sq 9910/SQ9910a universal high brightness led driver features >90% efficiency u niversal rectified 85 to 265 v ac input range constant - current led driver applicat ions from a few ma to more than 1a output led string from one to hundreds of diodes pwm low - f requency dimming via enable pin input voltage surge ratings up to 500v internal thermal protection (otp) 7.5v mosfet drive C SQ9910 1 0v mosfet drive C SQ9910a typical applications dc/dc or ac/dc led driver applicatio n rgb backlighting led driver back lighting of flat panel displays general purpose constant current source signage and decorative led lighting product description the sq 9910 is a pwm high - effi ciency led dr iver control ic. it allows effi cient operation of high brightness (hb) leds from vo ltage sources ranging from 85v ac up to 265v ac . the sq 9910 co ntrols an external mosfet at fi xed switching frequency up to 300khz. the frequency can be programmed using a single resistor. the led string is driven at constant current rather than constant voltage, thus providing constant light output and enhanced reliability. the output current can be programmed between a few milliamps and up to more than 1.0a. the sq 9910 uses a rugged high voltage junction isolated process that can withstand an input voltage surge of up to 50 0v. output current to an led string can be programmed to any value between zero and its maximum value by applying an external control voltage at the linear dimming control input of the sq 9910. the sq 9910 provides a low - fr equency pwm dimming input that can accept an external control signal with a duty ratio of 0 - 100% and a frequency of up to a few kilohertz application circuit
sq 9910/SQ9910a packaging information s q9910 /SQ9910a ms t 8 - pin plastic s. o.i.c. (top view) s q9910 /SQ9910a m 8 - pin plastic dip (top view ) absolute maximum ratings (note 1) v in to gnd - 0.5v to +520v cs - 0.3v to (vdd + 0.3v) ld, pwm_d to gnd - 0.3v to (vdd - 0.3v) gate to gnd - 0.3v to (vdd + 0.3v) v dd ( max ) 13.5v continuous power dissipation (ta = 25 ? c) (note 1) 8 pin dip (derate 9mw/ ? c above +25 ? c 900mw 8 pin so (derate 6.3mw/ ? c above +25 ? c 630mw operating temperature range - 40 ? c to +85 ? c junction temperature range +125 ? c storage temperature range - 65 c to 150 c note: exceeding these ratings could cause damage to the device. all voltages are with respect to ground . currents are positive into, negative out of the specified termina l v in cs gnd gate pwm_d v dd ld. r osc vin cs gnd. gate pwm_d v dd ld r osc
sq 9910/SQ9910a electrical characteristics (over recommended operating conditions unless otherwise specifi ed - t a = 25c) parameter symbol min typ max units conditions input dc supply voltage range v indc 15.0 500 v dc input voltage shut - down mode supply current i insd 1 - 0.5 1 ma pin pwm_d to gnd , v in = 8v i insd 2 0.65 1.2 internally regulated voltage v dd 1 7.0 7.5 8.0 v v in = 15 - 500v, l dd(ext) =0, pin gate open v dd 2 9.5 10 10.5 maximal pin vdd voltage v ddmax 13.5 v when an external voltage applied to pin vdd v dd current availab le for external circuitry 3 i dd(ext) 1.0 ma v in = 15 - 100v v dd u n der voltage lockout threshold uvlo 6.45 6.7 6.95 v vin rising v dd under voltage lockout hysteresis ? uvlo 500 mv vin falling pin pwm_d input low voltage v en( lo ) 1.0 v v in = 15 - 500v pin pwm_d input high voltage v en(hi) 2.4 v v in = 15 - 500v pin pwm_d pull - down resistance r en 1 50 2 00 2 50 k v en = 5v current sense pull - in threshold voltage v cs(hi) 2 25 250 275 mv @ta = - 40c to +85c gate high output voltage v gate(hi) v dd - 0.3 v dd v i out = 10ma gate low output voltage v gate( lo ) 0 0.3 v i out = - 10ma oscillator frequency f osc 20 25 30 khz r osc = 1.00m 80 100 120 r osc = 226k maximum oscillato r pwm duty cycle d maxhf 100 % f pwmhf = 25khz, at gate, cs to gnd. linear dimming pin voltage range v ld 0 - 250 mv @t a = <85c, v in = 12v current sense blanking interval t blank 150 215 280 ns v cs = 0.55v ld , v ld = v dd delay from cs trip to gate lo t dela y 300 ns vin = 20v, v ld = 0.15, v cs = 0 to 0.22v after t blank gate output rise time t rise 30 50 ns c gate = 500pf gate output fall time t fall 30 50 ns c gate = 500pf thermal shut down t sd 150 ? c 1 for SQ9910 2 for SQ9910a 3 also limited by package power dissipation limit, whichever is lower.
sq 9910/SQ9910a pin out pin no. pin name function 1 v in input voltage 2 cs senses led string current 3 gnd device ground 4 gate drives the gate of the external mosfet 5 pwm_d low frequency pwm dimming pin, also enab l e input. internal 100k pull - down to gnd 6 v dd internally regulated supply voltage. 7.5v nominal for SQ9910 and 10v nominal for SQ9910a . can supply up to 1 ma for external circuitry. a sufficient storage capacitor is used to provide storage when the recti fied ac input is near the zero crossings 7 ld linear dimming by changing the current limit threshold at current sense comparator 8 r osc oscillator control. a resistor connected between this pin and ground sets the pwm frequency. block diagram & typic al applications otp: over temperature protection at 12 5
sq 9910/SQ9910a application information ac/dc off - line applications the SQ9910 is a low - cost off - line buck or boost converter co ntrol ic specifi cally designed for driving multi - led stings or arrays. it can be operated from either universal ac line or any dc voltag e between 8 - 450v. optionally, a passive power factor correction circuit can be used in order to pass the ac harmonic limits set by en 61000 - 3 - 2 class c for lighting equipment having input power less than 25w. the SQ9910 can drive up to hundreds of high - bri ghtness (hb) leds or multiple strings of hb leds. the led arrays can be confi gured as a series or series/parallel connection. the SQ9910 regulates constant current that ensures controlled brightness and spectrum of the leds, and extends their lifetime. th e SQ9910 features an enable pin (pwm_d) that allows pwm control of brightness. the SQ9910 can also control brightness of leds by programming continuous output current of the led driver (so - called linear dimming) when a control voltage is applied to the ld pin. the SQ9910 is offered in a standard 8 - pin soic package. it is also available in a high voltage rated so - 16 package for applications that require v in greater than 250v. the SQ9910 includes an internal high - voltage linear regulator that powers all in ternal circuits and can also serve as a bias supply for low voltage external circuitry. led driver operation the SQ9910 can control all basic types of converters, isolated or non - isolated, operating in continuous or discontinuous conduction mode. when th e gate signal enhances the external power mosfet, the led driver stores the input energy in an inductor or in the primary inductance of a transformer and, depending on the converter type, may partially deliver the energy directly to leds the energy stored in the magnetic component is further delivered to the output during the off - cycle of the power mosfet producing current through the string of leds (flyback mode of operation). when the voltage at the v dd pin exceeds the uvlo threshold the gate drive is en abled. the output current is controlled by means of limiting peak current in the external power mosfet. a current sense resistor is connected in series with the source terminal of the mosfet. the voltage from the sense resistor is applied to the cs pin of the SQ9910 . when the voltage at cs pin exceeds a peak current sense voltage threshold, the gate drive signal terminates, and the power mosfet turns off. the threshold is internally set to 250mv, or it can be programmed externally by applying voltage to the ld pin. therefore, assuring that output current of the led ramps gradually . when soft start is required, a capacitor can be connected to the ld pin to allow this voltage to ramp at a desired rate . additionally , a simple passive power factor correction circuit, consisting of 3 diodes and 2 capacitors, can be added as shown in the typical application circuit diagram of figure 1 . supply current a current of 1ma is needed to start the SQ9910 . as shown in the block diagram on page 3, this current is intern ally generated in the SQ9910 without using bulky startup resistors typically required in the offl ine applications. moreover, in many applications the SQ9910 can be continuously powered using its internal linear regulator that provides a regulated voltage of 7.5v for all internal circuits . setting light output when the buck converter topology of figure 2 is selected, the peak cs voltage is a good representation of the average current in the led. however, there is a certain error associated with this curre nt sensing method that needs to be accounted for. this error is introduced by the difference between the peak and the average current in the inductor. for example if the peak - to - peak ripple current in the inductor is 150ma, to get a 500ma led current, the sense resistor should be 250mv/(500ma+ 0.5*150ma) = 0.43? . dimming dimming can be accomplished in two ways, separately or combined, depending on the application. light output of the led can be controlled either by linear change of its current, or by swit ching the current on and off while maintaining it constant. the second dimming method (so - called pwm dimming) controls the led brightness by varying the duty ratio of the output current. the linear dimming can be implemented by applying a control voltage from 0 to 250mv to the ld pin. this control voltage overrides the internally set 250mv threshold level of the cs pin and programs the output current accordingly. for example, a potentiometer connected between v dd and ground can program the control voltage at the cs pin. applying a control voltage higher than 250mv will not change the output current setting. when higher current is desired, select a smaller sense resistor.
sq 9910/SQ9910a the pwm dimming scheme can be implemented by applying an external pwm signal to the p wm_d pin . the pwm signal can be generated by a microcontroller or a pulse generator with a duty cycle proportional to the amount of desired light output. this signal enables and disables the converter modulating the led current in the pwm fashion. in this mode, led current can be in one of the two states : zero or the no minal current set by the current sense resistor . it is not possible to use this method to achieve average brightness levels higher than the one set by the current sense threshold level of th e SQ9910. by using the pwm control method of the SQ9910, the light output can be adjusted between zero and 100%. the accuracy of the pwm dimming method is limited only by the minimum gate pulse width, which is a fraction of a percentage of the low frequenc y duty cycle. pwm dimming of the led light can be achieved by turning on and off the converter with low frequency 50hz to 1000hz ttl logic level signal. programming operating frequency the operating frequency of the oscillator is programmed between 25 an d 300khz using an external resistor connected to the r t pin: equation: f osc = 25000/(r t [k?] + 22) [khz] be noted, r osc shall be 820k~1m for the case of v out 7v because it has to satisfy the condition of t on t blank . the efficiency can be improved as well. power factor correction when the input power to the led driver does not exceed 25w , a simple passive power factor correction circuit can be added to the SQ9910 typical application circuit on page 7 in order to pass the ac line harmonic limits of the en61000 - 3 - 2 standard for class c equipment. the typical application circuit diagram show s how this can be done without affecting the rest of the circuit signifi cantly. a simple circuit consisting of 3 diodes and 2 capacitors is added across the rectified ac line input to improve the line current harmonic distortion and to achieve a power fac tor greater than 0.85. inductor design t he buck circuit is usually selected and it has two operation modes: continuous and discontinuous conduction modes . a buck power stage can be designed to operate in continuous mode for load current above a certain l evel usually 15% to 30% of full load. usually, the input voltage range, the output voltage and load current are defined by the power stage specification. this leaves the inductor value as the only design parameter to maintain continuous conduction mode. the minimum value of inductor to maintain continuous conduction mode can be determined by the following example. referring to the typical buck application circuit on fig. 1 the value can be calculated from the desired peak - to - peak led ripple current in t he inductor. typically, such ripple current is selected to be 30% of the nominal led current. in the example given here, the nominal current i led is 350ma the next step is determining the total voltage drop across the led string. for example, when the stri ng consists of 10 high - brightness leds and each diode has a forward voltage drop of 3.0v at its nominal current; the total led voltage v leds is 30v equation assuming the nominal rectified input voltage v in = 120v*1.41 = 169v, the switching duty r atio can be determined, as: d = v leds /v in = 30/169 = 0.177 then, given the switching frequency, in this example f osc = 50khz, the required on - time of the mosfet transistor can be calculated: t on = d/f osc = 3.5 microsecond the required value of the ind uctor is given by: l = (v in - v leds ) * t on /(0.3 * i led ) = 4.6mh input bulk capacitor an input filter capacitor should be designed to hold the rectified ac voltage above twice the led string voltage throughout the ac line cycle. assuming 15% relative vo ltage ripple across the capacitor, a simplified formula for the minimum value of the bulk input capacitor is given by: ? osc f 22 25000 ? osc r ? d in vf leds v v ) ( ? on t osc f d ? l led on vf leds in i t v v ? ? ? 3 . 0 ) ( ) ( ? sense r )) 2 . 0 ( 5 . 0 ( 25 . 0 ? ? ? led led i i
sq 9910/SQ9910a equation : where : capacity charge work period, generally about 0.2~0.25 : input frequency for full range ( 85~265 ) should be set 10~15 of a nd c min = i led *v leds *0.06/v in ^2 c min = 22 f, a value 22f/250v can be used a passive pfc circuit at the input requires using two series connected capacitors at the place of calculated c min . each of these identical capacitors should b e rated for ? of the input voltage and have twice as much capacitance enable the SQ9910 can be turned off by pulling the pwm_d pin to ground. when disabled, the SQ9910 draws quiescent current of less than 1ma . output open circuit protection when the b uck topology is used, and the led is connected in series with the inductor, there is no need for any protection against an open circuit condition in the led string. open led connection means no switching and can be continuous. dc/dc low voltage applicatio ns buck converter operation SQ9910 is an offline ac - dc solution for led lighting system. due to its simplicity of buck topology when the led string voltage is needed to be lower than the input supply voltage , this solution can be designed to meet various non - isolation application including t - 8, led lamp s the design procedure for a buck led driver outlined in the previous chapters can be applied to the low voltage led drivers as well. however, the designer must keep in mind that the input voltage must be maintained higher than 2 times the forward voltage drop across the leds. this limitation is related to the output current instability that may develop when the SQ9910 buck converter operates at a duty cycle greater than 0.5. this instability reveals its elf as an oscillation of the output current at a sub - harmonic of the switching frequency. b enefiting from s q9910 inherit ed high voltage feature, rectified dc high voltage (vdc = vac x 1.414) can be directly fed into power pin of it to achieve high duty cy cle, which is only limited by vo / vin, to optimize design efficiency. t his solution can easily achiev e above 90% efficiency l. however , if the duty cycle is configured to reach above more than 50%, some instability called sub - harmonics oscillation (sbo) wi ll occur. the best solution is to adopt the so - called constant off - time operation as shown in fig. 2 . t he resistor (r2) is, connected to ground by default, to set operating frequency. we can alternatively connect this resistor to gate of mosfet to force s q9910 to enter constant off time mode which will decrease duty cycle from 50% by increase total period, toff + ton. o ne of the major scenarios which might induce sbo is that when s q9910 is bias ed right after passive pfc stage . t he dc voltage rail, vin, i s halved which will easily increase duty cycle up to more than 50% for general led lighting application, pfc becomes a necessary factor in order to meet the emergent international standard of solid state lighting. the following example as shown in fig. 2 can explain it in more details w here rsense is connected between p in 8, rosc, and p in 4, gate to set s q9910 to operate in fixed - off time mode example : v in - vac 110v with passive pfc v out - consist ing of 1w hb led with nominal v f = 3.3v. vin, after rectified and passing pfc stage, the actual dc rail will become 110v * 1.414 / 2 = 77.7vdc the duty cycle, d = vout / vin, will reach above 50% when voltage drop of led string, as the vout, is more than 77.7 / 2 = 38.8v. another word, if any s tring consisting of 38.8 / 3.3 = 12 leds in a series, sbo will occur. ? in c max _ min _ 2 2 ) 1 ( dc l line ch in v f v d p ? ? ? ? ? ch d in c l f rms v max _ dc v ? min _ 2 line v
sq 9910/SQ9910a figure 1: typical application circuit (without pfc) figure 2: typical application circuit (with p fc)
sq 9910/SQ9910a packaging information so - 8 dip - 8 marking information dip 8 so 8 yy = year, ww = working week SQ9910 yyww yyww SQ9910 (0.356 - 0.508) (0.406 - 0.270) 0.016 - 0.050 d 0.189 - 0.197 (4.800 - 5.004) seating plan 0.014 - 0.020 0.150 - 0.157 (3.810 - 3.988) 0.008 - 0.010 (0.203 - 0.254) 8.0 max 0.053 - 0.059 (1.346 - 1.753) 0.004 - 0.010 0.228 - 0.244 (5.791 - 6.198) 0.050 (1.270) typ 0.300 - 0.320 (7.620 - 8.128) 0.045 +/- 0.015 (1.143 +/- 0.183) 0.250 +/- 0.005 (6.350 +/- 0.127) 0.370 - 0.400 (9.474 - 10.150) 0.06 (1.524) 0.145 - 0.200 (3.683 - 5.080) 0.125 - 0.140 (3.175 - 3.556) 0.108 +/- 0.003 (0.457 +/- 0.076) 0.100 +/- 0.010 (2.540 +/- 0.254) j 0.009 - 0.010 (0.299 - 0.381) 95 +/- 5
sq 9910/SQ9910a s equoia microelectronics corp. (sequoia) reserves the right to make changes to its data sheets and/or products or to disc ontinue any integrated circuit product or service without notice, and advises its customers to obtain the latest version of r elevant information to verify, before placing orders, that the information being relied on is current and complete . any products ar e sold subject to the terms and conditions of sales supplied at the time of order acknowledgement, including those pertaining to warranty, patent infringement and limitation of liability. sequoia warrants performance of its products to the specifications applicable at the time of sales in accordance with sequoia s standard warranty. testing and other quality control techniques are utilized to the extent sequoia deems necessary to support this warranty. specific testing of all parameters of each device is n ot necessarily performed, except those mandated by government requirements. customer acknowledges that sequoia products are not designed, manufactured, intended, authorized, or warranted to be suitable for use in any systems or products intended for use i n connection with life support or other hazardous activities or environments in which the failure of the sequoia products could involve potential risks of death, personal injury, or severe property or environmental damage ( high risk activities ). sequoia hereby disclaims all warranties, and sequoia will have no liabilities to customer or any third party, relating to the use of sequoia s products in connection with any high risk activities.. any support, assistance, recommendation or information that sequ oia may provide to customer (including, without limitation, regarding the design, development or debugging of customer circuit board or other application) is provide as is . sequoia does not make, and hereby disclaims, any warranties regarding any such su pport , including, without limitation, any warranties of merchantability or fitness for a particular purpose, and any warranty that such support will be accurate or error free or that customer circuit board or other application will be operational or functi onal. sequoia will have no liability to customer under any legal theory in connection with customer use of or reliance on such support. copyright ? 2009, sequoia microelectronics corp.
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