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rev e: 3/2 /07 sp7655 wide input voltage range 8a, 300khz, buck regulator ? 2007 sipex corporation sp7655 features 2.5v to 28v step down achieved using dual input output voltage down to 0.8v 8a output capability built in low r dson power switches (15 m 1 typ) highly integrated design, minimal components 300 khz fixed frequency operation uvlo detects both v cc and v in over temperature protection short circuit protection with auto-restart wide bw amp allows type ii or iii compensation programmable soft start fast transient response high efficiency: greater than 95% possible non- synchronous start-up into a pre-charged output lead free, rohs compliant package: small 7mm x 4mm dfn u.s. patent #6,922,041 wide input voltage range, 8amp 300khz, buck regulator the sp7655 is a synchronous step-down switching regulator optimized for high efficiency. the part is designed to be especially attractive for dual supply, 12v or 24v distributed power systems stepped down with 5v used to power the controller. this lower v cc voltage minimizes power dissipation in the part and is used to drive the top switch. the sp7655 is designed to provide a fully integrated buck regulator solution using a fixed 300khz frequency, pwm voltage mode architecture. protection features include uvlo, thermal shutdown and output short circuit protection. the sp7655 is available in the space saving dfn package . typical application circuit description power blox tm 16v cbst 6,800pf l1 2.2uh, irate=8a c1 22uf cvcc 2.2uf u1 sp7655 pgnd 1 pgnd 2 pgnd 3 gnd 4 vfb 5 comp 6 uvin 7 gnd 8 ss 9 vin 10 vin 11 vin 12 vin 13 lx 14 lx 15 lx 16 nc 17 bst 18 gnd 19 gnd 20 gnd 21 vcc 22 lx 23 lx 24 lx 25 lx 26 dbst css 47nf cp1 22pf 3.30v 0-8a rset 21.5k 1 ,1% gnd c3 47uf c4 22uf notes: 12v vin sd101aws have three contacts isolated from one another: vin, swnode, and gnd. rz3 7.15k 1 1% vout cz3 150pf cz2 1,000pf r1 68.1k 1 ,1% rz2 15k 1 ,1% cf1 100pf f s=300khz enable +5v vcc 2. rset=54.48/(vout-0.8v) kohms (note 2) 6.3v 1. u1 bottom side layout should 16v 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 2 2 23 24 25 26 top view heatsink pad 1 connect to lx heatsink pad 2 connect to gnd heatsink pad 3 connect to v in p gnd p gnd gnd v fb com p uvin gnd ss v in lx lx lx lx v cc gnd gnd gnd bst nc lx lx lx dfn p ackage 7mm x 4m m sp7655 p gnd v in v in v in
2 rev e: 3/2 /07 sp7655 wide input voltage range 8a, 300khz, buck regulator ? 2007 sipex corporation electrical specifications unless otherwise specified: -40 c < t amb < 85 c, -40 c < tj< 125 c, 4.5v < v cc < 5.5v, 3v< vin< 28v, bst=lx + 5v, lx = gnd = 0.0v, uvin = 3.0v, cv cc = 1 f, c comp = 0.1 f, c ss = 50nf, typical measured at v cc = 5v. the z denotes the specifications which apply over the full temperature range, unless otherwise specified. v cc ............................................................... ................................... 7v v in .............................................................................................................................. ............. 30v i lx .............................................................................................................................. .............. 10a bst ............................................................... ................................ 35v lx-bst ............................................................... .............. -0.3v to 7v lx ............................................................... ........................ -1v to 30v all other pins .......................................................... -0.3v to v cc +0.3v storage temperature .................................................. -65 c to 150 c power dissipation ...................................... internally limited via otp esd rating ............................................................... ........... 2kv hbm thermal resistance v jc .................................................................................... 5 c/w absolute maximum ratings retemarap .nim .pyt .xam stinu snoitidnoc tnerructnecseiuq v cc )gnihctiwson(tnerrucylppus 5.1 3 am v bf v9.0= v cc )gnihctiws(tnerrucylppus 6 9 am ? )gnihctiwson(tnerrucylppustsb 2.0 4.0 am v bf v9.0= )gnihctiws(tnerrucylppustsb 5 8 am ? olvu:noitcetorp v cc dlohserhttratsolvu 00.4 52.4 5.4 v v cc siseretsyholvu 001 002 003 vm dlohserhttratsnivu 3.2 5.2 56.2 v ? siseretsyhnivu 002 003 004 vm tnerructupninivu 1 a v0.3=nivu ecnereferreifilpmarorre ecnereferreifilpmarorre 297.0 008.0 808.0 v erusaem,.gifnocniagx2 v;bfv cc co52=t,v5= ecnereferreifilpmarorre erutarepmetdnaenilrevo 887.0 008.0 218.0 v ? ecnatcudnocsnartreifilpmarorre 6 v/am niagreifilpmarorre 06 bd daolon tnerrucknispmoc 051 a v bf v9.0=pmoc,v9.0= tnerrucecruospmoc 051 a v bf v2..2=pmoc,v7.0= v bf tnerrucsaibtupni 05 002 an v bf v8.0= eloplanretni 4 zhm pmalcpmoc 5.2 v v bf co52=at,v7.0= tneiciffeoc.pmetpmalcpmoc 2- co/vm these are stress ratings only and functional operation of the device at these ratings or any other above those indicated in the operation sections of the specifications below is not implied. exposure to absolute maximum rating conditions for extended periods of time may affect reliability.
3 rev e: 3/2 /07 sp7655 wide input voltage range 8a, 300khz, buck regulator ? 2007 sipex corporation electrical specifications unless otherwise specified: -40 c < t amb < 85 c, -40 c< tj< 125 c, 4.5v < v cc < 5.5v, 3v< vin< 28v, bst=lx + 5v, lx = gnd = 0.0v, uvin = 3.0v, cv cc = 1 f, c comp = 0.1 f, c ss = 50nf, typical measured at v c c = 5v. the z denotes the specifications which apply over the full temperature range, unless otherwise specified. r e t e m a r a p .n i m . p y t . x a m s t i n u s n o i t i d n o c h t a p y a l e d p o o l & p m a r , r o t a r a p m o c m w p : p o o l l o r t n o c e d u t i l p m a p m a r 2 9 . 0 1 . 1 8 2 . 1 v t e s f f o p m a r 1 . 1 v t a p m o c p m a r , c o 5 2 = g n i h c t i w s s t r a t s h g l i t n u t n e i c i f f e o c . p m e t t e s f f o p m a r 2 - c o /v m h t d i w e s l u p m u m i n i m h g 0 9 0 8 1 s n ? o i t a r y t u d e l b a l l o r t n o c m u m i x a m 2 9 7 9 % o i t a r y t u d m u m i x a m e r o f e b t s u j d e r u s a e m s n i g e b g n i s l u p o i t a r y t u d m u m i x a m 0 0 1 % s e l c y c 0 2 r o f d i l a v o i t a r r o t a l l i c s o l a n r e t n i 240 300 360 z h k ? t r a t s t f o s : s r e m i t : t n e r r u c e g r a h c s s 01 a : t n e r r u c e g r a h c s i d s s 1 a m ? v 2 . 0 =s s , t n e s e r p t l u a f l a m r e h t & t i u c r i c t r o h s : n o i t c e t o r p e g a t l o v d l o h s e r h t t i u c r i c t r o h s 2 . 0 5 2 . 0 3 . 0 v ? v d e r u s a e m f e r - )v 8 . 0 ( v b f t u o e m i t p u c c i h 0 0 2 s m v b f v 5 . 0 = s e l c y c k c o l c e l b a w o l l a f o r e b m u n e l c y c y t u d % 0 0 1 t a 0 2 s e l c y c s e l c y c 0 2 r e t f a e s l u p l g m u m i n i m 5 . 0 s e l c y c v b f v 7 . 0 = e r u t a r e p m e t n w o d t u h s l a m r e h t 5 4 1 c o v b f v 7 . 0 = e r u t a r e p m e t y r e v o c e r l a m r e h t 5 3 1 c o s i s e r e t s y h l a m r e h t 01 c o e g a t s r e w o p : t u p t u o r e d i s h g i h n o s d 5 1 ? m ? v c c i ; v 5 = t u o a 8 = t b m a c o 5 2 = r t e f s u o n o r h c n y s n o s d 5 1 ? m ? v c c i ; v 5 = t u o a 8 = t b m a c o 5 2 = t n e r r u c t u p t u o m u m i x a m 8 a ?
rev e: 3/2 /07 sp7655 wide input voltage range 8a, 300khz, buck regulator ? 2007 sipex corporation general overview the sp7655 is a fixed frequency, voltage mode, synchronous pwm regulator optimized for high efficiency. the part has been designed to be especially attractive for high voltage applica- tions utilizing 5v to power the controller and 2.5v to 28v for step down conversion. the heart of the sp7655 is a wide bandwidth transconductance amplifier designed to accom- modate type ii and type iii compensation schemes. a precision 0.8v reference, present on the positive terminal of the error amplifier, permits the programming of the output voltage down to 0.8v via the v fb pin. the output of the error amplifier, comp, compared to a 1.1v peak-to-peak ramp is responsible for trailing edge pwm control. this voltage ramp, and pwm control logic are governed by the internal oscillator that accurately sets the pwm fre- quency to 300khz. theory of operation the sp7655 contains two unique control fea- tures that are very powerful in distributed appli- cations. first, asynchronous driver control is enabled during startup, to prohibit the low side switch from pulling down the output until the high side switch has attempted to turn on. sec- ond, a 100% duty cycle timeout ensures that the low side switch is periodically enhanced during extended periods at 100% duty cycle. this guar- antees the synchronized refreshing of the bst capacitor during very large duty cycle ratios. the sp7655 also contains a number of valuable protection features. programmable v in uvlo allows the user to set the exact value at which the conversion voltage can safely begin down con- version, and an internal v cc uvlo which en- sures that the controller itself has enough volt- age to operate properly. other protection fea- pin description pin # pin name description 1-3 p gnd ground connection for the synchronous rectifier 4,8,19-21 gnd ground pin. the control circuitry of the ic and lower power driver are referenced to this pin. return separately from other ground traces to the (-) terminal of c out . 5 v fb feedback voltage and short circuit detection pin. it is the inverting input of the error amplifier and serves as the output voltage feedback point for the buck converter. the output voltage is sensed and can be adjusted through an external resistor divider. whenever v fb drops 0.25v below the positive reference, a short circuit fault is detected and the ic enters hiccup mode. 6 comp output of the error amplifier. it is internally connected to the inverting input of the pwm comparator. an optimal filter combination is chosen and connected to this pin and either ground or v fb to stabilize the voltage mode loop. 7 uvin uvlo input for v in voltage. connect a resistor divider between v in and uv in to set minimum operating voltage. 9 ss soft start. connect an external capacitor between ss and gnd to set the soft start rate based on the 10a source current. the ss pin is held low via a 1ma (min) current during all fault conditions. 10-13 v in input connection to the high side n-channel mosfet. place a decoupling capacitor between this pin and pgnd. 14-16,23-26 lx connect an inductor between this pin and v out 17 nc no connect 18 bst high side driver supply pin. connect bst to the external boost diode and capacitor as shown in the typical application circuit on page 1. high side driver is connected between bst pin and swn pin. 22 vcc input for external 5v bias supply
5 rev e: 3/2 /07 sp7655 wide input voltage range 8a, 300khz, buck regulator ? 2007 sipex corporation tures include thermal shutdown and short-cir- cuit detection. in the event that either a thermal, short-circuit, or uvlo fault is detected, the sp7655 is forced into an idle state where the output drivers are held off for a finite period before a restart is attempted. soft start ?soft start? is achieved when a power converter ramps up the output voltage while controlling the magnitude of the input supply source cur- rent. in a modern step down converter, ramping up the positive terminal of the error amplifier controls soft start. as a result, excess source current can be defined as the current required to charge the output capacitor. iv in = c out * ( 6 v out / 6 t soft-start ) the sp7655 provides the user with the option to program the soft start rate by tying a capacitor from the ss pin to gnd. the selection of this capacitor is based on the 10 a pullup current present at the ss pin and the 0.8v reference voltage. therefore, the excess source can be redefined as: iv in = c out * ( 6 v out *10 a / (c ss * 0.8v) under voltage lock out (uvlo) the sp7655 contains two separate uvlo com- parators to monitor the bias (v cc ) and conver- sion (v in ) voltages independently. the v cc uvlo threshold is internally set to 4.25v, whereas the v in uvlo threshold is program- mable through the uvin pin. when the uvin pin is greater than 2.5v, the sp7655 is permitted to start up pending the removal of all other faults. both the v cc and v in uvlo compara- tors have been designed with hysteresis to pre- vent noise from resetting a fault. thermal and short-circuit protection because the sp7655 is designed to drive large output current, there is a chance that the power converter will become too hot. therefore, an internal thermal shutdown (145 c) has been included to prevent the ic from malfunctioning at extreme temperatures. a short-circuit detection comparator has also been included in the sp7655 to protect against an accidental short at the output of the power converter. this comparator constantly monitors the positive and negative terminals of the error amplifier, and if the v fb pin falls more than 250mv (typical) below the positive reference, a short-circuit fault is set. because the ss pin overrides the internal 0.8v reference during soft start, the sp7655 is capable of detecting short- circuit faults throughout the duration of soft start as well as in regular operation. handling of faults: upon the detection of power (uvlo), thermal, or short-circuit faults, the sp7655 is forced into an idle state where the ss and comp pins are pulled low and both switches are held off. in the event of uvlo fault, the sp7655 remains in this idle state until the uvlo fault is removed. upon the detection of a thermal or short-circuit fault, an internal 200ms timer is activated. in the event of a short-circuit fault, a restart is at- tempted immediately after the 200ms timeout expires. whereas, when a thermal fault is de- tected, the 200ms delay continuously recycles and a restart cannot be attempted until the ther- mal fault is removed and the timer expires. error amplifier and voltage loop since the heart of the sp7655 voltage error loop is a high performance, wide bandwidth current- limited (+/-150 a) transconductance ampli- fier, there are many ways to compensate the voltage loop or to control the comp pin exter- nally. if a simple, single pole, single zero response is desired, then compensation can be theory of operation
6 rev e: 3/2 /07 sp7655 wide input voltage range 8a, 300khz, buck regulator ? 2007 sipex corporation theory of operation as simple as an rc circuit to ground. if a more complex compensation is required, then the amplifier has enough bandwidth (45 at 4 mhz) and enough gain (60db) to run type iii compen- sation schemes with adequate gain and phase margins at crossover frequencies greater than 50khz. the common mode output of the error amplifier is 0.9v to 2.2v. therefore, the pwm voltage ramp has been set between 1.1v and 2.2v to ensure proper 0% to 100% duty cycle capability. the voltage loop also includes two other very important features. one is non-s ynchronous startup mode. basically, the synchronous recti- fier cannot turn on unless the high side switch has attempted to turn on or the ss pin has exceeded 1.7v. this feature prevents the con- troller from ?dragging down? the output voltage during startup or in fault modes. the second feature is a 100% duty cycle timeout that en- sures synchronized refreshing of the bst ca- pacitor at very high duty ratios. in the event that the high side nfet is on for 20 continuous clock cycles, a reset is given to the pwm flip- flop half way through the 21 st cycle. this forces gl to rise for the cycle, in turn refreshing the bst capacitor. the boost capacitor is used to generate a high voltage drive supply for the high side switch, which is 5v above v in . power mosfets the sp7655 contains a pair of integrated low resistance n-channel switches designed to drive up to 10 amps of output current. care should be taken to de-rate the output current based on the thermal conditions in the system such as ambi- ent temperature, airflow and heat sinking. maxi- mum output current could be limited by thermal limitations of a particular application by taking advantage of the integrated-over-temperature protective scheme employed in the sp7655. the sp7655 incorporates a built-in over-tem- perature protection to prevent internal overheat- ing. gh voltage gl voltage v(v in ) 0v -0v -v(diode) v v(v in )+v(v cc ) bst voltage v(v cc ) time swn voltage v bst v swn v(v cc) the sp7655 can be set to different output volt- ages. the relationship in the following formula is based on a voltage divider from the output to the feedback pin vfb, which is set to an internal reference voltage of 0.80v. standard 1% metal film resistors of surface mount size 0603 are recommended. vout = 0.80v ( r1 / r set + 1 ) => r set = r1 . [ ( vout / 0.80v ) ? 1 ] where r1 = 68.1k 1 and for v out = 0.80v setting, simply remove r set from the board. fur- thermore, one could select the value of the r1 and r set combination to meet the exact output voltage setting by restricting r1 resistance range such that 50k 1 < r1 < 100k 1 for overall system loop stability. setting output voltages
7 rev e: 3/2 /07 sp7655 wide input voltage range 8a, 300khz, buck regulator ? 2007 sipex corporation applications information inductor selection there are many factors to consider in selecting the inductor including core material, inductance vs. frequency, current handling capability, effi- ciency, size and emi. in a typical sp7655 cir- cuit, the inductor is chosen primarily for value, saturation current and dc resistance. increasing the inductor value will decrease output voltage ripple, but degrade transient response. low in- ductor values provide the smallest size, but cause large ripple currents, poor efficiency and require more output capacitance to smooth out the larger ripple current. the inductor must be able to handle the peak current at the switching frequency without saturating, and the copper resistance in the winding should be kept as low as possible to minimize resistive power loss. a good compromise between size, loss and cost is to set the inductor ripple current to be within 20% to 40% of the maximum output current. the switching frequency and the inductor oper- ating point determine the inductor value as fol- lows: ( max) (max) (max) ) ( outrs in out inout ikfv vvv l < = where: f s = switching frequency k r = ratio of the ac inductor ripple current to the maximum output current the peak-to-peak inductor ripple current is: lfv vvv i s i n out inout pp (max) (max) ) ( < = once the required inductor value is selected, the proper selection of core material is based on peak inductor current and efficiency require- ments. the core must be large enough not to saturate at the peak inductor current... 2 (max) p p out peak i ii += ...and provide low core loss at the high switch- ing frequency. low cost powdered-iron cores have a gradual saturation characteristic but can introduce considerable ac core loss, especially when the inductor value is relatively low and the ripple current is high. ferrite materials, although more expensive, have an abrupt saturation char- acteristic with the inductance dropping sharply when the peak design current is exceeded. nev- ertheless, they are preferred at high switching frequencies because they present very low core loss while the designer is only required to prevent saturation. in general, ferrite or molypermalloy materials are a better choice for all but the most cost sensitive applications. optimizing efficiency the power dissipated in the inductor is equal to the sum of the core and copper losses. to mini- mize copper losses, the winding resistance needs to be minimized, but this usually comes at the expense of a larger inductor. core losses have a more significant contribution at low output cur- rent where the copper losses are at a minimum, and can typically be neglected at higher output currents where the copper losses dominate. core loss information is usually available from the magnetics vendor. proper inductor selection can affect the resulting power supply efficiency by more than 15%! the copper loss in the inductor can be calculated using the following equation: winding rmslcul rip 2 )()( = where i l(rms) is the rms inductor current that can be calculated as follows: i l(rms) = i out(max) 1 + 1 ( i pp ) 2 3 i out(max)
8 rev e: 3/2 /07 sp7655 wide input voltage range 8a, 300khz, buck regulator ? 2007 sipex corporation output capacitor selection the required esr (equivalent series resis- tance) and capacitance drive the selection of the type and quantity of the output capacitors. the esr must be small enough that both the resis- tive voltage deviation due to a step change in the load current and the output ripple voltage do not exceed the tolerance limits expected on the output voltage. during an output load transient, the output capacitor must supply all the addi- tional current demanded by the load until the sp7655 adjusts the inductor current to the new value. in order to maintain v out ,the capacitance must be large enough so that the output voltage is held up while the inductor current ramps to the value corresponding to the new load current. addi- tionally, the esr in the output capacitor causes a step in the output voltage equal to the current. because of the fast transient response and inher- ent 0% to100% duty cycle capability provided by the sp7655 when exposed to an output load transient, the output capacitor is typically cho- sen for esr, not for capacitance value. the esr of the output capacitor, combined with the inductor ripple current, is typically the main contributor to output voltage ripple. the maxi- mum allowable esr required to maintain a specified output voltage ripple can be calculated by: r esr ) 6 v out i pk-pk where: 6 v out = peak-to-peak output voltage ripple i pk-pk = peak-to-peak inductor ripple current the total output ripple is a combination of the esr and the output capacitance value and can be calculated as follows: 6 v out = ( i pp (1 ? d) ) 2 + (i pp r esr ) 2 c out f s f s = switching frequency d = duty cycle c out = output capacitance value input capacitor selection the input capacitor should be selected for ripple current rating, capacitance and voltage rating. the input capacitor must meet the ripple current requirement imposed by the switching current. in continuous conduction mode, the source cur- rent of the high-side mosfet is approximately a square wave of duty cycle v out /v in . more accurately the current wave form is trapezoidal, given a finite turn-on and turn-off, switch tran- sition slope. most of this current is supplied by the input bypass capacitors. the rms current handling capability of the input capacitors is determined at maximum output current and under the assumption that the peak-to-peak in- ductor ripple current is low, it is given by: i cin(rms) = i out(max) 3 d(1 - d) the worst case occurs when the duty cycle d is 50% and gives an rms current value equal to i out /2. select input capacitors with adequate ripple current rating to ensure reliable operation. the power dissipated in the input capacitor is: )( 2 )( cinesr rmscin cin rip = this can become a significant part of power losses in a converter and hurt the overall energy transfer efficiency. the input voltage ripple primarily depends on the input capacitor esr and capacitance. ignoring the inductor ripple current, the input voltage ripple can be deter- mined by: applications information 2 )( )( (max) )( inins out i nout maxout cine sr out in vcf vvvi riv < + = 6
rev e: 3/2 /07 sp7655 wide input voltage range 8a, 300khz, buck regulator ? 2007 sipex corporation applications information the capacitor type suitable for the output capac- itors can also be used for the input capacitors. however, exercise additional caution when tanta- lum capacitors are used. tantalum capacitors are known for catastrophic failure when exposed to surge current, and input capacitors are prone to such surge current when power supplies are con- nected ?live? to low impedance power sources. although tantalum capacitors have been success- fully employed at the input, it is generally not recommended. loop compensation design the open loop gain of the whole system can be divided into the gain of the error amplifier, pwm modulator, buck converter output stage, and feedback resistor divider. in order to cross over at the desired frequency cut-off (fco), the gain of the error amplifier compensates for the attenuation caused by the rest of the loop at this frequency. the goal of loop compensation is to manipulate loop frequency response such that its cross-over gain at 0db, results in a slope of - 20db/dec. the first step of compensation design is to pick the loop crossover frequency. high crossover frequency is desirable for fast transient response, but often jeopardizes the power supply stability. crossover frequency should be higher than the esr zero but less than 1/5 of the switching frequency or 60khz. the esr zero is contrib- uted by the esr associated with the output capacitors and can be determined by: ? z(esr) = 1 2 / c out r esr the next step is to calculate the complex conju- gate poles contributed by the lc output filter, ? p(lc) = 1 2 / l c out when the output capacitors are of a ceramic type, the sp7655 evaluation board requires a type iii compensation circuit to give a phase boost of 180 in order to counteract the effects of an underdamped resonance of the output filter at the double pole frequency. sp7655 voltage mode control loop with loop dynamic (srz2cz2+1)(sr1cz3+1) (sr esr c out + 1) [s^2lc out +s(r esr +r dc ) c out +1] v in sr1cz2(srz3cz3+1)(srz2cp1+1) v ramp_pp v out (volts) + _ v ref (volts) notes: r esr = output capacitor equivalent series resistance. r dc = output inductor dc resistance. v ramp_pp = sp6132 internal ramp amplitude peak to peak voltage. condition: cz2 >> cp1 & r1 >> rz3 output load resistance >> r esr & r dc r 2 v ref (r 1 + r 2 ) or v out v fbk (volts) type iii voltage loop compensation g amp (s) gain block pwm stage g pwm gain block output stage g out (s) gain block voltage feedback g fbk gain block definitions: r esr = output capacitor equivalent series resistance r dc = output inductor dc resistance r ramp_pp = sp7655 internal ramp amplitude peak to peak voltage conditions: c z 2 >> cp1 and r1 >> rz3 output load resistance >> r esr and r dc
0 rev e: 3/2 /07 sp7655 wide input voltage range 8a, 300khz, buck regulator ? 2007 sipex corporation sp765x thermal resistance the sp765x family has been tested with a variety of footprint layouts along with different copper area and thermal resistance has been measured. the layouts were done on 4 layer fr4 pcb with the top and bottom layers using 3 ounces of copper and the power and ground layers using 1 ounce of copper. for the minimum footprint, only about 0.1 square inch (of 3 ounces of) copper was used on the top or footprint layer, and this layer had no vias to connect to the 3 other layers. for the medium footprint, about 0.7 square inches (of 3 ounces of) copper was used on the top layer, but vias were used to connect to the other 3 layers. for the maximum footprint, about 1.0 square inch (of 3 ounces of) copper was used on the top layer and many vias were used to connect to the 3 other layers. the results show that only about 0.7 square inches (of 3 ounces of) copper on the top layer and vias connecting to the 3 other layers are needed to get the best thermal resistance of 36 c/w. adding area on the top beyond the 0.7 square inches did not reduce thermal resistance. sp765x thermal resistance 4 layer board: top layer 3ounces copper gnd layer 1ounce copper power layer 1ounce copper bottom layer 3ounces copper minimum footprint: 44 c/w top layer: 0.1 square inch no vias to other 3 layers medium footprint: 36 c/w top layer: 0.7 square inch vias to other 3 layers maximum footprint: 36 c/w top layer: 1.0 square inch vias to other 3 layers applications information using a minimum of 0.1 square inches of (3 ounces of) copper on the top layer with no vias connecting to the 3 other layers produced a thermal resistance of 44 c/w. this thermal impedance is only 22% higher than the medium and large footprint layouts, indicating that space constrained designs can still benefit thermally from the powerblox family of ics. this indi- cates that a minimum footprint of 0.1 square inch, if used on a 4 layer board, can produce 44 c/w thermal resistance. this approach is still very worthwhile if used in a space con- strained design. the following page shows the footprint layouts from an orcad file. the thermal data was taken for still air, not with forced air. if forced air is used, some improvement in thermal resis- tance would be seen.
rev e: 3/2 /07 sp7655 wide input voltage range 8a, 300khz, buck regulator ? 2007 sipex corporation
2 rev e: 3/2 /07 sp7655 wide input voltage range 8a, 300khz, buck regulator ? 2007 sipex corporation bode plot of type iii error amplifier compensation. cp1 rz2 cz2 - + 6 5 vfb comp + - 0.8v cf1 v out r1 68.1k, 1% r set cz3 rz3 r set =54.48/ (vout -0.8) (k 1 ) type iii error amplifier compensation circuit applications information frequency (hz) error amplifier gain bandwidth product condition: c22 >> cp1, r1 >> rz3 20 log (rz2/r1) gain (db) 1/6.28(r22) (cz2) 1/6.28 (r1) (cz3) 1/6.28 (r1) (cz2) 1/6.28 (rz2) (cp1) 1/6.28 (rz3) (cz3)
3 rev e: 3/2 /07 sp7655 wide input voltage range 8a, 300khz, buck regulator ? 2007 sipex corporation typical performance characteristics efficiency vs load at 3.3vin 60 70 80 90 100 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 output load (a) vout=2.5v vout=1.8v vout=1.2v efficiency vs load at 5.0vin 60 70 80 90 100 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 output load (a) vout=3.3v vout=2.5v vout=1.8v vout=1.2v efficiency vs load at 12vin 60 70 80 90 100 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 output load (a) vout=5.0v vout=3.3v vout=2.5v vout=1.8v vout=1.2v efficiency vs load at 24vin 60 70 80 90 100 0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 output load (a) vout=12v vout=5.0v vout=3.3v vout=2.5v
rev e: 3/2 /07 sp7655 wide input voltage range 8a, 300khz, buck regulator ? 2007 sipex corporation typical performance characteristics sp7655 effi. v.s iout plots @ vin=12v, and vout=3.3v 83.0 84.0 85.0 86.0 87.0 88.0 89.0 90.0 91.0 92.0 1 2 3 4 5 6 7 8 load current (a) efficiency (%) sp7655 vout v.s iout plots @ vin=12v, and vout=3.3v 3.3 3.31 3.32 3.33 3.34 0 1 2 3 4 5 6 7 8 load current (a) output voltage (v) sp7655 effi. v.s iout plots @ vin=12v, and vout=5.0v 82.0 84.0 86.0 88.0 90.0 92.0 94.0 96.0 1 2 3 4 5 6 7 8 load current (a) efficiency (%) sp7655 vout v.s iout plots @ vin=12v, and vout=5.0v 4.9600 4.9700 4.9800 4.9900 5.0000 0 1 2 3 4 5 6 7 8 load current (a) output voltage (v)
5 rev e: 3/2 /07 sp7655 wide input voltage range 8a, 300khz, buck regulator ? 2007 sipex corporation typical performance characteristics sp7655 effi. v.s iout plots @ vin=12v, and vout=3.3v 83.0 84.0 85.0 86.0 87.0 88.0 89.0 90.0 91.0 92.0 1 2 3 4 5 6 7 8 load current (a) efficiency (%) sp7655 vout v.s iout plots @ vin=12v, and vout=3.3v 3.3 3.31 3.32 3.33 3.34 0 1 2 3 4 5 6 7 8 load current (a) output voltage (v) sp7655 effi. v.s iout plots @ vin=12v, and vout=5.0v 82.0 84.0 86.0 88.0 90.0 92.0 94.0 96.0 1 2 3 4 5 6 7 8 load current (a) efficiency (%) sp7655 vout v.s iout plots @ vin=12v, and vout=5.0v 4.9600 4.9700 4.9800 4.9900 5.0000 0 1 2 3 4 5 6 7 8 load current (a) output voltage (v) note: fused pin area for pins -3 and pins - 6 = (2e+b)xl - 2x(e-b) x l/2 = 0.376mm2 or 0.08 in2
6 rev e: 3/2 /07 sp7655 wide input voltage range 8a, 300khz, buck regulator ? 2007 sipex corporation ordering information part number temperature package sp7655er .............................................. -40 c to +85 c ................................. 26 pin 7 x 4 dfn sp7655er-l ........................................... -40 c to +85 c ............. (lead free) 26 pin 7 x 4 dfn sp7655er/tr ........................................ -40 c to +85 c ................................. 26 pin 7 x 4 dfn sp7655er-l/tr ..................................... -40 c to +85 c ............. (lead free) 26 pin 7 x 4 dfn bulk pack minimum quantity is 500. /tr = tape and reel. pack quantity is 3,000 dfn. sipex corporation headquarters and sales offce 233 south hillview drive milpitas, ca 5035 tel: (08) 3-7500 fax: ( 08) 35-7600 sipex corporation reserves the right to make changes to any products described herein. sipex does not assume any liability arising out of the application or use of any product or circuit described herein; neither does it convey any license under its patent rights nor the rights of others. s o l v e d b y t m

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