FAN5608 Serial / Parallel LED Driver with Current-Regulated, Step-Up DC/DC Converter Features Description Two independent channels drive up to six LEDs 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. per channel Adaptive output voltage drive to maximize efficiency 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 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< 1μA Open-load protection Minimal external components needed Space-saving 4x4mm 12-lead MLP packages Applications Cell phones Handheld computers PDAs, DSCs, MP3 players Keyboard backlights 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. LED displays Ordering Information Part Number Pb-Free Schottky Diode Package Packing Method FAN5608DHMPX Yes Internal MLP-12 4x4mm Tape and Reel © 2006 Fairchild Semiconductor Corporation FAN5608 Rev. 1.0.5 • 8/8/06 www.fairchildsemi.com 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 Block Diagram Figure 1. Block Diagram Pin Configuration TOP-VIEW NC INDB VOUT 12 11 10 GND 1 9 INDA CH1 2 8 CH2 B1 3 7 4 5 B2 6 A1 VIN A2 4x4mm 12-Lead MLP(QUAD) (Internal Schottky Diode) FAN5608DHMPX Figure 2. FAN5608M MLP package © 2006 Fairchild Semiconductor Corporation FAN5608 Rev. 1.0.5 • 8/8/06 www.fairchildsemi.com 2 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 Min. Max. Units VIN to GND VOUT to GND CH1,CH2 Voltage to GND All Other Pins Junction Temperature (TJ) Storage Temperature Lead Soldering Temperature, 10 seconds -0.3 -0.3 6.5 35 25 VIN+0.3 150 150 300 V V V V °C °C °C Electrostatic Discharge Protection (1,2) -0.3 -20 -65 HBM CDM 1.5 2 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 ) © 2006 Fairchild Semiconductor Corporation FAN5608 Rev. 1.0.5 • 8/8/06 Conditions POUT <0.6W, 2 channels evenly loaded Min. 2.7 VIN -40 Typ. Max. Units 25 5.5 24 85 V V °C www.fairchildsemi.com 3 FAN5608 Serial / Parallel LED Driver with Current-Regulated, Step-Up DC/DC Converter Pin Definitions FAN5608 Serial / Parallel LED Driver with Current-Regulated, Step-Up DC/DC Converter Typical Application Digital Brightness Control CIN L = 4.7µH 2.7V to 5.5V INDB INDA VIN VOUT A1 DAC Input For CH1 FAN5608DHMPX B1 DAC Input For CH2 VOUT 4.7µF GND CH2 A2 CH1 B2 NC Figure 3. FAN5608 Digital Brightness Circuit Analog Brightness Control CIN 2.7V to 5.5V L = 4.7µH VEXTERNAL INDB INDA VIN VOUT A1 A2 FAN5608DHMPX VOUT 4.7µF GND CH2 B1 CH1 B2 NC Figure 4. FAN5608 Analog Brightness Circuit © 2006 Fairchild Semiconductor Corporation FAN5608 Rev. 1.0.5 • 8/8/06 www.fairchildsemi.com 4 Recommended operating conditions and component values are per the Figure 18 test circuit. Typical values are at 25°C and VIN=3.6V. Boldface indicates specifications over ambient operating temperature (-40°C to +85°C). 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 Conditions A input LOW, B input LOW A input HIGH, B input HIGH A input HIGH, B input HIGH Min. Typ. Max. Units 18 0.1 20 1 22 3 µA mA % KHz V Analog Control Mode 850 VIN > 3V HIGH LOW Digital Control Mode VIN -0.7 0 Analog Control Mode Input B1, B2 threshold Digital Control Mode Input A1, A2 current Digital Control Mode Input B1, B2 current Digital Control Mode 500 1.2 1000 80 1150 % VIN 0.6 V 1.2 HIGH LOW VA = VIN VA =0 0.6 x VIN 0 50 VIN 0.3 x VIN 80 0.1 0.1 V µA µA 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 LED Brightness Control 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). 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. 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. 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 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. © 2006 Fairchild Semiconductor Corporation FAN5608 Rev. 1.0.5 • 8/8/06 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). www.fairchildsemi.com 5 FAN5608 Serial / Parallel LED Driver with Current-Regulated, Step-Up DC/DC Converter Electrical Specifications PWM Control in Digital Dynamic Mode The FAN5608’s digital decoder allows selection of the following modes of operation: OFF, 5mA, 10mA, and 20mA per channel. 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 10kΩ to ensure less than 0.7V dropout; VA > (VIN – 0.7V), as required for HIGH logic level. A B ILED 0 0 OFF 1 0 5mA 0 1 10mA 1 1 20mA The logic level HIGH (VH) and logic level LOW (VL) of the PWM signal should be: (VIN – 0.7V) < VH < VIN Analog Static Control EQ 3 and 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. 0 < VL < 0.6V. EQ 4 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. The ILED value can be calculated using the formula or the graph below: PWM Control in Analog Dynamic Mode In Analog Dynamic Mode, the logic level HIGH (VH) and logic level LOW (VL) of the PWM signal should be: EQ 2 where 1.2V < VEXT ≤ R(kΩ) 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 (10kΩ to 50kΩ) range. VH = VEXT and 0 < VL < 0.6V. 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. 25 R=10k 20 ILED (mA) EQ 5 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. 15 10 R=50k 5 Shutdown Mode 0 1.0 1.25 1.5 1.75 VEXT (V) 2 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 1μA. 2.25 Figure 7. Analog Control © 2006 Fairchild Semiconductor Corporation FAN5608 Rev. 1.0.5 • 8/8/06 www.fairchildsemi.com 6 FAN5608 Serial / Parallel LED Driver with Current-Regulated, Step-Up DC/DC Converter Digital Static Control (5) Figure 8. A is PWM controlled; B is LOW; ILED (average) – s x 5mA, where s is the duty cycle A Input B Input (PWM) 30% Duty Cycle 70% Duty Cycle 1KHz ILED 1KHz OFF 0mA (6) 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 70% Duty Cycle 1KHz 1KHz B Input (PWM) 30% Duty Cycle 70% Duty Cycle 1KHz ILED 1KHz 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. © 2006 Fairchild Semiconductor Corporation FAN5608 Rev. 1.0.5 • 8/8/06 www.fairchildsemi.com 7 FAN5608 Serial / Parallel LED Driver with Current-Regulated, Step-Up DC/DC Converter PWM Control 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 Figure 12. PWM Dimming VIN =3.6V, L=6.8uH, COUT=4.7uF, 3-LEDs/CH Voltage at DAC Inputs Output Voltage 10V/Div Input Current 500mA/Div LED Current 20mA/Div Startup Response Tim e 200µS/Div Figure 13. Startup Response Design and Component Selection Guidelines on the maximum output power (POUT) and the minimum input voltage (VIN): 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. L≤ EQ 6 where units of L, VIN, and POUT are in μH, Volt, and Watt, respectively and T = 0.4μs is a factor depending upon the FAN5608 internal architecture. The above relationship is applicable up to POUT = 0.8W and L ≥ 2.2μH . At lower inductor values, the efficiency To ensure proper operation of the current regulator over the entire range of conditions, select the inductor based © 2006 Fairchild Semiconductor Corporation FAN5608 Rev. 1.0.5 • 8/8/06 (VIN )2 × T POUT www.fairchildsemi.com 8 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: 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 μS × VIN max EQ 7 L which gives the maximum rated current for the inductor. For L =4.7μH 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 > 4.7μF/6.3V and COUT = 4.7μF/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 L = 4.7µH INDB 2.7V to 5.5V INDA GND DAC Inputs A1 B1 A2 B2 4.7µF Specific Layout Recommendations CH1 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. CH2 Figure 14. Digital Brightness Control CIN 2.7V to 5.5V L = 4.7µH INDB VIN VEXT INDA GND A1 CH1 A2 CH2 4.7µF Figure 15. Analog Brightness Control © 2006 Fairchild Semiconductor Corporation FAN5608 Rev. 1.0.5 • 8/8/06 www.fairchildsemi.com 9 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 = 3.3μΗ 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 = 4.7μH ensures proper operation for 2 x 4 white LEDs with regulated 20mA current if VIN > 2.7V. 2.7V to 5.5V L = 6.9µH DAC Input for CH1 DAC Input for CH2 INDB INDA VIN VOUT A1 FAN5608DHMPX A2 VOUT 4.7µF GND CH2 B1 CH1 B2 NC Figure 16. FAN5608 with four LEDs 2.7V to 5.5V Figure 17. FAN5608 efficiency with four LEDs L = 6.8µH DAC Input for CH1 DAC Input for CH2 INDB INDA VIN VOUT A1 FAN5608DHMPX A2 VOUT 4.7µF GND CH2 B1 CH1 B2 NC Figure 18. FAN5608 with six LEDs 2.7V to 5.5V Figure 19. FAN5608 efficiency with six LEDs L = 4.7µH DAC Input for CH1 DAC Input for CH2 INDB INDA VIN VOUT A1 A2 FAN5608DHMPX VOUT 4.7µF GND CH2 B1 CH1 B2 NC Figure 20. FAN5608 with eight LEDs © 2006 Fairchild Semiconductor Corporation FAN5608 Rev. 1.0.5 • 8/8/06 Figure 21. FAN5608 efficiency with eight LEDs www.fairchildsemi.com 10 FAN5608 Serial / Parallel LED Driver with Current-Regulated, Step-Up DC/DC Converter FAN5608 Efficiency Curves L = 3.3µH DAC Input for CH1 DAC Input for CH2 INDB INDA VIN VOUT A1 A2 FAN5608DHMPX VOUT 4.7µF GND CH2 B1 CH1 B2 NC Figure 22. FAN5608 with ten LEDs 2.7V to 5.5V Figure 23. FAN5608 efficiency with ten LEDs L = 2.7µH DAC Input for CH1 DAC Input for CH2 INDB INDA VIN VOUT A1 A2 FAN5608DHMPX VOUT 4.7µF GND CH2 B1 CH1 B2 NC Figure 24. FAN5608 with twelve LEDs © 2006 Fairchild Semiconductor Corporation FAN5608 Rev. 1.0.5 • 8/8/06 Figure 25. FAN5608 efficiency with twelve LEDs www.fairchildsemi.com 11 FAN5608 Serial / Parallel LED Driver with Current-Regulated, Step-Up DC/DC Converter 2.7V to 5.5V 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 © 2006 Fairchild Semiconductor Corporation FAN5608 Rev. 1.0.5 • 8/8/06 www.fairchildsemi.com 12 ACEx™ ActiveArray™ Bottomless™ Build it Now™ CoolFET™ CROSSVOLT™ DOME™ EcoSPARK™ 2 E CMOS™ EnSigna™ FACT™ FACT Quiet Series™ ® FAST FASTr™ FPS™ FRFET™ GlobalOptoisolator™ GTO™ HiSeC™ 2 I C™ i-Lo™ ImpliedDisconnect™ IntelliMAX™ ISOPLANAR™ LittleFET™ MICROCOUPLER™ MicroFET™ MicroPak™ MICROWIRE™ MSX™ MSXPro™ OCX™ OCXPro™ ® OPTOLOGIC OPTOPLANAR™ PACMAN™ POP™ Power247™ PowerEdge™ PowerSaver™ ® PowerTrench ® QFET QS™ QT Optoelectronics™ Quiet Series™ RapidConfigure™ RapidConnect™ ScalarPump™ μSerDes™ ® SILENT SWITCHER SMART START™ SPM™ Stealth™ SuperFET™ SuperSOT™-3 SuperSOT™-6 SuperSOT™-8 SyncFET™ TCM™ TinyBoost™ TinyBuck™ ® TinyLogic TINYOPTO™ TinyPower™ TinyPWM™ TruTranslation™ UHC™ ® UltraFET UniFET™ VCX™ Wire™ Across the board. Around the world.™ Programmable Active Droop™ ® The Power Franchise 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. THESE SPECIFICATIONS DO NOT EXPAND THE TERMS OF FAIRCHILD’S WORLDWIDE TERMS AND CONDITIONS, SPECIFICALLY THE WARRANTY THEREIN, WHICH COVERS THESE PRODUCTS. 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 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. PRODUCT STATUS DEFINITIONS Definition of Terms Datasheet Identification Product Status Advance Information Formative or In Design This datasheet contains the design specifications for product development. Specifications may change in any manner without notice. Definition Preliminary First Production 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. No Identification Needed Full Production This datasheet contains final specifications. Fairchild Semiconductor reserves the right to make changes at any time without notice to improve design. Obsolete Not In Production This datasheet contains specifications on a product that has been discontinued by Fairchild Semiconductor. The datasheet is printed for reference information only. Rev. I20 © 2006 Fairchild Semiconductor Corporation FAN5608 Rev. 1.0.5 • 8/8/06 www.fairchildsemi.com 13 FAN5608 Serial / Parallel LED Driver with Current-Regulated, Step-Up DC/DC Converter TRADEMARKS The following are registered and unregistered trademarks Fairchild Semiconductor owns or is authorized to use and is not intended to be an exhaustive list of all such trademarks.