shutdown Supply Current
Output Short Circuit Current
VEN = 0V
VIN = 5.5V,
VOUT = 0V
VOUT Over Voltage Protection
V
400
µA
1
µA
65
mA
5.1
V
VIN At Mode Transition From 1X to 1.5X
LED Vf = 3.5V,
IOUT = 4 x 20mA
3.76
V
VIN At Mode Transition From 1.5X to 2X
LED Vf = 3.5V,
IOUT = 4 x 20mA
2.85
V
VIN = 3.75V,
LED Vf = 3.5V,
ILED= 20mA
93
%
Peak Efficiency
Oscillator Frequency
0.8
1
1.2
MHz
Thermal Shutdown Threshold
145
ºC
Thermal Shutdown Hysteresis
15
ºC
EN Logic Input High Voltage
1.6
EN Logic Input Low Voltage
EN Input Bias Current
REV. 1.0.1 12/2/04
EN to VIN or GND
-1
V
0.4
V
1
µA
5
FAN5607
PRODUCT SPECIFICATION
Typical Performance Characteristics
TA = 25°C, CIN= COUT =4.7µF, CAP1 = CAP1 = 0.1µF, FAN5607 driving four LEDs with Vf = 3.5V at 20mA, unless
otherwise noted.
Upper Mode Change Voltage vs
LED Forward Voltage
Efficiency vs Battery Voltage
1.0
Efficiency
0.9
Battery Voltage (V)
4.5
ILED = 20mA
0.8
0.7
0.6
t I LED
4V a
VF =
4.0
mA
= 20
D
at I LE
3.5V
VF =
3.5
VF
3.0
mA
= 20
D
at I LE
= 3V
mA
= 20
ILED = 2mA
0.5
2.5
3.0
3.5
4.0
4.5
5.0
5.5
0
5
Battery Voltage (V)
LED CathodeVoltage vs Battery Voltage
15
20
25
LED Current vs BatteryVoltage
22
0.14
ILED = 20mA
High LED Current (mA)
LED Cathode Voltage (V)
10
LED Current (mA)
0.13
0.12
0.11
0.10
0.09
2.2
ILED = 2mA
21
2.1
20
2.0
19
1.9
ILED = 20mA
Low LED Current (mA)
2.5
ILED = 2mA
18
0.08
2.5
3.0
3.5
4.0
4.5
5.0
5.5
Battery Voltage (V)
1.8
2.5
3.0
3.5
4.0
4.5
5.0
5.5
Battery Voltage (V)
Supply Current vs Battery Voltage
Supply Current (mA)
180
160
140
120
100
80
60
2.5
3.0
3.5
4.0
4.5
5.0
5.5
Battery Voltage (V)
6
REV. 1.0.1 12/2/04
PRODUCT SPECIFICATION
FAN5607
Typical Performance Characteristics (cont.)
TA = 25°C, CIN = COUT = 4.7µF, CAP1 = CAP1 = 0.1µF, FAN5607 driving four LEDs with Vf = 3.5V at 20mA, unless
otherwise noted.
Startup at VIN = 5V
Startup at VIN = 3.6V
ILED = 20mA
LED Current
(10mA/div)
LED Current
(10mA/div)
ILED = 20mA
Input Current
(200mA/div)
Input Current
(200mA/div)
Input current when driving
4 LEDs x 20mA
Input current when driving
4 LEDs x 20mA
Time (100µs/div)
Time (100µs/div)
VIN = 4.2V
VIN = 3.2V
LED Current
(10mA/div)
Input Voltage
(1V/div)
Line Transient Response
Time (100µs/div)
REV. 1.0.1 12/2/04
7
FAN5607
PRODUCT SPECIFICATION
Block Diagram
1µF
VOUT
Linear
Regulator
Voltage
Selector
EN
Oscillator
5µF
Reference
Analog
Detector
Range Selection
Low Battery Ref.
Ref2
Ref1
Regulator
I. LIM.
Bandgap
Reference
I. LIM.
On Off
And
Current Range
Power
Good
P
U
M
P
I. LIM.
R
SET
D
R
I
V
E
R
S
I. LIM.
V
IN
Ref3
Mode Change
VIN
Ref4 (BG)
GND
1µF
Figure 2. Block Diagram
Circuit Description
The FAN5607’s switched capacitor DC/DC converter automatically configures its internal switches to achieve high
efficiency 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 battery 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 reconfigured to operate in 2:1 mode. As the battery discharges and
8
the voltage decays, the FAN5607 switches between modes to
maintain a constant current through LED throughout the battery life. The transition has hysteresis to prevent toggling.
Supply Voltage
The internal supply voltage for the device is automatically
selected from VIN or VOUT 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 controls the rate of the output voltage ramp-up to its final value.
Typical start-up time is 0.4ms. 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.
REV. 1.0.1 12/2/04
PRODUCT SPECIFICATION
FAN5607
Switch Configurations
VIN
VIN
VOUT
+
CAP1
VOUT = 2 X VIN
+
CAP2
GND
C
-
OUT
Figure 3. Step-up, 2:1 Configuration
Switch positions shown in charge phase
Reverse all switches for pump phase
GND
Figure 4. 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 maximum of 65mA.
The resistor value establishes the reference current needed
for a constant LED current. Value of RSET for a fixed LED
current are given in the table above and also in the graph
below, using the function: RSET = 250/ILED.
LED Brightness Control Methods
LED Current vs RSET
RSET Only-Analog
The basic method is to use external resistor to set the LED
current. Connect the resistor with the appropriate value
between RSET and GND to set the LED current.
RSET (KΩ) 8.25
12.5
25
50
62.5
ILED (mA)
20
10
5
4
30
LED Current (mA)
35
30
25
20
15
10
5
0
0
10
20
30
40
50
60
70
RSET (KΩ)
REV. 1.0.1 12/2/04
9
FAN5607
PRODUCT SPECIFICATION
PWM Control
Unless otherwise noted, RSET = 12.5KΩ, ILED_MAX = 20mA
Enable is Controlled by PWM Signal
ENABLE Input (PWM)
ss
30%
Duty Cycle
70%
Duty Cycle
1KHz
1KHz
ILED (Average) = 0.7 x ILED-MAX
ILED (Average) = 0.3 x ILED-MAX
ILED
0mA
PWM Control
Once RSET is chosen to set maximum LED current
(ILED_MAX), PWM modes can be used for brightness control. By turning the ENABLE pin ON and OFF, the current
can be modulated between 0 to ILED_MAX to achieve any
IAverage value. In PWM mode, the modulating frequency has
to be set sufficiently high in order to avoid a flickering effect
(50Hz to 100Hz).
The best LED to LED matching and the purest white light
are achieved over the entire range of average current settings,
when the PWM brightness control is used to modulate the
LED current between zero and the maximum value.
Application Information
Brightness Control
1. Dimming Using PWM at EN Pin
A PWM signal applied to EN can control the LED brightness
in direct dependence on the duty cycle. The recommended
PWM signal frequency is 100Hz to ensure a good match
between the input signal duty cycle and the LED average
current. If this ripple frequency is too low for a particular
noise sensitive application, then DC-based dimming control
circuits or higher-frequency-filtered PWM signals may be
used.
2. Dimming with DC Voltage
The brightness control using a variable DC voltage is shown
in Figure 5. If R1=125kΩ, R2=13.9kΩ, adjusting VEXT in the
(0V to 0.5V) range results in dimming the LED current from
20mA to 2mA.
10
ss
OFF
VEXT
R2
R1
ISET
FAN5607
Figure 5. DC Voltage Control
The FAN5607 internal circuit maintains a constant ISET voltage = 0.5V. Adjusting VEXT changes the ISET and ILED
accordingly.
Selecting different values for R1, R2 and VEXT range, the
ILED variation range can be changed according to the relation:
250 ( 250 – 500 × V EXT )
I LED = ---------- + --------------------------------------------------- mA
R2
R1
Where 0V < VEXT < 0.5V and R1 and R2 are in KΩ.
3. Dimming Using a Filtered PWM Signal
The external PWM signal is filtered by an R3C network
resulting in a DC component dependent on the PWM signal
duty cycle as shown in Figure 6. The resistor R3 needs to be
much smaller than R2 and the corner frequency of R3C
group is much smaller than the PWM signal frequency.
R3
R2
C
R1
ISET
FAN5607
Figure 6. Filtered PWM Control
REV. 1.0.1 12/2/04
PRODUCT SPECIFICATION
FAN5607
Selecting Capacitors
It is important to select the appropriate capacitor types and
the values for use with the FAN5607. These capacitors determine parameters such as power efficiency, maximum sustainable load current by the charge pump, input and output
ripple and start-up process.
through the RC input filter, as shown in Figure 7. Two low
ESR bucket capacitors of value between 0.1µF to 1µF,
should be used for best efficiency in boost mode. The bucket
capacitor, CAP1 = CAP2 = 1µF is recommended, if the
FAN5607 is required to start at battery voltage lower than
3V.
PC Board Layout
0.22Ω
Input
Power
Supply
VIN
10µF
4.7µF
FAN5607
GND
For best performance, a solid ground plane is recommended
on the back side of the PCB. The ground tails of CIN and
COUT should be connected together close to the GND pin of
IC.
Figure 7. Battery Ripple Reduction
In order to reduce ripple, both CIN and COUT should be low
ESR capacitors. Increasing the COUT capacitor reduces the
output ripple voltage. However this will increase the poweron time. The CIN value controls input ripple. If necessary,
this ripple can be further reduced by powering the FAN5607
REV. 1.0.1 12/2/04
11
FAN5607
PRODUCT SPECIFICATION
Mechanical Dimensions
4x4mm 16-Lead MLP Package
12
REV. 1.0.1 12/2/04
FAN5607
PRODUCT SPECIFICATION
Ordering Information
Product Number
Package Type
Order Code
FAN5607
4x4mm 16-Lead MLP
FAN5607HMPX
DISCLAIMER
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.
LIFE SUPPORT POLICY
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
12/2/04 0.0m 001
Stock#DS505607
2004 Fairchild Semiconductor Corporation
Mouser Electronics
Authorized Distributor
Click to View Pricing, Inventory, Delivery & Lifecycle Information:
Fairchild Semiconductor:
FAN5607HMPX
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