Preliminary Datasheet LP3382S High Performance, Constant Current Switching Regulator For 8PCS White LED In Series General Description Features The LP3382S is a 1.2MHz PWM boost switching regulator designed for constant- current white LED driver applications. The LP3382S can drive a string of up to 8 white LEDs in series, ensuring uniform brightness and eliminating several ballast resistors. The LP3382S implements a constant frequency 1.2MHz PWM control scheme. The high frequency PWM operation also saves board space by reducing external component sizes. To improve efficiency, the feedback voltage is set to 250 mV, which reduces the power dissipation in the current setting resistor. Highly integration and internal compensation network minimizes as 5 external component counts. Optimized operation frequency can meet the requirement of small LC filters value and low operation current with high efficiency. High Efficiency: 92% 1.2MHzFixed-Frequency PWM Operation Maximum Output Voltage up to 29V Operating Range : 2.7V to 5.5V Shutdown Supply Current:<1uA Available in SOT23-6 Package Built-in 29V Over Voltage Protection Minimize the External Component RoHS Compliant and 100% Lead (Pb)-Free Applications WLED Backlight driver OLED Backlight driver PDA MID/PTV Typical Application Circuit Ordering Information Vin 4.7uH Panel 1 4 EN OVP FB 5 3 2 Package: B6: SOT23-6 Vin LX 6 F: Pb-Free Cout 2.2uF GND Cin 10uF LP3382S LP3382S Pin Configurations Rset 2 Marking information Part Number LP3382SB6F Top Marking F5 Package SOT23-6 Other Information please view website: www.lowpowersemi.com. (SOT23-6) LP3382S – 00 Version 1.0 Datasheet OCT.-2012 www.lowpowersemi.com Page 1 of 9 Preliminary Datasheet LP3382S Functional pin description SOT-23-6 Pin Name Pin Function 1 SW Switch Pin. Connect this Pin to inductor and catch diode. Minimize the track area to reduce EMI. 2 GND Ground Pin FB Feedback Reference Voltage Pin. Series connect a resistor between WLED and ground as a current sense. Sense the current feedback voltage to set the current rating. 4 EN Chip Enable (Active High). Voltage sensing input to trigger the function of over voltage protection. Note that this pin is high impedance. There should be a pull low 100kΩ resistor connected to GND when the control signal is floating. 5 OVP Over voltage pin. 6 Vin Supply Input Voltage Pin. Bypass 1uF capacitor to GND to reduce the input noise. 3 Function Block Diagram LP3382S – 00 Version 1.0 Datasheet OCT.-2012 www.lowpowersemi.com Page 2 of 9 Preliminary Datasheet LP3382S Typical Application Circuit Vin Vin Panel Panel LX 6 4 1 4 3 FB Vin 5 OVP EN 3 FB 2 EN 6 5 OVP GND Vin Cout 2.2uF LX Cout 2.2uF 1 Cin 2.2uF 4.7uH Cin 2.2uF GND 4.7uH 2 LP3382S LP3382S 4.7uH Cout 2.2uF FB 4.7uH Cout 2.2uF 5 6 3 4 Vin EN OVP FB 5 3 2 EN OVP Cin 2.2uF Panel 2 4 Vin GND 6 LX 1 Cin 2.2uF Vin 1 Panel LP3382S for 2X6pcs Application Circuit LX Vin Rset 5.1 GND LP3382S for 6pcs Application Circuit Rset 12 LP3382S LP3382S LP3382S for 7pcs Application Circuit Rset 12 Rset 5.1 LP3382S for 2X7pcs Application Circuit Vin 4.7uH Panel 6 EN OVP FB 5 3 2 4 Vin LX 1 Cout 2.2uF GND Cin 10uF LP3382S Rset 2 LP3382S – 00 Version 1.0 Datasheet OCT.-2012 www.lowpowersemi.com Page 3 of 9 Preliminary Datasheet LP3382S Absolute Maximum Ratings Supply Input Voltage---------------------------------------------------------------------------------------------------−0.3V to 6.0V SW Input Voltage ---------------------------------------------------------------------------------------------------------−0.3V to 35V The Other Pins -----------------------------------------------------------------------------------------------------------−0.3V to 5.5V Power Dissipation, PD @ TA = 25°C SOT-23-6----------------------------------------------------------------------------0.455W Lead Temperature (Soldering, 10 sec.) -------------------------------------------------------------------------------------- 280°C Operation Temperature Range ------------------------------------------------------------------------------ −40°C to 80°C Storage Temperature Range ----------------------------------------------------------------------------------- −65°C to 150°C ESD Susceptibility HBM(Human Body Mode) ---------------------------------------------------------------------------------------MM((Machine Mode)) -------------------------------------------------------------------------------------------- 4KV 200V Electrical Characteristics Parameter Symbol Test Condition Min Typ. Max Units 6 V System Supply Input Operation voltage Range VDD Under Voltage Lock Out VDD Supply Current IDD Shut Down Current IDD 2.7 Line Regulation 2.4 V FB=0.2V, Switch 90 uA VEN < 0.4V 0.1 VIN : 3.0~4.3V 1 uA 2 % 1.2 MHz Oscillator Operation Frequency FOSC Maximum Duty Cycle 93 Feedback Voltage % LP3382S 250 mV On Resistance of MOSFET RDS(ON) 0.3 Ω SW Current Limit ILM 2 A VOVP 29 V 5 μA MOSFET Protection OVP Threshold OVP Sink Current Shut Down Voltage VEN Enable on Voltage VEN Minimum EN Dimming Threshold Minimum EN Dimming Threshold 0.4 0.7 0.7 V VFB=250Mv 1.4 V 100 Datasheet V VFB=0 V PWM EN Dimming range LP3382S – 00 Version 1.0 V OCT.-2012 www.lowpowersemi.com 200K Hz Page 4 of 9 Preliminary Datasheet LP3382S Typical Operating Characteristics LP3382S – 00 Version 1.0 Datasheet OCT.-2012 www.lowpowersemi.com Page 5 of 9 Preliminary Datasheet LP3382S Applications Information LED Current Control The LP3382S regulates the LED current by setting the current sense resistor (R1) connecting to feedback and ground. The internal feedback reference voltage is 250mV. The LED current can be set from following equation easily. ILED=250mV/R1 In order to have an accurate LED current, precision resistors are preferred (1% is recommended). The table for R1 selection is shown below. current will not increase over the current limiting threshold. OVP/UVLO/OTP The Over Voltage Protection is detected by a junction breakdown detecting circuit. Once VOUT goes over the detecting voltage, LX pin stops switching and the power N-MOSFET will be turned off. Then, the VOUT will be clamped to be near VOVP. As the output voltage is higher than a specified value or input voltage is lower than a specified value, the chip will enter protection mode to prevent abnormal function. As the die temperature is higher then 160℃, the chip also will enter protection mode. The power MOSFET will be turned off during protection mode to prevent abnormal operation. Inductor Selection The recommended value of inductor for 2 to 8WLEDs applications are 2.2 to 22µH. Small size and better efficiency are the major concerns for portable device, such as LP3382S used for mobile phone. The inductor should have low core loss at 1.3MHz and low DCR for better efficiency. To avoid inductor saturation current rating should be considered. Power Sequence In order to assure the normal soft start function for suppressing the inrush current the input voltage should be ready before EN pulls high. Capacitor Selection Input ceramic capacitor of 2.2uF and output ceramic capacitor of 1uF are recommended for the LP3382S applications for driving 8 series WLEDs. For better voltage filtering, ceramic capacitors with low ESR are recommended. X5R and X7R types are suitable because of their wider voltage and temperature ranges. Soft-Start The function of soft-start is made for suppressing the inrush current to an acceptable value at the beginning of power-on. The LP3382S provides a built-in soft-start function by clamping the output voltage of error amplifier so that the duty cycle of the PWM will be increased gradually in the soft-start period. Dimming control Current Limiting The current flow through inductor as charging period is detected by a current sensing circuit. As the value comes across the current limiting threshold, the N-MOSFET will be turned off so that the inductor will be forced to leave charging stage and enter discharging stage. Therefore, the inductor a. Using a PWM Signal to EN Pin For controlling the LED brightness, the LP3382S can perform the dimming control by applying a PWM signal to EN pin. The internal soft-start and wide range dimming frequency from 100Hz to 200KHz can insignificantly reduce audio noise when dimming. The average LED current is proportional to the PWM signal duty cycle. The LP3382S – 00 Version 1.0 Datasheet OCT.-2012 www.lowpowersemi.com Page 6 of 9 Preliminary Datasheet magnitude of the LP3382S selection of resistors in Figure 4 sets dimming control of LED current from 20mA to 0mA. Vin 4.7uH SS0520 Cout 1uF 1 Cin 10uF 6 Vin LX PWM signal should be higher than the maximum enable voltage of EN pin, in order to let the dimming control perform correctly. OVP 5 4 R2 100k EN OVP FB ON/OFF EN R4 100k FB 3 2 Cout 1uF LP3382S 5 R3 3 VFB=300mV Vin LX 1 SS14 GND 6 PWM 4 4.7uH R2 56K VDC 6.8K R1 12 2 Cin 10uF GND Vin LP3382S 0-1MHz R1 12 c. Using a Filtered PWM signal Another common application is using a filtered PWM signal as an adjustable DC voltage for LED dimming control. A filtered PWM signal acts as the DC voltage to regulate the output current. The recomended application circuit is shown in the Figure 6. In this circuit, the output ripple depends on the frequency of PWM signal. For smaller output voltage ripple (<100mV), the recommended frequency of 2.8V PWM signal should be above 2kHz. To fix the frequency of PWM signal and change the duty cycle of PWM signal can get different output current. According to the application circuit of Figure 5, output current is from 20.5mA to 5.5mA by adjusting the PWM duty cycle from 10% to 90%. Vin 4.7uH LP3382S – 00 Version 1.0 Datasheet OCT.-2012 Cout 1uF ON/OFF R4 100k EN LX OVP FB 5 3 LP3382S R69 PWM (0-100KHz) 100K www.lowpowersemi.com VFB=300mV 4 Vin GND 6 2 b. Using a DC Voltage Using a variable DC voltage to adjust the brightness is a popular method in some applications. The dimming control using a DC voltage circuit is shown in Figure 4. According to the Superposition Theorem, as the DC voltage increases, the voltage contributed to VFB increases and the voltage drop on R2 decreases, i.e. the LED current decreases. For example, if the VDC range is from 0V to 2.8V, the SS0520 1 Cin 10uF R2 R3 6.8K 56K C3 0.1uF Page 7 of 9 R1 15 Preliminary Datasheet LP3382S Layout Consideration For best performance of the LP3382S, the following guidelines must be strictly followed. ※ Input and Output capacitors should be placed close to the IC and connected to ground plane to reduce noise coupling. ※ The GND and Exposed Pad should be connected to a strong ground plane for heat sinking and noise protection. ※ Keep the main current traces as possible as short and wide. ※ LX node of DC-DC converter is with high frequency voltage swing. It should be kept at a small area. ※ Place the feedback components as close as possible to the IC and keep away from the noisy devices. LP3382S – 00 Version 1.0 Datasheet OCT.-2012 www.lowpowersemi.com Page 8 of 9 Preliminary Datasheet LP3382S Packing information LP3382S – 00 Version 1.0 Datasheet OCT.-2012 www.lowpowersemi.com Page 9 of 9