ts 1937 1 boost (step - up) wled driver with ovp 1 / 8 version: h14 sot - 2 6 general description the ts1937 1 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 c apacitor can be as small as 4.7 f, saving space versus alternative solutions. a low 95mv feedback voltage minimizes power loss for better efficiency. additional feature inclu de 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 inherently matched led current high efficienc y: 89 % t ypical drives up to 9 leds series @ vin 9~15v drives up to 126 leds (9s14p) @ vin 12~15v drives up to 6 (1w) leds series @ vin 12v over output voltage protection 30v (sot - 26) fast 1.2mhz switching frequency requires only 4.7 f output capacitor pwm d immin g c ontrol 1 k hz to 1 0 k hz analog d imming c ontrol ordering information part no. package packing ts 1937 1 cx6 rf sot - 2 6 3 k pcs / 7 reel ts 1937 1 cx6 rf g sot - 2 6 3 k pcs / 7 reel note: g denotes for halogen - and antimony - free as those which contain <900ppm brom ine, <900ppm chlorine (<1500ppm total br + cl) and <1000ppm antimony compounds . application cellular phones portable electronics devices pda, gps lcd display module white led backlightin g mr - 16 lighting input voltage vs. efficiency typical applicatio n circuit pin definition : 1. sw 6. vin 2. g nd 5. ovp 3. f b 4. ctrl
ts 1937 1 boost (step - up) wled driver with ovp 2 / 8 version: h14 absolute maximum rating (note 1) parameter symbol limit unit input voltage v in 20 v supply voltage (recommended) v in 2. 5 ~ 18 v fb voltage v fb 10 v sw voltage v sw 3 6 v ctrl voltage v ctrl 10 v ambient temperature range t a - 40 to +85 o c junction temperature range t j - 40 to +125 o c electrical specifications ( t c = 25 o c , v in = v ctrl =3v, c in =1uf, c out = 0.22 f unless otherwise noted ) parameter symbol test conditions min typ max units input voltage range v in 2. 5 -- 18 v feedback voltage v fb i sw = 18 0ma, v in =5v 80 95 1 10 mv fb pin bias current i b 10 45 100 n a supply current i q -- 2.1 3.0 ma ctrl= 0v -- 0 . 1 1 .0 a switching frequency f rsw 0.8 1.2 1.6 m hz switch current limit i cl -- 650 -- ma maximum duty cycle d tmx 85 90 -- % switch v cesat v sat at i sw = 2 5 0ma -- 350 -- mv switch leakage current i lkg v sw = 5 v -- 0.01 5 a voltage enable control v ctl h igh 1. 5 -- -- v low -- -- 0. 4 v ctrl pin bias current i ctl ctrl =2v -- 65 -- a over voltage protection ovp -- 30 -- v thermal information ( note 2 ) parameter symbol test conditions min typ max units thermal resistance - junction to ambient r ? -- 220 -- c/w 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, t j (max), the junction to ambient thermal resistance, r ja , and the ambient temperature. the maximum allowable, power dissipation at any ambient temperature is calculated using: pd(max) = [t j (max) - t a ]/ r ja . exceeding the maximum allowable power dissipation will cause excessive die temperature. all limits at temperat ure extremes are guaranteed via correlation using standard statistical methods .
ts 1937 1 boost (step - up) wled driver with ovp 3 / 8 version: h14 functional block pin description pin function description 1 sw switching pin. this is the collector of the internal npn power switch. connect 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. 3 fb feedb ack pin. reference voltage is 95 mv. connect leds and a resistor at this pin. led current is determined by the resis tance and ctrl voltage. 4 ctrl shutdown pin and dimming control pin. 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 o ver voltage protection, 30v . 6 vin input supply pin. bypass this pin with a capacitor as close to the device as possible .
ts 1937 1 boost (step - up) wled driver with ovp 4 / 8 version: h14 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 sim ply 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 amplifiers 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 ts1937 1 . the typical switch current is limited to about 650 ma b y the chip . o ver voltage protection the ts 1937 1 has design an i nternal latched off open - circuit protection circuit , the additional sense pin to detect the voltage w hen the leds are disconnected from the circuit or fail open, the ts 1937 1 will shutdown unti l input condition changes to bring it out of the shutdown mode. inductor selection a 10uh inductor is recommended for most ts 19371 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 l osses 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 vo ltage 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 cer amic capacitors makes them ideal for ts 1937 1 applications. x5r and x7r types are recommended because they retain their capacitance over wider voltage and temperature ranges than oth er types such as y5v or z5u. a 4.7f input capacitor and a 4.7 f output ca p acitor are sufficient for most TS19371 applications . led current control the led current is controlled by the feedback resistor (r1). the feedback reference is 95 mv. the led current is 95mv/r1 . the formula and table 3 for r1 selection are shown below. r1=9 5mv/i led i led (m a) r1(?) 19.1 10 9.53 12 7.87 15 6.34 20 4.75
ts 1937 1 boost (step - up) wled driver with ovp 5 / 8 version: h14 application information (continue) typical application circuit reference design informatio n vin range (v) v led (v) l ( h) led (series) led (parallel ) current ( series/ ma) resistor () efficiency ( %) 5 19.8 22 6pcs 14 20 4.75 81.2 9 29.7 33 9 pcs 1 4 20 4.75 8 3.6 12 29.7 47 9 pcs 14 20 4.75 87.2 15 29.7 68 9 pcs 14 20 4.75 88.4 typical application circuit for 1w x 6pcs led s reference design informatio n vin range (v) v led . (v) l ( h) 1w led (s eries) current (ma) resistor () efficiency (%) 12~1 5 19.8 68 6pcs 350 0.22 88
ts 1937 1 boost (step - up) wled driver with ovp 6 / 8 version: h14 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 app lied to the shdn pin, the ts 1937 1 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 ts 1937 1 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, t he 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 decrease s. 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 figu re 4 gives dimming control of led current from 0ma to 20 ma. dimming control using a dc voltage 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 so urce in dimming control. the circuit is shown as follow: 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. v dc (v) v fb i out (ma) 2 0 0 1.8 2.2 0.43 1.6 9.2 1.8 1.4 19.6 3.6 1.2 31.1 6 1 43.4 8.5 0.8 63 12.3 0.6 74 14.5 0.4 86.4 16.9 0.2 9 6.9 19 0 102 20 duty i out ( 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 ; 1 k hz ; vin=3.6v
ts 1937 1 boost (step - up) wled driver with ovp 7 / 8 version: h14 sot - 26 mechanical drawing marking diagram 7 1 = device code y = year code m = month code ( a =jan, b =feb, c =mar, d =apl, e =may, f =jun, g =jul, h =aug, i =sep, j =oct , k =nov, l =dec) l = lot code 71 = device code y = year code m = month code for halogen free product ( o =jan, p =feb, q =mar, r =apl, s =may, t =jun, u =jul, v =aug, w =sep, x =oct, y =nov, z =dec) l = lot code
ts 1937 1 boost (step - up) wled driver with ovp 8 / 8 version: h14 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 he rein 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 tscs terms and conditions of sale for such products, tsc assumes no liability wh atsoever, 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 intelle ctual 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.
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