ts19370 boost (step-up) wled driver with ovp 1/8 version: d08 sot - 2 6 general description the ts19370 is a step-up dc/dc converter specifical ly designed to drive white leds with a constant cur rent. the device can drive 2 ~ 9 leds in series from a li-ion cell. series connection of the leds provides ident ical led currents resulting in uniform brightness and elimin ating the need for ballast resistors. the output ca pacitor can be as small as 0.22f, saving space versus alternative solutions. a low 95mv feedback voltage minimizes p ower loss for better efficiency. additional feature incl ude over output voltage limiting when leds are disc onnected. the ts19370 switches at a fixed frequency of 1.2mhz , allowing the use of tiny, low profile inductors a nd capacitors to minimize footprint and cost in space consideration applications for cellular phone backl ighting or other hand held equipment. features inherently matched led current high efficiency: 88% typical drives up to 6 leds @ vin 5v drives up to 9 leds @ vin 9~15v over output voltage protection 30v fast 1.2mhz switching frequency requires only 0.22f output capacitor pwm dimming control 1khz to 10khz analog dimming control ordering information part no. package packing ts19370cx6 rf sot-26 3kpcs / 7 reel input voltage vs. efficiency application cellular phones portable electronics devices pda, gps lcd display module white led backlighting typical application circuit pin definition : 1. sw 6. input 2. ground 5. ovp 3. feedback 4. ctrl
ts19370 boost (step-up) wled driver with ovp 2/8 version: d08 absolute maximum rating 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 36 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 (ta = 25 o c, v in = v ctrl =3v, c in =1uf, c out =0.22uf unless otherwise noted) function parameter symbol test conditions min typ m ax units input voltage range v in 2.5 -- 18 v feedback voltage v fb i sw =100ma, 66% duty cycle 86 95 104 mv fb pin bias current i b 10 45 100 na supply current i q -- 1.9 2.5 ma ctrl = 0v -- 0.1 1.0 ua switching frequency f rsw 0.8 1.2 1.6 mhz switch current limit i cl -- 320 -- ma maximum duty cycle d tmx 85 90 -- % switch v cesat v sat at i sw = 250ma -- 350 -- mv switch leakage current i lkg v sw = 5v -- 0.01 5 a v ctrl v ctl high 1.5 -- -- v low -- -- 0.4 v ctrl pin bias current i ctl ctrl = 2v -- 65 -- a over voltage protection ovp -- 30 -- v thermal resistance ja -- 220 -- c/w note: absolute maximum ratings are limits beyond which da mage to the device may occur. the maximum allowable power dissipation is a functi on of maximum function temperature, tj(max), the ju nction to ambient thermal resistance, ja , and the ambient temperature. the maximum allow able, power dissipation at any ambient temperature is calculated using: pd(max)= [ tj(max)-ta]/ ja . exceeding the maximum allowable power dissipation will cause excessive die temperature. a ll limits at temperature extremes are guaranteed vi a correlation using standard statistical methods
ts19370 boost (step-up) wled driver with ovp 3/8 version: d08 functional block pin description pin function description 1 sw switching pin. this is the collector of the interna l npn power switch. connect to inductor and diode. minimize the metal trace area c onnected to this pin to reduce emi. 2 ground ground pin. connect directly to local grou nd plane. 3 feedback feedback pin. reference voltage is 95mv. connect le ds and a resistor at this pin. led current is determined by the resistance an d 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 over voltage protection, 30v 6 input input supply pin. bypass this pin with a capacitor as close to the device as possible
ts19370 boost (step-up) wled driver with ovp 4/8 version: d08 application information operation the ts19370 uses a constant frequency, current mode control scheme to provide excellent line and load regulation. operation can be best understood by ref erring to the block diagram. at the start of each o scillator cycle, the rs latch is set, which turns on the power switc h 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. whe n this voltage exceeds the level at the negative input of a2, the rs latch is reset turning off the power swi tch. the level at the negative input of a2 is set by the error amplif ier a1, and is simply an amplified version of the d ifference between the feedback voltage and the reference volt age of 95mv. in this manner, the error amplifier se ts the correct peak current level to keep the output in re gulation. if the error amplifiers output increases , more current is delivered to the output; if it decreases, less curr ent is delivered. minimum output current the ts19370 can regulate three series leds connecte d at low output currents, down to approximately 4ma from a 4.2v supply, without pulse skipping, using the same external components as specified for 20ma operatio n. as the current is further reduced, the device will begin s kipping pulses. this will result in some low freque ncy ripple, although the led current remains regulated on an av erage basis down to zero. soft start and current limit the internal soft start circuit minimizes the inrus h current during turning on ts19370. the typical sw itch current is limited to about 320ma by the chip. over voltage protection the ts19370 has design an internal latched off open -circuit protection circuit, the additional sense p in to detect the voltage when the leds are disconnected from the cir cuit or fail open, the ts19370 will shutdown until input condition changes to bring it out of the shutdown m ode. inductor selection a 22h inductor is recommended for most ts19370 app lications. 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 to maintain high efficiency, the average current ra ting of the schottky diode should be large than the peak inductor current, ipk. schottky diode with a low forward dro p and fast switching speeds are ideal for increase efficiency in portable application. choose a reverse breakdown of the schottky diode large than the output voltage. a schottky diode rated at 100ma to 200ma is sufficient for mos t ts19370 applications. capacitor selection the small size of ceramic capacitors makes them ide al for ts19370 applications. x5r and x7r types are recommended because they retain their capacitance o ver wider voltage and temperature ranges than other types such as y5v or z5u. a 1f input capacitor and a 0.2 2f output capacitor are sufficient for most.
ts19370 boost (step-up) wled driver with ovp 5/8 version: d08 application information (continue) led current control the led current is controlled by the feedback resis tor (r1). the feedback reference is 95mv. the led c urrent is 95mv/r1. in order to have accurate led current, pre cision resistors are preferred (1% is recommended). the formula and table 3 for r1 selection are shown belo w. r1 = 95mv/iled iled (ma) r1( ) 5 19.1 10 9.53 12 7.87 15 6.34 20 4.75 led dimming control there are some different types of dimming control c ircuits: 1. using a pwm signal to shdn pin with the pwm signal applied to the shdn pin, the ts 19370 is turned on or off by the pwm signal. the le ds 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 ts193 70 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 th an the minimum shdn voltage high. for some applications, the preferred method of brig htness control is a variable dc voltage to adjust t he led current. the dimming control using a dc voltage is shown in figure 4. as the dc voltage increases, the voltage drop on r2 increases and the voltage drop on r1 dec reases. thus, the led current decreases. the select ion of r2 and r3 will make the current from the variable d c 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 give s dimming control of led current from 0ma to 20ma. dimming control using a dc voltage vdc(v) vfb iout(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 96.9 19 0 102 20
ts19370 boost (step-up) wled driver with ovp 6/8 version: d08 application information (continue) 2. using a filtered pwm signal the filtered pwm signal can be considered as an adj ustable dc voltage. it can be used to replace the v ariable dc voltage source in dimming control. the circuit i s shown as follow: dimming control using a filtered pwm signa l 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
ts19370 boost (step-up) wled driver with ovp 7/8 version: d08 sot-26 mechanical drawing marking diagram 70 = device code y = ye ar 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 sot-26 dimension dim millimeters inches min typ max min typ max a 0.95 bsc 0.0374 bsc a1 1.9 bsc 0.0748 bsc b 2.60 2.80 3.00 0.1024 0.1102 0.1181 c 1.40 1.50 1.70 0.0551 0.0591 0.0669 d 2.80 2.90 3.10 0.1101 0.1142 0.1220 e 1.00 1.10 1.20 0.0394 0.0433 0.0472 f 0.00 -- 0.10 0.00 0.0039 g 0.35 0.40 0.50 0.0138 0.0157 0.0197 h 0.10 0.15 0.20 0.0039 0.0059 0.0079 i 0.30 -- 0.60 0.0118 -- 0.0236 j 5o -- 10o 5o -- 10o
ts19370 boost (step-up) wled driver with ovp 8/8 version: d08 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 erro rs 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 tscs terms and co nditions of sale for such products, tsc assumes no liability wh atsoever, and disclaims any express or implied warr anty, relating to sale and/or use of tsc products includi ng liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent, cop yright, or other intellectual property right. the products shown herein are not designed for use in medical, life-saving, or life-sustaining applica tions. customers using or selling these products for use i n such applications do so at their own risk and agr ee to fully indemnify tsc for any damages resulting from such i mproper use or sale.
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