HV9918 1235 bordeaux drive, sunnyvale, ca 94089 t el: 408-222-8888 www .supertex.com features hysteretic control with high-side current sensing integrated 40v 1.0 mosfet >90% ef?ciency wide input voltage range: 4.5 to 40v 5% led current accuracy up to 2.0mhz switching frequency adjustable constant led current analog or pwm control signal for pwm dimming over-temperature protection -40oc to +125oc operating temperature range applications low voltage industrial and architectural lighting general purpose constant current source signage and decorative led lighting indicator and emergency lighting ? ? ? ? ? ? ? ? ? ? ? ? ? ? general description the HV9918 is a pwm controller ic designed to drive high brightness leds using a buck topology. it operates from an input voltage of 4.5 to 40vdc and employs hysteretic control with a high-side current sense resistor to set the constant output current up to 700ma. the device is well suited for applications requiring a wide input voltage range. the high-side current sensing and an integrated current-setting circuitry minimize the number of external components while delivering an accurate average output. dedicated pulse-width modulation (pwm) input enables pulsed led dimming over a wide range of brightness levels. a hysteretic control method ensures excellent input supply rejection and fast response during load transients and pwm dimming. the HV9918 offers an analog-controlled pwm dimming feature that reduces the output current by applying an external dc voltage below the internal 2.0v threshold voltage from adim to gnd. adim can also accept input from a resistor divider including a negative temperature coef?cient (ntc) thermistor connected between adim and gnd, or a positive temperature coef?cient (ptc) thermistor connected between adim and vdd thus providing a pwm thermal-foldback feature that reduces the led current when the temperature of the led string exceeds a speci?ed temperature point. additional features include thermal-shutdown protection. the high switching frequency up to 2.0mhz permits the use of small inductors and capacitors, minimizing space and cost in the overall system. the HV9918 comes in a small 8-lead dfn package and is ideal for industrial and general lighting applications. typical application circuit hysteretic, buck, high brightness led driver with high-side current sensing c in 0 - 2.0v HV9918 r sense l vi n sw vdd gnd ram p adim dim cs
2 HV9918 1235 bordeaux drive, sunnyvale, ca 94089 t el: 408-222-8888 www .supertex.com -g indicates package is rohs compliant (green) absolute maximum ratings stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. these are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the speci?cations is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability . parameter value vin, cs, sw to gnd -0.3 to +45v vdd, ramp, dim, adim to gnd -0.3 to +6.0v cs to vin -1.0 to +0.3v continuous power dissipation, (t a = +25c) 1.6w operating temperature range -40c to +125c junction temperature +150c storage temperature range -65c to +150c sym description min typ max units conditions v in input dc supply voltage range 4.5 - 40 v dc input voltage v dd internally regulated voltage 4.5 - 5.5 v v in = 6.0 to 40v i in supply current - - 1.5 ma sw = gnd i in, sdn shutdown supply current - - 750 a dim < 0.7v i in, lim current limit - 30 - ma v in = 4.5v, v dd = 0v - 8.0 - v in = 4.5v, v dd = 4.0v f sw switchingr frequency - - 2.0 mhz --- uvlo v dd undervoltage lockout threshold - - 4.5 v v dd rising uvlo v dd undervoltage lockout hysteresis - 500 - mv v dd falling ordering information device package options 8-lead dfn 3.00x3.00mm body, 0.80mm height (max), 0.65mm pitch HV9918 HV9918k7-g pin description product marking 8-lead dfn (k7) 8-lead dfn (k7) (top view) electrical characteristics (v in = 12v, v dim = v dd , v ramp = gnd, c vdd = 1.0f, r cs = 0.5, t a = t j = -40 o c to +125 o c* unless otherwise noted) 8 1 2 3 4 7 6 5 cs vin sw ramp adim gnd vdd dim gnd 9 9 1 8 y w l l y = last digit of year sealed w = code for week sealed l = lot number = green packaging thermal resistance package ja 8-lead dfn (k7) 60 o c/w mounted on fr-4 board, 25mm x 25mm x 1.57mm * guaranteed by design and characterization, 100% tested at t a = 25 o c. typical characteristics are given at t a = 25 o c.
3 HV9918 1235 bordeaux drive, sunnyvale, ca 94089 t el: 408-222-8888 www .supertex.com sym description min typ max units conditions sense comparator v rs(hi) sense voltage threshold high 213 - 246 mv (v in - v cs ) rising v rs(lo) sense voltage threshold low 158 - 182 mv (v in - v cs ) falling t dpdl propagation delay to sw off - 70 - ns rising edge of (v in - v cs ) = v rs(hi) +70mv to v sw = 0.9 ? v in t dpdh propagation delay to sw on - 70 - ns falling edge of (v in - v cs ) = v rs(lo) -70mv to v sw = 0.1 ? v in i cs current-sense input current - - 1.0 a (v in - v cs ) = 200mv i cs(hys) current-sense threshold hysteresis - 56 70 mv --- dim input v ih pin dim input high voltage 2.2 - - v --- v il pin dim input low voltage - - 0.7 v --- t on turn-on time - 100 - ns dim rising edge to v sw = 0.9 ? v in t off turn-off time - 100 - ns dim falling edge to v sw = 0.1 ? v in output switch i dc sw continuous current - - 0.7 a --- r on on resistance - 1.0 2.0 --- i leak sw leakage current - 10 - a v in = 40v over-temperature protection t ot over temperature trip limit 128 140 - oc --- ?t hyst temperature hysteresis - 60 - oc --- analog control of pwm dimming f ramp dimming frequency 150 - 260 hz c ramp = 47nf 600 - 1100 c ramp = 10nf v low ramp threshold, low - 0.1 - v --- v high ramp threshold, high 1.8 - 2.1 v --- v os adim offset voltage -35 - 35 mv --- * guaranteed by design and characterization, 100% tested at t a = 25 o c. typical characteristics are given at t a = 25 o c. electrical characteristics (v in = 12v, v dim = v dd , v ramp = gnd, c vdd = 1.0f, r cs = 0.5, t a = t j = -40 o c to +125 o c* unless otherwise noted)
4 HV9918 1235 bordeaux drive, sunnyvale, ca 94089 t el: 408-222-8888 www .supertex.com application information block diagram current sens e co mpar at or uvlo co mpar at or vi n vd d cs ramp adim gn d di m sw HV9918 pw m ra mp 0.1~1.9v - + + - bandgap ref + - regula to r general description the HV9918 is a step-down, constant current, high-bright - ness led (hb led) driver. the device operates from a 4.5 to 40v input voltage range, and includes an internal 40v 1.0 n-channel mosfet. a high-side current sense resistor sets the output current and a dedicated pwm dimming input (dim) allows for a wide range of diming duty ratios. pwm dimming can also be achieved by applying a dc voltage be - tween 0 and 2.0v to the analog dimming input (adim). in this case, the dimming frequency can be programmed using a single capacitor at the ramp pin. the high-side current setting and sensing scheme minimizes the number of ex - ternal components while delivering led current with 5% accuracy using a 1% sense resistor. undervoltage lockout (uvlo) the HV9918 includes a 3.7v under-voltage lockout (uvlo) with 500mv hysteresis. when v in falls below 3.7v, switching of sw is disabled. switching of sw resumes once v in is 4.5v or higher. 5.0v regulator vdd is the output of a 5.0v regulator capable of sourcing 8ma. bypass vdd to gnd with a 1.0f capacitor. dim input the HV9918 allows dimming with a pwm signal at the dim input. a logic level below 0.7v at dim halts sw switching, turning the led current off. to turn the led current back on, the logic level at dim must be at least 2.2v. adim and ramp inputs the pwm dimming scheme can be also implemented by applying an analog control signal to adim pin. if an ana - log control signal of 0 ~ 2.0v is applied to adim, the device compares this analog input to a voltage ramp to pulse-width- modulate the led current. connecting an external capacitor to ramp programs the pwm dimming ramp frequency. f pwm = 10 -5 c ramp dim and adim inputs can be used simultaneously. in such case, f pwm(max) must be selected lower than the frequency of the dimming signal at dim. the smaller dimming duty cycle of adim and dim will determine the gate signal.
5 HV9918 1235 bordeaux drive, sunnyvale, ca 94089 t el: 408-222-8888 www .supertex.com one possible application of the adim feature of the HV9918 may include protection of the led load from over-tempera - ture by connecting an ntc thermistor at adim, as shown in figure 1. figure 1 setting led current with external resistor r sense the output current in the led is determined by the external current sense resistor (r sense ) connected between vin and cs. disregarding the effect of the propagation delays, the sense resistor can be calculated as: r sense 1 ? (v rs(hi) + v rs(lo) ) = 200mv 2 i led i led selecting buck inductor l the HV9918 regulates the led output current using an input comparator with hysteresis (figure 2). as the current through the inductor ramps up and the voltage across the sense re - sistor reaches the upper threshold, the internal mosfet at sw turns off. the mosfet turns on again when the inductor current ramps down through the freewheeling diode until the voltage across the sense resistor equals the lower threshold. use the following equation to determine the inductor value for a desired value of operating frequency f s : l = (v in - v out )v out - (v in - v out )t dpdl - v out t dpdh f s v in ?i o ?i o ?i o where: ?i o = v rs(hi) - v rs(lo) r sense and t dpdl , t dpdh are the propagation delays. note, that the cur - rent ripple ?i in the inductor l is greater than ?i o . this ripple can be calculated from the following equation: ?i = ?i o + (v in - v out )t dpdl + v out t dpdh l l for the purpose of the proper inductor selection, note that the maximum switching frequency occurs at the highest v in and v out = v in /2. figure 2 t t i led v di m v rs(hi ) r sense v rs(lo) r sense t dpdl t dpdh t s = 1 f s i i o nt c vd d adim gn d HV9918
6 HV9918 1235 bordeaux drive, sunnyvale, ca 94089 t el: 408-222-8888 www .supertex.com pin # pin description 1 cs current sense input. senses led string current. 2 vin input voltage 4.5 to 40v dc. 3 ramp analog pwm dimming ramp output. 4 adim analog 0 ~ 2.0v signal input for analog control of pwm dimming. 5 dim pwm signal input. 6 vdd internally regulated supply voltage. connect a capacitor from vdd to ground. 7 gnd device ground. 8 sw open drain output of an internal 40v 1.0 mosfet. tab gnd must be wired to pin 7 on pcb. pin description thermal shutdown the HV9918 thermal-shutdown feature turns off the sw driv - er when the junction temperature exceeds +140c. the sw driver turns back on when the junction temperature drops 60c below the shutdown temperature threshold. freewheeling diode selection the forward voltage of the freewheeling diode should be as low as possible for better ef?ciency. a schottky diode is a good choice as long as the breakdown voltage is high enough to withstand the maximum operating voltage. the forward current rating of the diode must be at least equal to the maximum led current. led current ripple the led current ripple is equal to the inductor current ripple. in cases when a lower led current ripple is needed, a ca - pacitor can be placed across the led terminals. pcb layout guidelines careful pcb layout is critical to achieve low switching losses and stable operation. use a multilayer board whenever pos - sible for better noise immunity. minimize ground noise by connecting high-current ground returns, the input bypass capacitor ground lead, and the output ?lter ground lead to a single point (star ground con?guration). the fast di/dt loop is formed by the input capacitor c in , the free-wheeling diode and the HV9918 switching mosfet. to minimize noise inter - action, this loop area should be as small as possible. place r sense as close as possible to the input ?lter and vin. for better noise immunity, a kelvin connection is strongly recom - mended between cs and r sense . connect the exposed tab of the ic to a large-area ground plane for improved power dissipation.
supertex inc. does not recommend the use of its products in life support applications, and will not knowingly sell them for use in such appl ications unless it receives an adequate product liability indemnification insurance agreement. supertex inc. does not assume responsibility for use of devices described, and limits its liabilit y to the replacement of the devices determined defective due to workmanship. no responsibility is assumed for possible omissions and inaccuracies. circuitry an d specifications are subject to change without notice. for the latest product specifications refer to the supertex inc . (website: http//ww w. supertex.com ) ?2009 supertex inc. all rights reserved. unauthorized use or reproduction is prohibited. supertex inc. 1235 bordeaux drive, sunnyvale, ca 94089 te l: 408-222-8888 www .supertex.com 7 (the package drawing(s) in this data sheet may not re?ect the most current speci?cations. for the latest package outline information go to http://www.supertex.com/packaging.htm l .) HV9918 doc.# dsfp-HV9918 a122109 8-lead dfn package outline (k7) 3.00x3.00mm body, 0.80mm height (max), 0.65mm pitch symbol a a1 a3 b d d2 e e2 e l l1 dimension (mm) min 0.70 0.00 0.20 ref 0.25 2.85* 1.60 2.85* 1.35 0.65 bsc 0.30 0.00* 0 o nom 0.75 0.02 0.30 3.00 - 3.00 - 0.40 - - max 0.80 0.05 0.35 3.15* 2.50 3.15* 1.75 0.50 0.15 14 o jedec registration mo-229, variation weec-2, issue c, aug. 2003. * this dimension is not speci?ed in the jedec drawing. drawings not to scale. supertex doc. #: dspd-8dfnk73x3p065, version c041009. seating plane to p v iew side v iew bottom v iew a a1 d e d2 e b e2 a3 l l1 vi ew b vi ew b note 1 (index area d/2 x e/2) note 3 note 2 note 1 (index area d/2 x e/2) 1 1 8 8 notes: a pin 1 identi?er must be located in the index area indicated. the pin 1 identi?er can be: a molded mark/identi?er; an embedded metal marker; or a printed indicator. depending on the method of manufacturing, a maximum of 0.15mm pullback (l1) may be present. the inner tip of the lead may be either rounded or square. 1. 2. 3.
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