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MAQ3203 high-brightness led driver controller with high-side current sense micrel inc. ? 2180 fortune drive ? san jose, ca 95131 ? usa ? tel +1 (408) 944-0800 ? fax + 1 (408) 474-1000 ? http://www.micrel.com general description the MAQ3203 is a hysteretic, step-down, constant- current, high-brightness led (hb led) driver. it provides an ideal solution for interior/exterior lighting, architectural and ambient lighting, led bulbs, and other general illumination applications. the MAQ3203 is well suited for lighting applications requiring a wide-input voltage ra nge. the hysteretic control gives good supply rejection and fast response during load transients and pwm dimming. the high-side current sensing and on-chip current-sense amplifier delivers led current with 5% accuracy. an exter nal high-side current- sense resistor is used to set the output current. the MAQ3203 offers a dedicated pwm input (dim) which enables a wide range of pulsed dimming. a high-frequency switching operation up to 1.5mhz allows the use of smaller external components minimizing space and cost. the MAQ3203 offers frequency dither feature for emi control. the MAQ3203 operates over a junction temperature from ? 40 c to + 125 c and is available in an 8-pin soic package. the MAQ3203 is aec-q100 qualified for automotive applications. datasheets and support documentation can be found on micrel?s web site at: www.micrel.com . features ? aec-q100 qualified ? 4.5v to 42v input voltage range ? high efficiency ( > 90%) ? 5% led current accuracy ? dither enabled for low emi ? high-side current sense ? dedicated dimming control input ? hysteretic control (no compensation!) ? up to 1.5mhz switching frequency ? adjustable constant led current ? over-temperature protection ? ? 40 c to + 125 c junction temperature range applications ? automotive lighting ? industrial lighting _________________________________________________________________________________________________________________________ typical application MAQ3203 step-down led driver march 2011 m9999-032411-a
micrel, inc. MAQ3203 march 2011 2 m9999-032411-a ordering information (1) part number marking junction temperature range package pwm MAQ3203ym MAQ3203ym ? 40c to + 125c 8-pin soic dither note: 1. ym ? is a green rohs compliant package. lead fini sh is nipdau. mold compound is halogen free. pin configuration 8-pin soic MAQ3203 pin description pin number pin name pin function 1 vcc voltage regulator output. the v cc pin supplies the power to the internal circuitry. the vcc in the output of a linear regulator which is powered from vin. a 1f ceramic capacitor is recommended for bypassing and should be placed as close as possible to the vcc and agnd pins. do not connect to an external load. 2 cs current-sense input. the cs pin provides the high-s ide current sense to set the led current with an external sense resistor. 3 vin input power supply. vin is the input supply pin to the internal circuitry and the positive input to the current sense comparator. due to the high frequenc y switching noise, a 10f ceramic capacitor is recommended to be placed as close as possible to vin and the power ground (pgnd) pin for bypassing. please refer to layout recommendations. 4 agnd ground pin for analog circuitry. internal signal ground for all low power sections. 5 en enable input. the en pin provides a logic level cont rol of the output and the vo ltage has to be 2.0v or higher to enable the current regul ator. the output stage is gated by the dim pin. when the en pin is pulled low, the regulator goes to off state and the s upply current of the device is greatly reduced (below 1a). in the off state, during this period the output drive is placed in a "tri-stated" condition, where mosfet is in an ?off? or non-conducting state. do not drive the en pin above the supply voltage. 6 dim pwm dimming input. the dim pin provides the contro l for brightness of the led. a pwm input can be used to control the brightness of led. dim high enables the output an d its voltage has to be at least 2.0v or higher. dim low disables the output, regardless of en ?high? state. 7 pgnd power ground pin for power fet. power ground (pgnd) is for the high-current switching with hysteretic mode. the current loop for the power gr ound should be as small as possible and separate from the analog ground (agnd) loop. refer to the layout considerations for more details. 8 drv gate-drive output. connec t to the gate of an external n-channe l mosfet. the drain of the external mosfet connects directly to the inductor and prov ides the switching current necessary to operate in hysteretic mode. due to the high frequency switching and high voltage associated with this pin, the switch node should be routed away from sensitive nodes.
micrel, inc. MAQ3203 march 2011 3 m9999-032411-a absolute maximum ratings (1) v in to pgnd .................................................. ? 0.3v to + 45v v cc to pgnd ................................................ ? 0.3v to + 6.0v cs to pgnd ........................................ ? 0.3v to (v in + 0.3v) en to agnd ........................................ ? 0.3v to (v in + 0.3v) dim to agnd ...................................... ? 0.3v to (v in + 0.3v) drv to pgnd .................................... ? 0.3v to (v cc + 0.3v) pgnd to agnd .......................................... ? 0.3v to + 0.3v junction temperature ................................................ 150 c storage temperat ure range .................... ? 60c to + 150 c lead temperature (sol dering, 10s ec) ....................... 260 c esd ratings (3) hbm ...................................................................... 1.5kv mm .........................................................................200v operating ratings (2) supply voltage (v in ).......................................... 4.5v to 42v enable voltage (v en) .............................................. 0v to v in dimming voltage (v dim ) ................................................................. 0v to v in junction temperature (t j ) ........................ ? 40 c to + 125 c junction thermal resistance soic ( ja ) .......................................................98.9 c/w soic ( jc ).......................................................48.8 c/w electrical characteristics (4) v in = v en = v dim = 12v; c vcc = 1.0f; t j = 25 c, bold values indicate ? 40 c t a + 125 c; unless noted. symbol parameter condition min. typ. max. units input supply v in input voltage range (v in ) 4.5 42 v i s supply current drv = open 1 3 ma i sd shutdown current v en = 0v 1 a uvlo v in uvlo threshold v in rinsing 3.2 4 4.5 v uvlo hys v in uvlo hysteresis 500 mv vcc supply vcc v cc output voltage v in = 12v, i cc = 10ma 4.5 5 5.5 v current limit 201.4 212 222.6 mv v cs(max) current sense upper threshold v cs(max ) = v in ? v cs 199 212 225 mv 168 177 186 mv v cs(min) sense voltage threshold low v cs(min ) = v in ? v cs 165 177 189 mv v cshys v cs hysteresis 35 mv v cs rising 50 ns current sense response time v cs falling 70 ns cs input current v in ? v cs = 220mv 0.5 10 a frequency f max switching frequency 1.5 mhz dithering (MAQ3203) v dith v cs hysteresis dithering range (5) 6 mv f dither frequency dithering range (5) % of switching frequency 12 %
micrel, inc. MAQ3203 march 2011 4 m9999-032411-a electrical characteristics (4) (continued) v in = v en = v dim = 12v; c vcc = 1.0f; t j = 25 c, bold values indicate ? 40 c t j + 125 c; unless noted. symbol parameter condition min. typ. max. units enable input en hi en logic level high 2.0 v en lo en logic level low 0.4 v v en = 12v 60 a en bias current v en = 0v 1 a start-up time from en pin going high to drv going high 30 s dimming input dim hi dim logic level high 2.0 v dim lo dim logic level low 0.4 v 20 50 dim bias current v dim = 0v 1 a dim delay time from dim pin going high to drv going high 450 ns f dim maximum dimming frequency 20 khz external fet driver pull up, i source = 10ma 2 drv on-resistance pull down, i sink = -10ma 1.5 ? rise time, c load = 1000pf 13 drv transition time fall time, c load = 1000pf 7 ns thermal protection t lim over-temperature shutdown t j rising 160 t limhys over-temperature shutdown hysteresis 20 c notes: 1. exceeding the absolute maximum rating may damage the device. 2. the device is not guaranteed to function outside its operating rating. 3. devices are esd sensitive. hand ling precautions recommended. human body model, 1.5k in series with 100pf. 4. specification for packaged product only. 5. guaranteed by design.
micrel, inc. MAQ3203 march 2011 5 m9999-032411-a typical characteristics efficiency vs input voltage 60 70 80 90 100 0 5 10 15 20 25 30 35 40 45 input voltage (v) efficiency (%) l=150h iled=1a 4led 6led 8led 10led efficiency vs input voltage 60 70 80 90 100 0 5 10 15 20 25 30 35 40 45 input voltage (v) efficiency (%) l=68h iled=1a 4led 6led 8led 10led normalized led currents vs input voltage 0.97 0.98 0.99 1 1.01 1.02 1.03 0 5 10 15 20 25 30 35 40 45 input voltage (v) led currents (a) l=150h iled=1a 4led 6led 8led 10led 1led 2led normalized led currents vs. input voltage 0.97 0.98 0.99 1 1.01 1.02 1.03 0 5 10 15 20 25 30 35 40 45 input voltage (v) led currents (a) l=68h iled=1a 4led 6led 8led 10led 1led 2led frequency vs. input voltage 0 50 100 150 200 250 300 350 0 5 10 15 20 25 30 35 40 45 input voltage (v) frequency (khz) l=150h iled=1a 4led 6led 8led 10led 1led 2led frequency vs. input voltage 0 100 200 300 400 500 600 700 0 5 10 15 20 25 30 35 40 45 input voltage (v) frequency (khz) l=68h iled=1a 4led 6led 8led 10led 1led 2led duty cycle vs. input voltage 0 25 50 75 100 0 5 10 15 20 25 30 35 40 45 input voltage (v) duty cycle (%) l=150h iled=1a 4led 6led 8led 10led 1led 2led duty cycle vs input voltage 0 25 50 75 100 0 5 10 15 20 25 30 35 40 45 input voltage (v) duty cycle (%) l=68h iled=1a 4led 6led 8led 10led 1led 2led supply current vs. input voltage 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 5 10 15 20 25 30 35 40 45 input voltage (v) supply current (ma) ta = 25c iled = 0a
micrel, inc. MAQ3203 march 2011 6 m9999-032411-a typical characteristics (continued) v cc vs. input voltage 0.0 1.0 2.0 3.0 4.0 5.0 6.0 0 5 10 15 20 25 30 35 40 45 input voltage (v) vcc (v) ta = 25c iled = 0a icc = 0a enable threshold vs. input voltage 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 0 5 10 15 20 25 30 35 40 45 input voltage (v) enable threshold (v) ta=25c 1led iled=1a current-sense voltage vs. input voltage 0 50 100 150 200 250 0 5 10 15 20 25 30 35 40 45 input voltage (v) current sense voltage (mv) vcs_max vcs_min l=100a iled=1a shutdown current vs. input voltage -5 0 5 10 15 20 25 30 35 40 0 5 10 15 20 25 30 35 40 45 input voltage (v) shutdown current (a) ta=25c iled=0a enable current vs. enable voltage 0 20 40 60 80 100 120 140 160 0 5 10 15 20 25 30 35 40 45 enable votlage (v) enable current (a) ta=25c icc limit vs. input voltage 0 20 40 60 80 100 120 140 160 180 200 0 5 10 15 20 25 30 35 40 45 input voltage (v) icc limit (ma) ta=25c vcc=4.2v iled=0a supply current vs. temperature 0.0 0.2 0.4 0.6 0.8 1.0 1.2 -40 -20 0 20 40 60 80 100 120 temperature (c) supply current (ma) vin=12v iled=0a vcc vs. temperature 0.0 1.0 2.0 3.0 4.0 5.0 6.0 -40 -20 0 20 40 60 80 100 120 temperature (c) vcc (v) vin=12v iled=0a icc=0a enable threshold vs. temperature 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 -40 -20 0 20 40 60 80 100 120 temperature (c) enable threshold (v) on off 1led iled=1a
micrel, inc. MAQ3203 march 2011 7 m9999-032411-a typical characteristics (continued) shutdown current vs. temperature 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 -40 -20 0 20 40 60 80 100 120 temperature (c) shutdown current (ua) vin=12v en=0v enable current vs. temperature 0 5 10 15 20 25 30 35 40 45 50 -40 -20 0 20 40 60 80 100 120 temperature (c) enable current (ua) vin=12v ven=vin current-sense voltage vs. temperature 0 50 100 150 200 250 -40 -20 0 20 40 60 80 100 120 temperature (c) current sense voltage (mv) vcs_max vcs_min 1led iled=1a d_vcs switching frequency vs. temperature 0 20 40 60 80 100 120 140 160 -40 -20 0 20 40 60 80 100 120 temperature (c) switching frequency (khz) vin=12v 1led iled=1a l=100h uvlo threshold vs. temperature 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 -40 -20 0 20 40 60 80 100 120 temperature (c) uvlo threshold (v) of on l=100a iled=1a thermal shutdown vs. input voltage 0 20 40 60 80 100 120 140 160 180 0 5 10 15 20 25 30 35 40 45 input voltage (v) thermal shutdown (c) of on
micrel, inc. MAQ3203 functional characteristics march 2010 8 m9999-031811-a
micrel, inc. MAQ3203 functional characteristics (continued) march 2010 9 m9999-031811-a
micrel, inc. MAQ3203 march 2011 10 m9999-032411-a functional diagram figure 1. MAQ3203 block diagram functional description the MAQ3203 is a hysteretic step-down driver which regulates the led current over wide input voltage range. the device operates from a 4.5v to 42v input mosfet voltage range and provides up to 0.5a source and 1a sink drive capability. when the input voltage reaches 4.5v, the internal 5v vcc is regulated and the drv pin is pulled high to turn on an external mosfet if en pin and dim pin are high. the inductor current builds up linearly. when the cs pin voltage hits the v cs(max) with respect to v in , the mosfet turns off and the schottky diode takes over and returns the current to v in . then the current through inductor and leds starts decreasing. when cs pin hits v cs(min) , the mosfet turns on and the cycle repeats. the frequency of operation depends upon input voltage, total leds voltage drop, led cu rrent and temperature. the calculation for frequency of operation is given in application section. the MAQ3203 has an on board 5v regulator which is for internal use only. connect a 1f capacitor on vcc pin to analog ground. the MAQ3203 has an en pin which gives the flexibility to enable and disable the output with logic high and low signals. the MAQ3203 also has a dim pin which can turn on and off the leds if en is in high st ate. this dim pin controls the brightness of the led by vary ing the duty cycle of dim pin from 1% to 99%.
micrel, inc. MAQ3203 march 2011 11 m9999-032411-a application information the internal block diagram of the MAQ3203 is shown in figure 1. the MAQ3203 is composed of a current-sense comparator, voltage and current reference, 5v regulator and mosfet driver. hysteretic mode control ? also called bang-bang control ? is a topology that does not employ an error amplifier, using an error comparator instead. the inductor current is cont rolled within a hysteretic window. if the inductor current is too small, the power mosfet is turned on; if the inductor current is large enough, the power mosfet is turned off. it is a simple control scheme with no oscillator and no loop compensation. since the control scheme does not need loop compensation, it makes a design easy, and avoids problems of instability. transient response to load and line variation is very fast and only depends on propagation delay. this makes the control scheme very popular for certain applications. led current and r cs the main feature in MAQ3203 is to control the led current accurately within 5% of set current. choosing a high-side r cs resistor helps for setting constant led current irrespective of wide input voltage range. the following equation gives the r cs value: ) i v+v (x 2 1 =r led )min(cs)max(cs cs table 1. r cs for led current r cs ( ? ) i led (a) i 2 r (w) size (smd) 1.33 0.15 0.03 0603 0.56 0.35 0.07 0805 0.4 0.5 0.1 0805 0.28 0.7 0.137 0805 0.2 1.0 0.2 1206 0.13 1.5 0.3 1206 0.1 2.0 0.4 2010 0.08 2.5 0.5 2010 0.068 3.0 0.6 2010 for v cs(max) and v cs(min), refer to the electrical characteristic table. frequency of operation to calculate the frequency spread across input supply: t ? i ? l=v l l l is the inductance, i l is fixed (the value of the hysteresis): cs )min(cs)max(cs l r v v =i ? - v l is the voltage across inductor l which varies by supply. for current rising (mosfet is on): rise_l l r v i ? l=t where: v l_rise = v in ? i led r cs ? v led for current falling (mosfet is off): fall_l l f v i ? l=t where: v l_fall = v d + i led r cs + v led fr t+t=t , t 1 =f sw )v+v(i ? l )vriv()v+ri+v( =f indl ledcs ledin led cs ledd sw -- where : ? v d is schottky diode forward drop ? v led is total leds voltage drop ? v in is input voltage ? i led is average led current
micrel, inc. MAQ3203 march 2011 12 m9999-032411-a inductor according to the above equation, choose the inductor to make the operating frequency no higher than 1.5mhz. the following tables give a reference inductor value and corresponding frequency for a given led current. for space-sensitive applications, smaller inductor with higher switching frequency could be used but efficiency of the regular will be reduced. table 2. inductor for vin = 12v, 1 led rcs ( ? ) i led (a) l (h) f sw (khz) 1.33 0.15 220 474 0.56 0.35 100 439 0.4 0.5 68 461 0.28 0.7 47 467 0.2 1.0 33 475 0.13 1.5 22 463 0.1 2.0 15 522 0.08 2.5 12 522 0.068 3.0 10 533 table 3. inductor for vin = 24v, 4 leds rcs ( ? ) i led (a) l (h) f sw (khz) 1.33 0.15 470 474 0.56 0.35 220 426 0.4 0.5 150 447 0.28 0.7 100 470 0.2 1.0 68 493 0.13 1.5 47 463 0.1 2.0 33 507 0.08 2.5 27 496 0.068 3.0 22 517 table 4. inductor for vin = 36v, 8 leds rcs ( ? ) i led (a) l (h) f sw (khz) 1.33 0.15 470 495 0.56 0.35 220 446 0.4 0.5 150 467 0.28 0.7 100 490 0.2 1.0 68 515 0.13 1.5 47 485 0.1 2.0 33 530 0.08 2.5 27 519 0.068 3.0 22 541 given an inductor value, the size of the inductor can be determined by its rms and peak current rating. 18.0= v+v v v 2= i i )min(cs)max(cs )min(cs)max(cs l l - l 2 l 2 l)rms(l i i 12 1 +i=i l l l)pk(l i09.1=i 2 1 +i=i where: i l is inductor average current. select an inductor with saturation current rating at least 30% higher than the peak current. mosfet mosfet selection depends upon the maximum input voltage, output led current and switching frequency. the selected mosfet should have 30% margin on maximum voltage rating for high reliability requirements. the mosfet channel resistance r dson is selected such that it helps to get the required efficiency at the required led currents as well as meets the cost requirement. logic level mosfets are preferred as the drive voltage is limited to 5v. the mosfet power loss has to be calculated for proper operation. the power loss consists of conduction loss and switching loss. the conduction loss can be found by: in led_total led)fet(rms dson 2 )fet(rms)con(loss v v =d di=i ri= p
micrel, inc. MAQ3203 march 2011 13 m9999-032411-a the switching loss occurs during the mosfet turn-on and turn-off transition and can be found by: gate drv drv gd2gs drv sw ledin )tran(loss r v =i )q+q( i fiv = p where: r gate is total mosfet resistance, q gs2 and q gd can be found in a mosfet manufacturer datasheet. the total power loss is: )tran(loss )con(loss )tot(loss p+ p= p the mosfet junction temperature is given by: aja )tot(loss j t+r p=t the t j must not exceed maximum junction temperature under any conditions. snubber a rc voltage snubber is used to damp out high frequency ringing on the switch node caused by parasitic inductance and capacitance. the capacitor is used to slow down the switch node rise and fall time and the resistor damps the ringing. excessive ringing can cause the MAQ3203 to operate erratically by prematurely tripping its current limit comparator circuitry. the snubber is connected across the schottky diode as shown in the evaluation board schematic. capacitor c s (c4) is used to block the dc voltage across the resistor, minimizing the power dissipation in the resistor. this capacitor value should be between two to five times the parasitic capacitance of the mosfet c oss and the schottky diode junction capacitance c j . a capacitor that is too small will have high impedance and prevent the resistor from damping the ringing. a capacitor that is too large causes unnecessary power dissipation in the resistor, which lowe rs efficiency. the snubber components should be placed as close as possible to the schottky diode. placing the snubber too far from the diode or using an etch that is too long or too thin adds inductance to the snubber and diminishes its effectiveness. proper snubber design requires the parasitic inductance and capacitance be known. a method of determining these values and calculating the damping resistor value is outlined below: 1. measure the ringing frequency at the switch node which is determined by parasitic l p and c p . define this frequency as f 1 . 2. add a capacitor c s (normally at least 3 times as big as the c oss of the diode) across the diode and measure the new ringing frequency. define this new (lower) frequency as f 2 . l p and c p can now be solved using the values of f 1 , f 2 and c s . 3. add a resistor r s in series with c s to generate critical damping. if the snubber resistance is equal to the characteristic impedance of the resonant circuit (1/sqrt(l p c p )), the resonant circuit will be critically damped and have no ringing. step 1: first measure the ringing frequency on the switch node voltage when the high-side mosfet turns on. this ringing is characterized by the equation: pp 1 cl2 1 f = w here: c p and l p are the parasitic capacitance and inductance. step 2: add a capacitor, c s , in parallel with the schottky diode. the capacitor value should be approximately 3 times the c oss of d1. measure the frequency of the switch node ringing, f 2. )c(cl2 1 f psp 2 + = define f? as: 2 1 f f f' = combining the equations for f 1 , f 2 and f? to derive c p , the parasitic capacitance: ? ? ? ? ? ? ? ? ? = 1)(f2 c c 2, s p
micrel, inc. MAQ3203 march 2011 14 m9999-032411-a l p is solved by re-arranging the equation for f 1 : () () 2 1p 2 p fc2 1 l = step 3: calculate the damping resistor. critical damping occurs at q = 1: 1 cc l r 1 q ps p s = + = solving for r s : ps p s cc l r + = the snubber capacitor, c s , is charged and discharged each switching cycle. the energy stored in c s is dissipated by the snubber resistor, r s , two times per switching period. this power is calculated in the equation below: 2 inss snubber vcf p = where: f s is the switching frequency for each phase. v in is the dc input voltage. an alternate method to reduce the switch node ringing is to place a 2.2 ? resistor in series with the n-channel mosfets gate pin. this will slow down both the rising and falling edge of the switch node waveform. freewheeling diode the diode provides a conduction path for the inductor current during the switch o ff time. the reverse voltage rating of the diode should be at least 1.2 times the maximum input voltage. a schottky diode is recommend for highest efficiency. the schottky diode can be the major source of power loss, especially at the maximum input voltage. the current through the diode is equal to the led current with a duty cycle of (v in ? v led )/v in . the diode dissipation is given by: f in led in ledd v v )v(v ip ? = v f is the forward voltage of the diode at i led . a schottky diode forward voltage is typically 0.6v at its full rated current. it is normal design practice to use a diode rated at 1.5 to 2 times output current to maintain efficiency. this derating allows v f to drop to approximately 0.5v. when calculating the ?worst case? power dissipation, use the maximum input voltage and the actual diode forward voltage drop at the maximum operating temperature; otherwise the calculated power dissipation will be artificially high. the forward voltage drop of a diode decrease as ambient temperature is increased, at a rate of ? 1.0mv/ c. input capacitor the ceramic input capacitor is selected by voltage rating and ripple current rating. to determine the input current ripple rating, the rms value of the input capacitor can be found by: () d1di i led cin(rms) ?= the power loss in the input capacitor is: esr in cin(rms) 2 loss(cin) c i p = the input capacitor current rating can be considered as i led /2 under the worst condition d = 50%. led ripple current the led current is the same as inductor current. if led ripple current needs to be reduced then place a 4.7f/50v ceramic capacitor across led.
micrel, inc. MAQ3203 march 2011 15 m9999-032411-a frequency dithering the MAQ3203 is designed to reduce emi by dithering the switching frequency 12% in order to spread the frequency spectrum over a wider range. this lowers the emi noise peaks (see figure 2) generated by the switching regulator. output voltage frequency spectrum with dither 0 10 20 30 40 50 60 70 80 90 100 100 1000 10000 frequency (khz) amplitude (dbv) figure 2. output voltage frequency spectrum without dither switching regulators generate noise by their nature and they are the main emi source to interference with nearby circuits. if the switching frequency of a regulator is modulated via frequency dithering, the energy of the emi is spread among many frequencies instead of concentrated at fundamental switching frequency and its harmonics. the MAQ3203 modulates the v cs(max) with amplitude 6mv by a pseudo random generator to generate the 12% of the switching frequency dithering to reduce the emi noise peaks.
micrel, inc. MAQ3203 march 2011 16 m9999-032411-a pcb layout guidelines warning!!! to minimize emi and output noise, follow these layout recommendations. pcb layout is critical to achieve reliable, stable and efficient performance. a ground plane is required to control emi and minimize the inductance in power, signal and return paths. the following guidelines should be followed to insure proper operation of the MAQ3203 regulator. ic use thick traces to route the input and output power lines. signal and power grounds should be kept separate and connected at only one location. input capacitor place the input capacitors on the same side of the board and as close to the ic as possible. keep both the vin and pgnd traces as short as possible. place several vias to the ground plane close to the input capacitor ground terminal, but not between the input capacitors and ic pins. use either x7r or x5r dielectric input capacitors. do not use y5v or z5u type capacitors. do not replace the ceramic input capacitor with any other type of capacitor. any type of capacitor can be placed in parallel with the input capacitor. if a tantalum input capacitor is placed in parallel with the input capacitor, it must be recommended for switching regulator applications and the operating voltage must be derated by 50%. in ?hot-plug? applications, a tantalum or electrolytic bypass capacitor must be placed in parallel to ceramic capacitor to limit the over-voltage spike seen on the input supply with power is suddenly applied. in this case an additional tantalum or electrolytic bypass input capacitor of 22f or higher is required at the input power connection if necessary. inductor keep the inductor connection to the switch node (mosfet drain) short. do not route any digital lines underneath or close to the inductor. to minimize noise, place a ground plane underneath the inductor. output capacitor if led ripple current needs to be reduced then place a 4.7f/50v capacitor across led. the capacitor must be placed as close to the led as possible. mosfet place the mostet as close as possible to the MAQ3203 to avoid the trace inductance. pr ovide sufficient copper area on mosfet ground to dissipate the heat. diode place the schottky diode on the same side of the board as the ic and input capacitor. the connection from the schottky diode?s anode to the switching node must be as short as possible. the diode?s cathode connection to the r cs must be keep as short as possible. rc snubber if a rc snubber is needed, place the rc snubber on the same side of the board and as close to the schottky diode as possible. r cs (current-sense resistor) vin pin and cs pin must be as close as possible to r cs. make a kelvin connection to the vin and cs pin respectively for current sensing. trace routing recommendation keep the power traces as short and wide as possible. one current flowing loop is during the mosfet on time, the traces connecting the input capacitor c in , r cs , leds, inductor, the mosfet and back to c in . the other current flowing loop is during the mosfet off time, the traces connecting r cs , led, inductor, free wheeling diode and back to r cs . these two loop areas should kept as small as possible to minimize the noise interference, keep all analog signal traces away from the switching node and its connecting traces.
micrel, inc. MAQ3203 march 2011 17 m9999-032411-a ripple measurements to properly measure ripple on either input or output of a switching regulator, a proper ring in tip measurement is required. standard oscilloscope probes come with a grounding clip, or a long wire with an alligator clip. unfortunately, for high-frequency measurements, this ground clip can pick-up high-frequency noise and erroneously inject it into the measured output ripple. the standard evaluation board accommodates a home made version by providing probe points for both the input and output supplies and their respective grounds. this requires the removing of the oscilloscope probe sheath and ground clip from a standard oscilloscope probe and wrapping a non-shielded bus wire around the oscilloscope probe. if there does not happen to be any non-shielded bus wire immediately available, the leads from axial resistors will work. by maintaining the shortest possible ground lengths on the oscilloscope probe, true ripple measurements can be obtained. figure 3. low noise measurement
micrel, inc. MAQ3203 march 2011 18 m9999-032411-a evaluation board schematic
micrel, inc. MAQ3203 march 2011 19 m9999-032411-a bill of materials item part number manufacturer description qty. 12105c475kaz2a avx (1) c1, c5 grm32er71h475ka88l murata (2) 4.7f/50v, ceramic capacitor, x7r, size 1210 2 12105c475kaz2a avx (1) grm32er71h475ka88l murata (2) c2 c3225x7s1h475m tdk (3) 4.7f/50v, ceramic capacitor, x5r, size 1210 1 08053d105kat2a avx (1) 1f/25v, ceramic capacitor, x5r, size 0805 1 grm21br71e105ka99l murata (2) c3 c2012x7r1e105k tdk (3) 1f/25v, ceramic capacitor, x7r, size 0805 1 (open) 08055a271jat2a avx (1) c4 (open) grm2165c2a271ja01d murata (2) 270pf/50v, ceramic capacitor npo, size 0805 1 sk36-tp mcc (4) sk36 fairchild (5) d1 sk36-7-f diodes, inc. (6) 60v, 3a, smc, schottky diode 1 l1 slf10145t-680m1r2 tdk (3) 68h, 1.2a, 0.14 ? , smt, power inductor 1 m1 fds5672 fairchild (7) mosfet, n-ch, 60v, 12a, so-8 1 r1 csr 1/2 0.2 1% i stackpole electronics, inc (8) 0.2 ? resistor, 1/2w, 1%, size 1206 1 r2, r3 crcw08051003fkea vishay (9) 100k ? resistor, 1% , size 0805 2 r4 crcw08050000fkea vishay (9) 0 ? resistor, 1%, size 0805 1 r5 (open) crcw08052r20fkea vishay (9) 2.2? resistor, 1%, size 0805 1 r6 crcw08051002fkea vishay (9) 10k ? resistor, 1% , size 0805 1 u1 MAQ3203ym micrel, inc. (10) high-brightness led driver controller with high-side current sense 1 notes: 1. avx: www.avx.com . 2. murata: www.murata.com . 3. tdk: www.tdk.com . 4. mcc: www.mccsemi.com . 5. fairchild: www.fairchildsemi.com . 6. diodes inc. : www.diodes.com . 7. fairchild : www.fairchildsemi.com . 8. stackpole electronics: www.seielect.com . 9. vishay: www.vishay.com . 10. diodes inc. : www.diodes.com . 11. micrel, inc.: www.micrel.com .
micrel, inc. MAQ3203 march 2011 20 m9999-032411-a pcb layout recommendation top assembly top layer
micrel, inc. MAQ3203 march 2011 21 m9999-032411-a pcb layout recommen dation (continued) bottom layer
micrel, inc. MAQ3203 march 2011 22 m9999-032411-a package information 8-pin soic
micrel, inc. MAQ3203 march 2011 23 m9999-032411-a recommended landing pattern 8-pin soic micrel, inc. 2180 fortune drive san jose, ca 95131 usa tel +1 (408) 944-0800 fax +1 (408) 474-1000 web http://www.micrel.com micrel makes no representations or warranties with respect to the accuracy or completeness of the information furnished in this data sheet. this information is not intended as a warranty and micrel does not assume responsibility for it s use. micrel reserves the right to change circuitry, specifications and descriptions at any time without notice. no license, whether express, implied, arising by estoppel or otherwise, to any in tellectual property rights is granted by this document. except as provided in micrel?s term s and conditions of sale for such products, micrel assumes no lia bility whatsoever, and micrel disclaims any express or implied warranty relating to t he sale and/or use of micrel pr oducts including liability or warr anties relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right micrel products are not designed or authori zed for use as components in life support app liances, devices or systems where malfu nction of a product can reasonably be expected to result in personal injury. life support devices or systems ar e devices or systems that (a) are intend ed for surgical implant into the body or (b) support or sustain life, and whose failure to per form can be reasonably expected to result in a significant inj ury to the user. a purchaser?s use or sale of micrel products for use in life support appliances, devices or system s is a purchaser?s own risk and purchaser agrees to fully indemnify micrel for any damages resulting from such use or sale. ? 2011 micrel, incorporated.

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