1.5a 280khz boost regulators AMC3202DMF descriptions o outline drawing: the amc3202 is a 280khz switching regulator with a high efficiency , 1.5a integrated switch. the part operates over a wide input voltage range, from 2.7v to 30v. the amc 3202 utilizes current mode architecture, which allows excellent load and line regulation, as well as a practical m eans for lim iting current. com b ining high frequency operation with a highly integrated regulator circuit results in an extrem ely com p act power supply solution. build-in therm a l protection to prevent the chip over heat dam a ge. f e a t u r e s integrated power switch: 1.5a guaranteed. wide input range: 2.7v to 30v. 40v power switch input voltage. high frequency allows for sm all com ponents. minim u m external com ponents. built in over current protection. application tft-lcd power managem e nt lcd monitor/tv led backlight driver 1/6 tiger electronic co.,ltd
AMC3202DMF block diagram and pi n co nfigura tion pin description pin no. pin nam e pin function 1 c o m p loop com p ensat i on pi n. thi s pi n i s t h e out put of t h e error am pl i f i e r and i s used for l oop com p ensat i on.loop com p ensat i on can be i m pl em ent e d by a si m p l e r c net w ork. 2 f b feedbac k p i n. sens e t h e o u t put volt a ge an d reference d to 1. 27 6 v . when th e vol tage at thi s pin f a lls bel o w 0.4v,c hip switching-frequency reduces to a m u ch lower frequency. 3 nc no connection.keep floating. 4 e n enable pin. a ttl low will shut down the chip and high enable the chip. this pin m a y also be used to sy nchronize the part to nearly twice the base frequency . if sy nchronization is not used, this pin should be either tied high or left floating for norm a l operation. 5 v c c input power supply pin. supply power to the ic and should have a bypass capacitor connected to agnd 6 a g n d analog gro und. provi de a clea n grou nd fo r the c o n t roller c i rcui try and s hou ld not be i n t h e pa th of large c u rrents.this pi n is c onn ec ted to the ic substrate. 7 p g n d power ground. th is pi n is the groun d co nne ctio n for the em itter of the power switchin g t r ansistor.c onne cti o n t o a g ood g r ound p l an e is essential. 8 v s w high current switch pin. connect to the collector of the internal power switch. the open voltage acr oss the power switch can be as high as 40v. to m i nim i ze radiation, use a trace as short as practical. 2/6
AMC3202DMF absolute maximum ra tings (t a=25 c) c h a r a c t e r i s t i c s y m b o l v a l u e unit input v o ltage vcc 30 v switch input v o ltage, vsw 40 v maxim u m operating junction t e m p erature tj 150 c s t orage t e m p erature t s tg -65 ?? +150 c lead t e m p erature(soldering,10seconds) 260 c * exceeding these ratings could cause dam a ge to the device. all voltages are with respect to ground. currents are positive into, negative out of the specified term inal. electrical characteristics (unless otherwise noted: 2.7v AMC3202DMF switch saturation v o ltage i swi t ch =1.5a i swi t ch =1.0a i swi t ch =10ma 0.8 0.75 0.09 1.5 0.45 v switch current lim it 50% duty cy cle 80% duty cy cle 1.5 1.4 1.8 1.6 2.3 2.1 a minimum pulse w i dth fb=0v , isw=1.0a 1 0 0 2 5 0 3 0 0 n s switch leakage vsw=40v ,vcc=0v 2 . 0 1 0 0 a ? icc/ ? ivsw 2.7v vcc 12v ,10ma isw 1.0a 12v vcc 30v ,10ma isw 1.0a 2.7v vcc 12v ,10ma isw 1.5a 12v vcc 30v ,10ma isw 1.5a 10 - 17 - 30 100 30 100 ma/ a operating current isw=0 5 . 5 8 . 0 ma shutdown mode current v co mp <0.8v , en=0v , 2.7v vcc 12v v co mp <0.8v , en=0v , 12v vcc 30v 12 60 100 a minimu m o p e r a t i o n i n p u t v o ltage vsw switching,ma ximum isw=10ma 2 . 4 5 2 . 7 0 v thermal shutdown 1 5 0 1 8 0 2 1 0 ?? therm a l hy s t eres is 2 5 ?? * guaranteed by design,not 100% tested in production. applica t ion circuit 4/6
AMC3202DMF application summary the amc 3202 incorporates a current mode control scheme, in which the duty cycle of the switch is directly controlled by switch current rather than by output voltage. the output of the oscillator turns on the power switch at a frequency of 280khz as shown in the block diagram . the power switch is turned o ff by the output of the pwm com p arator. a ttl low voltage will shut down the chip and high voltage enable the chip through en pin. this pin m a y also be used to sy nchronize the part to nearly twice the base oscillator frequency. in order to synchronize to a higher frequency, a positive transition turns on the power switch before the output of the oscillator goes high, thereby resetting the oscillator. the sy nchronization operation allows m u ltiple power supplies to operate at the sam e frequency . if sy nchronization is not used,this pin should be either tied high or left floating for norm a l operation. com ponent selection: the amc 3202 develops a 1.276v reference from the fb pin to ground. output voltage is set by connecting the fb pin to an output resistor divider and the m a xim u m output voltage is determ ined by the vsw pin m a xim u m voltage m i nus the output diode forward voltage. referring to ty pical application circuit, the output voltage is set by the below form ula(1): where, v f is the output diode d f forward voltage. when choosing the inductor, one m u st consider factors such as peak current, core and ferrite m a terial, output voltage ripple, emi, tem p erature range, phy sical size, and cost. 5/6
AMC3202DMF 6/6 lower values are chosen to reduce phy sical size of the inductor, and higher values reduce ripple voltage and core loss. in continuous conduction m ode, the peak inductor current is equal to average current plus half of the ripple current, which should not cause inductor saturation. based on the tolerance of the ripple current in the circuits, the following form ula (2) can be referenced: in boost circuits, the inductor becom e s part of the input filter. in continuous m ode, the input current waveform is triangular and does not contain a large pulsed current. this reduces the requirem e nts im posed on the input capacitor selection. capacitors in the range of 10uf to 100uf with an esr less than 0.3| ?m work well up to full 1.5a switch current. the v in ripple is determ ined by the product of the inductor current ripple and the esr of input capacitor, and the v out ripple com e s from two m a jor sources, nam e ly esr of output capacitor and the charging/discharging of the output capacitor. ceram i c capacitors have the lowest esr, but too low esr m a y cause loop stability problem s. alum inum electroly tic capacitors exhibit the highest esr, resulting in the poorest ac response. one option is to parallel a ceram ic capacitor with an alum inum electrolytic capacitor. the goal of frequency com p ensation is to achieve desirable transient response and dc regulation while ensuring the stability of the system . a typical com p ensation network, as shown in the ty pical application circuit, provides a frequency response of two poles and one zero. the loop frequency com p ensation is perform ed on the output of the error am plifier (comp pin) with a series rc networ k. the m a in pole is form ed by the series capacitor and the output im pedance of the error am plifier. the series resistor creates a zero, which im proves loop stability and transient response.a second capacitor,is som e tim es used to reduce the switching frequency ripple on the comp pin.
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