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a i t s em i c ond u ctor i n c . www.ait - ic.com a 74 42 dc - dc converter/ buck (step - down) 40v, 4.2a high performance cv/cc quick charger syn chronous rev1. 0 - j ul 201 7 released - - 1 - de s cri p t i o n f eat u r es ap7442 is a high efficiency synchronous dc - dc buck converters with cv / cc modes, which can output up to 4.2 a in a wide input range from 6 v to 36 v. the A7442 operates either in cv (constant voltage) mode or cc (constant current) mo de. with the cv / cc mode, adjustable current limit and output voltage, the A7442 is particularly suitable for qc 2.0 / 3.0 (12 v / 1.5a, 9v / 2a and 5v / 3 a), type -c pd (5 v / 3 a) and apple portable device (5v / 2.4 a) applications. the output voltage and cc limit can be programed through the fb, csp and csn pins respectively. in order to achieve better emi performance and comply with apples mfi standard, the switching frequency was fixed at 130 khz. A7442 is capable to operate in cc mode down to 3 v output voltage to protect the soft - short condition that is from the over current of the portable device a discharge circuitry is integrated to quickly and reliably discharge output capacitors to avoid the faulty voltage delivery in case of output over voltage a nd ensure safe operation for qc 2.0 / 3.0 application. the hiccup mode output under voltage protection(uvp) can reduce the average input current to 50ma. features such as output cord voltage drop compensation and low voltage drop operation is especially suitable for car charger. the a74 42 is available in psop8 package. o rde ri ng i nf o rm a t i o n p ac k ag e t y pe p ar t n um ber psop8 spq: 4,000pcs/reel mp8 a74 42 mp8 r A7442 mp8vr note v: halogen free package r: tape & reel ait provides all rohs products ? wide inpu t supply voltage range of 6 v ~ 40v ? up to 4.2 a output current ? up to 95 % efficiency ? 130 khz fixed switching frequency ? internal soft - start circuitry ? compensation for output cord voltage drop ? input under voltage lockout ? input over voltage protection ? adjustabl e constant current limit ? output over voltage protection ? output auto discharge ? cycle by cycle peak current limit ? hiccup mode output uvp for soft - short 3v ? thermal shutdown ? available in psop8 package appl i c at i o n ? car charger ? portable charging devices ? cv / cc regulation dc / dc converter t ypi c al ap pl i c at i o n
a i t s em i c ond u ctor i n c . www.ait - ic.com a 74 42 dc - dc converter/ buck (step - down) 40v, 4.2a high performance cv/cc quick charger syn chronous rev1. 0 - j ul 201 7 released - - 2 - p i n de s cri p t i o n top view p i n # s y mb ol f u nc t i on 1 v in input voltage supply. connect a decoupling capacitor between v in and gnd pins with least distance . 2 fb converter feedback input. connect to the center point of the output feedback resistors divider to program the output voltage. 3 csn current limit negative feedback pin. kevin sensing from this pin to the sensing resistor is recommended. 4 csp current limit positive feedback pin. kevin sensing from this pin to the sensing resistor is recommended. 5 cc cable compensation pin. connect a resistor to output to adjust wire compensation gain. 6 v cc internal 5v power supply. connect a 100nf capacitor between v cc and gnd pins for stability and noise de - coupling; 7 bst boot - strap pin. supply input for the gate drive circuit of high - side nfet. connect a 1 00 nf capacitor between bst and sw pins. 8 sw switch node between high - side nfet and low - side nfet. connect this pin to the switching node of inductor. dap(9) gnd ground and thermal pad on the bottom of ic. ground pin of internal circuitry and power return pin for sync - nfet source connection.
a i t s em i c ond u ctor i n c . www.ait - ic.com a 74 42 dc - dc converter/ buck (step - down) 40v, 4.2a high performance cv/cc quick charger syn chronous rev1. 0 - j ul 201 7 released - - 3 - abso l u t e m ax i m u m r at i n g s v in - 0.3v ~ 42v sw - 0.3 v ~ (v in + 0.2 v) 42 v bst to sw - 0.3v ~ 6 v csp, cs n , cc - 0.3v ~ 14 v v cc , fb - 0.3v ~ 6 v esd rating (human body model) 4 kv note1 package thermal resistance note2 ja 50c/w t j , min. operating - 40c t j , max. operating internally limited storage temperature - 55c ~ 150 c lead temperature (soldering 10 sec.) 260c stress beyond above listed absolute maximum ratings may lead permanent damage to the device. the se are stress ratings only and operations of the device at these or any other conditions beyond those indicated in the operational sections of the specifications are not implied. exposure to absolute maximum rating conditions for extended periods may affec t device reliability. note1: tested and classified as class 3a per esda/jedec jds - 001 - 2014. note2: thermal resistance is measured in the natural convection at t a = 25c on a low effective single layer thermal conductivity test board of jedec 51 - 3 thermal measurement standard.
a i t s em i c ond u ctor i n c . www.ait - ic.com a 74 42 dc - dc converter/ buck (step - down) 40v, 4.2a high performance cv/cc quick charger syn chronous rev1. 0 - j ul 201 7 released - - 4 - e l e ct ri ca l cha ra ct e ri s t i cs no t e 3 v in = 12 v, t a = 25 , unless otherwise noted. p ar a met er s y mb ol c ond i t i ons mi n. t y p. m ax . u n it i npu t s up pl y v o l t a ge input voltage v in 6 - 40 v i npu t u v lo & o v p input uvlo threshold v uvlo v in rising 4.0 4. 4 4.8 v input ovp threshold v in_ovp v in rising 36.5 39.5 - v input ovp hysteresis note4 v in_ovphys v in falling - 2.5 - v i npu t s up pl y c ur r ent quiescent current (non - switching) i q v fb = 1.5 v - 500 850 a o ut put v ol t ag e output voltage rang e v out 3.4 - 13.0 v feedback voltage threshold v fb_th 0.98 0 1 .000 1.02 0 v feedback current i fb - 10 50 na csp ovp threshold v csp_ovp v csp rising 13.2 14.0 14.9 v csp ovp hysteresis v csp_hys v csp falling - 840 - mv feedback ovp threshold v fb_ovp v fb rising, % of v fb_th - 11 3 - % feedback ovp threshold hysteresis v fb_hys v fb falling, % of v fb_th - 2 - % csp uvp threshold v uvp v csp falling 2.62 3.00 3.31 v uvp hiccup interval note4 t uvp - 0. 7 - s cable compensation voltage v ccomp r cc = 1 8 k, i load = 2.4 a, r s = 18 m - 200 - mv auto discharge threshold v th_dis % of v fb_th - 11 3 - % auto discharge current i dis - 60 - ma o s c il la t o r switching frequency f sw i load = 1a 10 9 130 160 khz maximum duty cycle note4 d max - 99 - %
a i t s em i c ond u ctor i n c . www.ait - ic.com a 74 42 dc - dc converter/ buck (step - down) 40v, 4.2a high performance cv/cc quick charger syn chronous rev1. 0 - j ul 201 7 released - - 5 - p ar a met er s y mb ol c ond i t i ons mi n. t y p. m ax . u n it m o sf et high side mosfet on resistance r ds(on)h - 52 - m low side mosfet on resistance r ds(on)l - 52 - m high - side mosfet leakage current i leak_h v sw = 0 v - - 9 a low - side mosfet leakage current i leak_l v sw = v in - - 7 a c ur r ent li mi t high side mosfet peak current limit note4 i lim_hs v out = 5 v - 7.5 - a constant current limit threshold i cs r s = 15 m, v out = 5 v 3.832 4.067 4.265 a r s = 1 7 m, v out = 5 v 3.381 3.588 3.763 a r s = 1 7 m, v out = 9 v 2.262 2.442 2.633 a r s = 1 7 m, v out = 12 v 1.572 1.769 1.951 a r egu l a t or v cc regulator v vcc_5 t a = 25 c, 0 < i cc <5 ma 4.541 4.896 5.109 v v cc output current i cc _10 v in = 12 v, v cc = 4.3 v, t a = 25 c 10 - - ma s of t - s t ar t soft - start time note4 t ss - 1.6 - ms t h er ma l s h ut d ow n thermal shutdown threshold note4 t sdn - 165 - c thermal shutdown hysteresis note4 t sdnhys - 40 - c note3: specifications over temperature range are guaranteed by design and characterization. note4: guaranteed by design and characterization only.
a i t s em i c ond u ctor i n c . www.ait - ic.com a 74 42 dc - dc converter/ buck (step - down) 40v, 4.2a high performance cv/cc quick charger syn chronous rev1. 0 - j ul 201 7 released - - 6 - t y p i ca l p e rf o rm a n ce cha ra ct e ri s t i cs all curves taken at v in = 12 v, v out = 5 v, rs = 15m with configuration in typical application circuit for high current output shown in this datasheet. t a = 25 c, unless otherwise specified. 1. efficiency vs. load current, v out = 5 v 2. efficiency vs. load current, v out = 9 v 3. efficiency v s. load current, v out = 12 v 4. efficiency vs. input voltage 5. v out regulation vs. load current, r cc = 0, r 1 = 100 k, r s = 0 6. cable compensation voltage vs. load current, r cc + r 1 = 100 k
a i t s em i c ond u ctor i n c . www.ait - ic.com a 74 42 dc - dc converter/ buck (step - down) 40v, 4.2a high performance cv/cc quick charger syn chronous rev1. 0 - j ul 201 7 released - - 7 - 7. ccm switching frequency vs. v in , i out = 1a 8. ccm switching frequency vs. temperature 9. reference voltage vs. temperature 10. mosfet r ds(on) vs. temperature 11. constant current limit threshold vs. temperature 12. q uiescent current vs. v in
a i t s em i c ond u ctor i n c . www.ait - ic.com a 74 42 dc - dc converter/ buck (step - down) 40v, 4.2a high performance cv/cc quick charger syn chronous rev1. 0 - j ul 201 7 released - - 8 - 13. output cc/cv curve, v in = 24v, r cc = 0 14. power up 15. power down 16. load transient 17. continuous mode operation 18. discontinuous mode operation
a i t s em i c ond u ctor i n c . www.ait - ic.com a 74 42 dc - dc converter/ buck (step - down) 40v, 4.2a high performance cv/cc quick charger syn chronous rev1. 0 - j ul 201 7 released - - 9 - 19. short circuit protection 20. short circuit protection
a i t s em i c ond u ctor i n c . www.ait - ic.com a 74 42 dc - dc converter/ buck (step - down) 40v, 4.2a high performance cv/cc quick charger syn chronous rev1. 0 - j ul 201 7 released - - 10 - bl o c k d i ag r am
a i t s em i c ond u ctor i n c . www.ait - ic.com a 74 42 dc - dc converter/ buck (step - down) 40v, 4.2a high performance cv/cc quick charger syn chronous rev1. 0 - j ul 201 7 released - - 11 - d e t a il e d in f or m a t ion o p er at i on the A7442 is a monolithic high efficiency synchronous buck converters with cv / cc modes. it utilizes internal mosfets to achieve high efficiency and up to 4.2a output current in a wide input range from 6v to 36 v. the output voltage and constant current limit can be programed through the fb, csp and csn pins respectively. the A7442 is capable to operate in cc mode down to 3v output voltage to protect the soft - short condition that is from the over current of the portable device. with the slope compensated current mode pwm control, provides stable switching and cycle - by - cycle current limit for excellent load and line responses and protection of the internal switches. during normal operation, the internal main switch is turned on for a certain time to ramp up the inductor current at each rising edge of the internal oscillator, and turned off when the peak inductor current is above the error voltage. the current comparator limits the peak inductor current. once the main switch is turned off, the synchronous rectifier will be turned on immediately and stay on until either the inductor current decay to zero, as indicated by the zero current comparator or the beginning of the next clock cycle. c omp ens a t i o n f or o ut p ut c or d v ol t ag e d r o p in charger applications, the voltage drop across the output cord is significant in high current charging process. in some cases, excessive voltage drop across the output cord will even extend the charging time if high impedance output cord is used. the A7442 integrated a cable compensation function. when the output current increases, the cc pin sinks current into the ic to increase the voltage drop across the resistor, r cc , in order to increase the output voltage. the sinking current of the cc pin is proportional to the voltage across csp and csn pins. thus, the cable compensation function can increase the output voltage according to the load. the increment of the voltage measured at csp pin(vcsp) is called cable compensation voltage(vccomp). the value of rcc determines the gain of the cable compensation. after taking the voltage drop across the sensing resistor, rs, the value of rcc can be calculated using equation 1. r cc = )k v r (i v os -s x out ccomp (1) where ? r cc is the value of the resistor between cc pin and the node of the inductor. ? v ccomp is the cable compensation voltage measured at the csp pin. ? i out is the output current of the converter. ? v os is the internal offset voltage which is equal to 3.3 mv ? k is a constant which is equal to 279. ? rs is the value of the sensing resistor.
a i t s em i c ond u ctor i n c . www.ait - ic.com a 74 42 dc - dc converter/ buck (step - down) 40v, 4.2a high performance cv/cc quick charger syn chronous rev1. 0 - j ul 201 7 released - - 12 - p r ogr a mm ab l e c v / c c mod e c ont r o l the A7442 features a cv / cc function. it operates either in cv mode or cc mode. the cv and the cc l imits can be programed through fb, csp and csn pins respectively. with the programmable output voltage and constant current limit. the device is particularly suitable for qc 2.0, qc 3.0 type - c pd and apple portable device applications. the cc mode provides an accurate current limiting function which is programed through the sensing resistor, r s . output current can increase until it reaches the cc limit set by the sensing resistor. at this point, the A7442 will transit from regulating output voltage to regul ating output current, and the output voltage will drop with increasing load. the A7442 can output up to 4.2a current at 5v output voltage. in general, 3 a output current is sufficient for charging purpose at 5 v output voltage. f i g ur e 1 shows the cc limit verse sensing resistor, r s . in this case, the cc limit should be set at a level which is a bout 10% higher than 3a. a 18 m sensing resistor should be selected for ensuring 3 a continuous output current. the cc limit is adaptive at different output voltages which is particularly useful in qc 2.0 / 3.0 application. f i gur e 1. c ons t ant c ur r e nt l i m i t v s . s e ns i n g r es i s t or in cv m ode, the feedback voltage is regulated at 1 v and the output voltage is programed by the feedback divider r cc , r 1 and r 2 . r cc and r 1 together form the upper feedback resistor and r 2 is the lower feedback resistor. the output voltage at no load can be calculated using equation 2. v out = 2 2 1 cc r r )r (r + + (2) w here ? v out is the output voltage at no load. ? r cc is the value of the resistor between cc pin and the node of the inductor. ? r 1 is the value of the resistor between cc and fb pins. ? r 2 is the va lue of the resistor between fb and gnd pins.
a i t s em i c ond u ctor i n c . www.ait - ic.com a 74 42 dc - dc converter/ buck (step - down) 40v, 4.2a high performance cv/cc quick charger syn chronous rev1. 0 - j ul 201 7 released - - 13 - c y c l e by c y c l e p eak c ur r en t l i m i t the peak current limit prevents the A7442 from high inductor current and drawing excessive current from the input voltage rail. excessive current might occur with a shorted or s aturated inductor or a heavy load or a shorted output circuit condition. if the inductor current reaches the peak limit threshold, the high - side mosfet is turned off and the low - side mosfet is turned on to ramp down the inductor current. o ut put a ut o d i s c h ar ge the A7442 is designed for working with usb interface ic (qc 2.0 / 3.0). regarding to the output voltage changing capability of this application, the A7442 integrates an output auto discharge path to discharge the output capacitor at 60 ma typically once the voltage at the fb pin raise above 11 3 % of feedback voltage threshold. the function is crucial in high voltage charging scheme. for instant, the output capacitor is charged - up by the high voltage which is set by the portable device. after the portable device is unplugged, the output capacitor takes time to be discharged if there is no high current discharge path. there is a chance that a conventional 5v portable device is damaged by a high voltage once it is connected to the power supply immediately af ter the detachment of qc 2.0 / 3.0 portable device. i npu t u n der - v ol t ag e l oc k ou t ( u v lo ) an input uvlo circuit prevents the converter from starting the operation until the input voltage rises above the typical uvlo threshold of 4. 4 v. i npu t o v er v ol t ag e p r o t ec t i o n( o v p ) the input ovp is an additional function to protect the device from damage in a condition which is above the specified input voltage range. once the input voltage is raising above input ovp threshold, 39.5 v typically, the A7442 stops switching to reduce the chance of damage by the voltage spike at sw pin. the device goes back to normal operation until the input voltage falls a hysteresis about 2.5v below the input ovp threshold. o ut put o v er v ol t ag e p r ot ec t i on( o v p ) there are two individual output ovp functions in the A7442 . those are csp ovp and fb ovp. the csp ovp senses the output voltage directly. if the voltage at csp pin is detected above csp ovp threshold of 14 v(typ.), the device stops switching immediately until the voltage at the csp pin drops the hysteresis voltage lower than csp ovp threshold. this function prevents the device as well as the output capacitors from damage by high voltage on the output even though the feedback resistors are faulty opened. the operation of fb ovp is very similar to the csp ovp except that it detects the voltage of the fb pin(v fb ). once v fb raises above 11 3 % of the feedback voltage threshold, the fb ovp will be triggered immediately and stop switching. this ovp condition will be remove until v fb drop 2% lower than fb ovp threshold.
a i t s em i c ond u ctor i n c . www.ait - ic.com a 74 42 dc - dc converter/ buck (step - down) 40v, 4.2a high performance cv/cc quick charger syn chronous rev1. 0 - j ul 201 7 released - - 14 - h i c c up mod e o ut put u n der v o l t a ge p r ot ec t i on( u v p ) there is a csp uvp threshold. if the threshold is hit, the hiccup mode output uvp will be triggered by disabling the converter and restarts soft - start after a predefined interval about 0. 7 s. the A7442 repeats this mode until the under voltage condition is removed. this function prevents the damage of the system from hard - short condition and a soft - short condition from the over current of portable device. s of t - s t ar t the A7442 implement s the soft - start function to reduce the inrush current during startup. the soft - start begins once the input voltage raises abov e typical uvl o threshold of 4. 4 v. the soft - start time is typically 1.6 ms. t h er ma l s h ut d ow n a thermal shutdown is implemented to prevent the damage due to excessive heat and power dissipation. typically, the thermal shutdown happens at the junction temperature of 165 c. when the thermal shutdown is triggered, the device stops switching until the junction temperature drops the hysteresis temperature lower than thermal shutdown threshold, then the device starts switching again.
a i t s em i c ond u ctor i n c . www.ait - ic.com a 74 42 dc - dc converter/ buck (step - down) 40v, 4.2a high performance cv/cc quick charger syn chronous rev1. 0 - j ul 201 7 released - - 15 - a p p l ic a t ion s in f or m a t ion d es i g n r e qu i r em ent d es i g n p ar a met er s t ar get v a l u es input voltage range 6v to 40 v typical input voltage 24 v output voltage 5v out put current rating 3.5 a v ccomp at full load 250 mv t a bl e 1. d es i gn p ar am et er s s et t i n g t he c c l i m i t the simplified application circuit is showed on the front page. f i gur e 1 shows the cc limit at 5 v output verse r s . according to this figure, r s should be set at around 15 m to output 3.5a continuous current. s et t i n g t he c ab l e c om pe ns a t i on r es i s t or the cable compensation resistor, r cc , determines the gain of the cable compensation. by subtitling v ccomp , i out , r s , v os and k into the equation 1, r cc = 18. 21 k . 18 k is the clo sest e24 standard value. t a bl e 2. shows the cable compensation voltage at different load with r cc = 18 k and r s = 15 m. i l oad ( a) v ccomp ( m v) 0 0 0.5 21 1 59 1.5 96 2 134 2.4 164 3 209 3.5 247 t a bl e 2. c a bl e c o mp ens at i o n v o l t a ge at d i f f er ent lo a d s et t i n g t he o u t pu t v ol t ag e the feedback resistors, r 1 and r 2 , together with the cable compensation resistor, r cc , program the output voltage at no load condition according to the equation 2. for qc 2.0 / 3.0 applications, the upper feedback resistor(r cc + r 1 ) is fixed at 100 k generally for compatibility. thus, r 1 = 100 k - 18 k = 82 k. by subtitling r cc , r 1 and v out into the equation 2, r 2 = 25 k (24.9 k is the closest standard value).
a i t s em i c ond u ctor i n c . www.ait - ic.com a 74 42 dc - dc converter/ buck (step - down) 40v, 4.2a high performance cv/cc quick charger syn chronous rev1. 0 - j ul 201 7 released - - 16 - i nduc t or s el ec t i o n since the selection of the inductor affects the power supplys steady state operation, transient behavior, loop stability, and overall efficiency, the inductor is the most important component in switch power regulator design. three most important specifications to the performance of the inductor are the inductor value, dc resistance, and saturation current. the A7442 designed to work with inductor values between 15 h to 47 h. a 15 h inductor is typically available in a smaller or lo wer - profile package, while a 47 h inductor produces lower inductor current ripple. if the output current is limited by the peak current limit of the ic, using a 47 h inductor can maximize the converters output current capability. the tolerance of inductors can be ranging from 10% to 30%. the inductance will further decrease 20% to 35% from the value of zero bias current depending on the definition of saturation by inductor manufacturers. the basic requirements of selecting an inductor are the saturation current must be higher than the peak switching current and the dc rated current is higher than the average inductor current in normal operation. in buck converter, the average inductor current is equal to the output current. the inductor value can be derived from the equation 3. l= sw l x in ccomp out in ccomp out fx i v ) v- v- (v x ) v (v ? + (3) where ? i l is the inductor peak - to - peak ripple current. ? v out is the output voltage at no load. ? v ccomp is the cable compensation voltage measured at the csp pin. ? v in is the input voltage. ? f sw is the switching frequency lower inductor value results in higher ripple current and vice versa. choose inductor ripple current approximately 30 % of the maximum load current, 3.5 a, or i l = 1.05 a. by subtitling v in (typ.), v out , i l and v ccomp , i l and f sw (typ.) into the above equation, the inductor value, l, is 31.3 h. the common inductor value is 33 h. the saturation current of the inductor must be higher than the maximum output current, 3.5 a, plus half of the inductor ripple current in the worst case, i.e. highest operating v in (36 v) lowest f sw (109 khz), lowest inductor value( - 10 ~ - 30% from nominal value), to prevent the core from saturation. t a b l e 3 lists a typical toroid inductor specifi cation that meets target application for the design requirement. c or e m an uf ac t ur er c or e p ar t n umb er l( h ) n o. o f t ur ns w ir e ? ( m m) al ( nh / n 2 ) s i z e [ o dx i dx h] ( m m) kdm magnetic powder cores ks040 - 125a 33 10% 23 0.7 125 66 1 0.20 x 5.08 x 3.96 t a bl e 3. r ec o mm end ed t or o i d i nd uc t or
a i t s em i c ond u ctor i n c . www.ait - ic.com a 74 42 dc - dc converter/ buck (step - down) 40v, 4.2a high performance cv/cc quick charger syn chronous rev1. 0 - j ul 201 7 released - - 17 - i npu t c a pac i t or s e l ec t i on the input capacitor reduces the surge current drawn from the input and the switching noise from the converter. the input capacitor impedance at the switching frequency should be less than the input source impedance to prevent high frequency switching current passing to the input. a low esr input capacitor sized for maximum rms current must be used. multilayer ceramic capacitor(mlcc) with x5r or x7r dielectric is highly recommended because of their low esr, low temperature coefficients and compact size characteristics. a 22 f mlcc is sufficient for most of applications. o ut put c a pac i t or s el ec t i on the output capacitor is required to keep the output voltage ripple small and to ensure regulation loop stability. the output capacitor must have low impedance at the switching freq uency. mlcc with x5r or x7r dielectric is recommended due to their low esr, low temperature coefficients and compact size characteristics. the output ripple, v out , is determined by: vout ?? ? ?? ? + out sw x sw x in out in outx cx f x 8 1 esr x l f v ) v- (v v (4) l ay out c o ns i d er at i ons when doing the pcb layout, the following suggestions should be taken into consideration to ensure proper operation of the A7442 . these suggestions are also illustrated graphically in f i gur e 2 and f i gur e 3 . 1. the power path including the gnd trace, the sw trace an d the v in trace should be as short as possible, direct and wide. 2. the fb pin should be connected directly to the center point of the output feedback resistors divider. 3. the resistor divider must be connected to the output capacitor and gnd pin directly. 4. the input decoupling mlcc should be placed as close to the v in and gnd pins as possible and connected to input power plane and ground plane directly. this capacitor provides the ac current to the internal power mosfet. 5. the power path between the output mlcc, c 5, and the power inductor should be kept short and the other terminal of the capacitor should connect to the ground plane directly to reduce noise emission. 6. keep the switching node, sw, away from the sensitive fb node. 7. keep the negative terminals of input capacitor and output capacitor as close as possible. 8. use kelvin sense connection techniques from the sensing resistor, rs, pads directly to the csp and csn pins to achieve accurate cc limit. 9. use large copper plane and thermal vias for gnd for the best heat dissipation and noise immunity.
a i t s em i c ond u ctor i n c . www.ait - ic.com a 74 42 dc - dc converter/ buck (step - down) 40v, 4.2a high performance cv/cc quick charger syn chronous rev1. 0 - j ul 201 7 released - - 18 - f i gur e 2 . t op lay er f i gur e 3 . b o t t o m l ay er t y p i c al a p pl i c at i o n c i r c ui t w i t h u s b i nt er f ac e i c t y p i c al a p pl i c at i o n c i r c ui t f or h i gh c ur r ent o ut p ut
a i t s em i c ond u ctor i n c . www.ait - ic.com a 74 42 dc - dc converter/ buck (step - down) 40v, 4.2a high performance cv/cc quick charger syn chronous rev1. 0 - j ul 201 7 released - - 19 - p a c k a ge in f or m a t ion dimension in psop8 (unit: mm) s y mb ol m i ll im e t e r s i nc hes m in m ax m in m ax a 1.300 1.700 0.051 0.067 a1 0.000 0.100 0.000 0.004 a2 1.350 1.550 0.053 0.061 b 0.330 0.510 0.013 0.020 c 0.170 0.250 0.00 7 0.010 d 4.700 5.100 0.185 0.20 1 d1 3.050 3.350 0.120 0.13 2 e 3.800 4.000 0.150 0.157 e1 5.800 6.200 0.228 0.244 e2 2.160 2.360 0.085 0.093 e 1.270 bsc 0.050 bsc l 0.400 1.270 0.016 0.050 0 8 0 8
a i t s em i c ond u ctor i n c . www.ait - ic.com a 74 42 dc - dc converter/ buck (step - down) 40v, 4.2a high performance cv/cc quick charger syn chronous rev1. 0 - j ul 201 7 released - - 20 - i m p o rt a nt no t i ce ait semiconductor inc. (ait) reserves the right to make changes to any its product, specifications, to discontinue any integrated circuit product or service without notice, and advises its customers to obtain the latest version of relevant information to verify, before placing orders, that the information being relied on is current. ait semiconductor inc.'s integrated circuit products are not designed, i ntended, authorized, or warranted to be suitable for use in life support applications, devices or systems or other critical applications. use of ait products in such applications is understood to be fully at the risk of the customer. as used herei n may involve potential risks of death, personal injury, or server property, or environmental damage. in order to minimize risks associated with the customer's applications, the customer should provide adeq uate design and operating safeguards. ait semiconductor inc . assumes to no liability to customer product design or application support. ait warrants the performance of its products of the specifications applicable at the time of sa le.

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