FC9910B FS | Alldatasheet
Document overview
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Technical content
Features
Constant current LED driver Applications from a few mA to more then 1A output LED string from one to hundreds of diodes 8.0 to 450V input range PWM Low-Frequency dimming via enable pin Input voltage surge ratings up to 500V >90% efficiency
Applications
DC/DC or AC/DC LED driver applications RGB backlighting LED driver Back lighting of flat panel displays General purpose constant current source Signage and decorative LED lighting Chargers General Description The FC9910B is a PWM high efficiency LED driver control IC. It allows efficient operation of High Brightness LEDs from voltage sources ranging from 8V DC up to 450V DC. The FC9910B controls an internal MOSFET at fixed switching frequency up to 300kHz. The frequency can be programmed using a single resister. The LED string is driven at constant current rather then constant voltage, thus providing constant light output and enhanced reliability. The output current can be programmed between afew milliampares and up to more then 1.0A. The FC9910B uses a rugged high voltage junction isolated process that can withstand an input voltage surge of up to 450V. Output current to an LED string can be programmed to any value between zero and its maximum value by appling an external control voltage at linear dimming control input of the FC9910B. The FC9910B provides a low frequency PWM dimming input that can accept an external control signal with a duty ratio of 0~100% and a frequency of up to a few kHz. Typical Application Circuit Universal High Brightness LED Driver CDD RT RCS D1 CO C N FC9910B VIN DRV PWM_D VDD LIN_D ISEN Rosc GND SEMICO NDUCTOR TECH NICAL DATA FC9910B 2013. 08. 29 1/10Revision No : 1 Figure 1. Typical Application Circuit of FC9910B
maximum rating conditions for extended periods may affect device reliability. Figure 2. Pin Assignment of FC9910B
- 08. 29 3/10Revision No : 1 Specifications (TA = 25°C unless noted otherwise) s n o i t i d n o C s t i n U x a M p y T n i M n o i t p i r c s e D l o b m y S VINDC Input DC supply voltage range 8.0 450 V DC input voltage IINsd Shut-Down mode supply current 0.5 1 mA Pin PWM_D to GND, V IN = 8V VDD V 0 . 8 5 . 7 0 . 7 e g a t l o v d e t a l u g e r y l l a n r e t n I VIN = 8–450V, IDD(ext)=0, pin Gate open VDDmax V 5 . 3 1 e g a t l o v d d V n i p l a m i x a M When an external voltage applied to pin Vdd IDD(ext) V DD current available for external circuitry 1.0 mA V IN = 8–100V UVLO V DD undervoltage lockout threshold 6.45 6.7 6.95 V Vin rising ∆UVLO VDD undervoltage lockout hysteresis 500 mV Vin falling VEN(lo) V V 0 . 1 e g a t l o v w o l t u p n i D _ M W P n i P IN = 8–450V VEN(hi) Pin PWM_D input high voltage 2.4 V V IN = 8–450V REN Pin PWM_D pull-down resistance 50 100 150 kΩ VEN = 5V VCS(hi) Current sense pull-in threshold voltage 225 250 275 mV @TA = -40°C to +85°C VGATE(hi) V e g a t l o v t u p t u o h g i h E T A G DD-0.3 V DD V I OUT = 10mA VGATE(lo) I V 3 . 0 0 e g a t l o v t u p t u o w o l E T A G OUT = -10mA fOSC Oscillator frequency 20 100 120 kHz kHz R OSC = 1.00MΩ ROSC = 226kΩ DMAXhf Maximum Oscillator PWM Duty Cycle 100 % FPWMhf = 25kHz, at GATE, CS to GND. GBD VLD Linear Dimming pin voltage range 0 250 mV @TA = <85°C, Vin = 12V TBLANK Current sense blanking interval 150 215 280 ns V CS = 0.55VLD, VLD = VDD tDELAY Delay from CS trip to GATE lo 300 ns Vin = 12V, VLD = 0.15, VCS = 0 to 0.22V after TBLANK tRISE C s n 0 5 0 3 e m i t e s i r t u p t u o E T A G GATE = 500pF tFALL C s n 0 5 0 3 e m i t l l a f t u p t u o E T A G GATE = 500pF Also limited by package power dissipation limit, whichever is lower.
- 08. 29 4/10Revision No : 1
Figure 3. Block Diagram of FC9910B No Connects (NC) are not internally connected and may be used for pass-thru PCB traces.
Description
VIN 1 1 Input voltage 8V to 450V DC CS 4 2 Senses LED string current GND 5 3 Device ground GATE 8 4 Drives the gate of the external MOSFET PWM_D 9 5 Low Frequency PWM Dimming pin, also Enable input. Internal 100kΩ pull-down to GND VDD 12 6 Internally regulated supply voltage. 7.5V nominal. Can supply up to 1mA for external circuitry. A sufficient storage capacitor is used to provide storage when the rectified AC input is near the zero crossings. LD 13 7 Linear Dimming by changing the current limit threshold at current sense comparator ROSC 14 8 Oscillator control. A resistor connected between this pin and ground sets the PWM frequency. VDD
The FC9910B is a low cost off line buck boost or buck- boost converter control IC specifically designed for driving enables fairly accurate LED current control without the need multi-LED strings or arrays. It can be operated from either universal AC line o r any DC voltage between 8~450V. Optionally, passive power factor collection circuit can be used in order to pass the AC harmonic limits set by EN 61000- 3-2 Class C for lighting equipment having input power less than 25W. The FC9910B can drive up to hundreds of high brightness LEDs or multiple strings of HB LEDs. The LED arrays can be configured as a series or series/ parallel connection. The FC9910B regulates constant current that ensures controlled brightness and spectrum of the LEDs. and extends their life time. The FC9910B features an enable pin(PWM_D) that allows PWM control of brightness. The FC9910B can also control brightness of LEDs by programming continuous output current of the LED driver (so called linear dimming) when a control voltage is applied to the LIN_D pin. The FC9910B is offered in standard SOP-8. It is also available in a high voltage rated SOP-16 package for applications that require Vin greater than 250V. The FC9910B includes an internal high voltage linear regulator that powers all internal circuits and can also serve as a bias supply for low voltage external circuitry. The FC9910B can control all basic types of converters, isolated or non-isolated operating in continuous or discontinuous conduction mode. When the gate signal enhances the internal power MOSFET, the LED driver stores the input energy in an inductor or in the primary inductance of a transformer and depending on the converter type may partially driver the energy directly to LEDs. delivered to the output during the off cycle of the power MOSFET producing current through the string of LEDs. (Flyback mode of operation) When the voltage at the Vcc pin e xceeds the UVLO threshold the gate drive is enabled. The output current is controlled by means of limiting peak current in the internal power MOSFET. A current sense resistor is connected in series with the source terminal of the MOSFET. The energy stored in the magnetic component is further The voltage from the sense resister is applied to the ISEN pin of the FC9910B. When the voltage at ISEN pin exceeds a peak current sense voltage threshold, the gate drive signal terminates, and the power MOSFET turn off. The threshold is internally set to 250mV, or it can be programmed externally by applying voltage to the LIN_D pin. When soft start is required, a capacitor can be connected to the LIN_D pin to allow this voltage to ramp Optionally a simple passive power factor correction circuit at a desired rate, therefore, assuring that output current of the LED ramps gradually. consisting of 3 diodes and 2 capacitors, can be added as as shown in the application circuit diagram of figure 1. A current of 1mA is needed to start the FC9910B. As shown in block diagram , this current is internally generated- in FC9910B without using bulky start up resistors typically required in the off line applications. Moreover, in many applications the FC9910B can be continuously powered using its internal linear regulator that provides a regulated voltage of 7.5V for all internal circuits. When the buck converter topology of Figure 1 is selected. The peak ISEN voltage is a good representation of the everage current in the LED. However there is a certain error associated with this current sensing methode that need to be accounted for. This error is i ntroduced by the difference between the peak and the everage current in the inductor is 150mA, to get a 500mA LED current, the sense resistor should be 250mV/(500mA+0.5*150mA) = 0.43 ohm. Dimming can be accomplished in two ways, seperately or combined, depending on the application. Light output of the LED can be controlled either by linear change of its current, or by switching the current on and off while maintaining it constant. The second dimming methode (so called PWM dimming) controls LED brightness by varying the duty ratio of the output current.
Application Information
- 08. 29 5/10Revision No : 1 1. LED Driver Operation 2. Supply current 3. Setting Light output 4. Dimming
The linear dimming can be implemented by applying a control voltage from 0mV to the 250mV to the LIN_D pin. This control voltage overrides the internally set 250mV threshold level of the ISEN pin and programs the output current accordingly. For example, a potentiometer connected between Vcc and ground can program the control voltage at the ISEN pin. Applying a control voltage higher then 250mV will not change the output current setting. When higher current is desired, select a smaller sense resistor. The PWM dimming scheme can be implemented by applying an external PWM signal to the PWM_D pin. The PWM signal can be generated by a microcontroller or a pulse generator with a duty cycle proportional to the amount of desired light output. This signal enables and disables the converter modulating the LED current in the PWM fashion. In this mode LED current can be in one of the two states, zero or the nominal current set by the current sense resistor. It is not possible to use this methode to achive everage brightness levels higher then the one set by the current sense threshold level of the FC9910. By using the PWM control methode of the FC9910, the l ight output can be adjusted between zero and 100%. the accuracy of the PWM dimming methode is limited only by the minimum gate pulse width, which is a fraction of a percent of the low frequency duty cycle. The operating frequency of the oscillator is programmed between 25 and 300kHz using an external resistor connected to the connected to the Rosc pin. Fosc = 25000/(Rosc[kΩ] +22) [kHz] FC9910B 2013. 05. 08 6/10Revision No : 0 Application Information (Continued) 5. Programming Operating Frequency 33% PWM Ratio at 500Hz Dimming 95% PWM Ratio at 500Hz Dimming 0.4% PWM Ratio at 500Hz Dimming
- 08. 29 7/10Revision No : 1 7. Inductor Design Reffering to t he typical application circuit below the value can be calculated from the desired peak to peak LED ripple current in the inductor. Typically such ripple current is selected to be 30% of the nominal LED current. In the example given here, the nominal current I is 350mA. The next step is determining the total voltage drop across the LED string. For example, when the string consists of 10 High Brightness LEDs and each didode has a forward voltage drop of 3.0V at its nominal current , the total LED voltage V is 30V. Knowing the nominal rectified input voltage Vin = 120V*1.41 = 169V, the switching duty ratio can be determined as: D = V / Vin = 30 / 169 = 0.177 8. Input Bulk Capacitor Then given the switching frequency , in the example f OSC = 50kHz, the required on time of the MOSFET transistor can be calculated: T = D/ f OSC = 3.5 microsecond The required value of the inductor is given by An input filter capacitor should be designed to hold the rectified AC voltage above twice the LED string voltage throughout the AC line cycle. Assuming 15% relative voltage ripple across the capacitor, a simplified formula for the minimum value of the bulk input capacitor is given by: A passive PFC circuit at the input requires using two series connected capacitors at the place of calculated C MIN . Each of these identical capacitors should be rated for 1/2 of the input voltage and have twice as much capacitance. The FC9910B can be turned off by pulling the PWM_D pin to ground. When disabled, the FC9910B draws quiescent current of less then 1mA. LED LED LED ON IN LEDS ON LED C = I * V * 0.06 / V LEDMIN LEDS N C = 22uF, a value 22uF / 250V can be used.MIN 9. Enable 6. Power Factor Correction When the input power to the LED driver does not exceed 25W, a simple passive power factor correction circuit can be added to the FC9910B application circuit of Figure 4 in order to pass the AC line harmonic limits of the EN61000-3-2 standard for Class C equipment. The typical application circuit diagram shows how this can be done without affecting the rest of the circuit significantly. A simple circuit consisting of 3 diodes and 2 capacitors is added across the rectified AC line input to improve the line current harmonic distortion and to achieve a power factor greater than 0.85.
When the buck topology is used, and the LED is connected in series with the inductor, there is no need for any protection against an open circuit condition in the LED string. Open LED connection means no switching and can be continuous. However, in the case of the buck-booster or the flyback topology the FC9910B may cause excessive voltage stress of the switching transistor and the rectifier diode and potential failure. In the case, the FC9910B can be disabled by pulling the PWM_D pin to ground when the over voltage condition is detected. Application Information (Continued) FC9910B 2013. 08. 29 8/10Revision No : 1 10. output Open Circuit Protection Figure 4：Typical Application Circuit 0.2 Ω AC Input 85-135V AC 68µ F, 160 V 750µΗ , LEDsES1B FTK4N60D/F coilcraft BUSH-2820R5B VIN VDD LD PWM_D GND RT CS GATE 0.1µF, 250 V 0.1µF, 250 V 1n F, 250 V 1n F, 250 V 2A, 250 V NTC 1N4007 1N40071N4007 1N4007 FC9910B 68µ F, 160 V 1N4007 1N4007 1µF, 10V optional for PFC 220nF, 400 V LED(s) – a string of HB LEDs , 16 diodes 280 kΩ 1N4007*4 = DF06 / DF06S
The buck power conversion topology can be used when the LED string voltage is needed to be lower then the input supply voltage. The design procedure for a buck LED driver outlined in the previous chapters can be applied to the low voltage LED drivers as well. However, the designer must keep in mind that the input voltage must be maintained higher than 2 times the forward voltage drop across the LEDs. This limitation is rated to the output current instability that may develop when the FC9910B buck converter operates at a duty cycle greater than 0.5. This instability reveals itself as an oscillation of the output current at a sub-harmonic of the switching frequency. The power conversion topology can be used when the forward voltage drop of the LED string is higher, equal or lower than the input supply voltage. For example, the buck-booster topology can be appropriate battery(12V) and output string consists of three to six HB LEDs, as the case ma be for fail and break signal lights. In the buck-booster converter, the energy from the input source is first stored in the inductor or a flyback transformer when the switching transistor is ON. The energy is then delivered to the output during the OFF time of the transistor. When the energy stored in the flyback inductor is not fully depleted by the next switching cycle (continuous conduction mode ) the DC conversion between input and output voltage is given by: Vout = -Vin * D / (1-D) The output voltage can be either higher or lower than the input voltage, depending on duty ratio. Let us discuss the above exanple of an auto-motive LED driver that needs to drive three HB LEDs at 350mA. Knowing the nominal input voltage VIN=12V, the nominal duty ratio can be determined, as 3. Output Capacitor Then, given the switching frequency, in this example f = 50kHz, the required on-time of the MOSFET transistor can be calculated: Unlike the buck topology, the buck-booster converter requires an output filter capacitor to deliver power to the LED string during the ON time of switching the transistor, when the flyback inductor current is diverted from the output of the converter. In the order to average the current in the LED, this capacitor must present impeadance to the switching output AC ripple current that is much lower than the dynamic impeadance Rout of the LED string. If we assume Rout=3 Ohm in our example, in order to attenuate the switching ripple by a factor of 10, a capacitor with equivarent series resistance (ESR) of 0.3 Ohm is needed. A chip SMT tantalium capacitor can be selected for this purpose. FC9910B 2013. 08. 29 9/10Revision No : 1 Application Information (Continued) DC DC Low Voltage Application 1. Buck Converter Operation 2. Flyback(Buck-Booster) Operation D = V / (Vin + V ) = 9 / (12+9) = 0.43LEDs LEDs OSC L = Vin * T / (0.3* I ) = 0.98mH, use 1mHON LED