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1 date: 1/19/05 sp6650 high efficiency 600ma synchronous buck regulator ?copyright 2005 sipex corporation high efficiency 600ma synchronous buck regulator ideal for portable designs powered with li ion battery sp6650 features 95% high efficiency proprietary control loop 2.7v to 6.5v input voltage range 3.3v or adjustable output voltage range 2% output voltage accuracy 600ma output current 100% duty cycle operation programmable inductor peak current limit (0.95a or 0.5a) no external fet's required 3v battery low indicator 2.7v undervoltage lockout shutdown control small 10-pin msop the sp6650 is ideal for portable applications that use a li-ion or 3 to 4 cell alkaline/nicd/nimh input. the sp6650 extends battery life with it? unique control loop scheme (patent pending), which maintains high efficiency levels (> than 90%) over a wide range of output currents. features such as inductor peak current control, protects the power supply from overload or short circuit conditions, controls the startup current to prevent output overshoot and excessive battery drop, and gives the user more flexibility in choosing an appropriate coil to optimize solution cost, size and performance. other features include a dedicated pin for manual shutdown, a battery low indicator, and thermal protection. typical applications circuit rb 100k ? 2.7-6.5 vdc 3.3v or 1.25v to 5.0v sp6650 10 9 8 7 6 1 2 3 4 5 r1 10 ? c1 1 f c2 47 f l1 22 h v out c3 47 f r2 164k r3 100k c4 470pf pv in v in blon i lim shdn lx pgnd gnd v out fb r4 100k ? description applications pda cd player adsl modem digital still camera now available in lead free packaging pv in v in blon i lim shdn sp6650 10 pin msop 1 2 3 4 5 10 9 8 7 6 lx pgnd gnd v out fb
2 date: 1/19/05 sp6650 high efficiency 600ma synchronous buck regulator ?copyright 2005 sipex corporation these are stress ratings only and functional operation of the device at these ratings or any other above those indicated in the operation sections of the specifications below is not implied. exposure to absolute maximum rating conditions for extended periods of time may affect reliability. specifications apply for -40 c to +85 c, v out = 3.3v, v in = 3.6v, i lim = shdn = v in , fb = gnd, l1 = 22 h, c out = c in = 47 f, unless otherwise noted. parameter min. typ. max. units conditions input voltage operating uvlo 6.5 v range undervoltage lockout threshold 2.6 2.7 2.8 v v in rising undervoltage lockout hysteresis 120 mv fb set voltage, v ref 1.23 1.25 1.27 v v out tied to fb pin v ref load regulation 0.5 % i load = 0 to 600ma v in = 3.6v, v out = 3.3v v ref line regulation 0.5 % v in = 3.6v to 6.5v v out = 3.3v, i load = 200ma v ref line and load regulation 0.65 % v in = 3.6v to 6.5v i load = 0 to 600ma v out accuracy 3.23 3.30 3.37 v i load = 100ma, v in = 3.6v v out line and load regulation 3.17 3.30 3.43 v v in = 3.6v to 6.5v i load = 0 to 600ma on-time constant - k on 2.7 s*v minimum t on = k on / (v in -v out ) pmos switch resistance 0.4 0.8 ? i pmos = 200ma nmos switch resistance 0.3 0.8 ? i nmos = 200ma v in pin quiescent current 70 150 a shdn = v in = fb = 1.5v v in pin shutdown current 0.3 500 na shdn = 0v v out pin quiescent current 7 12 a shdn = v in = fb = 1.5v v out pin shutdown current 0.1 500 na shdn = 0v power efficiency 92 % i load = 600ma 95 % i load = 100ma 88 % i load = 1ma minimum guaranteed load 600 700 ma i lim = v in current 300 350 ma i lim = 0v inductor current limit 0.75 0.95 1.15 a i lim = v in 0.40 0.50 0.60 a i lim = 0v inductor current limit -100 ppm/ c electrical characteristics pv in , v in . ........................................................... 7v all other pins .............................. -0.3v to v in +0.3v pv in , pgnd, lx current .................................... 2a storage temperature .................... -65 c to 150 c absolute maximum ratings
3 date: 1/19/05 sp6650 high efficiency 600ma synchronous buck regulator ?copyright 2005 sipex corporation block diagram specifications apply for -40 c to +85 c, v out = 3.3v, v in = 3.6v, i lim = shdn = v in , fb = gnd, l1 = 22 h, c out = c in = 47 f, unless otherwise noted. pv in internal supply v in min t off min t on ref shdn uvlo ref shdn i lim fb v out ref block ref ref/2 i lim /m overcurrent gnd blon uvlo i lim /m d v in clr ref/2 q v in q lx + - c + - c + - c + - c + - c m 1 pgnd tsd v in parameter min. typ. max. units conditions falling blon trip voltage 2.88 3.00 3.12 v blon trip voltage hysteresis 2.9 % blon low output voltage 0.4 v v in = v out = 3.0v, i sink = 1ma blon leakage current 1 av blon = 3.3v rising over-temperature trip 140 c point over-temperature hysteresis 14 c shdn, ilim leakage current 1 500 na shdn, ilim input threshold 0.60 0.90 1.8 v high to low transition voltage 0.60 1.25 1.8 v low to high transition electrical characteristics
4 date: 1/19/05 sp6650 high efficiency 600ma synchronous buck regulator ?copyright 2005 sipex corporation pin number pin name description 1pv in input voltage power pin. inductor charging current passes through this pin. 2v in internal supply voltage. control circuitry powered from this pin. 3 blon open drain battery low output. v in below battery low thresh- old pulls this node to ground. v in above threshold, this node is open. 4i lim inductor current limit programming pin. tie pin to v in for 0.95a peak inductor current limit. tie pin to ground for 0.5a peak inductor current limit. ttl input threshold. 5 shdn shutdown control input. tie to v in for normal operation, tie to ground for shutdown. ttl input threshold. 6f b external feedback network input connection. connect a resistor from fb to ground and fb to v out to control the output voltage externally. this pin regulates to the internal bandgap reference voltage of 1.25v. tie fb to ground to use the internal divider for a preset output voltage of 3.3v. 7v out output voltage sense pin. used for internal feedback divider and timing circuit. 8 gnd internal ground pin. control circuitry returns current to this pin. 9 pgnd power ground pin. synchronous rectifier current returns through this pin. 10 lx inductor switching node. inductor tied between this pin and the output capacitor to create regulated output voltage. pin description
5 date: 1/19/05 sp6650 high efficiency 600ma synchronous buck regulator ?copyright 2005 sipex corporation operation the sp6650 is a synchronous buck regulator with an input voltage range of +2.7v to +6.5v and an output that is either preset to +3.3v, or adjustable between +1.25v and v in . the sp6650 features a unique on-time control loop that runs in discontinuous conduction mode (dcm) or continuous conduction mode (ccm) using syn- chronous rectification. other features include overtemperature shutdown, overcurrent protec- tion, undervoltage lockout, digitally controlled enable, a battery low indicator, and an external feedback pin. the sp6650 operates with a light load quiescent current of 70 a using a 0.4 ? pmos main switch and a 0.3 ? nmos auxiliary switch. it operates with excellent efficiency across the entire load range, making it an ideal solution for battery powered applications and low current step-down conversions. the part smoothly tran- sitions into a 100% duty cycle under heavy load/ low input voltage conditions. on-time control the sp6650 uses a precision comparator and a minimum on-time one-shot to regulate the out- put voltage and control the inductor current under normal load conditions. as the feedback node (negative terminal of the loop comparator) drops below the reference, the loop comparator output goes high and closes the main switch. the minimum on-time one shot is triggered, setting a logic high for the duration defined by: t on = k on v in -v out where: k on = 2.7 s*v constant v in = v in pin voltage v out = v out pin voltage the outputs of the loop comparator and the on- time one shot are or'd together, inverted, and buffered to drive the gate of the high side pmos main switch. increasing inductor current causes the output to increase through the esr (equiva- lent series resistance) of the output capacitor. as v out rises above the regulation threshold, the loop comparator output resets low. termination of the on cycle occurs when both the loop comparator and the on-time one shot goes to logic low, or the inductor current limit has been reached. the discharge phase follows with the high side pmos switch opening and the low side nmos switch closing to provide a discharge path for the inductor current. the decreasing inductor current and the load current cause the output voltage to droop. under normal load conditions when the inductor current is below the pro- grammed limit, the off-time will continue until the output voltage falls below the regulation threshold, which initiates a new charge cycle via the loop comparator. the inductor current "floats" in continuous con- duction mode. during this mode the inductor peak current is below the programmed limit and the valley current is above zero. this is to satisfy load currents that are greater than half the mini- mum current ripple. the current ripple, i lr , is defined by the equation: i lr k on * v in -v out -i out *rch lv in -v out where: l= inductor value i out = load current rch = pmos on resistance, 0.4 ? typ. if the i out *rch term is negligible compared with (v in -v out ), the above equation simplifies to: i lr k on l for most applications, the inductor current ripple controlled by the sp6650 is constant regardless of input and output voltage. because the output voltage ripple is equal to: v out (ripple) = i lr *r esr where: r esr = esr of the output capacitor the output ripple of the sp6650 regulator is independent of the input and output voltages. for battery powered applications, where the battery voltage changes significantly, the sp6650 provides constant output voltage ripple through- out the battery lifetime. this greatly simplifies the lc filter design.
6 date: 1/19/05 sp6650 high efficiency 600ma synchronous buck regulator ?copyright 2005 sipex corporation r ds(on) of the p-channel mosfet and r l is the dc resistance of the inductor. the on-time control circuit seamlessly operates the converter between ccm, dcm, and low dropout modes without the need for compensa- tion. the converter's transient response is quick since there is no compensated error amplifier in the loop. inductor over-current protection the inductor over-current protection circuitry is programmed to limit the peak inductor current to 950ma (pin 4 tied to v in ) or 500ma (pin 4 to ground). this is done during the on-time by comparing the source to drain voltage drop of the pmos passing the inductor current with a second voltage drop representing the maximum allowable inductor current. as the two voltages become equal, the over-current comparator trig- gers a minimum off-time one shot. the off-time one shot forces the loop into the discharge phase for a minimum time causing the inductor current to decrease. at the end of the off-time loop, control is handed back to the or'd on-time signal. if the output voltage is still low, charging begins until the output is in regulation or the current limit has been reached again. during startup and over- load conditions, the converter behaves like a current source at the programmed limit minus half the current ripple. the minimum t off is 6 s (typ.) at v out = 0v and 2 s (typ.) for v out greater than 1.5v. under-voltage lockout the sp6650 is equipped with under-voltage lockout to protect the input battery source from excessive currents when substantially dis- charged. when the input supply is below the uvlo threshold both power switches are open to prevent inductor current from flowing. the internal reference and regulator circuitry are enabled drawing the 70 a light load quiescent current on pin 2. the rising input voltage uvlo threshold is +2.7v, with a typical hysteresis of 120mv to prevent chattering due to the imped- ance of the input source. on-time control: continued the maximum loop frequency in ccm is de- fined by the equation: f lp (v in -v out )*(v out +i out *rdc) k on *[v in +i out *(rdc-rch)] where: f lp = ccm loop frequency rdc = nmos on resistance, 0.3 ? typ. ignoring conduction losses simplifies the loop frequency to f lp = 1 * v out * (v in -v out ) k on v in or'ing the loop comparator and the on-time one shot reduces the switching frequency for load currents below half the inductor ripple current. this increases light load efficiency. the mini- mum on-time insures that the inductor current ripple is a minimum of k on /l, more than the load current demands. the converter goes in to a standard pulse frequency modulation (pfm) mode where the switching frequency is propor- tional to the load current. low dropout and load transient operation or'ing the loop comparator also increases the duty ratio past the ideal d=v out /v in up to and including 100%. under a light to heavy load transient, the loop comparator will hold the main switch on past the on-time one shot pulse until the output is brought back into regulation. also, as the input voltage supply drops down close to the output voltage, the main mosfet resistance loss will dictate a much higher duty ratio to regulate the output. eventually as the input voltage drops low enough, the output voltage will follow, causing the loop compara- tor to hold the converter at 100% duty cycle. this mode is critical in extending battery life when the output voltage is at or above the minimum usable input voltage. the dropout voltage is the minimum (v in - v out ) below which the output regulation cannot be main- tained. the dropout voltage of sp6650 is equal to i l (0.4 ? + r l ) where 0.4 ? is the typical
7 date: 1/19/05 sp6650 high efficiency 600ma synchronous buck regulator ?copyright 2005 sipex corporation under-current detection the synchronous rectifier is comprised of the inductor discharge switch, a voltage compara- tor, and a latch. during the off-time, positive inductor current flows into the pgnd pin 9 through the low side nmos switch to lx pin 10, through the inductor and the output capaci- tor, and back to pin 9. the comparator monitors the voltage drop across the discharge nmos. as the inductor current approaches zero, the channel voltage sign goes from negative to positive, causing the comparator to trigger the latch and open the switch to prevent inductor current reversal. this circuit along with the on- time one shot puts the converter into pfm mode and improves light load efficiency when the load current is less than half the inductor ripple current defined by k on /l. thermal shutdown the converter will open both power switches if the die junction temperature rises above 140 c. the die must cool down below 126 c before the regulator is re-enabled. this feature protects the sp6650 and surrounding circuitry from exces- sive power dissipation due to fault conditions. shutdown/enable control pin 5 of the device is a logic level control pin that shuts down the converter with a logic low, or enables the converter with a logic high. when the converter is shut down, the power switches are opened and all circuit biasing is extinguished leaving only junction leakage currents on sup- ply pins 1 and 2. after pin 5 is brought high to enable the converter, there is a turn on delay to allow the regulator circuitry to re-establish it- self. power conversion begins with the assertion of the internal reference ready signal which occurs approximately 150 s after the enable signal is received. battery low indicator the regulator bias voltage on pin 2 (v in ) is divided down and compared to the internal +1.25v reference voltage. when pin 2 voltage drops below +3.00v, an open drain nmos on pin 3 (blon) sinks current to ground. tying a resistor from pin 3 to v in or v out creates a logic level battery low indicator. a low bandwidth comparator and 2.9% hysteresis filter the input voltage ripple to prevent noisy transitions at the threshold. external feedback pin the sp6650 comes with a factory preset output voltage of +3.3v when pin 6 (fb) is grounded. otherwise, the output voltage can be externally programmed within the range +1.25v to +5.0v by tying a resistor from fb to ground and fb to v out (pin7). see the applications section for resistor selection information.
8 date: 1/19/05 sp6650 high efficiency 600ma synchronous buck regulator ?copyright 2005 sipex corporation typical performance characteristics figure 1. efficiency vs. output current, v out = 3.3v, l1 = 22 h (sumida cdrh6d28), i lim = v in figure 2. line/load rejection, v out = 3.3v, l1 = 22 h (sumida cdrh6d28), i lim = v in figure 3. no load battery current, v out = 3.3v, l1 = 22 h (sumida cdrh6d28), i lim = v in figure 4. efficiency vs. output current, v out = 2.5v, l1 = 22 h (sumida cdrh6d28), i lim = v in figure 5. line/load rejection, v out = 2.5v, l1 = 22 h (sumida cdrh6d28), i lim = v in figure 6. no load battery current, v out = 2.5v, l1 = 22 h (sumida cdrh6d28), i lim = v in 0 3.320 3.330 3.340 3.350 3.360 3.370 3.380 v out i load (ma) 100 200 300 400 500 600 v in = 3.67v v in = 4.2v v in = 5.0v v in = 6.5v 0 20 40 60 80 100 120 140 160 180 200 3.0 4.0 5.0 6.0 7.0 v in i in ( a) 100 65 70 75 80 85 90 95 1.0 10.0 100.0 600.0 iload (ma) efficiency (%) v in = 3.6v v in = 4.2v v in = 5.0v v in = 6.5v v in = 3.0v 0 2.445 2.455 2.465 2.475 2.485 2.495 v out iload (ma) 100 200 300 400 500 600 v in = 3.6v v in = 4.2v v in = 5.0v v in = 6.5v v in = 3.0v 0 20 40 60 80 100 120 140 160 180 200 3.0 4.0 5.0 6.0 7.0 v in i in ( a) 100 65 70 75 80 85 90 95 1.0 10.0 100.0 600.0 iload (ma) efficiency (%) v in = 3.0v v in = 4.2v v in = 5.0v v in = 6.5v
9 date: 1/19/05 sp6650 high efficiency 600ma synchronous buck regulator ?copyright 2005 sipex corporation figure 7. efficiency vs. output current, v out = 1.25v, l1 = 22 h (sumida cdrh6d28), i lim = v in figure 8. line/load rejection, v out = 1.25v, l1 = 22 h (sumida cdrh6d28), i lim = v in figure 9. no load battery current, v out = 1.25v, l1 = 22 h (sumida cdrh6d28), i lim = v in figure 10. quiescent current vs. temperature. v in = 3.6v, shdn = v in (enabled) figure 11. quiescent current vs. temperature. v in = 3.6v, shdn = gnd (shutdown) figure 12. load step transient response, v out = 2.5v, 10ma to 500ma. l1 = 22 h (sumida cdrh6d28), i lim = v in 50 55 60 65 70 75 80 85 90 95 100 1.0 10.0 100.0 600.0 iload (ma) efficiency (%) v in = 3.6v v in = 4.2v v in = 5.0v v in = 6.5v v in = 3.0v 0 20 40 60 80 100 120 140 160 180 200 3.0 4.0 5.0 6.0 7.0 v in i in ( a) 0 v out iload (ma) 100 200 300 400 500 600 1.267 1.272 1.277 1.282 1.287 1.292 v in = 3.6v v in = 4.2v v in = 5.0v v in = 6.5v v in = 3.0v 0 10 20 30 40 50 60 70 80 90 100 temperature ( c) i q op ( a) -50 -30 -10 -40 -20 0 20 40 10 30 60 80 50 70 100 90 i in i out 0 10 20 30 40 50 i q sd (na) -50 -30 -10 -40 -20 0 20 40 10 30 60 80 50 70 100 90 i in i out temperature ( c) typical performance characteristics
10 date: 1/19/05 sp6650 high efficiency 600ma synchronous buck regulator ?copyright 2005 sipex corporation figure 13. load step transient response, v out = 2.5v, 500ma to 10ma. l1 = 22 h (sumida cdrh6d28), i lim = v in figure 14. low i lim startup, v in = 4.2v, v out = 3.3v. i lim tied to gnd, internal feedback r load = 33 ? . figure 15. dead short. v in = 5.0v, i lim tied to gnd. start i out = 37ma, v out = 3.3v. finish i out = 500ma, v out = 20mv. typical performance characteristics
11 date: 1/19/05 sp6650 high efficiency 600ma synchronous buck regulator ?copyright 2005 sipex corporation external component selection inductor according to the pulse frequency modulation (pfm) algorithm, the peak to peak output ripple current can be calculated as: i lr k on l k on = 2.7 s*v is a constant for sp6650 and is set by the parameters of the internal on-time calculation circuitry. for the recommended 22 h inductor, typical ripple currents are i lr = 123ma in discontinuous conduction mode (dcm) op- eration. during continuous conduction mode, the speed of the loop comparator determines the current ripple. it is approximately equal to 200ma with a 22 h inductor. the value of the inductor is chosen based on the constant k on and acceptable current ripple. two additional inductor parameters are important: its current rating and its dc resistance. when the current through the inductor reaches the level of i sat , inductance drops down to 70% from the nominal. this non-linear change can cause stability problems or excessive fluctuation in current ripple. to avoid this, the inductor should be chosen with saturation current at least equal to the maximum output current of the converter plus half of the ripple. to provide the best converter performance in dynamic condi- tions such as start-up and load transients, induc- tors with saturation current close to the chosen i lim are recommended. the second important inductor parameter, dc resistance, directly defines the efficiency of the converter, therefore, the inductor should be cho- sen with the minimum possible dc resistance for a particular design. recommended types of the inductors for different applications are given in table 1. preferred inductors for on board power supplies with the sp6650 converter are shielded inductors to minimize radiated mag- netic fields emissions. all components recommended for typical de- signs like those shown in the applications sche- matics are given in table 1. input and output capacitors output capacitor is often selected based on the requirement on the output ripple voltage. in a buck regulator, the output ripple is determined by esr (equivalent series resistor) of the output capacitors and inductor ripple current v or = esr * i lr , where v or = peak to peak output ripple voltage. sp6650? adaptive on-time scheme provides a constant inductor ripple that is independent of input voltages and thus makes it easier to select the output capacitor. in many power supply designs, the ripple voltage needs to be less than 3% of the dc output voltage. using low esr tantalum or electrolytic capacitors to reduce the output ripple. due to the nature of the pfm control, certain output ripple is required for stable operation. the loop comparator requires minimum of 15mv ripple on the fb pin to reliably toggle the com- parator output. that translates to an output ripple of v or(min) = 15mv * v out v ref where v ref = 1.25v is the internal reference voltage. to reduce the output ripple and improve stabil- ity, a small capacitor can be paralleled with the feedback voltage divider as shown on page 1 . this capacitor forms a high pass filter with feedback resistor to increase the ripple voltage seen by the fb pin. the value of the capacitor should be in the range of 100pf to 500pf. although the 3.3v output can be programmed simply by connecting the fb pin to the ground, using this external feedback scheme can signifi- cantly reduce the output ripple. for output ripple less than 15mv, for instance when ceramic capacitors are used, an artificial ramp can be generated and superimposed onto the output. application information
12 date: 1/19/05 sp6650 high efficiency 600ma synchronous buck regulator ?copyright 2005 sipex corporation table 1. designation description manufacturer part number comments 22 h/0.77arms/0.104dcr tdk slf7030t-220mr86 shielded inductor 22 h/1.1arms/0.071dcr murata lqs66c220m04 l1 22 h/0.095dcr sumida cdrh6d28 shielded 47 h/0.76arms/0.15dcr murata lqs66c470m04 shielded 47 h/0.72arms/0.37dcr sumida cr54 c2, c3 47 f/350m ? /500ma nemco lsr47/10c-350 input, output 47 f/350m ? /500ma avx tpsc476010r0350 filter 33 f/375m ? /542ma avx tpsc336010r0375 capacitors 22 f/700m ? /348ma avx tpsb226010r0700 r2,r3 100k/63mw/1%tolerance any approved any package: r1 10/63mw/5%tolerance 0402,0505,0603 etc. the schematic and description is shown in ad- ditional application circuits . another function of the output capacitor is to hold up the output voltage during the load tran- sient, and thus prevent excessive overshoot and undershoot. for that, the recommended capaci- tor value is greater than 22uf. an input capacitor can reduce the peak current drawn from the battery, improve efficiency, and significantly reduce high frequency noises in- duced by a switching power supply. the appli- cable capacitors are tantalum, electrolytic and ceramic capacitors. an rc filter is recommended on the vin pin (pin 2) to effectively cut down the noise which can impact the ic control circuit. the time constant of the rc filter needs to be at least 5 times higher than the switching period, calculated as 1/f lp during ccm. output voltage program the output voltage can be programmed by the external voltage divider as shown on page 1. first pick a resistor value less than 100k for r3. a large r3 value would reduce the ac voltage seen by the loop comparator because the fb pin capacitance (can be as high as 10pf) can form a low pass filter with r3 paralleling with r2. lack of ac voltage to the loop comparator would give rise to pulse jittering and higher output ripple. once the r3 value is picked, r2 can be calculated from r 2 = ( v out - 1 ) r 3 v ref application information
13 date: 1/19/05 sp6650 high efficiency 600ma synchronous buck regulator ?copyright 2005 sipex corporation the additional rf/cf network used in figure 16 generates an artificial ramp from the lx pin voltage and superimposes it to the feedback pin. as a result, the internal loop comparator doesn? have to rely on output ripple to run pfm. now low esr output capacitors, such as ceramic capacitors, can be used, and the output ripple can be reduced by two to three times. for the best result, size the cf and rf values so the network would introduce 10 to 30mv ripples to the fb rb 100k sp6650 u1 10 9 8 7 6 1 2 3 4 5 l1 22 h c out 47 f r2 160k r3 100k cf 33nf pv in v in blon i lim shdn lx pgnd gnd v out fb rf 4.99k 3.3v/600ma v in 2.7-6.5 vdc cv in 1.0 f rv in 10.0 c in 47 f figure 16. additional application circuit with low output ripple pin. oversized ripple would compromise the load regulation and also cause oscillation during load transient. load transient response and out- put ripples from figure 16 circuit are shown in figure 17 and figure 18, respectively. the added ripple voltage can be calculated from ? v = k on rfcf figure 17. v out transient response from 50ma to 500ma load step. ch1- v out , ch4 - i load figure 18. output ripple ch1-output ripple. v in = 5, v out = 3.3v, i load = 600ma application information
14 date: 1/19/05 sp6650 high efficiency 600ma synchronous buck regulator ?copyright 2005 sipex corporation figure 19. additional application circuit: v in = 5.0v, v out = 12v, and max i load = 150ma. rb 100k sp6650 u1 10 9 8 7 6 1 2 3 4 5 l3 47 h c out1 100 f/16v r2 86k r3 10k pv in v in blon i lim shdn lx pgnd gnd v out fb 12v/150ma v in 4.5-6.5 vdc rv in 5.0 r2 4.02k c in 47 f d1 mbr0530ti q1 fds637an r1 11.3 k cv in 1.0 f figure 20. additional application circuit: v in = 5.0v, v out = 5.0v, i load = 250ma. rb 100k sp6650 u1 10 9 8 7 6 1 2 3 4 5 l1 47 h c out1 47 f r2 30.9k r3 10.2k pv in v in blon i lim shdn lx pgnd gnd v out fb 5v/250ma v in 4.5-6.5 vdc rv in 10.0 r2 4.02k c in 47 f d1 mbr0530t1 q1 fds637an cf2 470pf r1 1 1.3k cv in 4.7 f c out2 47 f sp6650 can also be configured with few external components to achieve buck-boost voltage con- version. efficiency of 75% to 87% can often be obtained depending on the load current and output voltage. figure 19 and figure 20 demonstrate two typical applications in which the usb input is converted to a 12v and a well regulated 5v. the operation of the circuit is as follows. when the internal high side pmos turns on, the lx pin swings to the input voltage which turns on the external nmos q1. a voltage equal to vin is then applied to the inductor to cause the inductor current rise linearly. since there? no current delivered to the output, the output capacitor is discharged by the load current. therefore, the internal pmos can be only turned off by the over-current comparator since the loop com- parator would never toggle during this state. when the internal pmos is open, the internal low side nmos is turned on. this pulls the lx pin to the ground and turns off the q1. as a result, the schottky d2 is forward biased and conducts the inductor current to the output. now the inductor experiences a reversed voltage equal to vout and its current ramps down linearly. as expressed in the operation section under in- ductor over-current protection , a minimum t off timer is activated after the over-current comparator is triggered in the previous state. before toff expires, the internal pmos will not turn on, and the inductor will not be recharged even when the output voltage drops below the regulation voltage. this reduces the maximum load current that can be delivered by this circuit. since t off is reverse proportional to the v out pin voltage, the v out pin is pulled up using a voltage divider tying to the input voltage. as a result, a 5v to 12v conversion can provide maximum 120ma load. this buck-boost circuit can regulate an output voltage higher, lower or equal to the input voltage. application information
15 date: 1/19/05 sp6650 high efficiency 600ma synchronous buck regulator ?copyright 2005 sipex corporation layout considerations proper layout is a very important part of the on- board power supply, affecting normal function- ality of the dc-dc converter itself and emi. because of the high frequency switching of the converter, the traces that couple an electric field can conduct currents under the ac voltages across the parasitic capacitance. magnetic field coupling traces can induce currents like trans- formers. to avoid an excessive interference between the converter and the other active components on the board, some rules should be followed. avoid injecting noise into the sensitive part of the circuit via the gnd plane. input and output capacitors conduct the current through the gnd plane and high frequency components of the current can degrade the sensitive circuitry. sepa- rate the power and signal grounds and connect them at one point to minimize the noise injected from the power ground to the signal ground. "star" connection of the ground traces is shown on figure 26, where gnd is the minus pole of the output capacitor. power loops on the input and output of the converter should be laid out with the shortest and widest traces possible. the longer and narrower the trace, the higher the resistance and induc- tance it will have. the ac current in long traces radiates emi noise affecting the sensitive cir- cuits. the length of traces in series with the capacitors increases its esr and esl and reduc- ing their effectiveness at high frequencies. there- fore put the input capacitor as close to the appropri- ate pins of the converter as possible and output capacitor close to the inductor. the external voltage feed back network should be placed very close to the fb pin as well as bypass capacitor c4. any noise traces like the lx pin should be kept away from the voltage feed back network and separated from it by using power ground copper to minimize emi. f igure 21. application circuit with highlighted power traces. gnd_ signal fb sdn gnd pgnd blon v out v in i lim pv in l x sp6650 2.7 - 6.5v dc c1 1 f c2 47 f + r1 10 ? c4 470pf r2 100k ? r3 100k ? 47 f c3 + 2.5v 1 2 3 4 5 6 7 8 9 10 3 1 l1 22 h 100k
16 date: 1/19/05 sp6650 high efficiency 600ma synchronous buck regulator ?copyright 2005 sipex corporation 1 e1 e pin #1 indentifier must be indicated within this shaded area (d/2 * e1/2) l1 l r1 1 r 1 seating plane gauge plane l2 b b symbol min nom max a--1.1 a1 0 - 0.15 a2 0.75 0.85 0.95 b0.17- 0.27 c0.08- 0.23 d e e1 e e1 l0.40. 60.8 l1 l2 n-10- r0.0 7- - r1 0.07 - - ?0o-8o ?1 0o - 15o note: dimensions in (mm) 10 pin msop jedec mo-187 (ba) variation 3.00 bsc 4.90 bsc 3.00 bsc 0.50 bsc 2.00 bsc 0.95 ref 0.25 bsc 1 2 e/2 e1 e d c with plating base metal b section b-b a2 a a1 b package: 10 pin msop
17 date: 1/19/05 sp6650 high efficiency 600ma synchronous buck regulator ?copyright 2005 sipex corporation part number temperature range package type sp6650eu .............................................. -40?c to +85?c ........................................ 10-pin msop sp6650eu/tr ........................................ -40?c to +85?c ........................................ 10-pin msop analog excellence sipex corporation reserves the right to make changes to any products described herein. sipex does not assume any liability aris ing out of the application or use of any product or circuit described herein; neither does it convey any license under its patent rights nor t he rights of others. corporation sipex corporation headquarters s 233 south hillview drive milpitas, ca 95035 tel: (408) 934-7500 fax: (408) 935-7600 /tr = tape and reel pack quantity is 2500 for msop. available in lead free packaging. to order add "-l" suffix to part number. example: sp6650eu/tr = standard; sp6650eu-l/tr = lead free ordering information

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