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FAN5608 Serial / Parallel LED Driver with Current-Regulated, Step-Up DC/DC Converter
August 2006
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 PFM mode of operation of the boost circuit Up to 85% efficiency Up to 2x20mA output Two built-in DACs for independent (digital) brightness control for both channels LED current can be duty-cycle-modulated, 0 to 20mA Digital, analog, and PWM brightness control 2.7V to 5.5V input voltage range 500KHz operating frequency Soft-start feature Low shutdown current: ICC< 1A Open-load protection Minimal external components needed Space-saving 4x4mm 12-lead MLP packages
Description
The FAN5608 is an integrated Schottky diode LED driver, which generates regulated output currents from a battery input voltage of 2.7V to 5V. An internal MOS switch and the external inductor deliver the necessary voltage to the load. The proprietary internal compensation loop continuously monitors the lowest LED cathode voltage of both channels and adjusts the VOUT voltage to the minimum value. The minimum VOUT is determined by the highest LED forward voltage of the selected channel. This adaptive nature allows the FAN5608 architecture to deliver high efficiency. Up to twelve LEDs can be connected in series as long as the summed forward voltage does not exceed the maximum specification of 24V. It is not required to match an equal number of LEDs serially within each channel; FAN5608 delivers the highest efficiency and best current regulation in the balanced configuration. FAN5608 has two internal two-bit D/A converters that provide independent programmability to each output channel. In analog programming, "B" pins must be GND (logic "0"); a resistor must be connected between pin "A" and a fixed supply voltage. The output current can be programmed to any desired value within the specified range. The FAN5608DHMPX is available in a 4x4mm 12-lead MLP package. A single external resistor sets the current and turns the device ON and OFF.
Applications
Cell phones Handheld computers PDAs, DSCs, MP3 players Keyboard backlights LED displays
Ordering Information
Part Number
FAN5608DHMPX
Pb-Free
Yes
Schottky Diode
Internal
Package
MLP-12 4x4mm
Packing Method
Tape and Reel
(c) 2006 Fairchild Semiconductor Corporation FAN5608 Rev. 1.0.5 * 8/8/06
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FAN5608 Serial / Parallel LED Driver with Current-Regulated, Step-Up DC/DC Converter
Block Diagram
Figure 1. Block Diagram
Pin Configuration
TOP-VIEW
NC
12
VOUT
11 10
INDB
GND CH1 B1
1 2 3
9 8 7
INDA CH2 B2
4
5
6
A1 VIN A2
4x4mm 12-Lead MLP(QUAD) (Internal Schottky Diode) FAN5608DHMPX
Figure 2. FAN5608M MLP package
(c) 2006 Fairchild Semiconductor Corporation FAN5608 Rev. 1.0.5 * 8/8/06
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FAN5608 Serial / Parallel LED Driver with Current-Regulated, Step-Up DC/DC Converter
Pin Definitions
Pin #
1 2 3 4 5 6 7 8 9 10 11 12
Name
GND CH1 B1 A1 VIN A2 B2 CH2 INDA INDB VOUT NC
Description
Ground First LED Cathode DAC B1 DAC A1 Input Voltage DAC A2 DAC B2 Second LED Cathode SD Anode. INDA and INDB must be connected together externally on the PCB. Inductor. INDA and INDB must be connected together externally on the PCB. Output LEDs Anode No Connection
Absolute Maximum Ratings
The "Absolute Maximum Ratings" are those values beyond which the safety of the device cannot be guaranteed. The device should not be operated at these limits. The parametric values defined in the Electrical Characteristics tables are not guaranteed at the absolute maximum ratings. The "Recommended Operating Conditions" table defines the conditions for actual device operation.
Parameter
VIN to GND VOUT to GND CH1,CH2 Voltage to GND All Other Pins Junction Temperature (TJ) Storage Temperature Lead Soldering Temperature, 10 seconds Electrostatic Discharge Protection (1,2) HBM CDM
Min.
-0.3 -0.3 -0.3 -20 -65 1.5 2
Max.
6.5 35 25 VIN+0.3 150 150 300
Units
V V V V C C C kV
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 (Schottky diode cathode <1.5kV).
Recommended Operating Conditions
Parameter
Supply Voltage VIN Output Voltage Range Ambient Temperature (TA )
Conditions
POUT <0.6W, 2 channels evenly loaded
Min.
2.7 VIN -40
Typ.
Max.
5.5 24 85
Units
V V C
25
(c) 2006 Fairchild Semiconductor Corporation FAN5608 Rev. 1.0.5 * 8/8/06
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FAN5608 Serial / Parallel LED Driver with Current-Regulated, Step-Up DC/DC Converter
Typical Application
Digital Brightness Control
CIN 2.7V to 5.5V L = 4.7H INDB VIN DAC Input For CH1 DAC Input For CH2 A1 B1 A2 B2 FAN5608DHMPX INDA VOUT GND CH2 CH1 NC 4.7F VOUT
Figure 3. FAN5608 Digital Brightness Circuit
Analog Brightness Control
CIN 2.7V to 5.5V L = 4.7H INDB VEXTERNAL VIN A1 A2 B1 B2 FAN5608DHMPX INDA VOUT GND CH2 CH1 NC 4.7F VOUT
Figure 4. FAN5608 Analog Brightness Circuit
(c) 2006 Fairchild Semiconductor Corporation FAN5608 Rev. 1.0.5 * 8/8/06
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FAN5608 Serial / Parallel LED Driver with Current-Regulated, Step-Up DC/DC Converter
Electrical Specifications
Recommended operating conditions and component values are per the Figure 18 test circuit. Typical values are at 25C and VIN=3.6V. Boldface indicates specifications over ambient operating temperature (-40C to +85C).
Parameter
Supply current in OFF mode LED current accuracy Current matching(3) Switching frequency Internal reference voltage, VA Current multiplication ratio Power efficiency (AVG)(4) Input A1, A2 threshold Input B1, B2 threshold Input A1, A2 current Input B1, B2 current
Conditions
A input LOW, B input LOW A input HIGH, B input HIGH A input HIGH, B input HIGH Analog Control Mode
Min.
18
Typ.
0.1 20 500 1.2 1000 80
Max.
1 22 3
Units
A mA % KHz V %
850 VIN > 3V Digital Control Mode Analog Control Mode Digital Control Mode Digital Control Mode Digital Control Mode HIGH LOW VA = VIN VA =0 0.6 x VIN 0 HIGH LOW VIN -0.7 0
1150 VIN 0.6
V V A A
1.2 VIN 0.3 x VIN 80 0.1 0.1
50
Notes: 3. Current matching is the absolute value of the difference in current of the two LEDs channels, divided by the average current in the two channels. 4. Power efficiency is the ratio between the electrical power to the LEDs and the total power consumed from the input power supply. Although this definition leads to a lower value than the boost converter efficiency, it more accurately reflects the system performance in an application.
Circuit Description
When power is applied to the VIN pin, the system is enabled, the bandgap reference acquires its nominal voltage (1.2V), and the soft-start cycle begins. Once "power good" is achieved (when 0.5mA voltage flows through the LEDs), the soft-start cycle stops, and the boost voltage increases to generate the current selected by the input control pins (A1, A2, B1, B2). If CH1 is not selected, the CH1 output pin is HIGH, its output measurement is approximately equal to VOUT, and its LEDs are OFF. The FAN5608 provides tightly regulated output currents for the selected LED's channel. An internal feedback loop determines which LED string requires the highest output voltage to sustain the pre-set current. It also adjusts the boost regulator based on CH1 and CH2 feedback voltage and A1, A2, B1, B2 input settings. System efficiency decreases if the channels' strings of LEDs have different forward voltage. If one channel is used, the other channel should be disabled by connecting the corresponding DAC inputs to logic LOW. If the external output capacitor VOUT is shorted to GND, the internal Schottky diode can be damaged, a condition which should be avoided.
LED Brightness Control
The control inputs are A1 and B1 for CH1 and A2 and B2 for CH2. B1 and B2 are digital inputs that require LOW (GND) and HIGH VIN 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. LED dimming can be controlled with static or dynamic inputs from CH1 and CH2. CH1 and CH2 outputs are driven directly by A1, B1 and A2, B2 inputs, respectively. Either channel can be configured as analog or digital. Inputs A1 and A2 are analog inputs that can be connected to an external regulated voltage source, which can be calculated by:
EQ 1 where current multiplication ratio is according to the Electrical Specifications table. Inputs B1 and B2 are digital inputs and can only be set by external logic of "0" (LOW) or "1" (HIGH).
(c) 2006 Fairchild Semiconductor Corporation FAN5608 Rev. 1.0.5 * 8/8/06
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FAN5608 Serial / Parallel LED Driver with Current-Regulated, Step-Up DC/DC Converter
Digital Static Control
The FAN5608's digital decoder allows selection of the following modes of operation: OFF, 5mA, 10mA, and 20mA per channel. A B ILED 0 0 OFF 1 0 5mA 0 1 10mA 1 1 20mA
PWM Control in Digital Dynamic Mode
In Digital Dynamic Mode, if inputs A1 and/or A2 are externally driven by an open-drain output, the pull-up resistance should be less than 10k to ensure less than 0.7V dropout; VA > (VIN - 0.7V), as required for HIGH logic level. The logic level HIGH (VH) and logic level LOW (VL) of the PWM signal should be: (VIN - 0.7V) < VH < VIN and 0 < VL < 0.6V. EQ 4 EQ 3
Analog Static Control
In Analog Mode, B1 and B2 inputs should be connected to GND or "0" logic. A1 and A2 control the LED current through an external resistor (R), as shown in Figure 4, or an external voltage (VEXT) input. The ILED value can be calculated using the formula or the graph below:
The frequency of the PWM signal should be within the 50Hz to 1kHz range, by default, or 30kHz at any input if the other input is kept HIGH.
PWM Control in Analog Dynamic Mode
EQ 2 where 1.2V < VEXT R(k) x 0.020(mA) + 1.2V and the current multiplication ratio is according to the Electrical Specifications table. The R value should be in the (10k to 50k) range. In Analog Dynamic Mode, the logic level HIGH (VH) and logic level LOW (VL) of the PWM signal should be: VH = VEXT and 0 < VL < 0.6V. EQ 5
25 R=10k 20 ILED (mA) 15 10 5 0 1.0 1.25 1.5 1.75 VEXT (V) 2 2.25 R=50k
The frequency of the PWM signal should be in the range from 50Hz to 1kHz. The VEXT amplitude sets the maximum LED current, while the duty cycle of the PWM signal sets the average current between 0mA and ILED maximum.
Open-Circuit Protection
The FAN5608 has an internal over-voltage protection mechanism that prevents damage to the IC in a no-load condition. If CH1 and/or CH2 LEDs are enabled in an open-circuit condition, FAN5608 automatically sets the duty cycle to 25%. The output voltage can reach as high as 50V at maximum VIN (5.5V). Depending on the capacitor's rating, the output capacitor may be at risk in this condition.
Shutdown Mode
Each channel can be independently disabled by applying LOW logic level voltage to the appropriate A and B inputs. When both channels are disabled, the FAN5608 enters shutdown mode and the supply current is reduced to less than 1A.
Figure 7. Analog Control
(c) 2006 Fairchild Semiconductor Corporation FAN5608 Rev. 1.0.5 * 8/8/06
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FAN5608 Serial / Parallel LED Driver with Current-Regulated, Step-Up DC/DC Converter
PWM Control
Figure 8. A is PWM controlled; B is LOW; ILED (average) - s x 5mA, where s is the duty cycle
A Input
(5)
B Input (PWM)
30% Duty Cycle 1KHz 70% Duty Cycle 1KHz
ILED
0mA
OFF
Figure 9. A is HIGH and B is PWM controlled; ILED (average) - s x 15mA +5mA, where s is the duty cycle
A Input (PWM)
30% Duty Cycle 1KHz 70% Duty Cycle 1KHz
(6)
B Input (PWM)
30% Duty Cycle 1KHz 70% Duty Cycle 1KHz
ILED
0mA
OFF
(7)
Figure 10. A and B are PWM controlled; ILED (average) - s x 20mA, where s is the duty cycle Notes: 5. Proportionally select the duty cycle to achieve a typical LED current from 1mA to 4mA. 6. Maximum PWM frequency can be 30KHz. 7. Proportionally select the duty cycle to achieve a typical LED current from 1mA to 19mA.
(c) 2006 Fairchild Semiconductor Corporation FAN5608 Rev. 1.0.5 * 8/8/06
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FAN5608 Serial / Parallel LED Driver with Current-Regulated, Step-Up DC/DC Converter
Typical Characteristics
TA=25C, VBAT = 3.6V, unless otherwise specified.
Figure 11. Peak power efficiency
Startup Response
LED Current 20mA/Div
Figure 12. PWM Dimming
Input Current 500mA/Div
VIN =3.6V, L=6.8uH, COUT=4.7uF, 3-LEDs/CH
Voltage at DAC Inputs
Output Voltage 10V/Div
Tim e 200S/Div
Figure 13. Startup Response
Design and Component Selection Guidelines
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 pulse-frequency modulation (PFM) and pulse-skipping techniques. In most cases, the FAN5608 operates in discontinuous conduction mode, resulting in higher inductor current ripple. To ensure proper operation of the current regulator over the entire range of conditions, select the inductor based
(c) 2006 Fairchild Semiconductor Corporation FAN5608 Rev. 1.0.5 * 8/8/06 8
on the maximum output power (POUT) and the minimum input voltage (VIN): L (VIN )2 x T POUT EQ 6
where units of L, VIN, and POUT are in H, Volt, and Watt, respectively and T = 0.4s is a factor depending upon the FAN5608 internal architecture. The above relationship is applicable up to POUT = 0.8W and L 2.2H . At lower inductor values, the efficiency
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FAN5608 Serial / Parallel LED Driver with Current-Regulated, Step-Up DC/DC Converter
decreases due to the resistive loss in the switching power FET. Using L = 3.3 and increasing the load to 12 LED x 20mA (POUT = 800mW) requires VIN > 3.5V to maintain a constant 20mA current through LEDs. An inductance L = 4.7H ensures proper operation for 2 x 4 white LEDs with regulated 20mA current if VIN > 2.7V. For any lighter load or higher VIN, the inductance may be increased to improve the system efficiency. Application examples are given in Figures 16 - 25. The peak current in the inductor depends on the maximum battery voltage and the inductance, according to the equation:
I pk = 1.4 S x VIN max L
The current feeding the string of LEDs is the sum of the currents programmed for each channel in digital or analog mode. Using all four inputs in digital mode, the LED current can be programmed within the 0 to 40mA range, according to the following table:
EQ 7
which gives the maximum rated current for the inductor. For L =4.7H and VIN = 4.2V, the inductor saturation current should be at least 1A.
Capacitors Selection
Low ESR capacitors should be used to minimize the input and output ripple voltage. Use of a CIN > 4.7F/6.3V and COUT = 4.7F/25V type X5R/X7R multilayer ceramic capacitor is recommended. 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 reduce the battery ripple to the level required by a particular application.
Driving Two Independent Strings of LEDs
For best efficiency, the two strings of LEDs driven by the FAN5608 should have close forward voltages. This recommendation is met when the same number and type of LEDs are serially connected in each channel. If the application requires the two channels be significantly unbalanced, an external resistor may be added in series with the shorter string of LEDs to reduce the voltage difference between the two channels and enhance performance. The maximum differential LEDs connected in series to CH1 and CH2 is not recommended to exceed three LEDs.
Driving Higher Current LEDs
To increase the LED current range to 50mA, the CH1 and CH2 outputs may be connected, as shown below:
CIN 2.7V to 5.5V
L = 4.7H INDB
INDA GND
4.7F
DAC Inputs
A1 B1 A2 B2
CH1 CH2
Specific Layout Recommendations
The FAN5608 is available in a dual Die Attach Pad (DAP) package. One DAP is connected to GND and another to VOUT, making it unnecessary to provide any external connection to the DAPs. Since the internal power dissipation is low, the 4x4mm MLP package is capable of dissipating maximum power without requiring an extra copper field on the printed circuit board. When viewing the bottom of the dual-DAP device package, two electrically isolated exposed metal islands are visible. The two IND pins should be connected externally. Depending on the application noise sensitivity, an external filter may be required between the battery and the IC input.
Figure 14. Digital Brightness Control
CIN 2.7V to 5.5V
L = 4.7H INDB VIN
INDA GND
4.7F
VEXT
A1 A2
CH1 CH2
Figure 15. Analog Brightness Control
(c) 2006 Fairchild Semiconductor Corporation FAN5608 Rev. 1.0.5 * 8/8/06
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FAN5608 Serial / Parallel LED Driver with Current-Regulated, Step-Up DC/DC Converter
FAN5608 Efficiency Curves
2.7V to 5.5V
L = 6.9H INDB VIN A1 A2 B1 B2 INDA VOUT FAN5608DHMPX GND CH2 CH1 NC 4.7F VOUT
DAC Input for CH1 DAC Input for CH2
Figure 16. FAN5608 with four LEDs
Figure 17. FAN5608 efficiency with four LEDs
2.7V to 5.5V
L = 6.8H INDB VIN A1 A2 B1 B2 INDA VOUT FAN5608DHMPX GND CH2 CH1 NC 4.7F VOUT
DAC Input for CH1 DAC Input for CH2
Figure 18. FAN5608 with six LEDs
Figure 19. FAN5608 efficiency with six LEDs
2.7V to 5.5V
L = 4.7H INDB VIN A1 A2 B1 B2 INDA VOUT FAN5608DHMPX GND CH2 CH1 NC 4.7F VOUT
DAC Input for CH1 DAC Input for CH2
Figure 20. FAN5608 with eight LEDs
Figure 21. FAN5608 efficiency with eight LEDs
(c) 2006 Fairchild Semiconductor Corporation FAN5608 Rev. 1.0.5 * 8/8/06
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FAN5608 Serial / Parallel LED Driver with Current-Regulated, Step-Up DC/DC Converter
2.7V to 5.5V
L = 3.3H INDB VIN A1 A2 B1 B2 INDA VOUT FAN5608DHMPX GND CH2 CH1 NC 4.7F VOUT
DAC Input for CH1 DAC Input for CH2
Figure 22. FAN5608 with ten LEDs
Figure 23. FAN5608 efficiency with ten LEDs
2.7V to 5.5V
L = 2.7H INDB VIN A1 A2 B1 B2 INDA VOUT FAN5608DHMPX GND CH2 CH1 NC 4.7F VOUT
DAC Input for CH1 DAC Input for CH2
Figure 24. FAN5608 with twelve LEDs
Figure 25. FAN5608 efficiency with twelve LEDs
(c) 2006 Fairchild Semiconductor Corporation FAN5608 Rev. 1.0.5 * 8/8/06
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FAN5608 Serial / Parallel LED Driver with Current-Regulated, Step-Up DC/DC Converter
Dimensional Outline Drawings
Dimensions are in millimeters unless otherwise noted.
Figure 26. 4x4mm 12-Lead MLP
(c) 2006 Fairchild Semiconductor Corporation FAN5608 Rev. 1.0.5 * 8/8/06
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FAN5608 Serial / Parallel LED Driver with Current-Regulated, Step-Up DC/DC Converter
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PRODUCT STATUS DEFINITIONS Definition of Terms Datasheet Identification Advance Information Product Status Formative or In Design First Production Definition This datasheet contains the design specifications for product development. Specifications may change in any manner without notice. This datasheet contains preliminary data; supplementary data will be published at a later date. Fairchild Semiconductor reserves the right to make changes at any time without notice to improve design. This datasheet contains final specifications. Fairchild Semiconductor reserves the right to make changes at any time without notice to improve design. This datasheet contains specifications on a product that has been discontinued by Fairchild Semiconductor. The datasheet is printed for reference information only.
Rev. I20
Preliminary
No Identification Needed
Full Production
Obsolete
Not In Production
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