FAN5346 Series Boost LED Driver with PWM Dimming Interface Description Features Asynchronous Boost Converter Drives LEDs in Series: − FAN5346S20X: 20V Output − FAN5346S30X: 30V Output 2.5V to 5.5V Input Voltage Range PWM Dimming for LED Brightness Control 5kHz to 100kHz PWM Dimming Frequency Range 1.2MHz Fixed Switching Frequency Soft-Start Capability Input Under-Voltage Lockout (UVLO) Output Over-Voltage Protection (OVP) Short-Circuit Detection Thermal Shutdown (TSD) Protection Small Form-Factor 6-Lead SSOT23 Package The FAN5346 is an asynchronous constant-current LED driver that drives LEDs in series to ensure equal brightness for all the LEDs. FAN5346S20X has an output voltage of 20V and can drive up to 5 LEDs in series. FAN5346S30X has an output voltage of 30V and up to 8 LEDs in series. Optimized for small form-factor applications, the 1.2MHz fixed switching frequency allows the use of small inductors and capacitors. The FAN5346 uses a PWM dimming control interface to set the brightness levels of the LEDs. A PWM signal of 5kHz to 100kHz is applied to the EN pin. For safety, the device features integrated over-voltage, overcurrent, short-circuit detection, and thermal-shutdown protections. In addition, input under-voltage lockout protection is triggered if the battery voltage is too low. The FAN5346 is available in a 6-lead SSOT23 package. It is “green” and RoHS compliant. (Please see http://www.fairchildsemi.com/company/green/index.html for Fairchild’s definition of green). Applications Cellular Mobile Handsets Mobile Internet Devices Portable Media Players PDA, DSC, MP3 Players Ordering Information Part Number Output Voltage Option FAN5346S20X 20V FAN5346S30X 30V Temperature Range Package -40 to 85°C 6-Lead, SuperSOT™-6, JEDEC MO-193, 1.6mm Wide (MA06A) . © 2011 Fairchild Semiconductor Corporation FAN5346 • Rev.1.0.1 www.fairchildsemi.com FAN5346 — Series Boost LED Driver with PWM Dimming Interface June 2012 FAN5346 — Series Boost LED Driver with PWM Dimming Interface Typical Application Diagram Figure 1. Typical Application Block Diagram Figure 2. Functional Block Diagram © 2011 Fairchild Semiconductor Corporation FAN5346 • Rev. 1.0.1 www.fairchildsemi.com 2 Figure 3. Pin Assignments, Top View Pin Definitions Pin # Name Description 5 VOUT 1 VIN Input Voltage. Connect to the power source and decouple with CIN to GND. 4 EN Enable Brightness Control. Program dimming levels by driving pin with the PWM signal. 3 FB Voltage Feedback. The boost regulator regulates this pin to 0.250V to control the LED string current. Tie this pin to a current setting resistor (RSET) between GND and the cathode of the LED string. 6 SW Switching node. Tie inductor L1 from VIN to SW pin. 2 GND Boost Output Voltage. Output of the boost regulator. Connect the LEDs to this pin. Connect COUT (output capacitor) to GND. Ground. Tie directly to a GND plane. © 2011 Fairchild Semiconductor Corporation FAN5346 • Rev. 1.0.1 www.fairchildsemi.com 3 FAN5346 — Series Boost LED Driver with PWM Dimming Interface Pin Configuration Stresses exceeding the absolute maximum ratings may damage the device. The device may not function or be operable above the recommended operating conditions and stressing the parts to these levels is not recommended. In addition, extended exposure to stresses above the recommended operating conditions may affect device reliability. The absolute maximum ratings are stress ratings only. Symbol VIN VFB, VEN VSW Parameter Min. Max. Unit VIN Pin -0.3 6.0 V FB, EN Pins -0.3 VIN + 0.3 V FAN5346S20X -0.3 22.0 V FAN5346S30X -0.3 33.0 V FAN5346S20X -0.3 22.0 V FAN5346S30X -0.3 33.0 V SW Pin VOUT VOUT Pin ESD Electrostatic Discharge Protection Human Body Model per JESD22-A114 1.5 Charged Device Model per JESD22-C101 1.5 kV TJ Junction Temperature -40 +150 °C TSTG Storage Temperature -65 +150 °C +260 °C TL Lead Soldering Temperature, 10 Seconds Recommended Operating Conditions The Recommended Operating Conditions table defines the conditions for actual device operation. Recommended operating conditions are specified to ensure optimal performance to the datasheet specifications. Fairchild does not recommend exceeding them or designing to absolute maximum ratings. Parameter Symbol VIN Min. VIN Supply Voltage VOUT VOUT Voltage(1) IOUT VOUT Load Current Max. Unit V 2.5 5.5 FAN5346S20X 6.2 18.5 FAN5346S30X 6.2 28.5 V 5 25 mA TA Ambient Temperature -40 +85 °C TJ Junction Temperature -40 +125 °C Note: 1. Application should guarantee that minimum and maximum duty cycle fall between 20-85% to meet the specified range. Thermal Properties Junction-to-ambient thermal resistance is a function of application and board layout. This data is measured with four-layer 2s2p boards in accordance to JEDEC standard JESD51. Special attention must be paid not to exceed junction temperature TJ(max) at a given ambient temperature TA. Symbol θJA Parameter Junction-to-Ambient Thermal Resistance, SSOT23-6 Package © 2011 Fairchild Semiconductor Corporation FAN5346 • Rev. 1.0.1 Typical Unit 151 °C/W www.fairchildsemi.com 4 FAN5346 — Series Boost LED Driver with PWM Dimming Interface Absolute Maximum Ratings VIN = 2.5V to 5.5V and TA = -40°C to +85°C unless otherwise noted. Typical values are at TA = +25°C and VIN = 3.6V. Symbol Parameter Conditions Min. Typ. Max. Unit 0.90 μA Power Supplies ISD Shutdown Supply Current EN = GND 0.30 IQ(ACTIVE) Quiescent Current at ILOAD = 0mA Device Not Switching, No Load 300 VUVLO Under-Voltage Lockout Threshold VUVHYST Under-Voltage Lockout Hysteresis μA VIN Rising 2.10 2.35 2.60 VIN Falling 1.80 2.05 2.30 250 V mV EN: Enable Pin VIH HIGH-Level Input Voltage VIL LOW-Level Input Voltage REN EN Pull-Down Resistance fPWM tSD 1.2 200 (3) PWM Dimming Frequency EN LOW, Shutdown Pulse Width V 0.4 V 400 kΩ 100 kHz 1 ms 250 270 mV 1.0 μA 300 5 VIN = 3.6V; from Falling Edge of EN Feedback and Reference VFB Feedback Voltage ILED = 20mA from -40°C to +85°C, 2.5V ≤ VIN ≤ 5.5V IFB Feedback Input Current VFB = 250mV 0.1 VIN = 3.6V, ISW = 100mA 600 VIN = 2.5V, ISW = 100mA 650 EN = 0, VIN = VSW = VOUT = 5.5V, VLED = 0V 0.1 2.0 230 Power Outputs RDS(ON)_Q1 Boost Switch On Resistance ISW(OFF) ILIM-PK SW Node Leakage(2) Boost Switch Peak Current Limit mΩ FAN5346S20X: VIN = 3.2V to 4.3V, TA =-20°C to +60°C, VF = 3.4V, 4 LEDs 200 300 400 FAN5346S30X 500 750 1000 0.95 1.15 1.35 FAN5346S20X 18.0 20.0 21.5 FAN5346S30X 27.5 30.0 32.5 μA mA Oscillator fSW Boost Regulator Switching Frequency MHz Output and Protection VOVP Boost Output Over-Voltage Protection OVP Hysteresis FAN5346S20X 0.8 FAN5346S30X 1.0 V VTLSC VOUT Short-Circuit Detection Threshold VOUT Falling VIN – 1.4 V VTHSC VOUT Short-Circuit Detection Threshold VOUT Rising VIN – 1.2 V DMAX Maximum Boost Duty Cycle(3,4) DMIN Minimum Boost Duty Cycle(3,4) TTSD Thermal Shutdown 150 °C THYS Thermal Shutdown Hysteresis 35 °C 85 20 % Notes: 2. SW leakage current includes the leakage current of two internal switches; SW to GND and SW to VOUT. 3. Not tested in production; guaranteed by design. 4. Application should guarantee that minimum and maximum duty cycle fall between 20-85% to meet the specified range. © 2011 Fairchild Semiconductor Corporation FAN5346 • Rev. 1.0.1 www.fairchildsemi.com 5 FAN5346 — Series Boost LED Driver with PWM Dimming Interface Electrical Specifications 90% 90% 80% 80% Efficiency Efficiency VIN = 3.6V, TA = 25°C, ILED = 25mA, L = 10µH, COUT = 1.0µF, and CIN = 10.0µF. 70% VIN=2.5V VIN=2.7V 60% 70% VIN=2.5V VIN=2.7V 60% VIN=3.6V VIN=3.6V VIN=4.2V VIN=4.2V VIN=4.5V VIN=4.5V 50% 50% 5 10 15 20 25 5 10 25 Figure 5. 4 LEDs: Efficiency vs. LED Current vs. Input Voltage 90% 90% 80% 80% Efficiency Efficiency Figure 4. 3 LEDs: Efficiency vs. LED Current vs. Input Voltage 70% VIN=2.5V VIN=2.7V 70% VIN=2.5V VIN=2.7V 60% VIN=3.6V VIN=3.6V VIN=4.2V VIN=4.2V VIN=4.5V VIN=4.5V 50% 50% 5 10 15 20 5 25 10 Figure 6. 5 LEDs: Efficiency vs. LED Current vs. Input Voltage 20 25 Figure 7. 6 LEDs: Efficiency vs. LED Current vs. Input Voltage 90% 80% 80% Efficiency 90% 70% VIN=2.5V 70% VIN=2.9V VIN=2.7V 60% 15 LED Current (mA) LED Current (mA) Efficiency 20 LED Current (mA) LED Current (mA) 60% 15 60% VIN=3.6V VIN=3.6V VIN=4.2V VIN=4.2V VIN=4.5V VIN=4.5V 50% 50% 5 10 15 20 5 25 LED Current (mA) 15 20 25 LED Current (mA) Figure 8. 7 LEDs: Efficiency vs. LED Current vs. Input Voltage © 2011 Fairchild Semiconductor Corporation FAN5346 • Rev. 1.0.1 10 Figure 9. 8 LEDs: Efficiency vs. LED Current vs. Input Voltage www.fairchildsemi.com 6 FAN5346 — Series Boost LED Driver with PWM Dimming Interface Typical Characteristics 90% 90% 80% 80% Efficiency Efficiency VIN = 3.6V, TA = 25°C, ILED = 25mA, L = 10µH, COUT = 1.0µF, and CIN = 10.0µF. 70% 60% 70% 60% -40C -40C +25C +25C +85C +85C 50% 50% 2.5 3.0 3.5 4.0 2.5 4.5 3.0 0.2 1250 0.1 1200 0.0 -0.1 4.5 -0.2 -40°C 1150 1100 -40°C 1050 +25°C +25°C +85°C +85°C -0.4 1000 2.5 3.0 3.5 4.0 4.5 2.5 3.0 Input Voltage (V) 3.5 4.0 4.5 Input Voltage (V) Figure 12. Delta of VFB Over Input Voltage and Temperature for 7 LEDs with L=10µH and COUT=1.0µF Figure 13. Frequency vs. Input Voltage vs. Temperature 31.5 21.0 5 LEDs L = 10µH COUT = 1.0µF ILED = 25mA 7 LEDs L = 10µH COUT = 1.0µF ILED = 25mA 31.0 OVP (V) 20.5 OVP (V) 4.0 Figure 11. Efficiency vs. Input Voltage vs. Temperature for 7 LEDs in Series Frequency (kHz) Delta Feedback (mV) Figure 10. Efficiency vs. Input Voltage vs. Temperature for 5 LEDs in Series -0.3 3.5 Input Voltage (V) Input Voltage (V) 20.0 19.5 30.5 30.0 29.5 19.0 29.0 18.5 2.5 3.0 3.5 4.0 2.5 4.5 3.5 4.0 4.5 Input Voltage (V) Input Voltage (V) Figure 14. OVP vs. Input Voltage: FAN5346S20X © 2011 Fairchild Semiconductor Corporation FAN5346 • Rev. 1.0.1 3.0 Figure 15. OVP vs. Input Voltage: FAN5346S30X www.fairchildsemi.com 7 FAN5346 — Series Boost LED Driver with PWM Dimming Interface Typical Characteristics VIN = 3.6V, TA = 25°C, ILED = 25mA, L = 10µH, COUT = 1.0µF, and CIN = 10.0µF. 265 Quiescent Current (µA) Shutdown Current (µA) 0.80 0.60 0.40 0.20 0.00 2.50 3.00 3.50 4.00 260 255 250 245 240 235 230 225 2.50 4.50 3.00 3.50 4.00 4.50 VIN (V) VIN (V) Figure 16. Shutdown Current vs. Input Voltage Figure 17. Quiescent Current vs. Input Voltage LED Current (mA) 25 20 15 10 5 0 0 20 40 60 80 100 Duty Cycle (%) Figure 18. LED Current vs. Duty Cycle, fPWM = 20kHz Figure 19. Line Transient Response for 5 LEDs Figure 20. Line Transient Response for 6 LEDs Figure 21. Line Transient Response for 7 LEDs © 2011 Fairchild Semiconductor Corporation FAN5346 • Rev. 1.0.1 www.fairchildsemi.com 8 FAN5346 — Series Boost LED Driver with PWM Dimming Interface Typical Characteristics VIN = 3.6V, TA = 25°C, ILED = 25mA, L = 10µH, COUT = 1.0µF, and CIN = 10.0µF. Figure 22. Startup Waveform for Switch Voltage, Inductor Current, VFB, and EN for 5 LEDs Figure 23. Steady-State Waveform for VOUT, Switch Voltage, and Inductor Current for 5 LEDs Figure 24. Startup Waveform for Switch Voltage, Inductor Current, VFB, and EN for 6 LEDs Figure 25. Steady-State Waveform for VOUT, Switch Voltage, and Inductor Current for 6 LEDs Figure 26. Startup Waveform for Switch Voltage, Inductor Current, VFB, and EN for 7 LEDs Figure 27. Steady-State Waveform for VOUT, Switch Voltage, and Inductor Current for 7 LEDs © 2011 Fairchild Semiconductor Corporation FAN5346 • Rev. 1.0.1 www.fairchildsemi.com 9 FAN5346 — Series Boost LED Driver with PWM Dimming Interface Typical Characteristics Overview The FAN5346 is an inductive current-mode boost serial LED driver that achieves LED current regulation by maintaining 0.250V across the RSET resistor. The current through the LED string (ILED) is given by: I LED = 0.250 R SET (1) The voltage VOUT is determined by the sum of the forward voltages across each LED, plus the voltage across RSET, which is always 250mV. Driving Eight LEDs in Series FAN5346S30X can drive 8 LEDs in series, but the minimum input voltage (VIN) must be greater than or equal to 2.9V, while the forward voltage of the white LED should be less than or equal to 3.2V, and the maximum LED current cannot exceed 20mA to maintain stable operation. UVLO and Soft-Start If EN has been LOW for more than 1ms, the IC may initiate a “cold start” soft-start cycle when EN rises, provided VIN is above the UVLO threshold. PWM Dimming The FAN5346 uses a PWM signal to directly modulate output current in the LED string to vary the perceived LED brightness. When the EN pin is held HIGH, the FB voltage is 250mV. This voltage is reduced when a PWM signal is applied to the EN pin, thereby enabling the LEDs to be dimmed. The FB voltage is given by the equation: VFB = DutyCycle × 250mV (2) where DutyCycle = the duty cycle of the PWM signal and 250mV is the internal reference voltage. Figure 28. Block Diagram of FB and EN Circuit for PWM Dimming Over-Current and Short-Circuit Detection The boost regulator employs a cycle-by-cycle peak inductor current limit of 300mA (typical) and 750mA (typical) for FAN5346S20X and FAN5346S30X, respectively. Over-Voltage / Open-Circuit Protection If the LED string is an open circuit, FB remains at 0V and the output voltage continues to increase in the absence of an overvoltage protection (OVP) circuit. The FAN5346S20X OVP circuit disables the boost regulator when VOUT exceeds 20V and continues to keep the regulator off until VOUT drops below 19V. For FAN5346S30X, the OVP is 30V and it turns back on when VOUT is below 29V Thermal Shutdown When the die temperature exceeds 150°C, a reset occurs and remains in effect until the die cools to 115°C; at which time, the circuit is allowed to begin the soft-start sequence. Figure 28 illustrates how the FAN5346 divides the internal 250mV reference voltage at the duty cycle of the PWM signal. A low-pass filter filters the PWM signal, which then is input into the error amplifier as the reference voltage for the FB pin. © 2011 Fairchild Semiconductor Corporation FAN5346 • Rev. 1.0.1 www.fairchildsemi.com 10 FAN5346 — Series Boost LED Driver with PWM Dimming Interface Circuit Description The reference schematic diagram is shown in Figure 29. FAN5346 is able to drive up to eight LEDs with input voltage equal to or greater than 2.9V (VIN ≥ 2.9V). However, the number of LEDs that can be used FAN5346 depends on forward voltage. It is recommended that the forward voltage (VF) of the white LED be no greater than 3.2V and the maximum LED current be 20mA. FAN5345 can be also used as a boost convertor by connect the VOUT point to the load directly. The return trace of the load should also return to GND through a sense resistor (R1). Figure 29. Reference Application Schematic Diagram Component Placement and PCB Recommendations Input Capacitor and Return Trace FAN5346 switches at 1.2MHz to boost the output voltage. Component placement and PCB layout need to be carefully taken into consideration to ensure stable output and to prevent generation of noise. Figure 30 is a portion of the evaluation board layout. The critical layout elements are: the L1, CIN, CIN return trace, COUT, and the COUT return trace. The input capacitor is the first priority in a switching buck or boost regulator PCB layout. A stable input source (VIN) enables a switching regulator to deliver its best performance. During the regulator’s operation, it is switching at a high frequency, which makes the load of CIN change dynamically since it is trying to make the input source vary at the same switching frequency as the regulator. To ensure a stable input source, CIN needs to hold enough energy to minimize the variation at the input pin of the regulator. For CIN to have a fast response of charge / discharge, the trace from CIN to the input pin of the regulator and the return trace from GND of the regulator to CIN should be as short and wide as possible to minimize trace resistance, inductance, and capacitance. During operation, the current flow from CIN through the regulator to the load and back to CIN contains high-frequency variation due to switching. Trace resistance reduces the overall efficiency due to I2R loss. Even a small trace inductance could effectively yield ground variation to add noise on VOUT. The input capacitor should be placed close to the VIN and GND pins of the regulator and traces should be as short as possible. Avoid routing the return trace through different layers because vias have strong inductance effect at high frequencies. If routing to other PCB layers is unavoidable, place vias next to the VIN and GND pins of the regulator to minimize the trace distance. Output Capacitor and Return Trace The output capacitor serves the same purpose as the input capacitor, but also maintains a stable output voltage. As explained above, the current travels to the load and back to the COUT GND terminal. COUT should be placed close to the VOUT pin. The traces of COUT to L1, VOUT, and the return Figure 30. Reference PCB Layout © 2011 Fairchild Semiconductor Corporation FAN5346 • Rev. 1.0.1 www.fairchildsemi.com 11 FAN5346 — Series Boost LED Driver with PWM Dimming Interface Application Information Inductor Inductor (L1) should be placed as close to the regulator as possible to minimize trace resistance and inductance for the reasons explained above. As shown in Figure 30; CIN, COUT, and L1 are all placed next to the regulator. All traces are on the same layer to minimize trace resistance and inductance. Total PCB area, not including the sense resistor, is 67.2mm2 (7.47mm x 8.99mm). Sense Resistor The sense resistor provides a feedback signal for the regulator to control output voltage. A long trace from the sense resistor to the FB pin couples noise into the FB pin. If Table 1. Recommended External Components Inductor (L) Part Number Manufacturer LQH43MN100K03 Murata NLCV32T-100K-PFR TDK VLF3010AT-100MR49-1 TDK DEM2810C 1224-AS-H-100M TOKO CV105X5R105K25AT AVX / Kyocera GRM21BR71A106KE51L Murata N/A RBS520S30 Fairchild Semiconductor N/A RB520S-30 Rohm 10.0µH Minimum COUT 1.0µF Minimum CIN 10.0µF Schottky Diode © 2011 Fairchild Semiconductor Corporation FAN5346 • Rev. 1.0.1 www.fairchildsemi.com 12 FAN5346 — Series Boost LED Driver with PWM Dimming Interface noise is coupled into the FB pin, it causes unstable operation of the switching regulator, which affects application performance. The return trace from the sense resistor to the FB pin should be short and away from any fast-switching signal traces. The ground plane under the return trace is not necessary. If the ground plane under the return trace is noisy; but not the same ground plane as the regulator; the noise could be coupled into the FB pin through PCB parasitic capacitance, yielding noisy output. trace from load to COUT should be as short and wide as possible to minimize trace resistance and inductance. To minimize noise coupling to load, a small-value capacitor can be placed between VOUT and COUT to route high-frequency noise back to GND before it gets to the load. FAN5346 — Series Boost LED Driver with PWM Dimming Interface Physical Dimensions Figure 31. 6-Lead, SuperSOT™-6, JEDEC MO-193, 1.6mm Wide Package drawings are provided as a service to customers considering Fairchild components. Drawings may change in any manner without notice. Please note the revision and/or date on the drawing and contact a Fairchild Semiconductor representative to verify or obtain the most recent revision. Package specifications do not expand the terms of Fairchild’s worldwide terms and conditions, specifically the warranty therein, which covers Fairchild products. Always visit Fairchild Semiconductor’s online packaging area for the most recent package drawings: http://www.fairchildsemi.com/packaging/. © 2011 Fairchild Semiconductor Corporation FAN5346 • Rev. 1.0.1 www.fairchildsemi.com 13 FAN5346 — Series Boost LED Driver with PWM Dimming Interface © 2011 Fairchild Semiconductor Corporation FAN5346 • Rev. 1.0.1 www.fairchildsemi.com 14