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SS6577 re v .1.02 3/26/2004 external nmos step-down pwm controller features n-channel mosfet drive operating input voltage from 4.5v to 24v wide output range : 0.8v to 20v reference: 1.5% 0.8v reference low dropout operation : 95% duty cycle fixed constant frequency - 500khz low standby current, i q typically 720a logic-control m icropower shutdown output overvoltage protection internal diode for bootstrapped gate drive current-mode operation for excellent line and load transient response available in 8-lead so or msop packages applications lcd monitor palmtop computers, pdas wireless modems on-card switching regulators dc power distribution systems description the SS6577 is a current-mode switching regulator controller that drives an external n-channel power mosfet using a fixed fre- quency architecture. it uses an external divider to adjust the output voltage from 0.8v to 20v with excellent line and load regulation. a maximum high duty-cycle limit of 95% provides low dropout operation which extends operating time in battery-operated systems. a constant switching frequency of 500khz is used thus allowing smaller sized filter components. the operating current level is user-programmable via an external current sense resistor. it also provides output overvolt- age protection under fault conditions. a multifunction pin (i th /run) allows external compensation for optimum load step re- sponse plus shutdown. soft start can also be implemented with this pin to properly se- quence supplies. packages available are sop-8 and msop-8 for smd. www.siliconstandard.com 1 of 14 www.datasheet.in
www.siliconstandard.com 2 of 14 ss 65 77 re v . 1 .02 3 / 2 6 /2004 typical application circuit v in 6v~ 2 4 v + c in 1 22 p f r s 33m m1 c3 0. 1 p f d1 sl43 l1 10 p h v ou t 3.3v 3 a c1 1 000 pf c5 330 pf r3 24 k r2 62 k r1 20k vi n 8 i t h/ run 2 fb 3 gn d 4 sw 5 dr i 6 boos t 7 cs 1 SS6577 + c in 2 22 p f c2 0. 1 p f c ou t 220 p f c4 1n f c6 2. 2 p f c in 1 , c in 2 : her- m e i 22 p f / 35 v el ect r ol y t i c ca paci t or s m1: n-mosfet ssm6680m d1: gs sl43 l1: t d k slf 125 55 t - 100 m 3 r 4 c ou t : her- m e i 220 p f / 1 6 v el ect r ol y t i c ca paci t or c6: t a i y o y u d e n lm k2 12 bj 225 kg- t cer a m i c cap a ci t o r ordering information pin configuration SS6577c(x)xxx packing type tb: tube t r : tape and reel package outline s: so-8 o: m s op-8 g: pb-free lead finish exam p l e: SS6577cotr sw fb i th / run gnd cs 1 3 4 2 8 6 5 7 www.datasheet.in
www.siliconstandard.com 3 of 14 ss 65 77 re v . 1 .02 3 / 2 6 /2004 absolute maximum ratings (note 1) supply voltage (vin) ????......?????...............????????.................25v drive supply voltage (boost) ???????????????????..????32v switch voltage (sw) ????????????????????????? 25v differential boost voltage (boost to sw ) ??????????????????..8v i th /run,vfb voltages ?????????????????????????.7v peak drive output current < 10 s (dri ) ???????????????????.2a operating temperatur e range ??............... ??.???????.......-40 c ~ 85 c thermal resistance ( ja ) (assuming no ambient airflow, no heatsink) sop8 ??????????????????????????160 c/w msop8 ?????????????????????????? 180 c/w storage temperature range ?................... ???????. -65 c ~ 150 c lead temperature ( soldering, 10sec ) ??????????????.300 c test circuit refer to typical application circuit. electrical characteristics (t a =25c, v in =15v, unless otherwise noted.) parameter test conditions min. typ. max. unit input voltage 4.5 24 v normal mode (note 2) 720 900 a input supply current shutdown mode, v ith/run = 0 v 1 6 2 0 a feedback v o l t a g e 0 . 7 8 8 0 . 8 0 . 8 1 2 v ? output overvoltage lockout v fb connect to vout, ? v ov l =v ov l - v fb 2 0 5 5 9 0 m v reference voltage line regulation v in = 4.5v to 20 v 0.002 0.015 %/v output voltage load regula- tion i th sinking 5 a i th sourcing 5 a 0.7 -0.4 1.1 -0.8 % run threshold 0.6 0.8 0.9 v maximum current sense threshold v fb = 0 . 7 2 v 1 2 5 1 5 0 1 7 5 m v oscillator f r e q u e n c y 4 5 0 5 0 0 5 5 0 khz www.datasheet.in
www.siliconstandard.com 4 of 14 ss 65 77 re v . 1 .02 3 / 2 6 /2004 electrical characteristics (continued) parameter test conditions min. typ. max. unit dri rise time c load = 3000 p f 5 0 7 5 ns dri fall time c load = 3000 p f 5 0 7 5 ns boost voltage v in =8v , i b oos t =5ma, s w = 0 v 4 . 9 5 . 3 5 . 7 v maximum duty cycle 90 94 % soft start time 5 7.5 ms run current source v ith/run =0v , v fb = 0 v 1 . 0 2 . 3 4 . 0 p a run pullup current v ith/run = 1 v 1 0 0 1 9 0 2 5 0 p a note 1: absolute maximum ratings are those values bey ond w h ich the life of a device may be impaired. note 2: dy namic supply current is higher due to the gat e charge being delivered at the sw itching frequency . typical performance characteristics 1 10 10 0 100 0 10 00 0 70 75 80 85 90 95 10 0 v in =6v e f ficienc y ( % ) load c u r r ent ( ma) v in =12v v in =19v v out =3. 3 v fi g. 1 ef f i c i enc y vs load cur r ent ( v ou t =3. 3 v ) e f ficienc y ( % ) load c u r r ent ( ma) fi g. 2 ef f i c i enc y vs load cu r r ent ( v ou t =5. 0 v) 1 10 10 0 10 00 100 00 70 75 80 85 90 95 10 0 v out =5 v v in =6 v v in =12v v in =19 v www.datasheet.in
www.siliconstandard.com 5 of 14 ss 65 77 re v . 1 .02 3 / 2 6 /2004 typical performance characteristics (continued) efficienc y (%) input voltage (v) fig. 3 e ffic i enc y v s in put v o ltage 0 5 10 15 20 25 30 70 75 80 85 90 95 10 0 v out =3.3v i load =1a i load =0.1 a efficienc y ( % ) input voltage (v) fig. 4 effic i enc y v s input voltage 0 5 10 15 20 25 30 70 75 80 85 90 95 10 0 v out =5v i load =1a i lo a d =0.1a s u pp l y c u r r en t ( a) i nput vol t age ( v ) fi g. 5 suppl y cu r r en t vs i nput vol t age 0 5 10 15 20 25 30 0 20 40 500 600 700 800 900 no r m a l mo de shut do wn b oos t v o lta g e ( v ) boos t load c u r r ent ( ma) fi g. 6 boos t load r egul at i on 0 v cc =5v v cc =15v v ph ase =0v 0 51 0 15 20 1 2 3 4 5 6 7 b oos t v o lta ge (v ) i nput vol t age ( v ) fi g. 7 boos t li ne r egul at i on i bo ost =2ma v ph ase =0v 0 5 10 15 20 25 30 1 3 5 7 0 2 4 6 vc c dow n vcc up r e ferenc e v o lta g e ( v ) temper at ur e ( c) fi g. 8 ref e r enc e vol t age vs temper at ur e -4 0 - 2 0 0 20 40 60 80 10 0 12 0 14 0 0. 7 9 0 0. 7 9 1 0. 7 9 2 0. 7 9 3 0. 7 9 4 0. 7 9 5 0. 7 9 6 0. 7 9 7 0. 7 9 8 0. 7 9 9 0. 8 0 0 0. 8 0 1 0. 8 0 2 0. 8 0 3 0. 8 0 4 0. 8 0 5 www.datasheet.in
www.siliconstandard.com 6 of 14 ss 65 77 re v . 1 .02 3 / 2 6 /2004 typical performance characteristics (continued) b oos t v o lta ge (v ) temper at ur e ( c) fi g. 9 boos t vol t age vs te mper at ur e -4 0 -2 0 0 20 40 60 80 10 0 120 140 4. 0 4. 5 5. 0 5. 5 6. 0 i boost =1m a v ph ase =0 v fr e q u enc y ( khz ) temper at ur e ( c) fi g. 10 o per at i ng fr equenc y vs temper at ur e - 40 -20 0 20 40 60 80 100 12 0 14 0 40 0 42 0 44 0 46 0 48 0 50 0 c u rren t s ens e t h res hold (m v ) temper at ur e ( c) fi g. 11 max i mum c u r r ent sens e thr e s hol d vs tem per at ur e -40 -20 0 20 40 60 80 10 0 12 0 14 0 12 0 12 5 13 0 13 5 14 0 14 5 15 0 15 5 16 0 www.datasheet.in
www.siliconstandard.com 7 of 14 ss 65 77 re v . 1 .02 3 / 2 6 /2004 block diagram + m1 * dr op ou t de t os c vin int v c c 1_ s h u t q2 * q1 * q3 q4 ss re f 0. 8v th erm a l dri v e r fl o a t i n g le b bl an k - + ea vint vi n vin t vi n t 0. 8 v 1. 2 v 2. 4v 0.8 v 1. 3 3 v 0 . 85 5v - + lc _c o m p - + bur s t_ m o de - + sd + ov d t r s q 2. 5 www.datasheet.in
www.siliconstandard.com 8 of 14 ss 65 77 re v . 1 .02 3 / 2 6 /2004 pin descriptions pin 1: cs - current sense comparator invert- ing input, not to exceed v in volt- age. built in offsets between the cs and v in pins in conjunction with r sense set the current trip thresholds. pin 2: i th /run -combination of error amplifier compensation point and run con- trol inputs. the current compara- tor threshold increases with this control voltage. forcing this pin below 0.8v causes the device to be shutdown. pin 3: fb - feedback error amplifier input, to compare the feedback voltage with the internal reference voltage. connecting a resistor r2 to con- verter output node and a resistor r1 to ground yields the output voltage: v out =0.8 x (r1+r2)/ r1 pin4: gnd - singal gnd for ic. all voltage lev- els are measured with respect to this pin. pin 5: sw - switch node connection to induc- tor. in buck converter applications the voltage swing at this pin is from a schottky diode voltage drop below ground to v in pin 6: dri - external high-side n-mosfet gate drive pin. connect dri to gate of the external high-side n- mosfet. pin 7: boost - supply to high-side floating driver. the bootstrap capacitor c3 is returned to this pin. pin 8: vin - the chip power supply pin. it also provides the gate bias charge for all the mosfets controlled by the ic. recommend supply volt- age is 4.5v~24v. application information introduction the SS6577 is a current mode switching regulator controller that drives an external n-channel power mosfet with constant frequency architecture. it uses an external divider to adjust output voltage with excellent line regulation and load regulation. a maximum high duty cycle limit of 95% provides low dropout operation, which extends operating time in battery-operated system. wide input voltage ranges from 4.5v to 24v, and a switching frequency of 500khz allows smaller sized filter components. the operating current level is user-programmable via an external current sense resistor and it automatically enters pfm operation at low output current to boost circuit efficiency. a multifunction pin (i th /run) allows external com- pensation plus shutdown. a built-in soft start can properly provide sequenced supplies. available p ackages are sop8 and msop8 for smd. principle of operation the SS6577 uses a current mode with a constant frequency architecture. normally high-side mosfet turns on each cycle when oscillator sets rs latch and it turns off when internal current comparator re- sets rs latch. voltage on i th /run pin, which is the output voltage of voltage error amplifier, will control peak inductor current. the output voltage feeds back to v fb pin so that the error amplifier receives a voltage through external resistor divider. when load current increases, it causes a slight decrease www.datasheet.in
www.siliconstandard.com 9 of 14 ss 65 77 re v . 1 .02 3 / 2 6 /2004 max i 100mv s r in the volt age of v fb pin. thus the i th /run volt age remains increasing until the average inductor cur- rent matches new load current. while the high-side mosfet turns of f, the low-side mosfet is turned on to recharge boot strap cap a citor c3. inductor selection with the high operating frequency of 500khz, smaller inductor values are possible. in general, operating at high frequency will cause low efficiency because of large mosfet switching loss. thus the ef fect of inductor value on ripple current and low current operation must be considered as well. main control loop is shut down when i th /run goes below 0.8v . when i th /run pulled up to 0.8v or up by error amplifier , main control loop is enabled. low current operation during heavy load current operation, the SS6577 op- erates in pwm mode with a frequency of 500khz. decreasing of the current will cause a drop in i th /run below 1.33v so that the SS6577 enters pfm mode operation for better ef ficiency . if the volt age across r s does not exceed the of fset of current comp arator within a cycle, then the high-side and internal mosfet s will disable until i th /run goes over 1.33v . the inductor value has a direct influence on ripple current ( ? www.datasheet.in
www.siliconstandard.com 10 of 14 ss 65 77 re v . 1 .02 3 / 2 6 /2004 output diode selection ? 1 ? 1 r 2 r 1 v 8 . 0 v out in order not to exceed the diode ratings, it is impor- t ant to specify the diode peak current and average power dissip a tion. the feedback reference volt age 0.8v allows low output volt ages from 0.8v to input volt age. a small cap a citor at 1nf in p a rallel to the upper feedback resistor is required for a st able feedback. c in and c out selection t o prevent the high volt age spike resulted from high frequency switching, a low esr input cap a citor for the maximum rms current must be used. usually cap a citors may be p a ralleled to meet size or height requirement s in the design. i th /run function the i th /run pin, also as a dual-purpose pin, pro- vides loop compensation as well as shut down func- tion. an internal current source at 2.5 p a charges up the external cap a citor c5. when the volt age on i th /run pin reaches 0.8v , the SS6577 begins to operate. the selection of c out depends on the required ef - fective series resist ance (esr). in general once the esr requirement is met, the cap a cit ance is suit able for filtering. the output ripple volt age ( www.datasheet.in
www.siliconstandard.com 11 of 14 ss 65 77 re v . 1 .02 3 / 2 6 /2004 return to its designed value when the peak inductor value no longer exceeds over current protection point. ov er voltage protection over voltage protection occurs when the fb pin voltage (the negative input of error amplifier) ex- ceeds 0.855v. the over voltage comparator will force driver to pull low until output over voltage is removed. pcb lay out since operating at a high switching frequency, 500khz, proper pcb layout and component place- ment may enhance the performance of the SS6577 application circuit. for a better ef ficiency , major loop from input terminal to output terminal should be as short as possible. in addition, in the case of a large current loop, the track wid t h of each component in the loop should maint a in as wide as possible. in order to prevent the ef fect from noise, the gnd pin should be placed close to the ground. also keep the ic? s gnd pin and the ground leads in the short- est dist ance. recommended layout diagrams and component placement are as shown as figures 13 to 16. no sensitive component s, which may cause noise interference to the circuit, should be allowed to be close to sw pin. furthermore, the SS6577 is a current-mode controller. keeping the sense resistor close to both vin and cs pins is recommended for better ef ficiency and output performance. in addition, all filtering and de- coupling cap a citors, such as c1 and c2, should connect to the SS6577 as close as possible. fig. 12 top layer fig. 13 bottom layer www.datasheet.in
www.siliconstandard.com 12 of 14 ss 65 77 re v . 1 .02 3 / 2 6 /2004 fig. 14 plac ement (top overlay) fig. 15 plac ement (bottom overlay) application examples v in 6v~ 2 4 v + c in 1 22 f r s 33m m1 ssm6680m c3 0. 1 f d1 sl 43 l1 10 h v out 3. 3v 3 a c1 1 000p f c5 330pf r3 24k r2 62 k r1 20 k vin 8 it h / ru n 2 fb 3 gnd 4 sw 5 dri 6 boos t 7 cs 1 SS6577 + c in 2 22 f c2 0. 1 f c out 22 0 f c4 1n f d2 l l414 8 c7 1 f r4 1. 2m v in 6v ~ 2 4v ** c6 2. 2 f fig. 16 3.3v step-down converter with external soft-start circ uit www.datasheet.in
www.siliconstandard.com 13 of 14 ss 65 77 re v . 1 .02 3 / 2 6 /2004 v in 5v + c in1 22 p f r s 33m m1 ssm6680m c3 ll4148 d1 sl43 l1 10 p h v out 3.3v 3a c1 1000pf c5 330pf r3 24k r2 62k r1 20k vin 8 ith/run 2 fb 3 gnd 4 sw 5 dri 6 boost 7 cs 1 SS6577 + c in2 22 p f c2 0.1 p f c out 220 p f c4 1nf d2 c6 2.2 p f c7 1nf fig. 17 5v to 3.3v step-down converter www.datasheet.in
in formation furnished by silicon standard corporation is believed to be accurate and reliable. however, silicon standard corporation makes no guarantee or warranty, expre ss or implied, as to the reliability, accuracy, timeliness or completeness of such information and assumes no responsibility for its use, or for infringement of any patent or other intellectual property rights of third parties that may result from its use. silicon standard reserves the right to make changes as it deems necessary to any products described herein for any reason, including without limitation enhancement in reliability, functionality or design. no license is granted, whether expressly or by im plication, in relation to the use of any products described herein or to the use of any information provided herein, under any patent or other intellectual property rights of silicon standard corporation or any third parties. www.siliconstandard.com 14 of 14 ss 65 77 re v . 1 .02 3 / 2 6 /2004 msop 8 (co) symbol min max a 0.76 0.97 a1 -- 0.20 b 0.28 0.38 c 0.13 0.23 d 2.90 3.10 e 2.90 3.10 e 0.65 h 4.80 5.00 l 0.40 0.66 d h e a b a1 c e l physical dimensions (unit: mm) 8 lead plastic so (cs) symbol min max a 1.35 1.75 a1 0.10 0.25 b 0.33 0.51 c 0.19 0.25 d 4.80 5.00 e 3.80 4.00 e 1.27(typ) h 5.80 6.20 l 0.40 1.27 d h e a b a1 c e l www.datasheet.in

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