TS19371 Boost (Step-up) WLED Driver with OVP SOT-26 Pin Definition: 1. SW 6. VIN 2. GND 5. OVP 3. FB 4. CTRL General Description The TS19371 is a step-up DC/DC converter specifically designed to drive white LEDs with a constant current. The device can drive up to 126 LEDs (9S14P) from a 12V supply. The output capacitor can be as small as 4.7µF, saving space versus alternative solutions. A low 95mV feedback voltage minimizes power loss for better efficiency. Additional feature include over output voltage limiting when LEDs are disconnected. The TS19371 switches at a fixed frequency of 1.2MHz, allowing the use of tiny, low profile inductors and capacitors to minimize footprint and cost in space consideration applications for cellular phone backlighting or other hand held equipment. Features Ordering Information ● Inherently Matched LED Current ● High Efficiency: 89% Typical ● Drives Up to 9 LEDs Series @ Vin 9~15V ● Drives Up to 126 LEDs (9S14P) @ Vin 12~15V Note: “G” denotes for Halogen- and Antimony-free as those which ● Drives Up to 6 (1W) LEDs Series @ Vin 12V contain <900ppm bromine, <900ppm chlorine (<1500ppm total Br + ● Over Output Voltage Protection 30V (SOT-26) Cl) and <1000ppm antimony compounds. ● Fast 1.2MHz Switching Frequency ● Requires Only 4.7µF Output Capacitor ● PWM Dimming Control 1kHz to 10kHz ● Analog Dimming Control Application ● Cellular Phones ● Portable Electronics Devices PDA, GPS ● LCD Display Module ● White LED Backlighting ● MR-16 Lighting Part No. TS19371CX6 RFG Package Packing SOT-26 3,000pcs / 7” Reel Input Voltage vs. Efficiency Typical Application Circuit Document Number: DS_P0000242 1 Version: I15 TS19371 Boost (Step-up) WLED Driver with OVP Absolute Maximum Rating (Note 1) Parameter Symbol Limit Unit VIN 20 V Supply Voltage (Recommended) VIN 2.5 ~ 18 V FB Voltage VFB 10 V SW Voltage VSW 36 V VCTRL 10 Input Voltage CTRL Voltage Ambient Temperature Range TA Junction Temperature Range TJ V -40 to +85 o -40 to +125 o C C Electrical Specifications (TC = 25oC, VIN= VCTRL=3V, CIN=1uF, COUT=0.22µF unless otherwise noted) Parameter Symbol Input Voltage Range VIN Feedback Voltage VFB FB Pin Bias Current IB Supply Current IQ Test Conditions ISW =180mA, VIN=5V CTRL=0V Min Typ Max Units 2.5 -- 18 V 80 95 110 mV 10 45 100 nA -- 2.1 3.0 mA -- 0.1 1.0 µA Switching Frequency FRSW 0.8 1.2 1.6 MHz Switch Current Limit ICL -- 650 -- mA Maximum Duty Cycle DTMX 85 90 -- % Switch VCESAT VSAT At ISW = 250mA -- 350 -- mV Switch Leakage Current ILKG VSW =5V -- 0.01 5 µA Voltage Enable Control VCTL High 1.5 -- -- V Low -- -- 0.4 V CTRL Pin Bias Current ICTL Ctrl=2V -- 65 -- µA Over Voltage Protection OVP -- 30 -- V Min Typ Max Units -- 220 -- °C/W Thermal Information (Note 2) Parameter Thermal Resistance - Junction to Ambient Symbol Test Conditions RӨJA Note 1: Absolute maximum ratings are limits beyond which damage to the device may occur. Note 2: The maximum allowable power dissipation is a function of maximum function temperature, TJ(max), the junction to ambient thermal resistance, RθJA, and the ambient temperature. The maximum allowable, power dissipation at any ambient temperature is calculated using: PD(MAX)=[TJ(max)-TA]/RθJA . Exceeding the maximum allowable power dissipation will cause excessive die temperature. All limits at temperature extremes are guaranteed via correlation using standard statistical methods. Document Number: DS_P0000242 2 Version: I15 TS19371 Boost (Step-up) WLED Driver with OVP Functional Block Pin Description Pin Function Description Switching Pin. This is the collector of the internal NPN power switch. Connect 1 SW to inductor and diode. Minimize the metal trace area connected to this pin to reduce EMI. 2 Ground Ground Pin. Connect directly to local ground plane. Feedback Pin. Reference voltage is 95mV. Connect LEDs and a resistor at this 3 FB pin. LED current is determined by the resistance and CTRL voltage. Shutdown Pin and Dimming Control Pin. 4 CTRL VCTRL > 1.8V generates full-scale LED current. VCTRL < 0.4V chip is off. Switching from 04V to 2.0V, PWM duty cycle controls the LED current. 5 OVP 6 VIN Over Voltage Protection, 30V. Input Supply Pin. Bypass this pin with a capacitor as close to the device as possible. Document Number: DS_P0000242 3 Version: I15 TS19371 Boost (Step-up) WLED Driver with OVP Application Information Operation The TS19371 uses a constant frequency, current mode control scheme to provide excellent line and load regulation. Operation can be best understood by referring to the block diagram. At the start of each oscillator cycle, the RS latch is set, which turns on the power switch Q1. A voltage proportional to the switch current is added to a stabilizing ramp and the resulting sum is fed into the positive terminal of the PWM comparator A2. When this voltage exceeds the level at the negative input of A2, the RS latch is reset turning off the power switch. The level at the negative input of A2 is set by the error amplifier A1, and is simply an amplified version of the difference between the feedback voltage and the reference voltage of 95mV. In this manner, the error amplifier sets the correct peak current level to keep the output in regulation. If the error amplifier’s output increases, more current is delivered to the output; if it decreases, less current is delivered. Soft Start and Current Limit The internal soft start circuit minimizes the inrush current during turning on TS19371. The Typical switch current is limited to about 650mA by the chip. Over Voltage Protection The TS19371 has design an internal latched off open-circuit protection circuit, the additional sense pin to detect the voltage when the LEDs are disconnected from the circuit or fail open, the TS19371 will shutdown until input condition changes to bring it out of the shutdown mode. Inductor Selection A 10uH inductor is recommended for most TS19371 applications. Although small size and high efficiency are major concerns, the inductor should have low core losses at 1.2MHz and low DCR (copper wire resistance). Diode Selection Schottky diodes, with their low forward voltage drop and fast reverse recovery, are the ideal choices for TS19371 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 1.2MHz switching frequency of the TS19371. A Schottky diode rated at 1000mA is sufficient for most TS19371 applications. Capacitor Selection The small size of ceramic capacitors makes them ideal for TS19371 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 4.7µF input capacitor and a 4.7µF output capacitor are sufficient for most TS19371 applications. LED Current Control The LED current is controlled by the feedback resistor (R1). The feedback reference is 95mV. The LED current is 95mV/R1. The formula and table 3 for R1 selection are shown below. R1=95mV/ILED ILED (mA) R1(Ω) 5 19.1 10 9.53 12 7.87 15 6.34 20 4.75 Document Number: DS_P0000242 4 Version: I15 TS19371 Boost (Step-up) WLED Driver with OVP Application Information (Continue) Typical Application Circuit Reference Design Information VIN Range (V) 5 9 12 15 VLED (V) 19.8 29.7 29.7 29.7 L (µH) 22 33 47 68 LED (Series) 6pcs 9pcs 9pcs 9pcs LED (Parallel) 14 14 14 14 Current (Series/mA) 20 20 20 20 Resistor (Ω) 4.75 4.75 4.75 4.75 Efficiency (%) 81.2 83.6 87.2 88.4 Typical Application Circuit for 1W x 6pcs LEDs Reference Design Information VIN Range (V) VLED. (V) L (µH) 1W LED (Series) Current (mA) Resistor (Ω) Efficiency (%) 12~15 19.8 68 6pcs 350 0.22 88 Document Number: DS_P0000242 5 Version: I15 TS19371 Boost (Step-up) WLED Driver with OVP Application Information (Continue) LED Dimming Control There are some different types of dimming control circuits: 1. Using a PWM Signal to SHDN Pin With the PWM signal applied to the SHDN pin, the TS19371 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 will turn off the TS19371 and corresponds to zero LED current. A 100% duty cycle corresponds to full current. The typical frequency range of the PWM signal is 1kHz to 10kHz. The magnitude of the PWM signal should be higher than the minimum SHDN voltage high. 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 below figure. 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. For VDC range from 0V to 2V, the selection of resistors in Figure 4 gives dimming control of LED current from 0mA to 20mA. VDC(V) 2 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 Dimming Control using a DC Voltage VFB 0 2.2 9.2 19.6 31.1 43.4 63 74 86.4 96.9 102 IOUT(mA) 0 0.43 1.8 3.6 6 8.5 12.3 14.5 16.9 19 20 2. 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. The circuit is shown as follow: Duty IOUT ( mA) 0% 20 20% 17.4 30% 15 40% 12.4 50% 10 60% 8 70% 6.4 80% 4.07 100% 0 PWM : 2V ; 1kHz ; Vin=3.6V Dimming Control using a Filtered PWM Signal 3. Using Control pin for dimming The PWM signal can be considered as TTL signal to control pin to change the power on/off time. Document Number: DS_P0000242 6 Version: I15 TS19371 Boost (Step-up) WLED Driver with OVP SOT-26 Mechanical Drawing Marking Diagram 71 = Device Code Y = Year Code M = Month Code for Halogen Free Product O =Jan P =Feb Q =Mar R =Apr S =May T =Jun U =Jul V =Aug W =Sep X =Oct Y =Nov Z =Dec L = Lot Code Document Number: DS_P0000242 7 Version: I15 TS19371 Boost (Step-up) WLED Driver with OVP Notice Specifications of the products displayed herein are subject to change without notice. TSC or anyone on its behalf, assumes no responsibility or liability for any errors or inaccuracies. Information contained herein is intended to provide a product description only. No license, express or implied, to any intellectual property rights is granted by this document. Except as provided in TSC’s terms and conditions of sale for such products, TSC assumes no liability whatsoever, and disclaims any express or implied warranty, relating to sale and/or use of TSC products including liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright, or other intellectual property right. The products shown herein are not designed for use in medical, life-saving, or life-sustaining applications. Customers using or selling these products for use in such applications do so at their own risk and agree to fully indemnify TSC for any damages resulting from such improper use or sale. Document Number: DS_P0000242 8 Version: I15