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cm2576 3a s tep d own v oltage r egulator 2003/08/07 preliminary rev. 1.1 champion microelectronic corporation page 1 general description features the cm2576 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 output version. the cm2576 series offers a high-efficiency replacement for popular three-terminal linear regulators. also it requires a minimum number of external components. it substantially not only reduces the area of board size but also the size of the heat sink, and in some cases no heat sink is required. 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, featuring 70a (typical) standby current. the output switch includes cycle-by-cycle current limiting, as well as thermal shutdown for full protection under 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 adjustable version output voltage range, from 1.23v to 37v4% max over line and load conditions low standby current, typ. 70a, at shutdown mode requires only 4 external components thermal shutdown and current limit protection p+ product enhancement tested applications lcd monitors add-on cards switching regulators high efficiency step-down regulators efficient pre-regulator for linear regulators ordering information package type to-220 to-263 temperature range output voltage cm2576scn220 cm2576scn263 -40 ~ +125 3.3v cm2576zjcn220 CM2576ZJCN263 -40 ~ +125 5.0v cm2576cn220 cm2576cn263 -40 ~ +125 adj.
cm2576 3a s tep d own v oltage r egulator 2003/08/07 preliminary rev. 1.1 champion microelectronic corporation page 2 pin configuration to-220 top view 12 3 v in 45 v out gnd fb enable to-263 top view 3 2 1 v in 4 5 v out gnd fb enable absolute maximum ratings input voltage (v power ) ??.????????????????.??. +45v enable pin input voltage ?.?????????????. ?0.3v Q v Q v in operating junction temperature range, t j ?????...? 0 to +150 storage temperature ?????????????.?.?... -65 to +150 lead temperature (10 sec.) ??..????????..?.?????.... 260 power dissipation table package ja ( /w) derating factor (mw/ ) t a >= 25 t a <= 25 power rating (mw) t a = 70 power rating (mw) t a = 85 power rating (mw) to-220 45 22.2 2775 1776 1443 to-263 45 22.2 2775 1776 1443 note: 1. ja : thermal resistance-junction to ambient, d f : derating factor, p o : power consumption. junction temperature calculation: t j = t a + (p d x ja ), p o = d f x (t j ? t a ) the ja numbers are guidelines for the thermal performance of the device/pc-board system. all of the above assume no ambient airflow. 2. jt : thermal resistance-junction to ambient, t c : case (tab) temperature, t j = t c + (p d x ja ) resommended operating conditions parameter symbol min. typ. max units input voltage (v in ) v in 40 v temperature range t j -40 125
cm2576 3a s tep d own v oltage r egulator 2003/08/07 preliminary rev. 1.1 champion microelectronic corporation page 3 electrical characteristics electrical characteristics at i out = 0ma, and t j = +25 ; unless otherwise noted cm2576 parameter device test conditions min. typ. max. unit cm2576s 3.234 3.300 3.366 v output voltage (note 1) cm2576zj test circuit of figure 1 4.900 5.000 5.100 v cm2576s 6v<=v in <=40v 3.168 3.300 3.432 v output voltage (note 1) cm2576zj 8v<=v in <=40v 0.5a<=i load <=3a 4.800 5.000 5.200 v cm2576s 6v<=v in <=40v 3.135 3.300 3.482 v output voltage (note 1) cm2576zj 8v<=v in <=40v 0.5a<=i load <=3a, -40 <=t j <=125 test circuit of figure 1 4.750 5.000 5.250 v feedback voltage (note 1) cm2576 (adj) test circuit of figure 2 v out =5v 1.217 1.230 1.243 v feedback voltage (note 1) cm2576 (adj) 8v<=v in <=40v, v out =5v test circuit of figure 2 0.5a<=i load <=3a 1.193 1.230 1.267 v feedback voltage (note 1) cm2576 (adj) 8v<=v in <=40v, v out =5v test circuit of figure 2 0.5a<=i load <=3a, -40 <=t j <=125 1.180 1.230 1.286 v cm2576s 75 cm2576zj i load =3a 77 % efficiency cm2576(adj) i load =3a, v out =5v 77 % t j =25 47 52 58 oscillator frequency note 2 -40 <=t j <=125 42 52 63 khz quiescent current note 3 5 10 ma standby current enable = 5v 70 200 a t j =25 1.4 1.8 saturation voltage i load =3a (note 4) -40 <=t j <=125 2.0 v t j =25 50 100 feedback bias current v out =5v (adj. version only) -40 <=t j <=125 500 na duty cycle (on) note 5 93 98 % t j =25 4.2 7 8.8 current limit note 2,4 -40 <=t j <=125 3.5 7.2 9.0 a v out =0v 0.3 2 output leakage current note 3 v out =-1v 9 20 ma t j =25 2.2 1.4 v ih (v out =0v) -40 <=t j <=125 2.4 v t j =25 1.2 1.0 enable threshold voltage v il (v out = normal output voltage) -40 <=t j <=125 0.8 v i ih ( enable = 5v) 12 30 enable input current i ih ( enable = 0v) 0 10 a
cm2576 3a s tep d own v oltage r egulator 2003/08/07 preliminary rev. 1.1 champion microelectronic corporation page 4 note 1: external components such as the catch diode, inductor, input and output capacitors can affect switching regulator system performance. refer to application 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. this self-protection feature lowers the average power dissipation by lowering the minimum duty 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. block diagram
cm2576 3a s tep d own v oltage r egulator 2003/08/07 preliminary rev. 1.1 champion microelectronic corporation page 5 application circuit
cm2576 3a s tep d own v oltage r egulator 2003/08/07 preliminary rev. 1.1 champion microelectronic corporation page 6 typical characteristics
cm2576 3a s tep d own v oltage r egulator 2003/08/07 preliminary rev. 1.1 champion microelectronic corporation page 7
cm2576 3a s tep d own v oltage r egulator 2003/08/07 preliminary rev. 1.1 champion microelectronic corporation page 8 application information it is required that vin must be bypassed with at least a 100uf electrolytic capacitor for stability. also, it is strongly recom mended the capacitor?s leads must be dept short, and located near the regulator as possible. for low operating temperature range, for example, below -25 , the input capacitor value may need to be larger. this is due to the reason that the capacitance value of electrolytic capacitors decreases and the esr increases with lower temperatures and age. 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 loc ated near the cm2576 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. fo r example, the lower capacitor values (220uf ? 1000uf) will yield typically 50mv to 150mv of output ripple voltage, while larger-value capacitors will reduce the ripple to approximately 20mv to 50mv. the amount of output ripple voltage is primarily a function of the esr (equivalent series resistance) of the output capacitor a nd the amplitude of the inductor ripple current ( i ind ). output ripple voltage = ( i ind ) x (esr of c out ) some 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 tantalum capacitors, should be carefully evaluated. catch diode this diode is required to provide a return path for the inductor current when the switch is off. it should be located close to the cm2576 using short leads and short printed circuit traces as possible. to satisfy the need of fast switching speed and low forward voltage drop, schottky diodes are widely used to provide the best efficiency, especially in low output voltage switching regulators (less than 5v). besides, fast-recovery, high-efficiency, or ultra-fast recovery diodes are also suitable. but some types with an abrupt turn-off characteristic may cause instability and e mi problems. a fast-recovery diode with soft recovery characteristics is better choice.
cm2576 3a s tep d own v oltage r egulator 2003/08/07 preliminary rev. 1.1 champion microelectronic corporation page 9 output voltage ripple 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 voltages at the switcher frequency, typically about 1% of the output voltages, and may also contain short voltage spikes of the sawtooth waveform. due to the fast switching action, and the parasitic inductance of the output filter capacitor, there is voltage spikes presenti ng at the peaks of the sawtooth waveform. cautions must be taken for stray capacitance, wiring inductance, and even the scope probes used for transients evaluation. to minimize these voltage spikes, shortening the lead length and pcb traces is always th e first thought. further more, an additional small lc filter (30uh & 100uf) (as shown in figure 3) will possibly provide a 10x reduction in output ripple voltage and transients. inductor selection the cm2576 can 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 in the continuous mode (inductor current always flowing), but under l ight load conditions, the circuit will be forced to the discontinuous mode (inductor current falls to zero for a period of time). fo r light loads (less than approximately 300ma) it may be desirable to operate the regulator in the discontinuous mode, primarily because of the lower inductor values required for the discontinuous mode. inductors are available in different styles such as pot core, toriod, e-frame, bobbin core, et., as well as different core mate rials, 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 voltages in the scope probe.
cm2576 3a s tep d own v oltage r egulator 2003/08/07 preliminary rev. 1.1 champion microelectronic corporation page 10 an inductor should not be operated beyond 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 very rapidly. different inductor types have different saturation characteristics, an d 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 adjustable version, it is important to place the output voltage ratio resistors near cm2576 as possible in order to minimize the noise introduction. enable it is required that the enable must not 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 +v in without a resistor in series with it. grounding to maintain output voltage stability, the power ground 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 either connection may be used. heatsink and thermal consideration although the cm2576 requires only a small heatsink for most cases, the following thermal consideration is important for all operation. with the package thermal resistances ja and jc, 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 junction temperature rise can be determined by the following: ? t j = p d x ja ; with the ambient temerpature, 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 temperature (typically 125 ), then a heatsink is required. when using a heatsink, the junction temperature rise will be reduced by the following: ? t j = p d x ( jc + interface + heatsink ); also one can see from the above, it is important to choose an heatsink with adequate size and thermal resistance, such that to maintain the regulator?s junction temperature below the maximum operating temperature.
cm2576 3a s tep d own v oltage r egulator 2003/08/07 preliminary rev. 1.1 champion microelectronic corporation page 11 package dimension to-220 (n220) r s j k n a c b d f g 1 23 t s c t j r b a f 45 d g n k to-263 (n263) a d c b i e l f g k
cm2576 3a s tep d own v oltage r egulator 2003/08/07 preliminary rev. 1.1 champion microelectronic corporation page 12 important notice champion microelectronic corporation (cmc) reserves the right to make changes to its products or to discontinue any integrated circuit product or service without notice, and advises its customers to obtain the latest version of relevant information to ve rify, before placing orders, that the information being relied on is current. a few applications using integrated circuit products may involve potential risks of death, personal injury, or severe property or environmental damage. cmc integrated circuit products are not designed, intended, authorized, or warranted to be suitable for use in life-support applications, devices or systems or other critical applications. use of cmc products in such applications is understood to be fully at the risk of the customer. in order to minimize risks associated with the customer?s applications, th e customer should provide adequate design and operating safeguards. hsinchu headquarter sales & marketing 5f, no. 11, park avenue ii, science-based industrial park, hsinchu city, taiwan 11f, no. 306-3, sec. 1, ta tung road, hsichih, taipei hsien 221, taiwan t e l : +886-3-567 9979 t e l : +886-2-8692 1591 f a x : +886-3-567 9909 f a x : +886-2-8692 1596

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