Techcode® ÓÉ Foxit PDF Editor ±à¼°æȨËùÓÐ (c) by Foxit Software Company, 2004 ½öÓÃÓÚÆÀ¹À¡£ DATASHEET TD8203 White LED Step-up Converter 汪工 ＴＥＬ：１３８２８７１９４１０ ＱＱ：１９２９７９４２３８ General Description Features The TD8203 is a current‐mode and fixed frequency boost converter with an integrated N‐FET to drive white LEDs. The series connection allows the LED current to be identical for uniform brightness. Its low on‐resistance of NFET and low feedback voltage reduce power loss and achieve high efficiency. Fast switching frequency(1.5MHz typical) allows using small‐size inductor and both of input and output capacitors. An over voltage protection function,which monitors the output voltage via OVP pin, stops switching of the IC if the OVP voltage exceeds the over voltage threshold. An internal soft‐start circuit eliminates the inrush current during start‐up. The TD8203 also integrates under‐voltage lockout, overtemperature protection, and current limit circuits to protect the IC in abnormal conditions. The TD8203 is available in a TSOT‐23‐6A z z z z z z z z z z z z z Applications z z z z Wide Input Voltage from 2.7V to 6V Fixed 1.5MHz Switching Frequency Reference Voltage : 0.2V PWM Brightness Control with Wide Frequency Range of 100Hz to 100kHz Build‐In Power MOSFET : 0.2W Open‐LED Protection Under‐Voltage Lockout Protection Over‐Temperature Protection <1mA Quiescent Current during Shutdown TSOT‐23‐6A Halogen and Lead Free Available RoHS Compliant White LED Display Backlighting Cell Phone and Smart Phone PDA, PMP, MP3 Digital Camera December, 20, 2011 Techcode Semiconductor Limited www.techcodesemi.com 1 Techcode® DATASHEET TD8203 White LED Step-up Converter Pin Assignments Pin Description Pin Number Pin Name 1 LX 2 GND 3 FB 4 EN Description Switch pin. Connect this pin to inductor/diode here. Ground Feedback Pin. Connect this pin to cathode of the lowest LED and current‐sense resistor (R1). Calculate resistor value according to R1=VREF/ILED . Enable Control Input. Forcing this pin above 1.0V enables the device, or forcing this pin below 0.4V to shut it down. In shutdown, all functions are disabled to decrease the supply current below 1μA. Do not leave this pin floating. 5 OVP 6 IN Converter Output and Over‐Voltage Protection Input Pin. Main Supply Pin. Must be closely decoupled to GND with a 4.7μF or greater ceramic capacitor. December, 20, 2011 Techcode Semiconductor Limited www.techcodesemi.com 2 Techcode® DATASHEET TD8203 White LED Step-up Converter Ordering Information TD8203 □ □ Circuit Type Packing: Blank：Tube Package T:SOT23 Functional Block Diagram Functional Block Diagram of TD8203 December, 20, 2011 Techcode Semiconductor Limited www.techcodesemi.com 3 Techcode® DATASHEET TD8203 White LED Step-up Converter Absolute Maximum Ratings Parameter Symbol Rating VIN VIN Supply Voltage (VIN to GND) ‐0.3 ~ 7 VLX FB, EN to GND ‐0.3 ~ VIN LX to GND Voltage ‐0.3 ~ 27.5 VOVP OVP to GND ‐0.3 ~ 27.5 PD TJ TSTG TSDR Power Dissipation Internally Limit Maximum Junction Temperature 150 Storage Temperature ‐65 ~ 150 Maximum Lead Soldering Temperature, 10 Seconds 260 Unit V V V V W ℃ ℃ ℃ Recommended Operating Conditions Symbol θJA θJC VIN VOVP CIN COUT L1 TA TJ Parameter Junction-to-Ambient Resistance in Free Air Junction-to-Case Resistance VIN Supply Voltage(VIN to GND) VOUT to GND Input Capacitor Output Capacitor Converter Output Inductor Ambient Temperature Junction Temperature Typical 220 120 2.7‐6 VIN‐22 4.7~ 4.7~ 2.2‐10 ‐40~85 ‐40~125 Value Unit C/W o C/W o V V uF uF uH o C o C December, 20, 2011 Techcode Semiconductor Limited www.techcodesemi.com 4 Techcode® DATASHEET TD8203 White LED Step-up Converter Electrical Characteristics The following specifications apply for VIN =3.6V TA=25 oC, unless specified otherwise. Symbol Parameter Test Conditions VIN Input Voltage TD8203 Min. Typ. 2.5 IDD1 VFB=0.4V,no switching ‐ 300 ‐ uA IDD2 ISD VREF Input DC Bias Current UVLO Threshold Voltage UVLO Hysteresis Voltage VFB=0V, switching EN=GND VIN Rising VIN Falling Regulated Feedback Voltage VIN=2.7V~6V, TA = 25 oC VIN=2.7V~6V, TA = -40 ~ 85 oC IFB FSW RON FB Input Current Power Switch On Resistance 2 ‐ 2.2 100 0.2 1.5 0.2 5 1 2.4 150 0.215 0.22 50 1.75 mA µA V mV V ‐ ‐ 2.0 50 0.185 0.18 ‐50 1.25 ILIM DMAX TOTP Power Switch Current Limit 2 95 24 3 50 ‐ ‐ ‐ 800 150 40 1 98 27.5 ‐ ‐ ‐ 0.4 2 ‐ A uA % V V A V V A ns o C o C Switching Frequency LX Leakage Current LX Maximum Duty Cycle Over Voltage Threshold Over Voltage Hysteresis OVP Leakage Enable Voltage Threshold Shutdown Voltage Threshold EN Leakage Current EN Minimum On Pluse Width Over‐Temperature Protection Over‐Temperature Protection VEN = 0V, VLX = 0V or 6V, VIN = 6V ‐1 92 VOUT Rising 22 VOVP Falling ‐ VOVP =20V ‐ VEN Rising 1 VEN Falling ‐ VEN = 0 ~ 6V, VIN = 6V ‐2 VEN = 0 ~ 6V, VIN = 6V, PWM ‐ TJ Rising TJ Falling Max. 6 Unit V nA MHz Ω December, 20, 2011 Techcode Semiconductor Limited www.techcodesemi.com 5 Techcode® DATASHEET TD8203 White LED Step-up Converter Typical Operating Characteristics December, 20, 2011 Techcode Semiconductor Limited www.techcodesemi.com 6 Techcode® DATASHEET TD8203 White LED Step-up Converter Typical Operating Characteristics(Cont.) Operating Waveforms December, 20, 2011 Techcode Semiconductor Limited www.techcodesemi.com 7 Techcode® DATASHEET TD8203 White LED Step-up Converter Operating Waveforms(Cont.) December, 20, 2011 Techcode Semiconductor Limited www.techcodesemi.com 8 Techcode® White LED Step-up Converter DATASHEET TD8203 Typical Application Circuit December, 20, 2011 Techcode Semiconductor Limited www.techcodesemi.com 9 Techcode® DATASHEET TD8203 White LED Step-up Converter Function Description Main Control Loop Over-Temperature Protection (OTP) The TD8203 is a constant frequency current-mode switching The over-temperature circuit limits the junction temperature of the regulator. During normal operation, the internal N-channel power TD8203. When the junction temperature exceeds 150oC, a thermal MOSFET is turned on each cycle when the oscillator sets an sensor turns off the power MOSFET, allowing the device to cool. internal RS latch and turned off when an internal comparator The thermal sensor allows the converter to start a soft-start (ICMP) resets the latch. The peak inductor current at which ICMP process and regulate the LEDs current again after the junction resets the RS latch is controlled by the voltage on the COMP temperature cools by 40oC. The OTP is designed with a 40oC node, which is the output of the error amplifier (EAMP). An hysteresis to lower the average Junction Temperature (TJ) during external current-sense resistor connected between cathode of continuous thermal overload conditions, increasing the lifetime of the lowest LED and ground allows the EAMP to receive a current the device. feedback voltage VFB at FB pin. When the LEDs voltage Enable/Shutdown decreases to cause the LEDs current to decrease,it causes a Driving EN to ground places the TD8203 in shutdown mode. When slightly decrease in VFB relative to the reference voltage, which in in shutdown, the internal power MOSFET turns off, all internal turn causes the COMP voltage to increase until the LEDs current circuitry shuts down and the quiescent supply current reduces to reaches the set point. 1μA maximum. This pin also could be used as a digital input VIN Under-Voltage Lockout (UVLO) allowing brightness controlled by using a PWM signal with The Under-Voltage Lockout (UVLO) circuit compares the input frequency from 100Hz to 100kHz. The 0% duty cycle of PWM voltage at VIN with the UVLO threshold (2.2V rising,typical) to signal corresponds to zero LEDs current and 100% corresponds to ensure the input voltage is high enough for reliable operation. full one. Suggestion dimmimg duty range is from 8% to 100% at The 100mV (typ) hysteresis prevents supply transients from 100kHz dimmimg frequency. causing a restart. Once the input voltage exceeds the UVLO Open-LED Protection rising threshold, startup begins.When the input voltage falls In driving LED applications, the feedback voltage on FB pin falls below the UVLO falling threshold, the controller turns off the down if one of the LEDs, in series, is failed.Meanwhile, the converter. converter unceasingly boosts the output voltage like an open-loop Soft-Start operation. Therefore, an overvoltage protection monitoring the The TD8203 has a built-in soft-start to control the N channel output voltage via OVP pin is integrated into the chip to prevent the MOSFET current raises during start-up. During soft-start, an LX and the output voltages from exceeding their maximum voltage internal ramp voltage connected to one of the inverting inputs of ratings. Once the voltage on the OVP pin rises above the OVP the current limit comparator. The inductor current limit is threshold, the converter stops switching and prevents the output proportional to the voltage. When the threshold voltage of the voltage from rising. The converter can work again when the OVP internal soft-start comparator is reached, the full current limit is voltage falls below the falling of OVP voltage threshold. released. Current-Limit Protection The TD8203 monitors the inductor current, flowing through the N-channel MOSFET, and limits the current peak at current-limit level to prevent loads and the device from damages in overload conditions. December, 20, 2011 Techcode Semiconductor Limited www.techcodesemi.com 10 Techcode® DATASHEET TD8203 White LED Step-up Converter Application Information Input Capacitor Selection The input capacitor (CIN) reduces the current peaks drawn from the input supply and reduces noise injection into the IC. The The peak inductor current is calculated as the following equation: reflected ripple voltage will be smaller with larger CIN. For reliable operation, it is recommended to select the capacitor voltage rating at least 1.2 times higher than the maximum input voltage. The capacitors should be placed close to the VIN and GND. Inductor Selection For high efficiencies, the inductor should have a low dc resistance to minimize conduction losses. Especially at high-switching frequencies the core material has a higher impact on efficiency. When using small chip inductors, the efficiency is reduced mainly due to higher inductor core losses. This needs to be considered when selecting the appropriate inductor. The inductor value determines the inductor ripple current. The larger the inductor value, the smaller the inductor ripple current and the lower the conduction losses of the converter. Conversely, larger inductor values cause a slower load transient response. A reasonable starting point for setting ripple current, ΔIL,is 30% to 50% of the average inductor current. The recommended inductor value can be calculated as below: where VIN = input voltage Output Capacitor Selection VOUT = output voltage The current-mode control scheme of the TD8203 allows the usage FSW = switching frequency in MHz of tiny ceramic capacitors. The higher capacitor value provides IOUT = maximum output current in amp. good load transient response.Ceramic capacitors with low ESR η = Efficiency values have the lowest output voltage ripple and are recommended. If required,tantalum capacitors may be used as ΔIL /IL(AVG) = inductor ripple current/average current (0.3 to 0.5 well. The output ripple is the sum of the voltages across the ESR typical) and the ideal output capacitor. To avoid saturation of the inductor, the inductor should be rated at least for the maximum input current of the converter plus the inductor ripple current. The maximum input current is calculated as below: where IPEAK is the peak inductor current. December, 20, 2011 Techcode Semiconductor Limited www.techcodesemi.com 11 Techcode® White LED Step-up Converter DATASHEET TD8203 Application Information(Cont.) Output Capacitor Selection (Cont.) For ceramic capacitor application, the output voltage ripple is dominated by the ΔVCOUT. When choosing the input and output ceramic capacitors, the X5R or X7R with their good temperature and voltage characteristics are recommended. Setting the LED Current In figure 1, the converter regulates the voltage on FB pin, connected with the cathod of the lowest LED and the currentsense resistor R1, at 0.2V (typical). Therefore, the current (ILED), flowing via the LEDs and the R1, is calculated by the following equation: Layout Considerations For all switching power supplies, the layout is an important step in the design; especially at high peak currents and switching frequencies. If the layout is not carefully done, the regulator might show noise problems and duty cycle jitter. 1. The input capacitor should be placed close to the VIN and GND. Connecting the capacitor with VIN and GND pins by short and wide tracks without using any via holes for good filtering and minimizing the voltage ripple. 2. To minimize copper trace connections that can inject noise into the system, the inductor should be placed as close as possible to the LX pin to minimize the noise coupling into other circuits. 3. The feedback network should be routed away from the inductor. The feedback pin and feedback network should be shielded with a ground plane or trace to minimize noise coupling into this circuit. 4. A star ground connection or ground plane minimizes ground shifts and noise is recommended. December, 20, 2011 Techcode Semiconductor Limited www.techcodesemi.com 12 Techcode® DATASHEET TD8203 White LED Step-up Converter Package Information SOT23‐6 December, 20, 2011 Techcode Semiconductor Limited www.techcodesemi.com 13 Techcode® DATASHEET White LED Step-up Converter TD8203 Design Notes December, 20, 2011 Techcode Semiconductor Limited www.techcodesemi.com 14