Techcode® ÓÉ Foxit PDF Editor ±à¼°æȨËùÓÐ (c) by Foxit Software Company, 2004 ½öÓÃÓÚÆÀ¹À¡£ DATASHEET TD8201 White LED Step-up Converter 汪工 ＴＥＬ：１３８２８７１９４１０ ＱＱ：１９２９７９４２３８ General Description Features The TD8201 is a step‐up DC/DC converter designed for driving up to 5 white LEDs in series from a single cell Lithium Ion battery with constant current. Because it directly regulates output current, the TD8201 is ideal for driving light emitting diodes (LEDs) whose light intensity is proportional to the current passing through them, not the voltage across their terminals. A single external resistor sets LED current between 2mA and 20mA, which can then be easily adjusted using either a DC voltage or a pulse width modulated (PWM) signal up to 100KHz. Its low 104mV feedback voltage reduces power loss and improves efficiency. The OV pin monitors the output voltage and turns off the converter if an over‐voltage condition is present due to an open circuit condition. The TD8201 is available in SOT23‐6 packages. z z z z z z z z Drives Up to 5 Series White LEDs from 3V Up to 87% Efficiency 1.25MHz Fixed Switching Frequency Low 104mV Feedback Voltage Open Load Shutdown PWM Dimming SOT23‐6 Packages RoHS compliant Applications z z z z Cell Phones Handheld Computers and PDAs Digital Cameras Small LCD Displays December, 20, 2011 Techcode Semiconductor Limited www.tongchuangwei.com 1 Techcode® DATASHEET TD8201 White LED Step-up Converter Pin Assignments Pin Description Description Pin Number Pin Name 1 SW Power Switch Output. Connect the inductor and the blocking Schottky diode to SW. 2 GND Ground 3 FB Feedback input pin. The reference voltage at this pin is 104mV. Connect the cathode of the lowest LED to FB and a current sense resistor between FB and GND. 4 EN Enable pin. A high input at EN enables the device and a low input disables the devices. When not used, connect EN to the input source for automatic startup. 5 OV Over Voltage Input. OV measures the output voltage for open circuit protection. Connect OV to the output at the top of the LED string. 6 IN Input Supply Pin. Must be locally bypassed. December, 20, 2011 Techcode Semiconductor Limited www.tongchuangwei.com 2 Techcode® DATASHEET TD8201 White LED Step-up Converter Ordering Information TD8201 □ □ Circuit Type Packing: Blank：Tube Package T:SOT23 Functional Block Diagram Functional Block Diagram of TD8201 December, 20, 2011 Techcode Semiconductor Limited www.tongchuangwei.com 3 Techcode® DATASHEET TD8201 White LED Step-up Converter Absolute Maximum Ratings Parameter Symbol Rating Unit VIO PDMAX PTR1 Input Voltage Voltage at SW Pin All Other I/O Pins Power Dissipation (Note 2) Thermal Resistance，SOT‐23‐6, ΘJA Tstg Tsolder Storage Temperature Package Lead Soldering Temperature ‐0.3～6 ‐0.5～25 GND‐0.3 to VDD+0.3 Internally Limited 220 ‐55 to 150 260℃, 10s ESD Susceptibility (Note 3) 3 VIN VSW V V V W ℃/W ℃ kV Recommended Operating Conditions Symbol VIN VSW TOPT Parameter VIN Supply Voltage Output Voltage Operating Temperature Range 3 to 5.5 VIN to 20 ‐40 to +85 Unit V V ℃ December, 20, 2011 Techcode Semiconductor Limited www.tongchuangwei.com 4 Techcode® DATASHEET TD8201 White LED Step-up Converter Electrical Characteristics The following specifications apply for VIN= VEN =3.6V TA=25 oC, unless specified otherwise. Symbol Parameter Test Conditions VIN Input Voltage TD8201 Min. Typ. 3.0 VFB FB Pin Voltage Driving 4xLED@20mA 94 Isw Ioff Isby Fsw Dmax VEN_H VEN_L SW Pin leakage Current Operating Current（Shutdown） Operating Current（Quiescent） Switching Frequency Maximum Duty Cycle EN Minimum High Level EN Maximum Low Level VEN =0, VSW =20V 0.1 100 1.25 90 RON ILIMIT VOV VIN SW On Resistance SW Current Limit Open Circuit Shutdown Threshold Input Voltage VFB=0.5V VFB=0V 1.0 85 1.5 VOV Rising 3.0 Max. 5.5 Unit V 104 114 mV 1 1 350 1.5 µA µA µA MHz % V V 0.4 1.4 400 20 5.5 Ω mA V V December, 20, 2011 Techcode Semiconductor Limited www.tongchuangwei.com 5 Techcode® White LED Step-up Converter DATASHEET TD8201 Typical Operating Characteristics Efficiency vs Number of LEDs Dimming Control using PWM signal to EN pin VFB VS Temperature Fequency VS Temperature December, 20, 2011 Techcode Semiconductor Limited www.tongchuangwei.com 6 Techcode® White LED Step-up Converter DATASHEET TD8201 Typical Application Circuit OPERATION DESCRIPTION The TD8201 uses a constant frequency, peak current mode boost regulator architecture to regulate the series string of white LEDs. The operation of the TD8201can be understood by referring to the simplified block diagram shown above. At the start of each oscillator cycle, the control logic turns on the power switch M1. The signal at the non‐inverting input of the PWM comparator is proportional to the switch current, summed together with a portion of the oscillator ramp When this signal reaches the level set by the output of error amplifier, the PWM comparator resets the latch in the control logic and turns off the power switch. In this manner, error amplifier sets the correct peak current level to keep the LED current in regulation. If the feedback voltage starts to drop, the output of the error amplifier increases. This results in more current to flow through M1, hence increasing the power delivered to the output. December, 20, 2011 Techcode Semiconductor Limited www.tongchuangwei.com 7 Techcode® DATASHEET TD8201 White LED Step-up Converter Function Description Driving Capability Inductor Selections frequency of the TD8201. A Schottky diode rated at 100mA to 200mA is sufficient for most TD8201 applications. Some recommended Schottky diodes are listed in the following table: PART FORWARD VOLTAGE DROP DIODE NUMBER CURRENT CAPACITAN MANUFACTURER （V） CE （mA） CMDSH‐3 100 0.58@100mA 7.0@10V Central CMDSH2‐3 200 0.49@200mA 15@10v Central BAT54 200 0.53@100mA 10@25v Zetex LED Current Control PARTNUMBER CDRH3D16‐220 0.53 LB2012B220M 1.7 LEM2520‐220 5.5 EJPC220KF 4.0 LQH3C220 DCR（Ω） CURRENT RATING（mA）MANUFACTURER 0.71 350 75 125 160 250 SUMIDA MURATA TAIYO YUDEN PANASONIC TAIYO YUDEN The LED current is controlled by the feedback resistor. The feedback reference is 104mV. The LED current is 104mV/Rfb. In order to have accurate LED current, precision resistors are preferred (1% is recommended). The formula and table for RFB selection are shown below Capacitor Selection The small size of ceramic capacitors makes them ideal for TD8201 applications. X5R and X7R types are recommended because they retain their capacitance over wider voltage and temperature ranges than other types such as Y5V or Z5U. A 1μF input capacitor and a 0.22 μF output capacitor are sufficient for most TD8201 applications. Diodes Selection Schottky diodes, with their low forward voltage drop and fast reverse recovery, are the ideal choices for TD8201 applications. The forward voltage drop of a Schottky diode represents the conduction losses in the diode, while the diode capacitance (CT or CD) represents the switching losses. For diode selection, both forward voltage drop and diode capacitance need to be considered. Schottky diodes with higher current ratings usually have lower forward voltage drop and larger diode capacitance, which can cause significant switching losses at the 1.25MHz switching ILED（mA） RFB Value（Ω） 5 20.8 10 10.4 15 6.93 20 5.1 Open Circuit Protection Open circuit protection will shut off the TD8201 if the output voltage goes too high when the OV pin is tied to the output. In some cases an LED may fail, which will result in the feedback voltage always being zero. The TD8201 will then switch at its maximum duty cycle boosting the output voltage higher and higher. By connecting the OV pin to the top of the LED string the TD8201 checks this condition and if the output ever exceeds 20V, the TD8201 will shut down. The part will not switch again until the power is recycled. December, 20, 2011 Techcode Semiconductor Limited www.tongchuangwei.com 8 Techcode® DATASHEET TD8201 White LED Step-up Converter Function Description(Cont.) Dimming Control There are three different types of dimming control circuits: 1. Using a DC Voltage For some applications, the preferred method of brightness control is a variable DC voltage to adjust the LED current. The dimming control using a DC voltage is shown in Figure 3. As the DC voltage increases, the voltage drop on R2 increases and the voltage drop on R1 decreases. Thus, the LED current decreases. The selection of R2 and R3 will make the current from the variable DC source much smaller than the LED current and much larger than the FB pin bias current. 3. Using a Filtered PWM Signal The filtered PWM signal can be considered as an adjustable DC voltage. It can be used to replace the variable DC voltage source in dimming control. Board Layout Consideration 2. Using a PWM Signal to EN Pin With the PWM signal applied to the EN pin, the TD8201 is turned on or off by the PWM signal. The LEDs operate at either zero or full current. The average LED current increases proportionally with the duty cycle of the PWM signal. A 0% duty cycle corresponds to zero LED current. A 100% duty cycle corresponds to full current. The frequency range of the PWM signal should be up to 100KHz As with all switching regulators, careful attention must be paid to the PCB board layout and component placement. To maximize efficiency, switch rise and fall times are made as short as possible. To prevent electromagnetic interference (EMI) problems, proper layout of the high frequency switching path is essential. The voltage signal of the SW pin has sharp rise and fall edges. Minimize the length and area of all traces connected to the SW pin and always use a ground plane under the switching regulator to minimize interplane coupling. In addition, the ground connection for the feedback resistor R1 should be tied directly to the GND pin and not shared with any other component, ensuring a clean, noise‐free connection. December, 20, 2011 Techcode Semiconductor Limited www.tongchuangwei.com 9 Techcode® DATASHEET TD8201 White LED Step-up Converter Package Information SOT23‐6 December, 20, 2011 Techcode Semiconductor Limited www.tongchuangwei.com 10 Techcode® DATASHEET White LED Step-up Converter TD8201 Design Notes December, 20, 2011 Techcode Semiconductor Limited www.tongchuangwei.com 11