pj 2576 3a step down switching voltage regulator 1 - 6 2003/02.ver.a he pj 2576 series are step - down switching regulators with all required active functions. it is capable of driving 3a load with excellent line and load regulations. these devices are available in fixed output voltages of 3.3v, 5v, and an adjustable outp ut version. the pj2576 series offers a high - efficiency replacement for popular three - terminal linear regulators. also it requires a minimum number of external components. it substantially not onl y reduces the area of board size but also the si z e of heat s ink, and in some cases no heat sink is required. t he ? 4% tolerance on output voltage within specified input voltages and output load conditions is guaranteed. also, the oscillator frequency accuracy is within ? 10%. external shutdown is included. f eaturing 70 a (typical) standby current. the output switch includes cycle - by - cycle current limiting, as well as thermal shutdown for full protection u nder fault conditions . guaranteed 3a output current 3.3v, 5v, and adjustable versions wide input voltage range, up to 40v internal oscillator of 52khz fixed frequency wide adjust version output voltage range, from 1.23v to 37v ? 4% max . over line and load conditions. low standby current, typ. 70 a, at shutdown mode. requires only 4 external components thermal shutdown a nd current limit protection p+ product enhancement tested l cd monitors add - on cards switching regulators high efficiency step - down regulators efficient pre - regulator for linear regulators positive to negative converter (buck - b oost) t to - 220 - 5l to - 263 - 5l features block diagram pin : 1. v in 2. v out 3. gnd 4. fb 5. enable ordering information device operating temperature packa gge pj2576cz - adj pj2576cz - 3.3v pj2576cz - 5.0v to - 220 - 5l pj 2576cm - adj pj2576cm - 3.3v pj2576cm - 5.0v - 20 j?? +85 j to - 263 - 5l applications
pj 2576 3a step down switching voltage regulator 2 - 6 2003/02.ver.a parameter value unit input voltage (v power ) +45 v e nable pin input voltage - 0.3v ?? v ?? v in v operating junction temperature range 0 j to +150 j storage temperature - 65 j to +150 j lead temperature 260 j j power dissipation to - 220 - 5l / to - 263 - 5l ? j a derating factor t a ? 25 j t a ?? 25 j power rating t a ?? 70 j power rating t a ?? 85 j power rating 45 22.2 2775 1776 1443 j /w mw/ j mw mw mw note: 1. ? j a : thermal resistance - junction to ambient, d f : during factor, po: power consumption junction temperature calculation: t j =t a + (p d x ? j a ), po=d f x (t j - t a ) the ? j a numbers are guidelines for the the rmal performance of the device/pc - board system. all of the above assume no ambient airflow. 2. ? j t : thermal resistance - junction to ambient, t c : case (tab) temperature, t j =t c + (p d x ? j a ) parameter symbol min. typ. max. units input voltage (v in ) v i n -- -- 40 v temperature range t j - 40 -- 125 j figure 1. fixed output voltage versions figure 2 . adjustable output voltage versions absolute maximum ratings application circuit resomm ended operating conditions
pj 2576 3a step down switching voltage regulator 3 - 6 2003/02.ver.a parameter device test conditions min. typ. max. unit pj2576 - 3.3v 3.234 3.300 3.366 output voltage (note 1) pj2576 - 5.0v t est circuit of figure 1 4.900 5.000 5.100 v pj2576 - 3.3v 6v ?? v in ?? 40v 3.168 3.300 3.432 output voltage (note 1) pj2576 - 5.0v 8v ?? v in ?? 40v 0.5a ?? i load ?? 3a 4.800 5.000 5.200 v pj2576 - 3.3v 6v ?? v in ?? 40v 3.135 3.300 3.482 output voltage (note 1) pj2576 - 5.0v 8v ?? v in ?? 40v 0.5 a ?? i load ?? 3a, t est circuit of figure 1 4.750 5.000 5.250 v feedback voltage (note 1) pj2576 - adj test circuit of figure 2 v out =5v 1.217 1.23 1.243 v feedback voltage (note 1) pj2576 - adj 8v ?? v in ?? 40v , v out =5v test c ircuit of figure 2 0.5a ?? i load ?? 3a 1.193 1.23 1.267 v feedback voltage (note 1) pj2576 - adj 8v ?? v in ?? 40v , v out =5v test circuit of figure 2 0.5a ?? i load ?? 3a, - 40 j ?? t j ?? 125 j 1.18 1.23 1.286 v pj2576 - 3.3v -- 75 -- pj2576 - 5.0v i load =3a -- 77 -- efficiency pj25 76 - adj i load =3a, v out =5v -- 77 -- % t j = 25 j 47 52 58 oscillator frequency note 2 - 40 j ?? t j ?? 125 j 42 52 63 khz quiescent current note 3 -- 5 .0 10 ma standby current enable =5v -- 70 200 a t j = 25 j -- 1.4 1.8 saturation voltage i load =3a(note 4) - 40 j ?? t j ?? 125 j -- -- 2.0 v t j = 25 j -- 50 100 feedback bias current v out =5v (adj. version only) - 40 j ?? t j ?? 125 j -- -- 500 na duty cycle (on) note 5 93 98 -- % t j = 25 j 4.2 7.0 8.8 current limit note 2, 4 - 40 j ?? t j ?? 125 j 3.5 7.2 9.0 a v out =0 v -- 0.3 2.0 output leakage current n ote 3 v out = - 1 v -- 9.0 20 ma t j = 25 j 2.2 1.4 -- v ih (v out =0v) - 40 j ?? t j ?? 125 j 2.4 -- -- t j = 25 j -- 1.2 1.0 enable threshold voltage v il (v out =normal output voltage) - 40 j ?? t j ?? 125 j -- -- 0.8 v i ih (enable =5v) -- 12 30 enable input current i ih (enable =0v) -- 0 10 a note 1: external components such as the catch diode, inductor, input and output capacitors can affect switching regulator system performance. refer to appli cation information for details. note 2: the oscillator frequency reduces to approximately 11khz in the event of fault conditions, such as output short or overload. and the regulated output voltage will drop approximately 40% from the nominal output voltage . th i s self - protection feature lowers the average power dissipation by lowering the minimum d uty cycle from 5% down to approximately 2%. note 3: for these parameters, fb is removed from v out and connected to +12v to force the output transistor off. note 4: v out pin sourcing current. no diode, inductor or capacitor connect to v out. note 5 : fb is removed from v out and connected to 0v. electrical characteristics i out =0ma, and t j = +25 j ; unless otherwise noted
pj 2576 3a step down switching voltage regulator 4 - 6 2003/02.ver.a application information it is required that vin must be bypassed with at least a 100 f electrolytic capacitor for sta bility. also, it is strongly recommended the capacitor ? s leads must be dept short, and located near the regulator as possible. for low operating temperature range, for example, below - 25 j , the input capacitor value may need to be larger. this is due to th e reason that the capacitance value of electrolytic capacitors decreases and the esr increases with lower temperatures and ago. paralleling a ceramic or solid tantalum capacitor will increase the regulator stability at cold temperatures. output capacitors (c out ) an output capacitor is also required to filter the output voltage and is needed for loop stability. the capacitor should be located near the pj2576 using short pc board traces. low esr types capacitors are recommended for low output ripple voltage and good stability. generally, low value or low voltage (less than 12v) electrolytic capacitors usually have higher esr numbers, for example, the lower capacitor values (220 f - 1000 f) will yield typically 50mv to 150mv of output ripple voltage, while lar ger - value capacitors will reduce the ripple to approximately 20mv to 50mv. the amount of output ripple voltage is primarily a function of the esr (e quivalent series resistance) of the output capacitor and the amplitude of the inductor ripple current ( ? i in d ) output ripple voltage = ( ? i ind ) x (esr of c out ) s ome capacitors called ? high - frequency ? , ? low - inductance ? , or ? low - esr ? are recommended to use to further reduce the output ripple voltage to 10mv or 20mv. however, very low esr capacitors, such as tanta lum capacitors, should be carefully evaluated. catch diode this diode is required to return path for the inductor current when the switch is off. it should be located close to the pj2576 using short leads and short printed circuit traces as possible. to satisfy the need to fast switching speed and low forward voltage drop, schottky diodes are widely used to provide the best efficiency, especially in low output voltage swit ching regulators (less than 5v). beside, fast - recovery, high - efficiency, or ultra f ast recovery diodes are also suitable. but some types with an abrupt turn - off characteristic may cause instability and emi problems. a fast recovery diode with soft recovery characteristics is better choice. output voltage r i pple and transients the output ripple voltage is due mainly to the inductor sawtooth ripple current multiplied by the esr of the output capacitor. the output ripple voltage of a switching power supply will contain a sawtooth ripple voltage at the switcher frequency, typically about 1% of the output voltages, and may also contain short voltage spokes of the sawtooth waveform. due to the fast switching action, and the parasitic inductance of the output filter capacitor, there is voltage spikes presenting at the peaks of the sawtooth wave form. cautions must be taken for stray capacitance. w iring inductance, and even the scope probes used for transients evaluation. to minimize these voltage spikes, shortening the lead length and pcb traces is always the first thought . further more, an additional small lc filter (30 h & 100 f) (as shown in figure 3) will possibly provide a 10x reduction in output ripple voltage and transients. figure 3 . lc filter for low output ripple
pj 2576 3a step down switching voltage regulator 5 - 6 2003/02.ver.a inductor selection the pj2576 c an be used for either continuous or discontinuous modes of operation. each mode has distinctively different operating characteristics, which can affect the regulator performance and requirements. with relatively heavy load currents , the circuit operates i n the continuous mode (inductor current always flowing). but under light l oad conditions, the circuit will be f orce to the discontinuous mode (inductor current falls to zero for a period of time). for light loads (less than approximately 300ma) it may be d esirable to operate the regulator in the discontinuous mode, primarily because of the lower inductor values required for the discontinuous mode. indictors are available in different styles such as pot core, tor o i d, e - frame, bobbin core, et., as well as di fferent core materials such as ferrites and powdered iron . the least expensive, the bobbin core type, consists of wire wrapped on a ferrite rod core. this type of construction makes for an inexpensive inductor, but since the magnetic flux is not completely contained within the core, it generates more electromagnetic interference (emi). this emi can cause problems in sensitive circuits, or can give incorrect scope readings because of induced voltage in the scope probe. an inductor should not be operated bey ond its maximum rated current because it may saturate. when an inductor begins to saturate, the inductance decreases rapidly and the inductor begins to look mainly resistive (the dc resistance of the winding). this will cause the switch current to rise ver y rapidly. different inductor types have different saturation characteristics, and this should be well considered when selecting as inductor. feedback connection for fixed output voltage version, the fb (feedback) pin must be connected to v out . for the ad justable version, it is important to place the output volta ge ratio resistors near pj2576 as possible in order to minimize the noise introduction. enable it is required that the enable must n ot be left open. for normal operation, connect this pin to a ? low ? voltage (typically, below 1.6v). on the other hand, for standby mode, connect this pin with a ? high ? voltage. this pin can be safely pulled up to + vin without a resistor in series with it. grounding to maintain output voltage stability , the power gr ound connections must be low - impedance. for the 5 - lead to - 220 and to - 263 style package, both the tab and pin 3 are ground and rather connection may be used. heats ink and thermal consideration a l though the pj2576 requires only a small heatsink for most cas es, the following thermal consideration is important for all operation. with the package thermal resistances ? j a and ? j c , total power dissipation can be estimated as follows: p d = ( v in x i q ) + (v out / v in ) ( i load x v sat ) ; when no heatsink is used, the ju nction temperature rise can be determined by the following : ? t j = p d x ? j a with the ambient temperature, the actual junction temperature will be: t j = ? t j + t a if the actual operating junction temperature is out of the safe operating junction temperatu re (typically 125 j ), then a heatsink is required. when using a heatsink, the junction temperature rise will be reduced by the following : ? t j = p d x ( ? j c + ? interface + ? heatsink ); also one can see from the above, it is important to choose an heatsink wit h adequate size and thermal resistance, such that to maintain the regulator ? s junction temperature below the maximum operating temperature.
pj 2576 3a step down switching voltage regulator 6 - 6 2003/02.ver.a to - 220 - 5l machanical drawing to - 263 - 5l machanical drawing inches m l n e f d 1.top view a c b i k n m j k j l 6.01 14.29 0.297 2.175 8.28 0.237 6.51 15.31 0.563 0.477 2.925 8.8 0.012 0.086 0.326 c b a dim g f e h d g i h 2.side view 4.475 13.31 1.17 27.6 2.44 3.24 1.57 0.26 1.37 29.44 5.225 14.13 0.176 0.524 1.087 0.046 2.94 3.90 1.83 1.02 0.096 0.128 0.062 0.010 millimeters 10.00 min to-220-5l dimension 10.50 max 0.394 min 0.256 0.603 0.019 0.115 0.346 0.206 0.556 0.054 1.159 0.116 0.154 0.072 0.040 0.413 max i j b c d 1.top view a max 10.50 15.875 1.015 1.827 4.83 1.40 2.785 8.80 1.40 0.73 to-263-5l dimension 4.31 e h g 1.14 2.285 8.28 1.14 0.45 h i j f g f e 2.side view dim millimeters 10.00 14.595 0.255 1.573 b c d a min 0.190 0.169 0.017 0.044 0.325 0.044 0.089 0.029 0.055 0.346 0.055 0.110 inches 0.574 0.010 0.061 0.393 min 0.625 0.040 0.072 max 0.413
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