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description the a6214 is a single-ic switching regulator that provides constant-current output to drive high-power leds. it integrates a high-side n-channel dmos switch for dc-to-dc step- down (buck) conversion. a true average current is output using a cycle-by-cycle, controlled on-time method. output current is user-selectable by an external current sense resistor. output voltage is automatically adjusted to drive various numbers of leds in a single string. this ensures the optimal system efficiency. led dimming is accomplished by a direct logic input pulse-width-modulation (pwm) signal at the enable pin. alternatively, an analog dimming input can be used to calibrate the led current, or implement thermal foldback in conjunction with external ntc thermistor. the a6216 has the added capability to generate its own pwm dimming frequency and duty cycle in stand-alone mode. the a6214 is provided in a compact 10-pin narrow soic package (suffix lk). the a6216 is in 16-pin tssop (suffix lp), both with exposed pad for enhanced thermal dissipation. it is lead (pb) free, with 100% matte-tin leadframe plating. a6214-16-ds, rev. 4 features and benefits ? aec-q100 qualified ? supply voltage 4.5 to 55 v ? 2 a maximum output over operating temperature range ? integrated mosfet switch ? able to use either schottky or silicon low-side diode ? t rue average output current control ? internal control loop compensation ? integrated 5 v , 10 ma regulator for driving external load ? pwm dimming via direct logic input down to 0.1% at 200 hz ? standalone internal pwm dimming (a6216) ? analog dimming for brightness calibration and thermal foldback ? low-power shutdown (1 a typical) ? fault flag output (a6216) ? led string open and short protection ? cycle-by-cycle current limit ? undervoltage lockout (uvlo) and thermal shutdown (tsd) ? robust protection against: adjacent pin-to-pin short pin-to-gnd short component open/short faults automotive-grade, constant-current 2 a pwm dimmable buck regulator led driver packages: not to scale a6214 and a6216 figure 1: a6214 (lk package) typical application circuit applications: automotive lighting ? daytime runni ng lights ? front and rear fog lights ? t urn/stop lights ? map light ? dimmable inte rior lights january 21, 2013 a6214: 10-pin soicn (suffix lk) a6216: 16-pin etssop (suffix lp) not to scale led+ gnd v in (4.5 to 55 v) en/pwm c boot r on l1 c2 r sense gnd d1 1 2 3 4 5 10 9 8 7 6 sw boot gnd csh csl vin ton en adim vcc a6214 adim external pwm dimming signal external analog dimming signal c in c led november 1, 2016
2 selection guide part number internal pwm and fault flag package packing A6214KLKTR-T no 10-pin soicn with exposed thermal pad 3000 pieces per 13-in reel a6216klptr-t yes 16-pin tssop with exposed thermal pad 4000 pieces per 13-in reel table of contents features and benefits 1 description 1 applications 1 packages 1 t ypical application circuit (a6214) 1 t ypical application circuit (a6216) 2 selection guide 2 specifications 3 absolute maximum ratings 3 thermal characteristics 3 pinout diagrams and terminal list tables 4 functional block diagrams 5 electrical characteristics 7 characteristic performance 9 functional description 11 application circuit diagrams 18 system failure detection and protection 21 package outline drawings 23 figure 2: a6216 (lp package) typical application circuit led+ gnd v in (4.5 to 55 v) c in en/pwm l1 gnd d1 adim r1* * r1, r2, r3 used in stand-alone mode for internal pwm dimming v cc vcc fault external pwm dimming signal external analog dimming signal 3 4 6 7 5 range boot gnd csh csl full ton en/pwm adim vcc a6216 1 2 8 dr gnd fpwm 14 13 11 10 12 16 15 9 fault sw vin full full = ?high? = 100% duty cycle full = ?low? = dr controls duty cycle range range = ?high? = 0 to 100% duty cycle range = ?low? = 0 to 30% duty cycle r on c bias r2* r3* c boot c led r sense automotive-grade, constant-current 2 a pwm dimmable buck regulator led driver a6214 and a6216 allegro microsystems, llc 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com
3 absolute maximum ratings characteristic symbol notes rating unit supply voltage v in C0.3 to 60 v bootstrap drive voltage v boot C0.3 to v in + 8 v switching v oltage v sw continuous C1.5 to v in + 0.3 v pulsed, t < 20 ns C0.3 to v in + 3 v enable and ton voltage v en , v ton C0.3 to v in + 0.3 v linear regulator terminal v cc C0.3 to 7 v adim pin voltage v adim C0.3 to 7 v current sense voltages v csh , v csl C0.3 to v in + 0.3 v f ault, full, range, and fpwm voltages v fault , v full, v range , v fpwm a6216 only C0.3 to 7 v dr pin voltage v dr a6216 only; dr pin voltage must not be higher than v cc even when device is off (v cc = 0 v) C0.3 to v cc + 0.3 v operating ambient temperature t a k temperature range for automotive C40 to 125 c maximum junction temperature t j (max) 150 c storage temperature t stg C55 to 150 c thermal characteristics*: may require derating at maximum conditions; see application section for optimization characteristic symbol test conditions* value unit package thermal resistance (junction to ambient) r ja a6214 package lk on 4-layer pcb based on jedec standard 35 c/w a6216 package lp on 4-layer pcb based on jedec standard 34 c/w on 2-layer pcb with 3.8 in. 2 of copper area each side 43 c/w package thermal resistance (junction to pad) r jp 2 c/w *additional thermal information available on the allegro ? website. specifications automotive-grade, constant-current 2 a pwm dimmable buck regulator led driver a6214 and a6216 allegro microsystems, llc 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com
4 pinout diagram for a6214 (lk package) terminal list table for a6214 (lk package) number name function 1 vin supply voltage input voltage for ic and buck regulator 2 ton regulator on-time setting resistor terminal. connect a resistor between vin and ton to set the switching frequency. 3 en/pwm logic input for enable and pwm dimming 4 adim analog dimming control voltage input 5 vcc internal ic bias regulator output. connect 1uf mlcc to gnd. can be used to supply up to 10ma for external load. 6 gnd ground terminal 7 csl current sense (lower end) feedback input for led current 8 csh current sense (higher end) feedback input for led current 9 boot dmos gate driver bootstrap terminal 10 sw switched output terminal - pad exposed pad for enhanced thermal dissipation; connect to gnd pinout diagram for a6216 (lp package) vin ton en adim vcc sw boot csh csl gnd pad 1 2 3 4 5 10 9 8 7 6 vin ton en/pwm adim vcc dr gnd full sw boot csh csl gnd fault fpwm range 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 pad terminal list table for a6216 (lp package) number name function 1 vin supply voltage input voltage for ic and buck regulator 2 ton regulator on-time setting resistor terminal. connect a resistor between vin and ton to set the switching frequency 3 en/pwm logic input for enable and pwm dimming 4 adim analog dimming control voltage input 5 vcc internal ic bias regulator output. connect 1uf mlcc to gnd. can be used to supply up to 10ma for external load 6 dr dimming ratio control. in stand-alone mode: connect to resistor divider network from vcc to set the dimming pwm duty cycle 7 gnd ground terminal 8 full selects 100% dimming duty cycle or dr control of duty cycle 9 range selects dr control range, high range gives dr control from 5% to 100%, low range gives dr control from 5% to 33%. 10 fpwm dimming pwm frequency control. in stand-alone mode, connect a resistor to gnd to set the dimming pwm frequency 11 fault open-drain output which is pulled low in case of fault. connect through an external pull-up resistor to the desired logic level. 12 gnd ground terminal 13 csl current sense (lower end) feedback input for led current 14 csh current sense (higher end) feedback input for led current 15 boot dmos gate driver bootstrap terminal 16 sw switched output terminal - pad exposed pad for enhanced thermal dissipation; connect to gnd automotive-grade, constant-current 2 a pwm dimmable buck regulator led driver a6214 and a6216 allegro microsystems, llc 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com
5 functional block diagrams figure 3 : simplifed functional block diagram for a6214 led+ gnd l1 gnd d1 sw boot gnd csh csl v in vcc on-time select duty cycle control ldo enable internal 5 v i led reference adim adim r adj is optional. it can be used to fine-adjust the led current in case the desired value of r sense is not available. a6214 v in (4.5 to 55 v) r adj c led r sense r on c in en/pwm v out v cc vin ton en/pwm v in on-time c bias v ref c boot v out automotive-grade, constant-current 2 a pwm dimmable buck regulator led driver a6214 and a6216 allegro microsystems, llc 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com
6 figure 4 : simplifed functional block diagram for a6216 led+ gnd l1 gnd d1 sw boot gnd csh csl ton vcc vin ldo adim adim fault mode fault fault osc fpwm dr r1 r2 enable r fpwm up to 10 ma external load range full a6216 v cc v in (4.5 to 55 v) c in r on on-time select v out c bias internal 5 v bias v in en/pwm en/pwm v cc internal pwm duty cycle generator (200 hz to 1 khz) v ref (0 to 200 mv) i led reference buck converter duty cycle control on-time led current differential amp gate driver v in c boot v cc r sense r adj c led v out automotive-grade, constant-current 2 a pwm dimmable buck regulator led driver a6214 and a6216 allegro microsystems, llc 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com
7 electrical characteristics: valid at v in = 12 v, v out = 6 v, t a = C40c to 125c, typical values at t a = 25c, unless otherwise noted characteristics symbol test conditions min. typ. max. unit input supply voltage v in 4.5 C 55 v v in undervoltage lockout threshold v uvlo v in increasing C C 4.3 v v in undervoltage lockout hysteresis v uvlo _ hys v in decreasing C 150 300 mv vin pin supply current i in v csh C v csl = 0.5 v, en = v ih , r on = 402 k C 5 C ma vin pin shutdown current i insd en = v il C 1 10 a buck switch current limit threshold i swlim 2.5 3.25 4 a buck switch on-resistance r ds(on) v boot = v in + 4.3 v, t a = 25c, i sw = 0.5 a C 0.25 0.4 boot undervoltage lockout threshold v bootuv v boot to v sw increasing 3.1 3.4 3.7 v boot undervoltage lockout hysteresis v botuvhys v boot to v sw decreasing C 750 C mv switching minimum off-time t offmin v csh C v csl = 0 v C 75 100 ns switching minimum on-time t onmin v csh C v csl = 0.3 v C 75 100 ns selected on-time t on r on = 402 k 800 1000 1200 ns regulation comparator and error amplifier load current sense regulation threshold at 100% 1 v csreg v csh C v csl decreasing, sw turns on, adim tied to vcc 194 200 206 mv output current sense common mode voltage (measured at csl pin) v out v in = 55 v, f sw = 500 khz, i led = 0.5 a 2.65 C 50 v csh input sense current i csh v csh C v csl = 0.2 v C C190 C a csl input sense current i csl v csh C v csl = 0.2 v 50 75 100 a internal linear regulator vcc regulated output v cc 0 ma < i cc < 5 ma, v in > 6 v 4.85 5 5.15 v vcc current limit 2 i vcclim vcc 4.75 v 10 20 C ma vcc dropout voltage v ldo measure v in C v cc . v in = 5 v, i vcc = 9 ma C 0.15 0.35 v enable/pwm input logic high voltage v ih v en increasing 1.8 C C v logic low voltage v il v en decreasing C C 0.4 v en pin pull-down resistance r enpd v en = 5 v C 100 C k maximum pwm dimming off-time t pwml measured while en = low, during dimming control, and internal references are powered-on (exceeding t pwml results in shutdown) 10 17 C ms internal pwm dimming (a6216 only) internal pwm dimming frequency f pwm external r fpwm = 30 k from fpwm pin to gnd 180 200 220 hz full, range pins input low voltage v il C C 0.8 v full, range pins input high voltage v ih 2 C C v internal pwm duty cycle d pwm5(l) vdr driven by resistor divider from vcc, v cc / v dr = 9.72, f pwm = 200 hz, range = low 4.75 5 5.25 % d pwm5(h) vdr driven by resistor divider from vcc, v cc / v dr = 29.2, f pwm = 200 hz, range = high 4.5 5 5.5 % d pwm90(h) vdr driven by resistor divider from vcc, v cc / v dr = 1.62, f pwm = 200 hz, range = high 87 90 93 % continued on the next page automotive-grade, constant-current 2 a pwm dimmable buck regulator led driver a6214 and a6216 allegro microsystems, llc 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com
8 characteristics symbol test conditions min. typ. max. unit analog dimming input input voltage for 100% led current v adimh v csh C v csl = v csreg 2.1 C C v regulation threshold at 50% analog dimming v csreg50 v adim = 1 v C 100 C mv regulaton threshold at 20% analog dimming v csreg20 v adim = 0.4 v 38.4 40 41.4 mv f ault pin (a6216 only) fault pull-down voltage v fault(pd) fault condition asserted, pull-up current = 1 ma C C 0.4 v f ault pin leakage current v fault(lkg) fault condition cleared, pull-up to 5 v C C 1 a timers cool down timer for fault retry t retry C 1 C ms delay timer for reporting led open fault t open C 50 C s thermal shutdown thermal shutdown threshold 3 t sd 150 165 180 c thermal shutdown hysteresis t sdhys C 25 C c 1 in test mode, a ramp signal is applied across csh and csl pins to determine the cs regulation threshold voltage. in actual application, the average cs voltage is regulated at v csreg regardless of ripple voltage. 2 the internal linear regulator is capable of supplying up to 10 ma to external devices. 3 determined by design and characterization. not production tested. electrical characteristics (continued): valid at v in = 12 v, v out = 6 v, t a = C40c to 125c, typical values at t a = 25c, unless otherwise noted automotive-grade, constant-current 2 a pwm dimmable buck regulator led driver a6214 and a6216 allegro microsystems, llc 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com
9 characteristic performance 0 10 20 30 40 50 60 70 80 90 100 0 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2 3.6 4 duty cycle (%) v dr (v) internal pwm duty cycle vs dr pin voltage (v in = 12 v, vout = 6 v, r ton = 300 k , f pwm = 300 hz, t a = 25 o c) measured for range=h target for range=h measured for range=l target for range=l 0% 20% 40% 60% 80% 100% 0 0.4 0.8 1.2 1.6 2 2.4 normalized led current (%) adim voltage (v) normalized led current vs adim voltage (v in = 12 v, v out = 6 v, i led = 1 a, t a = 25c) measured current target figure 5: analog dimming performance C led current can be reduced linearly down to 10% using the adim pin voltage. figure 6: pwm dimming performance C duty cycle down to ~0.1% (1000:1) can be achieved with higher v in or lower inductance. figure 7: internal pwm dimming operation (a6216 only) C duty cycle is controlled by the voltage at dr pin. figure 8: internal pwm dimming frequency (a6216 only) as a function of fpwm resistance 0.001 0.01 0.1 1 0.1 1 10 100 normalize led current pwm duty cycle (%) average led current vs. pwm duty cycle (r ton = 442 k , load = 2 led at 1.5 a, f pwm = 200 hz) v in = 24 v, l = 47 h v in = 12 v, l = 22 h v in = 12 v, l = 47 h ideal 0 200 400 600 800 1000 1200 1400 1600 0 10 20 30 f pwm (hz) r fpwm (k ? ) frequency of internal pwm vs. fpwm resistance (v in = 12 v, v out = 6 v, v dr = 1.7 v, t a = 25c ) calculated measured automotive-grade, constant-current 2 a pwm dimmable buck regulator led driver a6214 and a6216 allegro microsystems, llc 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com
10 characteristic performance (continued) figure 9: startup for pwm dimming operation C r ton = 442 k, l = 22 h, v in = 12 v, output = 2 led at 1.5 a, pwm = 1 khz 50%. note that there is a ~150 s delay for the frst pwm = h pulse, but none for subsequent pulses. figure 10: pwm dimming with on-time of just 10 s C r ton = 442 k, l = 22 h, v in = 12 v, output = 2 led at 1 a. note that the led current takes ~5s to ramp up to its steady-state value. ch1 = v pwm (5 v/div) ch2 = v sw (5 v/div) ch3 = v out (5 v/div) ch4 = i led (500 ma/div) t ime scale= 500 s/div ch1 = v pwm (5 v/div) ch2 = v sw (5 v/div) ch3 = v out (5 v/div) ch4 = i led (500 ma/div) t ime scale= 5 s/div automotive-grade, constant-current 2 a pwm dimmable buck regulator led driver a6214 and a6216 allegro microsystems, llc 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com
11 the a6214 is a buck regulator designed for driving a high-current led string. it utilizes average current mode control to maintain constant led current and consistent brightness. the led current level is easily programmable by selection of an external sense resistor, with a value determined as follows: r sense = v csreg / i led where v csreg = v csh C v csl = 0.2 v typical. if necessary, a resistor can be inserted in series with the csl pin to fine-tune the led current, as shown below: csh csl r adj r sense v csreg + v sense ? i led i csh i csl ? + i csl r adj v csreg = i led r sense + i csl r adj therefore i led = (v csreg ? i csl r adj ) / r sense figure 11: how to fine-tune led current using r adj for example, with a desired led current of 1.4 a, the required r sense = 0.2 v / 1.4 a = 0.143 . but the closest power resistor available is 0.13 . therefore, the difference is r adj i csl = 0.2 v C 1.4 a 0.13 ? = 0.018 v where i csl = 75 a typical r adj = 0.018 v / 75 a = 240 the led current is further modulated by the adim (analog dimming) pin voltage. this feature can be used for led bright- ness calibration, or for thermal foldback protection. see analog dimming section for details. switching frequency the a6214 operates in fixed on-time mode during switching. the on-time (and hence switching frequency) is programmed using an external resistor connected between the vin and ton pins, as given by the following equation: t on = k (r ton + r int ) ( v out / v in ) f sw = 1 / [ k (r ton + r int )] where k = 0.00434, with f sw in mhz, t on in s, and r on and r int (internal resistance, 20 k) in k. 0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 0 100 200 300 400 500 600 700 800 900 1000 f sw (khz) r ton (k ) figure 12: switching frequency vs. ton resistance enable and dimming the ic is activated when a logic high signal is applied to the en (enable) pin. the buck converter ramps up the led current to a target level set by r sense . when the en pin is forced from high to low, the buck converter is turned off, but the ic remains in standby mode for up to 10 ms. if en goes high again within this period, the led current is turned on immediately. active dimming of the led is achieved by sending a pwm (pulse-width modulation) signal to the en pin. the resulting led brightness is proportional to the duty cycle (t on / period) of the pwm signal. a practical range for pwm dim - ming frequency is between 100 hz (period = 10 ms) and 2 khz. if en is low for more than 17 ms, the ic enters shutdown mode to reduce power consumption. the next high signal on en will initialize a full startup sequence, which includes a startup delay of approximately 150 s. this startup delay is not present during pwm operation. the en pin is high-voltage tolerant and can be directly connected to a power supply. however, if en is higher than the v in voltage at any time, a series resistor (1-10 k) is required to limit the cur - rent flowing into the en pin. this series resistor is not necessary if en is driven from a logic input. functional description automotive-grade, constant-current 2 a pwm dimmable buck regulator led driver a6214 and a6216 allegro microsystems, llc 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com
12 pwm dimming ratio the brightness of the led string can be reduced by adjusting the pwm duty cycle at the en pin as follows: dimming ratio = pwm on-time / pwm period for example, by selecting a pwm period of 5 ms (200 hz pwm frequency) and a pwm on-time of 5 s, a dimming ratio of 0.1% can be achieved. this is sometimes referred to as 1000:1 dim- ming. in an actual application, the minimum dimming ratio is deter- mined by various system parameters, including: v in , v out , inductance, led current, switching frequency, and pwm frequency. as a general guideline, the minimum pwm on-time should be kept at 5 s or longer. a shorter pwm on-time is acceptable under more favorable operating conditions, such as higher v in and lower inductance. internal pwm dimming (a6216 only) in addition to external pwm dimming through en pin, the a6216 is able to generate an internal pwm dimming signal in stand-alone mode. frequency of the internal pwm signal can be set by connecting a resistor between fpwm pin and gnd, as given by the following equation: f pwm = c / (r fpwm + r int ) where c = 6400, with f pwm in hz, and r fpwm and r int (internal resistance, 0.5 k) in k. this frequency can be between 200 hz and 1 khz when range is high, or 200 hz and 500 hz when range is low. duty cycle of pwm signal is linearly proportion to the voltage at dr (dim- ming ratio) pin. this is illustrated by the following chart: dr pin voltage (v) 3.43 90% 0% internal pwm duty cycle 5% 0.17 100% 3.08 0 v 30% range = high range = low 0.514 5 ~4 33% figure 13: variation of pwm duty cycle with respect to dr pin voltage it should be noted that the internal pwm duty cycle depends on the ratio between v cc and v dr . the voltages shown in the chart are with v cc = 5 v . for better accuracy, derive the dr pin volt- age using a resistor divider connected between vcc and gnd. a practical range of internal pwm duty cycle when range = high is between 5% (v dr = 0.17 v) and 90% (v dr = 3.08 v). t o improve accuracy at low duty cycles between 5% and 30%, set range to low. if dr pin is above 3.4 v , duty cycle stays at around 99% if range = high, 33% if low. to disable internal pwm generation, tie dr pin to vcc pin. (do not leave dr pin floating or connected to gnd.) the fpwm pin can be either left open, or tied to vcc. note that at any time during stand-alone pwm dimming mode, if en pin goes low, the led is turned off immediately. this is illustrated in figure below. internal pwm external pwm (en pin) led current figure 14: led current when both internal and exter- nal pwm dimming signals are applied analog dimming in addition to pwm dimming, the a6214/16 also provides an analog dimming feature. when v adim is over 2 v , the led cur- rent is at 100% level (as defined by the sense resistor). when v adim is below 2 v , the led current decreases linearly down to 20% at v adim = 0.4 v . this is shown in the following figure: adim pin voltage 2 v 200 mv 6 mv (100%) 0 0.4 v 40 mv 100 mv 1 v v csreg figure 15: adim pin voltage controls sense reference voltage (hence led current) it is possible to pull adim pin below 0.4 v to achieve lower than 20% analog dimming. however, the linearity may suffer if the led ripple current become too large compared to the aver- age current. for example, if the led ripple current is 100 ma, then the average current can only be dimmed down to 100 ma linearly. automotive-grade, constant-current 2 a pwm dimmable buck regulator led driver a6214 and a6216 allegro microsystems, llc 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com
13 adim pin can be used in conjunction with pwm dimming to provide wider led dimming range over 1000:1. in addition, the ic can provide thermal foldback protection by using an external ntc (negative temperature coefficient) thermistor, as shown below: ntc r1 r p r s vcc adim figure 16: using an external ntc thermistor to implement thermal foldback if analog dimming is not required, the adim pin must be con- nected to vcc pin. (do not leave adim pin floating or con- nected to gnd.) output voltage and duty cycle the figure below provides simplified equations for approximat- ing output voltage. the output voltage of a buck converter is approximately given as: v out = v in d C v d (1 C d ) v in d, if v d << v in d = t on / (t on + t off ) where d is the duty cycle, and v d is the forward drop of the diode d1 (typically under 0.5 v for schottky diode). during sw on-time: i ripple = (v in C v out ) / l t on = (v in C v out ) / l t d where d = t on / t. during sw off-time: i ripple = (v out + v d ) / l t off = (v out + v d ) / l t (1 C d) simplified equation for output voltage: v out = v in d C v d (1 C d) if v d << v in , then v out = v in d approximately. more precisely: v out = (v in C i avg r ds(on) ) d C v d (1 C d) C i avg (dcr + r sc ) where dcr is ther internal resistance of inductor and r sc is the sense resistance. v in v out sw gnd mos c in l d i l r sc v sw i l t t v in 0 t on period, t ?v d t off i ripple figure 17 : simplifed waveforms for a buck converter automotive-grade, constant-current 2 a pwm dimmable buck regulator led driver a6214 and a6216 allegro microsystems, llc 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com
14 minimum and maximum output voltages for a given input voltage, the maximum output voltage depends on the switching frequency and minimum t off . for example, if t off (min) = 150 ns and f sw = 2 mhz, then the maximum duty cycle is 80%. so for a 12.5 v input, the maximum output is approximately 10 v (based on the simplified equation of v out = v in d). this means up to 3 leds can be operated in series, assuming v f = 3.2 v or less for each led. the minimum output voltage depends on minimum t on and switching frequency. for example, if the minimum t on = 100 ns and f sw = 1 mhz, then the minimum duty cycle is 10%. that means with v in = 24 v , the theoretical minimum v out is just 2.4 v . however, the internal current sense amplifier is designed to operate down to v out = 2.65 v . therefore the output voltage should not go lower than 2.65 v , or else the current accuracy will suffer. to a lesser degree, the output voltage is also affected by other factors such as led current, on-resistance of the high-side switch, dcr of the inductor, and forward drop of the low-side diode. as a general rule, switching at lower frequencies allows a wider range of v out , and hence more flexible led configurations. 0 2 4 6 8 10 12 14 16 18 20 22 24 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 v out (v) frequency (mhz) v out (max) (v) v out (min) (v) figure 18: minimum and maximum output voltage vs. switching freqency (v in = 24 v, minimum t on and t off of 100 ns) if the required output voltage is lower than that permitted by the minimum t on , the controller will automatically extend the t off , in order to maintain the correct duty cycle. this means that the switching frequency will drop lower when necessary, in order to keep the led current in regulation. if the led string is completely shorted (v out = 0 v), led current regulation will become impossible. the output current will increase until it trips sw overcurrent protection. the ic then shuts down and retries after approximately 1 ms cooldown period. thermal budgeting the a6214 is capable of supplying a 2 a current through its high-side switch. however, depending on the duty cycle, the conduction loss in the high-side switch may cause the package to overheat. therefore care must be taken to ensure the total power loss of package is within budget. for example, if the maximum temperature rise allowed is ? t = 50c at the device case surface, then the maximum power dissipation of the ic is 1.4 w . assum- ing the maximum r ds(on) = 0.4 and a duty cycle of 85%, then the maximum led current is limited to 2 a approximately. at a lower duty cycle, the led current can be higher. fault handling the a6214 is designed to handle the following faults: ? pin-to-ground short ? pin-to-neighboring pin short ? pin open ? external component open or short ? output short to gnd the waveform in the figure below illustrates how the a6214 responds in the case in which the current sense resistor or the csh and csl pins are shorted together. note that the sw pin overcurrent protection is tripped at around 3.5 a, and the part shuts down immediately . the part then goes through startup retry after approximately 1 ms of cooldown period. figure 19: in case of sense resistor short fault C output current rises until it trips sw ocp at ~3.5 a. the ic shuts off and retries after ~1 ms cooldown period. ch1 = v pwm (5 v/div) ch2 = v sw (5 v/div) ch3 = v out (5 v/div) ch4 = i led (1 a/div) t ime scale = 200 s/div automotive-grade, constant-current 2 a pwm dimmable buck regulator led driver a6214 and a6216 allegro microsystems, llc 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com
15 as another example, the waveform in figure below shows the fault case where external diode d1 is missing or open. as led current builds up, a larger-than-normal negative voltage is developed at the sw node during off-time. this voltage trips the missing detection function of the ic. the ic then shuts down immediately, and waits for a cooldown period before retry. figure 20: in case of missing low-side diode C sw voltage fall below C2 v and trips missing-diode fault. fault pin (a6216 only) is pulled low immediate- ly. the ic shuts off and retries after cooldown period. component selections the inductor is often the most critical component in a buck con- verter. follow the procedure below to derive the correct param- eters for the inductor: 1. determine the saturation current of the inductor. this can be done by simply adding 20% to the average led current: i sat i led 1.2. 2. determine the ripple current amplitude (peak-to-peak value). as a general rule, ripple current should be kept between 10% and 30% of the average led current: 0.1 < i ripple(pk-pk) / i led < 0.3. 3. calculate the inductance bas ed on the following equations: l = (v in C v out ) d t / i ripple , and d = (v out + v d ) / ( v in + v d ) , where d is the duty cycle, t is the period 1/ f sw , and v d is the forward voltage drop of the schottky diode d1. output filter capacitor the a6214 is designed to operate in current regulation mode. therefore it does not require a large output capacitor to stabilize the output voltage. this results in lower cost and smaller pcb area. in fact, having a large output capacitor is not recommended. in most applications, however, it is beneficial to add a small filter capacitor (around 0.1 f) across the led string. this cap serves as a filter to eliminate switching spikes seen by the led string. this is very important in reducing emi noises, and may also help in esd testing. additional notes on ripple current ? for consistent switching frequency, it is recommended to choose the inductor and switching frequency to ensure the induc- tor ripple current percentage is at least 10% over normal operat- ing voltage range (ripple current is lowest at lowest v in ). if ripple current is less than 10%, the switching frequency may jitter due to insufficient ripple voltage across csh and csl pins. however, the average led current is still regulated. ? for best accuracy in led current regulation, a low current ripple of less than 20% is required. ? there is no hard limit on the highest ripple current percentage allowed. a 40% ripple current is still acceptable, as long as both the inductor and leds can handle the peak current (average cur- rent 1.2 in this case). however, higher ripple current % affects the accuracy of led current, and limits the minimum current that can be regulated when using adim. ? in general, allowing a higher ripple current percentage enables lower-inductance inductors to be used, which results in smaller size and lower cost. ? if lower ripple current is required for the led string, one solu- tion is to add a small capacitor (such as 1 to 2.2 f) across the led string from led+ to gnd. in this case, the inductor ripple current remains high while the led ripple current is greatly reduced. ? the effectiveness of this filter capacitor depends on many fac- tors, such as: switching frequency, inductors used, pcb layout, led voltage and current, and so forth. ? the addition of this capacitor introduces a longer delay in led current during pwm dimming operation. therefore the accuracy of average led current is reduced at short pwm on-time. ch1 = v fault (5 v/div) ch2 = v sw (5 v/div) ch3 = v out (5 v/div) ch4 = i led (1 a/div) t ime scale = 1 s/div automotive-grade, constant-current 2 a pwm dimmable buck regulator led driver a6214 and a6216 allegro microsystems, llc 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com
16 inductor selection chart the chart in figure below summarizes the relationship between led current, switching frequency, and inductor value. based on this chart: assuming led current = 1 a and l = 22 h, then mini - mum f sw = 0.7 mhz in order to keep the ripple current at 20% or lower . (note: v out = v in / 2 is the worst case for ripple current). if the switching frequency is lower, then a larger inductance must be used to meet the same ripple current requirement. 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 0 0.5 1 1.5 2 switching frequency (mhz) led current (a) l = 10 h l = 15 h l = 22 h l = 33 h l = 47 h figure 21: relation between minimum switching frequen- cy and led current, given different inductance used (v in = 12 v, v out = 6 v, ripple current = 20%) automotive-grade, constant-current 2 a pwm dimmable buck regulator led driver a6214 and a6216 allegro microsystems, llc 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com
17 v in gnd l1 d1 r sense led+ i ripple v in gnd l1 d1 r sense led+ i ripple i ripple without output capacitor: the same inductor ripple current flows through sense resistor and led string. with a small capacitor across led string: ripple current through led string is reducted, while ripple voltage across r sense remains high. figure 22: using an output filter capacitor to reduce ripple current in led string effects of output capacitor on led ripple current automotive-grade, constant-current 2 a pwm dimmable buck regulator led driver a6214 and a6216 allegro microsystems, llc 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com
18 application circuit diagrams figure 23: application circuit example for a6214 (for driving 15 v led at 1.3 a, f sw = 500 khz) led+ gnd v in (20 to 55 v) en/pwm c4 0.1 f r1 442 k l1 47 h 2 a c5 1 f r sense 0.15 gnd d1 60 v 2 a 1 2 3 4 5 10 9 8 7 6 sw boot gnd csh csl vin ton en adim vcc a6214 r adj 71.5 c3 0.1 f 100 v c2 4.7 f 100 v c1 33 f 63 v led string (~15 v) i led = (v csreg ? i csl r adj ) / r sense = (0.2 ? 0.000007 71.5) / 0.15 = 1.3 a suggested components symbol part number manufacturer c1 hhxa630ara330mha0g united chemi-con c2 c3225x7s2a475m200ab tdk c3 cga4j2x7r2a104m125aa tdk l1 cdrh105rnp-470nc sumida d1 10mq060ntrpbf vishay r sense rl1632r-r150-f susumu figure 24: application circuit example for a6216 (with external pwm and thermal foldback) led+ gnd v in (4.5 to 55 v) c in en/pwm gnd v cc vcc fault external pwm dimming signal 3 4 6 7 5 range boot gnd csh csl full ton en/pwm adim vcc a6216 1 2 8 dr gnd fpwm 14 13 11 10 12 16 15 9 fault sw vin r on 442 k c bias 1 f c boot 0.1 f c led 0.1 f r sense 0.2 10 k l1 47 h 2 a d1 60 v 2 a i led = 1 a before foldback vcc r s r1 r p ntc thermal foldback using ntc automotive-grade, constant-current 2 a pwm dimmable buck regulator led driver a6214 and a6216 allegro microsystems, llc 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com
19 application circuit diagrams (continued) figure 25: using two (or more) a6214/16 in parallel to drive the same led string. total led current is the sum of currents from each driver. led? l1 r cs1 d1 sw gnd csh csl c led vin led+ l2 r cs2 d2 sw gnd csh csl c led vin i led1 i led2 a6214/6 a6214/6 automotive-grade, constant-current 2 a pwm dimmable buck regulator led driver a6214 and a6216 allegro microsystems, llc 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com
20 application circuit diagrams (continued) protection from output lc-resonance during normal operation, if the led load becomes disconnected (due to a bad connector, for example), the output capacitor c led will be charged up to v out = v in . later, when the led load is reconnected, higher voltage stored in c led will create a huge current spike through the load. normally this does not create any problems, since the current spike will decay within a few microseconds. however, if the led load is connected through long cables, the parasitic inductance l k in the cable will form an lc-resonant circuit with c led . if the resonant circuit is under- damped, v out may oscillate and becomes negative. this could subject csh and csl pins to negative spike voltage exceeding their absolute maximum ratings. therefore the following pre- cautions are recommended to avoid output oscillation: ? use shortest possible led cables to reduce l k . ? use lower capacitance for c led to reduce stored energy (e c = 0.5 c led v in 2 ). ? critically damp the output lc-resonant circuit, as shown in figure 26. the drawback is additional power loss during pwm dimming operation (since c1 is charged and discharged through r1 during each pwm cycle). in case the output lc resonance cannot be eliminated (due to long led cables, for example), consider adding a schottky bar- rier diode (sbd) in parallel with c led , as shown in figure 28. the sbd clamps the negative spike of the lc resonance, so csh and csl pins are protected. this is the most effective protection with minimal side effects. in underdamped circuit, v out goes negative in critically-damped circuit, v out stays positive c led initially charged to v out = 50 v when load is open time/s figure 26: countermeasure to prevent v out oscillation during output intermittent open/short fault figure 27: simulation results showing difference in v out between underdamped and critically-damped circuits figure 28: using schottky diode to clamp the negative spike from output lc-resonance gnd l1 r sense csl c led add d2 to clamp the negative voltage of lc-resonant circuit s1 l k v led csh d2 (60 v 1 a) total parasitic inductance of cable v out v led gnd l1 r sense c led 0.1 f ic = 50 v r out 1 csh csl total resistance of output path l k 0.4 h ic = 0 a c1 0.22 f r1 1 esr 10 m s1 v out add r1 and c1 to critically damp the lc-resonant circuit large current spike when s1 is closed total parasitic inductance of cable automotive-grade, constant-current 2 a pwm dimmable buck regulator led driver a6214 and a6216 allegro microsystems, llc 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com
21 system failure detection and protection led+ gnd v in en/pwm l1 = open or short r sense open or short gnd 1 2 3 4 5 10 9 8 7 6 sw boot gnd csh csl vin ton en adim vcc a6214 d1 = open or short c4 open or short c1, c2 = open or short r1 = open or short c5 = open or short c3 open or short led string open or short to gnd figure 29: showing various possible fault cases in an application circuit ic-level failure modes protected against: ? any pin open ? any pin shorted to gnd ? adjacent pin-to-pin short system-level failure modes protected against open/short fault for all external components, including: ? led string ? sense resistor ? inductor ? diode ? input/output caps, etc. failure mode symptom observed fault flag (a6216) asserted? a6214/16 response inductor shorted dim light from led yes current spike trips sw secondary ocp and turns off switching. retries after 1 ms. sense resistor open no light from led yes high differential sense voltage causes ic to shut off switching. retries after 1 ms. sense resistor shorted dim light from led yes increases sw current, which eventually trips sw secondary ocp fault. retries after 1 ms. diode open dim light from led yes detects missing diode fault and shuts off switching. retries after 1 ms. diode shorted no light from led yes trips sw secondary ocp and turns off switching. retries after 1 ms. led string open no light from led yes* continue to switch at maximum t on (since this fault cannot be distinguished from v in too low for led forward drop) led string shorted to gnd, or output cap shorted no light from led yes* ic unable to regulate led current at v out = 0 v. sw current increases and trips ocp . ic shuts down and retries after 1 ms. led string partially shorted some leds are not on no normal operation (since ic has no way to know how many led is supposed to be in series). continued on the next page system failure mode table (partial) automotive-grade, constant-current 2 a pwm dimmable buck regulator led driver a6214 and a6216 allegro microsystems, llc 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com
22 failure mode symptom observed fault flag (a6216) asserted? a6214/16 response output cap open normal light from led no normal operation (since ic only monitors inductor current). boot cap open dim light from led yes* ic attempts to switch but cant fully turn on sw. short current spikes through led string. boot cap shorted no light from led yes* ic detects undervoltage fault across boot cap and will not start switching. ton resistor open dim light from led yes sw turns on and hits secondary current limit, then shuts down. retries after 1 ms. ton resistor shorted dim light from led no operates at maximum switching frequency (minimum t on and t off ). may hit thermal limit. note (*) ? in case of led current not in regulation, fault fag is asserted after approximately 50 s timeout delay. ? for pwm dimming operation with on-time < 50 s, fault fag is asserted if led current fails to reach regulation after 16 pwm = h pulses. ? for pwm dimming operation with on-time > 50 s, fault fag is only asserted when pwm = h. however, if the fault persists for 16 consecutive pwm cycles, fault fag will be pulled low and then it stays low until the fault is cleared. system failure mode table (partial) (continued) figure 30: v in too low for led regulation. pwm = 500 hz 2% (40 s). fault = l after 16 pwm pulses. figure 31: vin too low for led regulation. pwm = 500 hz 20% (400 s). fault toggles each time pwm = h, but stays low after 16 pwm pulses. ch1 = v pwm (5 v/div) ch2 = v fault (5 v/div) ch3 = v out (5 v/div) ch4 = i led (500 ma/div) t ime scale = 5 ms/div ch1 = v pwm (5 v/div) ch2 = v fault (5 v/div) ch3 = v out (5 v/div) ch4 = i led (500 ma/div) t ime scale = 5 ms/div automotive-grade, constant-current 2 a pwm dimmable buck regulator led driver a6214 and a6216 allegro microsystems, llc 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com
23 package lk, 10-pin soicn with exposed thermal pad package outline drawings for reference only? not for tooling use not to scale dimensions in millimeters dimensions exclusive of mold ?ash, gate burrs, and dambar protrusions exact case and lead con?guration at supplier discretion within limits shown a 0.40 0.30 0.25 0.19 8o 0o 0.685 0.20 c seating plane seating plane c 0.10 10x 1.00 bsc 0.25 bsc 21 10 4.90 +0.08 ?0.10 3.91 +0.08 ?0.10 2.41 0.25 6.00 0.20 1.55 0.10 0.10 0.05 gauge plane a b b c exposed thermal pad (bottom surface) 5.60 1.00 0.55 1.75 2.41 3.30 10 21 c branded face 3.30 0.25 pcb layout reference v iew t erminal #1 mark area reference land pattern layout; all pads a minimum of 0.20 mm from all adjacent pads; adjust as necessary to meet application process requirements and pcb layout tolerances; when mounting on a multilayer pcb, thermal vias at the exposed thermal pad land can improve thermal dissipation (reference eia/jedec standard jesd51-5) automotive-grade, constant-current 2 a pwm dimmable buck regulator led driver a6214 and a6216 allegro microsystems, llc 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com
24 package lp, 16-pin tssop with exposed thermal pad a 1.20 max 0.15 0.00 0.30 0.19 0.20 0.09 8o 0o 0.60 0.15 1.00 ref c seating plane c 0.10 16x 0.65 bsc 0.25 bsc 21 16 5.00 0.10 4.40 0.10 6.40 0.20 gauge plane seating plane a b b c d exposed thermal pad (bottom surface); dimensions may vary with device 6.10 0.65 0.45 1.70 3.00 3.00 16 21 1 c d branded face 3 nom 3 nom for reference only ? not for tooling use (reference mo-153 abt) dimensions in millimeters. not to scale dimensions exclusive of mold ?ash, gate burrs, and dambar protrusions exact case and lead con?guration at supplier discretion within limits shown pcb layout reference view terminal #1 mark area reference land pattern layout (reference ipc7351 sop65p640x110-17m); all pads a minimum of 0.20 mm from all adjacent pads; adjust as necessary to meet application process requirements and pcb layout tolerances; when mounting on a multilayer pcb, thermal vias at the exposed thermal pad land can improve thermal dissipation (reference eia/jedec standard jesd51-5) branding scale and appearance at supplier discretion standard branding reference view yyww nnnnnnn llll = device part number = supplier emblem = last two digits of year of manufacture = week of manufacture = characters 5-8 of lot number n y w l automotive-grade, constant-current 2 a pwm dimmable buck regulator led driver a6214 and a6216 allegro microsystems, llc 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com
25 for the latest version of this document, visit our website: www.allegromicro.com revision history number date description C september 23, 2015 initial release 1 march 17, 2016 added load current sense regulation threshold footnote (page 7-8); updated additional notes on ripple current (page 15). 2 april 6, 2016 added parallel operation figure (page 19) and sbd protection figure (page 20); updated protection from output lc-resonance (page 19); corrected lk package drawing dimension (page 23). 3 june 17, 2016 updated k value (page 11). 4 november 1, 2016 updated functional description (page 11); added table of contents. copyright ?2016, allegro microsystems, llc allegro microsystems, llc reserves the right to make, from time to time, such departures from the detail specifications as may be required to permit improvements in the performance, reliability, or manufacturability of its products. before placing an order, the user is cautioned to verify that the information being relied upon is current. allegros products are not to be used in any devices or systems, including but not limited to life support devices or systems, in which a failure of allegros product can reasonably be expected to cause bodily harm. the information included herein is believed to be accurate and reliable. however, allegro microsystems, llc assumes no responsibility for its use; nor for any infringement of patents or other rights of third parties which may result from its use. automotive-grade, constant-current 2 a pwm dimmable buck regulator led driver a6214 and a6216 allegro microsystems, llc 115 northeast cutoff worcester, massachusetts 01615-0036 u.s.a. 1.508.853.5000; www.allegromicro.com

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