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FAN5607
LED Driver with Adaptive Charge Pump DC/DC Converter
Features
* * * * * * * * * * * * * * * * * 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 x 30mA ) 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 < 1A 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
Description
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 0.1F to 1F bucket capacitors and two 4.7F 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. Soft-start circuitry prevents excessive current draw during power on. The device has built-in short circuit protection. The device is available in 4x4mm 16-lead MLP package.
Applications
* * * * * Cell Phones Handheld Computers PDA, DSC, MP3 Players Keyboard Backlight LED Displays
Typical Application
VOUT COUT
VIN CIN
VOUT VIN EN RSET RSET
LED-
LED-
LED-
LEDCAPCAP2 CAP+ CAP+ CAP1
FAN5607
GND
CAP-
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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 - I OUT programmed ) x 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 ) x 100 Current Matching (%) = ---------------------------------------------------------------------------------------------------( I LED branch 1 + I LED 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
Efficiency = -------------------------------------------V IN x 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%.
i=1
VLEDi x ILEDi
2
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PRODUCT SPECIFICATION
FAN5607
Pin Assignments
Top-View
LED15
LED14
16
LED-
13 12 11 10 9
LEDGND CAP2+ CAP2CAP18
EN NC NC NC
1 2 3 4 5 6 7
RSET
FAN5607 4x4mm 16-Lead MLP
Pin Descriptions
Pin No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Pin Name EN NC NC NC RSET VOUT VIN CAP1+ CAP1CAP2CAP2+ GND LEDLEDLEDLEDPin Function Description Enable Pin No Connection No Connection No Connection External resistor to set LED current Output to LEDs Anode Input Bucket capacitor positive connection Bucket capacitor negative terminal Bucket capacitor negative connection Bucket capacitor positive terminal Ground 4th LED Cathode 3rd LED Cathode 2nd LED Cathode 1st LED Cathode
Test Circuit
To VOUT Pin
16
EN NC NC NC
1
13 12
CAP1+
CAP2
1F
OUT
FAN5607
4 5 8 9
V
VIN
CAP1
1F
4 White LEDs Fairchild QTLP670C-IW Super Bright LED
RSET
VIN = 2.7V to 5.5V
CIN
VOUT 4.7F COUT
4.7F
All capacitors are Ceramic chip capacitors
Figure 1. Test Circuit
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FAN5607
PRODUCT SPECIFICATION
Absolute Maximum Ratings (Note 2)
Parameter VIN, VOUT Voltage to GND Any other Pin Voltage to GND Power Dissipation Lead Soldering Temperature (10 seconds) Operating Junction Temperature Range Storage Temperature Electrostatic Discharge Protection Level (Note 3) HBM CDM -55 4 2 Min -0.3 -0.3 Max 6.0 VIN + 0.3 Internally Limited 300 150 150 C C C kV Unit V V
Recommended Operating Conditions
Parameter Input Voltage Range, VIN Operating Ambient Temperature Range LED Forward Voltage Current through each LED 2
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)
Min 2.4 -40
Typ 25
Max 5.5 85 4 30
Unit V C V mA
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PRODUCT SPECIFICATION
FAN5607
Electrical Characteristics
VIN = 2.7V to 5.5V, TA = -40C to +85C, Test Circuit Figure 1, Unless otherwise noted. Typical values are at TA = 25C
Parameter Conditions
I LED 20mA I LED 20mA
Min.
Typ.
Max.
Units
Input Undervoltage Lockout ILED Accuracy Current Matching Output Voltage (VOUT = Vf + VCathode) Quiescent Current, IQ Shutdown Supply Current Output Short Circuit Current VOUT Over Voltage Protection VIN At Mode Transition From 1X to 1.5X VIN At Mode Transition From 1.5X to 2X Peak Efficiency LED Vf = 3.5V, IOUT = 4 x 20mA LED Vf = 3.5V, IOUT = 4 x 20mA VIN = 3.75V, LED Vf = 3.5V, ILED= 20mA
1.7
1.8 5 3 3.62 130
2.3
V % % V
LED Vf = 3.5V VIN = 5.5V, IOUT = 0mA VEN = 0V VIN = 5.5V, VOUT = 0V
400 1
A A mA V V V %
65 5.1 3.76 2.85 93
Oscillator Frequency Thermal Shutdown Threshold Thermal Shutdown Hysteresis EN Logic Input High Voltage EN Logic Input Low Voltage EN Input Bias Current EN to VIN or GND
0.8
1 145 15
1.2
MHz C C V
1.6 0.4 -1 1
V A
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FAN5607
PRODUCT SPECIFICATION
Typical Performance Characteristics
TA = 25C, CIN= COUT =4.7F, CAP1 = CAP1 = 0.1F, FAN5607 driving four LEDs with Vf = 3.5V at 20mA, unless otherwise noted.
Efficiency vs Battery Voltage
1.0 4.5
Upper Mode Change Voltage vs LED Forward Voltage
Battery Voltage (V)
mA = 20 mA = 20 mA = 20
0.9
ILED = 20mA
4.0
t I LED 4V a VF =
Efficiency
0.8
3.5
D at I LE 3.5V VF =
0.7
0.6
3.0
t I LED 3V a VF =
ILED = 2mA
0.5 2.5 3.0 3.5 4.0 4.5 5.0 5.5 2.5 0 5 10 15 20 25
Battery Voltage (V)
LED Current (mA)
LED CathodeVoltage vs Battery Voltage
0.14 22
LED Current vs BatteryVoltage
2.2
LED Cathode Voltage (V)
High LED Current (mA)
0.13 0.12 0.11 0.10 0.09
ILED = 2mA
21 2.1
20
2.0
19
1.9
ILED = 20mA
18 1.8 2.5 3.0 3.5 4.0 4.5 5.0 5.5
ILED = 2mA
0.08 2.5 3.0 3.5 4.0 4.5 5.0 5.5
Battery Voltage (V)
Battery Voltage (V)
Supply Current vs Battery Voltage
180
Supply Current (mA)
160 140 120 100 80 60 2.5 3.0 3.5 4.0 4.5 5.0 5.5
Battery Voltage (V)
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Low LED Current (mA)
ILED = 20mA
PRODUCT SPECIFICATION
FAN5607
Typical Performance Characteristics (cont.)
TA = 25C, CIN = COUT = 4.7F, CAP1 = CAP1 = 0.1F, FAN5607 driving four LEDs with Vf = 3.5V at 20mA, unless otherwise noted.
Startup at VIN = 3.6V
ILED = 20mA
Startup at VIN = 5V
ILED = 20mA
LED Current (10mA/div)
Input current when driving 4 LEDs x 20mA
LED Current (10mA/div)
Input Current (200mA/div)
Input Current (200mA/div)
Input current when driving 4 LEDs x 20mA
Time (100s/div)
Time (100s/div)
Line Transient Response
Input Voltage (1V/div)
VIN = 4.2V VIN = 3.2V
LED Current (10mA/div)
Time (100s/div)
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FAN5607
PRODUCT SPECIFICATION
Block Diagram
1F
VOUT V IN Linear Regulator Voltage Selector
EN
R SET
On Off And Current Range
Oscillator
D R I V E R S
Power Good P U M P
Bandgap Reference Range Selection Low Battery Ref.
Reference Analog Detector
5F
I. LIM.
I. LIM.
I. LIM.
Ref2 Ref1 Regulator Ref3
Mode Change VIN Ref4 (BG)
GND
1F
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
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.
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I. LIM.
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
RSET Only-Analog
LED Current (mA)
LED Current vs RSET
35 30 25 20 15 10 5 0 0 10 20 30 40 50 60 70
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 (K) 8.25 ILED (mA) 30 12.5 20 25 10 50 5 62.5 4
RSET (K)
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FAN5607
PRODUCT SPECIFICATION
PWM Control
Unless otherwise noted, RSET = 12.5K, ILED_MAX = 20mA
Enable is Controlled by PWM Signal
ENABLE Input (PWM)
30% Duty Cycle 1KHz
ss
70% Duty Cycle 1KHz
ILED (Average) = 0.7 x ILED-MAX ILED (Average) = 0.3 x ILED-MAX ILED 0mA
ss
OFF
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).
VEXT
R2
R1
ISET
FAN5607
Figure 5. DC Voltage Control
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.
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 x V EXT ) I LED = --------- + -------------------------------------------------- mA R2 R1
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=125k, R2=13.9k, adjusting VEXT in the (0V to 0.5V) range results in dimming the LED current from 20mA to 2mA.
Where 0V < VEXT < 0.5V and R1 and R2 are in K. 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 C
R2
R1 ISET
FAN5607
Figure 6. Filtered PWM Control
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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 0.1F to 1F, should be used for best efficiency in boost mode. The bucket capacitor, CAP1 = CAP2 = 1F is recommended, if the FAN5607 is required to start at battery voltage lower than 3V.
PC Board Layout
0.22 Input Power Supply VIN 10F 4.7F
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
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FAN5607
PRODUCT SPECIFICATION
Mechanical Dimensions
4x4mm 16-Lead MLP Package
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FAN5607
PRODUCT SPECIFICATION
Ordering Information
Product Number FAN5607 Package Type 4x4mm 16-Lead MLP Order Code 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. www.fairchildsemi.com
6/22/04 0.0m 001 Stock#DS505607 2004 Fairchild Semiconductor Corporation
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.

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