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rev.3.0 _00 step-down, built-in fet, synchronous rectification, pwm control switching regulators s-8550/8551 series seiko instruments inc. 1 the s-8550/8551 series is a cmos sy nchronous rectification step-down switching regulator which mainly consists of a reference voltage circuit, an oscillator, an error amplifier, a phase compensation circuit, a pwm controller, an under voltage lockout circuit (uvlo), a current limit circuit, and a power mos fet. the oscillation frequency is high at 1.2 mhz, so a high efficiency, large output current, step-down switching regulator can be achieved by using small external parts. the built-in synchronous rectification circuit makes achieving high efficiency easier compared with conventional step-down switching regulators. a ceramic capacitor can be used as an output c apacitor. high-density mounting is supported by adopting packages small sot-23-5 and super-small and thin snt-8a. the s-8550 and s-8551 series are offered according to different pin configuration. ? features ? oscillation frequency : 1.2 mhz ? input voltage range : 2.0 v to 5.5 v ? output voltage range : arbitrarily settable by external output voltage setting resistor ? output current : 600 ma ? reference voltage : 0.6 v 2.0% ? efficiency : 92% ? soft-start function : 1 ms typ. ? shutdown function : shutdown current consumption : 1.0 a max. ? built-in current limit circuit ? pch power mos fet on-resistance : 0.4 ? typ. ? nch power mos fet on-resistance : 0.3 ? typ. ? constant continuous mode operation (no light load mode) ? small package : sot-23-5, snt-8a ? lead-free products ? applications ? mobile devices, such as mobile phones, bluetooth devices , wireless devices, digital audio players, digital still cameras, portable dvd players, and portable cd players ? package drawing code package name package tape reel land sot-23-5 mp005-a mp005-a mp005-a ? snt-8a ph008-a ph00 8-a ph008-a ph008-a
step-down , built-in fet , synchronous rectification , pwm control switching regulators s-8550/8551 series rev.3.0 _00 2 seiko instruments inc. ? block diagram 1. sot-23-5 l on/off v in + ? + ? c in fb vin cont vss c fb r fb1 r fb2 v out c out *1 *1 reference voltage pwm comparator pwm control circuit uvlo circuit on/off circuit ic internal power supply current limit circuit error amplifier t r i angu l ar wave generation circuit *1. parasitic diode figure 1 2. snt-8a l on/off v in + ? + ? c in fb vin cont pvss c fb r fb1 r fb2 v out c out *1 *1 reference voltage pwm comparator pwm control circuit uvlo circuit on/off circuit ic internal power supply current limit circuit error amplifier t r i angu l ar wave generation circuit vss *1. parasitic diode figure 2
step-down , built-in fet , synchronous rectification , pwm control switching regulators rev.3.0 _00 s-8550/8551 series seiko instruments inc. 3 ? product name structure product name s-855 x a a - xxxx g package name (abbreviation) and packing specification *1 m5t1 : sot-23-5 , tape i8t1 : snt-8a, tape oscillation frequency a : 1.2 mhz pin configuration setting *2 0 : pin configuration 1 (sot-23-5), pin configuration 3 (snt-8a) 1 : pin configuration 2 (sot-23-5) *1. refer to the tape specifications at the end of this book. *2. refer to table 1 and table 3 of ? ? pin configurations ?.
step-down , built-in fet , synchronous rectification , pwm control switching regulators s-8550/8551 series rev.3.0 _00 4 seiko instruments inc. ? pin configurations table 1 s-8550 series (sot-23-5, pin configuration 1) pin no. symbol description 1 vin ic power supply pin 2 vss gnd pin 3 on/off shutdown pin ?h? : power on (normal operation) ?l? : power off (standby) 4 fb output voltage feedback pin 5 cont external inductor connection pin sot-23-5 top view 5 4 3 2 1 figure 3 table 2 s-8551 series (sot-23- 5, pin configuration 2) pin no. symbol description 1 on/off shutdown pin ?h? : power on (normal operation) ?l? : power off (standby) 2 vss gnd pin 3 cont external inductor connection pin 4 vin ic power supply pin 5 fb output voltage feedback pin table 3 s-8550 series (snt-8a, pin configuration 3) pin no. symbol description 1 fb output voltage feedback pin 2 nc *1 no connection 3 vss *2 small signal gnd pin 4 off on/ shutdown pin ?h? power on (normal operation) ?l? power off (standby) 5 vin ic power supply pin 1 2 3 4 snt-8a top view 8 7 6 5 6 pvss *2 power gnd pin figure 4 7 nc *1 no connection 8 cont external inductor connection pin *1. the nc pin is electrically open. the nc pin can be connecte d to vin, vss or pvss. *2 . connect vss and pvss to gnd.
step-down , built-in fet , synchronous rectification , pwm control switching regulators rev.3.0 _00 s-8550/8551 series seiko instruments inc. 5 ? absolute maximum ratings table 4 absolute maximum ratings (unless otherwise specified: ta = 25 c, v ss = 0 v) parameter symbol absolu te maximum rating unit vin pin voltage v in v ss ? 0.3 to v ss + 6.0 v fb pin voltage v fb v ss ? 0.3 to v in + 0.3 v cont pin voltage v cont v ss ? 0.3 to v in + 0.3 v on/off pin voltage v on/off v ss ? 0.3 to v in + 0.3 v cont pin current i cont 1300 ma sot-23-5 600 *1 mw power dissipation snt-8a p d 450 *1 mw operating temperature t opr ? 40 to +85 c storage temperature t stg ? 40 to +125 c *1. when mounted on printed circuit board [mounted board] (1) board size: 114.3 mm 76.2 mm t1.6 mm (2) board name: jedec standard51-7 caution 1. the absolute maximum ratings are rated values exceeding which the product could suffer physical damage. these values must therefore not be exceeded under any conditions. 2. since this ic has a built-in power mos fet, make sure that dissipation of the power mos fet does not exceed the allowable power dissipation of the package. (refer to figure 5.) generally, dissipation of a switching regulator can be calculated by the following equation. dissipation = (100 (%) ? efficiency (%)) / efficiency (%) output voltage load current the greater part of dissipation depends on the built-in power mos fet, however, dissipation of the inductor is also included. in addition, since power dissipation of th e package also changes according to a mounting board or a mounting state, fully check them using an actually mounted mode. 0 400 0 power dissipation ( p d ) [mw] ambient temperature (ta) [ c] 200 500 300 100 600 700 50 100 150 snt-8a sot-23-5 figure 5 power dissipation of package (mounted on board)
step-down , built-in fet , synchronous rectification , pwm control switching regulators s-8550/8551 series rev.3.0 _00 6 seiko instruments inc. ? electrical characteristics table 5 electrical characteristics ( unless otherwise specified: v in = 3.6 v, v out = 1.8 v (the conditions in table 6 ), ta = +25 c ) parameter symbol conditions min. typ. max. unit test circuit operating input voltage v in ? 2.0 ? 5.5 v 2 output voltage range *1 v out v in = v out(s) + 0.4 v to 5.5 v 1.1 ? 4.0 v 2 fb voltage v fb v in = v out(s) + 0.4 v to 5.5 v 0.588 0.6 0.612 v 2 fb voltage temperature coefficient ? v fb ? ta ta = ? 40 c to +85 c ? 100 ? ppm/ c 2 fb pin input current i fb v in = 2.0 v to 5.5 v, fb pin ? 0.1 ? +0.1 a 1 current consumption during shutdown i sss v in = 2.0 v to 5.5 v, v on/off = 0 v ? ? 1.0 a 1 current consumption 1 i ss1 f osc = 1.2 mhz, no external parts, v fb = v fb(s) 1.1 v ? 200 400 a 1 r pfet i cont = 100 ma ? 0.4 0.6 power mos fet on-resistance r nfet i cont = ? 100 ma ? 0.3 0.5 ? 1 power mos fet leakage current i lsw v in = 2.0 v to 5.5 v, v on/off = 0 v, v cont = 0 or 3.6 v ? 0.01 0.5 a 1 limit current i lim ? 800 1000 1200 ma 1 oscillation frequency f osc ? 1.02 1.2 1.38 mhz 2 soft-start time t ss time required to reach 90% of v out(s) 0.7 1.0 1.3 ms 2 high level input voltage v sh v in = 2.0 v to 5.5 v, on/off pin 0.9 ? ? v 2 low level input voltage v sl v in = 2.0 v to 5.5 v, on/off pin ? ? 0.3 v 2 high level input current i sh v in = 2.0 v to 5.5 v, on/off pin ? 0.1 ? 0.1 a 1 low level input current i sl v in = 2.0 v to 5.5 v, on/off pin ? 0.1 ? 0.1 a 1 uvlo detection voltage v uvlo ? 1.4 1.6 1.78 v 2 *1. v out(s) is the output voltage set value, and v out is the typ. value of t he actual output voltage. v out(s) can be set depending on the ratio between the v fb value and output voltage set resistors (r fb1 , r fb2 ). for details, refer to ? ? external parts selection ? . ? external parts when measuri ng electrical characteristics table 6 external parts element name symbol constant manufacturer part number inductor l 3.3 h taiyo yuden co., ltd. nr4018t3r3m input capacitor c in 4.7 f tdk corporation c3216x7r1e475k output capacitor c out 10 f tdk corporation c3216x7r1c106k output voltage set resistor 1 r fb1 36 k ? rohm co., ltd. mcr03 series 3602 output voltage set resistor 2 r fb2 18 k ? rohm co., ltd. mcr03 series 1802 phase compensation capacitor c fb 68 pf murata manufacturing co., ltd. grm1882c1h680j
step-down , built-in fet , synchronous rectification , pwm control switching regulators rev.3.0 _00 s-8550/8551 series seiko instruments inc. 7 ? test circuits 1. s-8550/8551series on/off a c in cont fb vss vin pvss *1 *1 . pvss pin is unavailable for the s-8550/8551 series with sot-23-5. figure 6 2. l s-8550/8551series on/off c in cont fb vss vin v v i out v out c fb c out r fb1 r fb2 pvss *1 *1 . pvss pin is unavailable for the s-8550/8551 series with sot-23-5. figure 7
step-down , built-in fet , synchronous rectification , pwm control switching regulators s-8550/8551 series rev.3.0 _00 8 seiko instruments inc. ? operation 1. synchronous rectification pwm c ontrol step-down switching regulator 1.1 synchronous rectification the synchronous rectification method lo wers voltage drop to greatly reduce power dissipation since an nch power mos fet, having resistance much lower th an conventional switching regulators, is used. in conventional switching regulators, current flows in the diode connected between the gnd and cont pins when the pch power mos fet is off. the forward drop voltage (v f ) of such diodes is large, between 0.3 v to 0.7 v, so the power dissipation used to be very la rge. synchronous rectification ultra-low resistance nch transistors repeat on and off, in sync hronization with the operat ion of the pch driver, in the reverse cycle of the pch driver. moreover, the built-in p and n through prevention circuit helps much reduction of power consumption during operation. 1.2 pwm control the s-8550/8551 series is a switching regulator using a pulse width modulation method (pwm) and features low current consumption. in conventional pwm control switching regulators, pulses are skipped when the output load current is low, causing a fluctuation in the ripple fr equency of the output voltage, resu lting in an increase in the ripple voltage. in the s-8550/8551 series, the switching frequency does not change, although the pulse width changes from 0% to 100% corresponding to each load current. the ripple voltage generated from switching can thus be removed easily using a filter because the switching frequency is constant. 2. soft-start function the soft-start circuit built in the s-8550/8551 series co ntrols the rush current and the overshoot of the output voltage when powering on, the on/off pin is switched from the ?l? level to the ?h? level, or the uvlo operation is released. a reference voltage adjustment method is adopted as the soft-start method. 3. shutdown pin this pin stops or starts step-up operations. switching the shutdown pin to the ?l? level stops operation of all the internal circuits and reduces the current consumption significantly. do not use the shutdown pin in a floating st ate because it is not pulled up or pulled down internally. do not apply voltage of be tween 0.3 v and 0.9 v to the shutdown pin because applying such a voltage increases the current consumption. if the shutdown pin is not used, connect it to the vin pin. table 7 shutdown pin cr oscillation circuit output voltage ?h? operates set value ?l? stops hi-z vin on/off vss figure 8
step-down , built-in fet , synchronous rectification , pwm control switching regulators rev.3.0 _00 s-8550/8551 series seiko instruments inc. 9 4. current limit circuit a current limit circuit is built in the s-8550/8551 series. the current limit circuit monitors the current that flow s in the pch power mos fet and limits current in order to prevent thermal destructi on of the ic due to an overload or ma gnetic saturation of the inductor. when a current exceeding the current limit detection value flows in the pc h power mos fet, the current limit circuit operates and turns off the pch power mos fet si nce the current limit detecti on until one clock of the oscillator ends. the pch power mos fet is turned on in the next clock and the current limit circuit resumes current detection operation. if the value of the current that flows in the pch power mos fet remains the current limit detection value or more, the current limit circuit functions agai n and the same operation is repeated. once the value of the current that flows in the pch power mos fet is lo wered up to the specified value, the normal operation status restores. a slight overshoot is generated in the output voltage when the current limit is released. the current limit detection value is fixed to 1 a (typ.) in the ic. if the time taken for the current limit to be detected is shorter than the time required for the current li mit circuit in the ic to detect, the current value that is actually limited increases. generally, the voltage di fference between the vin and vout pins is large, the current limit detection status is reached faster and the current value increases. 5. 100% duty cycle the s-8550/8551 series operates up to the maximum duty cycle at 100%. even when the input voltage is lowered up to the output voltage value set using the ex ternal output voltage setting resistor, the pch power mos fet is kept on and current can be supplied to the load. the output voltage at this time is the input voltage from which the voltage drop due to the direct resistance of the inductor and the on-resistance of the pch power mos fet are subtracted. 6. uvlo function the s-8550/8551 series includes a uvlo (under-voltage locko ut) circuit to prevent the ic from malfunctioning due to a transient status when power is applied or a mo mentary drop of the supply voltage. when uvlo is in the detection state, the pch and nch power mos fets stop switchin g operation, and the cont pin become hi-z. once the s-8550/8551 is in t he uvlo detection status, the soft-start function is reset, but the soft-start operates by the releasing operation of uvlo after that. note that the other internal circuits operate normally and that the status is different from the power-off status. the hysteresis width is set for the uvlo circuit to prev ent a malfunction due to a nois e that is generated in the input voltage. a voltage about 150 mv (typ.) higher th an the uvlo detection volta ge is the release voltage.
step-down , built-in fet , synchronous rectification , pwm control switching regulators s-8550/8551 series rev.3.0 _00 10 seiko instruments inc. ? operation principle the s-8550/8551 series is a step-down synchronous rectif ication switching regulator based on constant pwm control. figure 9 shows the basic circuit diagram. a step-down switching regulator starts current supply by the input voltage (v in ) when the pch power mos fet is turned on and holds energy in the in ductor at the same time. when the pch power mos fet is turned off, the current held in the inductor is released. the released cu rrent flows in the smoothing circuit, with the energy loss held minimum, supplies the output voltage (v out ) lower than v in . v out is kept constant by controlling the switching frequency (f osc ) and on time (t on ). with the pwm control method, v out is made constant by controlling the on time with f osc unchanged. l control circuit pch power mos fet nch power mos fet v in v out c out i 1 i 2 figure 9 basic circuit drawing of step-down switching regulator 1. continuous mode the following explains how the current flows to the in ductor when the step-down operation is constant and stable. when the pch power mos fet is turned on, current i 1 flows in the direction shown by the arrow in figure 9 , and energy is stored in the inductor (l). when the output capacitor (c out ) is charged, supply of the output current (i out ) is started at the same time. the inductor current (i l ) gradually increases in proportion to the on time (t on ) of the pch power mos fet as shown in figure 10 (changes from i l min. to i l max.). when the pch power mos fet is turned off, the nch power mos fet is turned on and i l tries to hold i l max. consequently, current i 2 flows in the direction shown by the arrow in figure 9 . as a result, i l gradually decreases and reaches i l min. when the off time (t off ) has elapsed. when t off has elapsed, the nch power mos fet is turned off and the next cycle is entered. the above sequence is repeated. as explained in the above, the co ntinuous mode refers to the operation in the current cycle in which i l linearly changes from i l min. to i l max. even if i l min. is less than 0 a, i l min. keeps flowing (backflow current flows). t on t off t = 1/f osc i l i l max. i l min. t figure 10 continuous mode (current cycle of inductor current (i l ))
step-down , built-in fet , synchronous rectification , pwm control switching regulators rev.3.0 _00 s-8550/8551 series seiko instruments inc. 11 2. backflow current the s-8550/8551 series performs pwm sy nchronous rectification even if i l min. is less than 0 a, so a backflow current is generated in v in and the backflow current becomes maximum when no load is applied (see figure 11 ). use the following equation to calculate the maximum backflow current value, which should be taken into consideration when designing. duty (i out = 0) = v out / v in example : v in = 3.6 v, v out = 1.8 v ?? duty = 50% ? i l = ? v / l t on = (v in ? v out ) duty / (l f osc ) example : v in = 3.6 v, v out = 1.8 v, f osc = 1.2 mhz, l = 3.3 h ?? ? i l = 227 ma i l max. = ? i l / 2 = 113.5 ma, i l min. = ?? i l / 2 = ? 113.5 ma the current value waveform of the inductor is a tr iangular wave, of which the maximum value is i l max. and the minimum value is i l min. (negative value), and the negative value (the portion marked by diagonal lines in figure 11 ) backflows when no load is applied (see figure 11 ). if about 113.5 ma of i out flows in the above conditions, the minimum value (i l min.) of the triangular wave is made 0 ma and no backflow current flows. when an input capacitor (c in ) is connected, the backflow current is absorbed by c in , thus reducing the backflow current to flow in the power supply. be sure to co nnect an input capacitor to reduce backflow current to the power supply (see figure 12 ). the above presents the conditions required to prevent backflow current from flowing, which is only a guideline. perform sufficient confirmation using an actual application. inductor current with no load inductor current when load is a current of 113.5 ma backflow current ? 113.5 ma 113.5 ma i l min. i l max. ? i l i l 0 ma backflow current = 0 ma 0 ma i out 113.5 ma i out 227 ma i l min. i l max. ? i l i l figure 11 example of conditions to prevent backflow current from flowing v out v in cont backflow current inductor current i l c in vin figure 12 backflow current
step-down , built-in fet , synchronous rectification , pwm control switching regulators s-8550/8551 series rev.3.0 _00 12 seiko instruments inc. ? external parts selection 1. inductor the inductance (l value) has a strong infl uence on the maximum output current (i out ) and efficiency ( ). the peak current (i pk ) increases by decreasing l and the stability of the circuit improves and i out increases. if l is decreased further, the current drive capabilit y of the external transistor is insufficient and i out decreases. if the l value is increased, the loss due to i pk of the power mos fet decreases and the efficiency becomes maximum at a certain l value. further increasing l de creases the efficiency due to the increased loss of the dc resistance of the inductor. the recommended l value for the s-8550/8551 series is 3.3 h. when selecting an inductor, note the allo wable current of the inductor. if a current exceeding this allowable current flows through the inductor, magnetic satura tion occurs, substantially lowering the efficiency. therefore, select an inductor so that i pk does not exceed the allowable current. i pk is expressed by the following equations in the discontinuous mode and continuous mode. 2 f osc l v in i pk = i out + v out (v in ? v out ) f osc = oscillation frequency table 8 typical inductors manufacturer part number l value dc resistance rated current dimensions (l w h) [mm] nr4018t3r3m 3.3 h 0.07 ? max. 1.23 a max. 4.0 4.0 1.8 taiyo yuden co., ltd. nr3012t3r3m 3.3 h0.1 ? max. 0.91 a max. 3.0 3.0 1.2 cdrh3d16/hp-3r3 3.3 h0.085 ? max. 1.40 a max. 4.0 4.0 1.8 sumida corporation cdrh2d11/hp-3r3 3.3 h0.173 ? max. 0.9 a max. 3.2 3.2 1.2 vlf4012at-3r3m 3.3 h 0.12 ? max. 1.3 a max. 3.7 3.5 1.2 tdk corporation vlf3010at-3r3m 3.3 h 0.17 ? max. 0.87 a max. 2.6 2.8 1.0 mip3226d3r3m 3.3 h0.104 ? max. 1.2 a max. 3.2 2.6 1.0 fdk corporation mips2520d3r3m 3.3 h0.156 ? max. 1.0 a max. 2.5 2.0 1.0
step-down , built-in fet , synchronous rectification , pwm control switching regulators rev.3.0 _00 s-8550/8551 series seiko instruments inc. 13 2. capacitors (c in , c out ) a ceramic capacitor can be used for the input (c in ) and output (c out ) sides. c in lowers the power supply impedance and averages the input current to improve efficiency. select c in according to the impedance of the power supply to be used. the recommended capacitance is 4.7 f for the s-8550/8551 series when a general lithium ion rechargeable battery is used. select as c out a capacitor with large capacitance and sma ll esr for smoothing the ripple voltage. the optimum capacitor selection depends on the l value, capa citance value, wiring, and application (output load). select c out after sufficient evaluation under actual use conditions. 3. output voltage setting resistors (r fb1 , r fb2 ), capacitor for phase compensation (c fb ) with the s-8550/8551 series, v out can be set to any value by external divider resistors. connect the divider resistors across the vout and vss pins. because v fb = 0.6 v typ., v out can be calculated by this equation. r fb2 v out = (r fb1 + r fb2 ) 0.6 connect divider resistors r fb1 and r fb2 as close to the ic to minimize effect s from of noise. if noise does have an effect, adjust the values of r fb1 and r fb2 so that r fb1 + r fb2 < 100 k ? . c fb connected in parallel with r fb1 is a capacitor for phase compensation. by setting the zero point (the phase feedback) by adding capacitor c fb to output voltage setting resistor r fb1 in parallel, the feedback loop gains the phase margin. as a re sult, the stability can be obtained. in principle, to use the portion how much the phase has feed back by the zero point effectively, define c fb referring to the following equation. khz 70 x r x x 2 1 c 1 fb fb ? this equation is the reference. the followings are explanation regarding the proper setting. to use the portion how much the phase has feed back by the zero point effectively, set r fb1 and c fb so that the zero point goes into the higher frequency than the pole frequency of l and c out . the following equations are the pole frequency of l and c out and the zero point frequency by c fb and r fb1 . out c x l x x 2 1 f pole ? fb 1 fb zero c x r x x 2 1 f ? the transient response can be improved by setting the zero point frequency in the range of lower frequency. however, since the gain becomes higher in the range of high frequency, the total phase of feedback loop delays 180 or more by setting the zero point frequency in the sign ificantly lower range. as a result, the gain cannot be 0 db or lower in the frequency rang e thus the operation might be unstable. determine the proper value after the sufficient evaluation under the actual condition. the typical constants by our evaluation are in table 9 . table 9 constant for external parts v out (s) [v] r fb1 [k ? ] r fb2 [k ? ] c fb [pf] l [ h] *1 c out [ f] *1 1.1 36 43 56 3.3 10 1.8 36 18 68 3.3 10 3.3 36 8 120 3.3 10 4.0 51 9 100 3.3 10 *1. the recommended parts in table 6
step-down , built-in fet , synchronous rectification , pwm control switching regulators s-8550/8551 series rev.3.0 _00 14 seiko instruments inc. ? standard circuit 1. sot-23-5 l on/off v in + ? + ? c in fb vin cont vss c fb r fb1 r fb2 v out c out *1 *1 4.7 f 3.3 h 36 k ? 18 k ? 10 f 68 pf 1.0 f reference voltage pwm comparator pwm control circuit uvlo circuit on/off circuit ic internal power supply current limit circuit error amplifier ground point triangular wave generation circuit *1. parasitic diode figure 13 2. snt-8a l on/off v in + ? + ? c in fb vin cont vss c fb r fb1 r fb2 v out c out *1 *1 4.7 f 3.3 h 36 k ? 18 k ? 10 f 68 pf 1.0 f reference voltage pwm comparator pwm control circuit uvlo circuit on/off circuit ic internal power supply current limit circuit error amplifier ground point triangular wave generation circuit pvss *1. parasitic diode figure 14 caution the above connection diagram and constant will not guarantee successful operation. perform thorough evaluation using an actual application to set the constants.
step-down , built-in fet , synchronous rectification , pwm control switching regulators rev.3.0 _00 s-8550/8551 series seiko instruments inc. 15 ? precaution ? mount external capacitors, diodes, and inductor as close as possible to the ic. ? characteristics ripple voltage and spike noise occur in ic containing switching regulators. moreover rush current flows at the time of a power supply injection. because these largely depend on the inductor, the capacitor and impedance of power supply used, fully che ck them using an actually mounted model. ? the 1.0 f capacitance connected between the vin and vss pins is a bypass capacitor. it stabilizes the power supply in the ic when application is used with a heav y load, and thus effectively works for stable switching regulator operation. allocate the bypass capacitor as cl ose to the ic as possible, prioritized over other parts. ? although the ic contains a static elec tricity protection circuit, static electric ity or voltage that exceeds the limit of the protection circuit should not be applied. ? the power dissipation of the ic greatly varies depending on the size and material of the board to be connected. perform sufficient evaluation using an actual application before designing. ? seiko instruments inc. assumes no resp onsibility for the way in which this ic is used on products created using this ic or for the specifications of that product, nor does seiko instruments inc. assume any responsibility for any infringement of patents or copyrights by products that include this ic either in japan or in other countries.
step-down , built-in fet , synchronous rectification , pwm control switching regulators s-8550/8551 series rev.3.0 _00 16 seiko instruments inc. ? characteristics (typical data) 1. example of major power supply dependence characteristics (ta = 25 c) 1. 1 current consumption 1 (i ss1 ) vs. input voltage (v in ) 1. 2 current consumption during shutdown (i sss ) vs. input voltage (v in ) 2.0 4.0 5.0 5.5 i ss1 [ a] 500 400 300 200 100 0 v in [v] 2.5 3.0 3.5 4.5 2.0 4.0 5.0 5.5 i sss [ a] 1.0 0.8 0.6 0.4 0.2 0 v in [v] 2.5 3.0 3.5 4.5 1. 3 oscillation frequency (f osc ) vs. input voltage (v in ) 1. 4 soft-start time (t ss ) vs. input voltage (v in ) 2.0 4.0 5.0 5.5 f osc [mhz] 1.38 1.30 1.18 1.10 1.02 v in [v] 2.5 3.0 3.5 4.5 1.06 1.14 1.22 1.26 1.34 2.0 4.0 5.0 5.5 t ss [ms] 1.3 1.1 1.0 0.9 0.7 v in [v] 2.5 3.0 3.5 4.5 0.8 1.2 1. 5 power mos fet on-resistance (r fet ) vs. input voltage (v in ) 1. 6 power mos fet leakage current (i lsw ) vs. input voltage (v in ) 2.0 4.0 5.0 5.5 r fet [ ? ] 0.8 0.6 0.5 0.4 0.2 v in [v] 2.5 3.0 3.5 4.5 0.3 0.7 nch pch 2.0 4.0 5.0 5.5 i lsw [ a] 0.5 0.1 0 ? 0.1 ? 0.5 v in [v] 2.5 3.0 3.5 4.5 ? 0.4 0.4 nch pch 0.2 0.3 ? 0.2 ? 0.3 1. 7 on/off pin input voltage?h? (v sh ) vs. input voltage (v in ) 1. 8 on/off pin input voltage?l? (v sl ) vs. input voltage (v in ) 2.0 4.0 5.0 5.5 v sh [v] 0.9 0.6 0.3 v in [v] 2.5 3.0 3.5 4.5 0.7 0.8 0.5 0.4 2.0 4.0 5.0 5.5 v sl [v] 0.9 0.6 0.3 v in [v] 2.5 3.0 3.5 4.5 0.7 0.8 0.5 0.4
step-down , built-in fet , synchronous rectification , pwm control switching regulators rev.3.0 _00 s-8550/8551 series seiko instruments inc. 17 1. 9 fb voltage (v fb ) vs. input voltage (v in ) 2.0 4.0 5.0 5.5 v fb [mv] 612 600 588 v in [v] 2.5 3.0 3.5 4.5 604 608 596 592 2. example of major temperature characteristics (ta = ? 40 to 85 c) 2. 1 current consumption 1 (i ss1 ) vs. temperature (ta) 2. 2 current consumption during shutdown (i sss ) vs. temperature (ta) ? 40 75 85 i ss1 [ a ] 500 0 ? 25 0 25 50 300 400 200 100 ta [ c] v in = 5.5 v v in = 3.6 v v in = 2.0 v ? 40 75 85 i sss [ a ] 1.0 0 ? 25 0 25 50 0.6 0.8 0.4 0.2 ta [ c] v in = 5.5 v v in = 3.6 v v in = 2.0 v 2. 3 oscillation frequency (f osc ) vs. temperature (ta) 2. 4 soft-start time (t ss ) vs. temperature (ta) ? 40 75 85 f osc [mhz] 1.32 1.08 ? 25 0 25 50 1.28 1.20 1.16 ta [ c] v in = 5.5 v v in = 3.6 v v in = 2.0 v 1.12 1.24 ? 40 75 85 t ss [ms] 1.3 0.7 ? 25 0 25 50 1.1 1.0 0.9 ta [ c] v in = 5.5 v v in = 3.6 v v in = 2.0 v 0.8 1.2 2. 5 power mos fet on-resistance (r fet ) vs. temperature (ta) 2. 6 power mos fet leakage current (i lsw ) vs. temperature (ta) ? 40 75 85 r fet [ ? ] 0.8 0.2 ? 25 0 25 50 ta [ c] v in = 5.5 v v in = 3.6 v v in = 2.0 v v in = 5.5 v v in = 3.6 v v in = 2.0 v pch nch 0.6 0.5 0.4 0.3 0.7 ? 40 75 85 i lsw [ a] 0.5 ? 0.5 ? 25 0 25 50 ta [ c] v in = 5.5 v v in = 5.5 v pch nch 0.1 0 ? 0.1 ? 0.4 0.4 0.2 0.3 ? 0.2 ? 0.3
step-down , built-in fet , synchronous rectification , pwm control switching regulators s-8550/8551 series rev.3.0 _00 18 seiko instruments inc. 2. 7 on/off pin input voltage?h? (v sh ) vs. temperature (ta) 2. 8 on/off pin input voltage?l? (v sl ) vs. temperature (ta) ? 40 75 85 v sh [v] 0.9 0.3 ? 25 0 25 50 ta [ c] 0.6 0.7 0.8 0.5 0.4 v in = 3.6 v v in = 5.5 v v in = 2.0 v ? 40 75 85 v sl [v] 0.9 0.3 ? 25 0 25 50 ta [ c] 0.6 0.7 0.8 0.5 0.4 v in = 5.5 v v in = 3.6 v v in = 2.0 v 2. 9 uvlo detection voltage (v uvlo ) vs. temperature (ta) 2. 10 fb voltage (v fb ) vs. temperature (ta) ? 40 75 85 v uvlo [v] 1.80 1.40 ? 25 0 25 50 ta [ c] 1.60 1.70 1.75 1.55 1.45 1.50 1.65 ? 40 75 85 v fb [mv] 612 588 ? 25 0 25 50 ta [ c] 600 604 608 596 592 v in = 5.5 v v in = 3.6 v v in = 2.0 v 3. examples of transient response characteristics (unless otherwise specified, the used parts are ones shown in ? external parts when measuring electrical characteristics .) 3. 1 powering on (v out = 1.8 v, v in = 0 v 3.6 v, ta = 25 c) (1) i out = 1 ma (2) i out = 600 ma ? 0.2 0.6 1.0 1.6 v in , v out [v] 4 3 1 0 ? 1 t [ms] i l [a] 0.6 0.2 0.4 ? 0.2 0 0 0.2 0.4 0.8 v out v in i l 2 1.2 1.4 ? 0.2 0.6 1.0 1.6 v in , v out [v] 4 3 1 0 ? 1 t [ms] i l [a] 1.5 0.5 1.0 ? 0.5 0 0 0.2 0.4 0.8 2 1.2 1.4 v out v in i l 3. 2 shutdown pin response (v out = 1.8 v, v in = 3.6 v, v on/off = 0 v 3.6 v, ta = 25 c) (1) i out = 1 ma (2) i out = 600 ma ? 0.2 0.6 1.0 1.6 v on/off , v out [v] 4 3 1 0 ? 1 t [ms] i l [a] 0.6 0.2 0.4 ? 0.2 0 0 0.2 0.4 0.8 2 1.2 1.4 v out v on/off i l ? 0.2 0.6 1.0 1.6 v on/off , v out [v] 4 3 1 0 ? 1 t [ms] i l [a] 1.5 0.5 1.0 ? 0.5 0 0 0.2 0.4 0.8 2 1.2 1.4 v out v on/off i l
step-down , built-in fet , synchronous rectification , pwm control switching regulators rev.3.0 _00 s-8550/8551 series seiko instruments inc. 19 3. 3 power supply fluctuations (v out = 1.8 v, ta = 25 c) (1) i out = 1 ma, v in = 2.6 v 3.6 v 2.6 v (2) i out = 600 ma, v in = 2.6 v 3.6 v 2.6 v ? 0.1 0.3 0.5 0.7 v out [v] 2.2 2.0 1.8 1.6 1.4 t [ms] v in [v] 3.5 2.5 1.5 0.5 4.5 0 0.1 0.2 0.4 0.6 v out v in ? 0.1 0.3 0.5 0.7 v out [v] 2.2 2.0 1.8 1.6 1.4 t [ms] v in [v] 3.5 2.5 1.5 0.5 4.5 0 0.1 0.2 0.4 0.6 v out v in 3. 4 load fluctuations (v out = 1.8 v, v in = 3.6 v, ta = 25 c) (1) i out = 0.1 ma 100 ma 0.1 ma (2) i out = 0.1 ma 300 ma 0.1 ma ? 0.1 0.3 0.5 0.7 v out [v] 1.90 1.85 1.80 1.75 1.70 t [ms] i out [ma] 200 100 0 ? 100 400 0 0.1 0.2 0.4 0.6 v out i out 300 ? 0.1 0.3 0.5 0.7 v out [v] 1.90 1.85 1.80 1.75 1.70 t [ms] i out [ma] 200 100 0 ? 100 400 0 0.1 0.2 0.4 0.6 300 v out i out
step-down , built-in fet , synchronous rectification , pwm control switching regulators s-8550/8551 series rev.3.0 _00 20 seiko instruments inc. ? reference data 1. reference data for external parts properties of external parts element name product name manufacture characteristics inductor nr4018t3r3m taiyo yuden co., ltd 3.3 h, dcr max = 0.07 ? , i max = 1.23 a input capacitor c3216x7r1e475k tdk corporation 4.7 f output capacitor c3216x7r1c106k tdk corporation 10 f caution the values of the external parts are based on the materials provided by each manufacturer. however, consider the characteristics of the original materials when using the above products. 2. output current (i out ) vs. efficiency ( ) characteristics and output current (i out ) vs. output voltage (v out ) characteristics 2. 1 v out = 1.1 v (r fb1 = 36 k ? , r fb2 = 43 k ? ) (1) output current (i out ) vs. efficiency ( ) (2) output current (i out ) vs. output voltage (v out ) 0 1000 [%] 100 0 1 10 100 i out [ma] 50 70 80 30 10 20 40 60 90 v in = 2.0 v v in = 3.6 v v in = 5.5 v 0 1000 v out [v] 1.3 0.9 1 10 100 i out [ma] 1.1 1.2 1.0 v in = 5.5 v v in = 3.6 v v in = 2.0 v 2. 2 v out = 1.8 v (r fb1 = 36 k ? , r fb2 = 18 k ? ) (1) output current (i out ) vs. efficiency ( ) (2) output current (i out ) vs. output voltage (v out ) 0 1000 [%] 100 0 1 10 100 i out [ma] 50 70 80 30 10 20 40 60 90 v in = 2.2 v v in = 3.6 v v in = 5.5 v 0 1000 v out [v] 2.0 1.6 1 10 100 i out [ma] 1.8 1.9 1.7 v in = 5.5 v v in = 3.6 v v in = 2.0 v
step-down , built-in fet , synchronous rectification , pwm control switching regulators rev.3.0 _00 s-8550/8551 series seiko instruments inc. 21 2. 3 v out = 3.3 v (r fb1 = 36 k ? , r fb2 = 8 k ? ) (1) output current (i out ) vs. efficiency ( ) (2) output current (i out ) vs. output voltage (v out ) 0 1000 [%] 100 0 1 10 100 i out [ma] 50 70 80 30 10 20 40 60 90 v in = 3.7 v v in = 5.5 v 0 1000 v out [v] 3.5 3.1 1 10 100 i out [ma] 3.3 3.4 3.2 v in = 5.5 v v in = 3.7 v 2. 4 v out = 4.0 v (r fb1 = 51 k ? , r fb2 = 9 k ? ) (1) output current (i out ) vs. efficiency ( ) (2) output current (i out ) vs. output voltage (v out ) 0 1000 [%] 100 0 1 10 100 i out [ma] 50 70 80 30 10 20 40 60 90 v in = 4.4 v v in = 5.5 v 0 1000 v out [v] 4.2 3.8 1 10 100 i out [ma] 4.0 4.1 3.9 v in = 5.5 v v in = 4.4 v 3. output current (i out ) vs. ripple voltage (v r ) characteristics 3. 1 v out = 1.1 v (r fb1 = 36 k ? , r fb2 = 43 k ? ) (1) v in = 3.6 v (2) v in = 5.5 v 0 1000 v r [mv] 50 0 1 10 100 i out [ma] 30 40 10 20 0 1000 v r [mv] 50 0 1 10 100 i out [ma] 30 40 10 20
step-down , built-in fet , synchronous rectification , pwm control switching regulators s-8550/8551 series rev.3.0 _00 22 seiko instruments inc. 3. 2 v out = 1.8 v (r fb1 = 36 k ? , r fb2 = 18 k ? ) (1) v in = 3.6 v (2) v in = 5.5 v 0 1000 v r [mv] 50 0 1 10 100 i out [ma] 30 40 10 20 0 1000 v r [mv] 50 0 1 10 100 i out [ma] 30 40 10 20 3. 3 v out = 3.3 v (r fb1 = 36 k ? , r fb2 = 8 k ? ) (1) v in = 3.6 v (2) v in = 5.5 v 0 1000 v r [mv] 50 0 1 10 100 i out [ma] 30 40 10 20 0 1000 v r [mv] 50 0 1 10 100 i out [ma] 30 40 10 20 3. 4 v out = 4.0 v (r fb1 = 51 k ? , r fb2 = 9 k ? ) (1) v in = 5.5 v 0 1000 v r [mv] 50 0 1 10 100 i out [ma] 30 40 10 20
step-down , built-in fet , synchronous rectification , pwm control switching regulators rev.3.0 _00 s-8550/8551 series seiko instruments inc. 23 ? marking specification (1) sot-23-5 (1) to (3) : product code (refer to product name vs. product code .) (4) : lot number 5 4 1 3 2 (1) (2) (3) (4) sot-23-5 to p vie w product name vs. product code (a) s-8550 series (b) s-8551 series product code product code product name (1) (2) (3) product name (1) (2) (3) S-8550AA-M5T1G r 5 a s-8551aa-m5t1g r 5 c (2) snt-8a (1) blank (2) to (4) product code (refer to product name vs. product code ) (5), (6) blank (7) to (11) lot number snt-8a top view 1 4 8 5 (9) (6) (2) (10) (7) (3) (11) (8) (4) (5) (1) product name vs. product code (a) s-8550 series product code product name 2 3 4 s-8550aa-i8t1g r 5 a

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the information described herein is subject to change without notice. seiko instruments inc. is not responsible for any problems caused by circuits or diagrams described herein whose related industrial properties, patents, or other rights belong to third parties. the application circuit examples explain typical applications of the products, and do not guarantee the success of any specific mass-production design. when the products described herein are regulated products subject to the wassenaar arrangement or other agreements, they may not be exported without authorization from the appropriate governmental authority. use of the information described herein for other purposes and/or reproduction or copying without the express permission of seiko instruments inc. is strictly prohibited. the products described herein cannot be used as part of any device or equipment affecting the human body, such as exercise equipment, medical equipment, security systems, gas equipment, or any apparatus installed in airplanes and other vehicles, without prior written permission of seiko instruments inc. although seiko instruments inc. exerts the greatest possible effort to ensure high quality and reliability, the failure or malfunction of semiconductor products may occur. the user of these products should therefore give thorough consideration to safety design, including redundancy, fire-prevention measures, and malfunction prevention, to prevent any accidents, fires, or community damage that may ensue.

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