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mar 29-07 revd sp6126 : tsot-6 pfet buck controller ? 2007 sipex corporation 1 features wide 4.5v ? 29v input voltage range internal compensation built-in high current pmos driver adjustable overcurrent protection internal soft-start 600khz constant frequency operation 0.6v reference voltage 1% output setpoint accuracy lead free, rohs compliant package: small 6-pin tsot description the sp6126 is a pwm controlled step down (buck) vol tage mode regulator with v in feedforward and internal type-ii compensation. it operates from 4.5 v to 29v making is suitable for 5v, 12v, and 24v applications. by using a pmos driver, this device i s capable of operating at 100% duty cycle. the high side driver is designed to drive the gate 5v b elow v in . the programmable overcurrent protection is based on high-side mosfet?s on resist ance sensing and allows setting the overcurrent protection value up to 300mv threshold (measured from v in -lx). the sp6126 is available in a space-saving 6-pin tsot package maki ng it the smallest controller available capable of operating from 24vdc supplies. typical application circuit 6 5 4 1 2 3 sp6126 6 pintsot gnd lx gate fb v in vdr high=of f l1, ihlp-2525cz 6.8uh, 60mohm, 4.5a c4 22uf ds mbra340t3g r1 200k, 1% rz 2k r2 44.2k, 1% q1 si2343ds cz 62pf c7 0.1uf c1 10uf rs=1k d1 1n4148 12v shdn vin gnd gnd vout vin gnd vdr vfb gate lx sp6126 3.3v 0-2.0a 5 3 1 26 4 solved by tm sp612 6 high-voltage, step down controller in tsot6
mar 29-07 revd sp6126 : tsot-6 pfet buck controller ? 2007 sipex corporation 2 these are stress ratings only, and functional opera tion of the device at these ratings or any other above thos e indicated in the operation sections of the specific ations below is not implied. exposure to absolute maximum rating conditions for extended periods of time may affect reliability. absolute maximum ratings input voltage?..................................... ............-0.3v to 30v lx??????????????? ?? ??.? -2v to 30v fb????? ..................................................- 0.3v to 5.5v storage temperature..?????? ...?? -65 c to 150 c junction temperature............................... ....-40 c to 125 c lead temperature (soldering, 10 sec)?.?.???..300 c esd rating?? ?.?.?1kv lx, 2kv all other nodes, hbm electrical specifications specifications are for t amb =t j =25 c, and those denoted by ? apply over the full operating range, -40 c< t j <85 c. unless otherwise specified: v in =4.5v to 29v, c in = 4.7 f. parameter min typ max units ? conditions uvlo turn-on threshold 4.2 4.35 4.5 v 0 c< t j <85 c uvlo turn-off threshold 4.0 4.2 4.4 v 0 c< t j <85 c uvlo hysterisis 0.2 v operating input voltage range 4.5 29 v 0 c< t j <85 c operating input voltage range 7 29 v ? operating vcc current 0.3 3 ma vfb=1.2v reference voltage accuracy 0.5 1 % reference voltage accuracy 0.5 2 % ? reference voltage 0.594 0.6 0.606 v reference voltage 0.588 0.6 0.612 v ? switching frequency 510 600 690 khz peak-to-peak ramp modulator v in /5 v minimum on-time duration 40 100 ns ? minimum duty cycle 0 % maximum duty cycle 100 % gate driver turn-off resistance 50 60 k internal resistor between gate and v in gate driver pull-down resistance 4 8 v in =12v, v fb =0.5v, measure resistance between gate and vdr gate driver pull-up resistance 3 6 v in =12v, v fb =0.7v, measure resistance between gate and v in v in - vdr voltage difference 4.5 5.5 v ? measure v in ? vdr, v in >7v overcurrent threshold 270 300 330 mv measure v in - lx lx pin input current 25 30 35 ua v lx = v in off interval during hiccup 100 ms soft start time 3 5 9 ms vfb=0.58v, measure between v in =4.5v and first gate pulse shdn threshold 0.9 1.0 1.1 v ? apply voltage to fb shdn threshold hysteresis 100 mv
mar 29-07 revd sp6126 : tsot-6 pfet buck controller ? 2007 sipex corporation 3 pin description pin # pin name description 1 v in input power supply for the controller. place input decoupling capacitor as close as possible to this pin. 2 gate connect to the gate terminal of the external p-channel mosfet. 3 vdr power supply for the internal driver. this voltage is internally regulated to about 5v below v in . place a 0.1uf decoupling capacitor between vdr an d v in as close as possible to the ic. 4 fb regulator feedback input. connect to a resistive vo ltage-divider network to set the output voltage. this pin can be also used for o n/off control. if this pin is pulled above 1v the p-channel driver is disabled an d controller resets internal soft start circuit. 5 gnd ground pin. 6 lx this pin is used as a current limit input for the i nternal current limit comparator. connect to the drain pin of the external mosfet thr ough an optional resistor. internal threshold is pre-set to 300mv nominal and can be decreased by changing the external resistor based on the followi ng formula: v trshld = 300mv ? 30ua * r block diagram fault register set dominant por +- enbl 4-bit counter vdr vin gate 5v internal ldo vin - 0.3v overcurrent comparator lx vdr 30ua gnd 5v +- +- vref fault fb oscillator vin sr i = k x vin error amplifier pwm comparator pwm latch reset dominant vin - 5v ldo fault +- 1v fault 200ms delay uvlo s r r
mar 29-07 revd sp6126 : tsot-6 pfet buck controller ? 2007 sipex corporation 4 the sp6126 is a fixed frequency, voltage- mode, non-synchronous pwm controller optimized for minimum component, small form factor and cost effectiveness. it has been designed for single-supply operation ranging from 4.5v to 29v. sp6126 has type-ii internal compensation for use with electrolytic/tantalum output capacitors. for ceramic capacitors type-iii compensation can be implemented by simply adding an r and c between output and feedback. a precision 0.6v reference, present on the positive terminal of the error amplifier, permits programming of the output voltage down to 0.6v via the fb pin. the output of the error amplifier is internally compared to a feed-forward (v in /5 peak-to- peak) ramp and generates the pwm control. timing is governed by an internal oscillator that sets the pwm frequency at 600khz. sp6126 contains useful protection features. over-current protection is based on high-side mosfet?s rds(on) and is programmable via a resistor placed at lx node. under-voltage lock-out (uvlo) ensures that the controller starts functioning only when sufficient voltage exists for powering ic?s internal circuitry. sp6126 loop compensation the sp6126 includes type-ii internal compensation components for loop compensation. external compensation components are not required for systems with tantalum or aluminum electrolytic output capacitors with sufficiently high esr. use the condition below as a guideline to determine whether or not the internal compensation is sufficient for your design. type-ii internal compensation is sufficient if the following condition is met: dbpole esrzero f f < ??????. (1) where: out esr esrzero c r f . . .2 1 = ???.. (2) out dbpole c l f ? = . .2 1 ?? ?? (3) creating a type-iii compensation network the above condition requires the esr zero to be at a lower frequency than the double-pole from the lc filter. if this condition is not met, type-iii compensation should be used and can be accomplished by placing a series rc combination in parallel with r1 as shown below. the value of cz can be calculated as follows and rz selected from table 1. 1 r c l cz ? = ????.. (4) table1- selection of rz figure 1- rz and cz in conjunction with internal compensation components form a type-iii compensation f esrzero f dbpole rz 1x 50k 2x 40k 3x 30k 5x 10k >= 10x 2k r1 200k, 1% r2 sp6126 vfb +- rz2 200k cz2 130pf cp1 2pf error amplif ier vref =0.6v vout rz cz general overview
mar 29-07 revd sp6126 : tsot-6 pfet buck controller ? 2007 sipex corporation 5 loop compensation example 1- a converter utilizing a sp6126 has a 6.8uh inductor and a 22uf/5m ceramic capacitor. determine whether type-iii compensation is needed. from equation (2) f esrzero = 1.45mhz. from equation (3) f dbpole = 13 khz. since the condition specified in (1) is not met, type-iii compensation has to be used by adding external components rz and cz. using equation (4) cz is calculated 61.2pf (use 62 pf). following the guideline given in table 1, a 2k rz should be used. the steps followed in example 1 were used to compensate the typical application circuit shown on page 1. satisfactory frequency response of the circuit, seen in figure 2, validates the above procedure. loop compensation example 2- a converter utilizing a sp6126 has a 6.8uh inductor and a 150uf, 82m aluminum electrolytic capacitor. determine whether type-iii compensation is needed. from equation (2) f esrzero = 13khz. from equation (3) f dbpole = 5 khz. since the condition specified in (1) is not met, type-iii compensation has to be used by adding external components rz and cz. using equation (4) cz is calculated 160pf (use 150 pf). since f esrzero f dbpole is approximately 3, rz has to be set at 30k . figure 2- satisfactory frequency response of typica l application circuit shown on page 1. crossover frequency fc is 80khz with a correspon ding phase margin of 65 degrees. general overview
mar 29-07 revd sp6126 : tsot-6 pfet buck controller ? 2007 sipex corporation 6 overcurrent protection ds q1 rs sp6126 gate lx 30ua +- vin - 0.3v vin ov er-current comparator figure 3- overcurrent protection circuit the overcurrent protection circuit functions by monitoring the voltage across the high-side fet q1. when this voltage exceeds 0.3v, the overcurrent comparator triggers and the controller enters hiccup mode. for example if q1 has rds(on)=0.1 , then the overcurrent will trigger at i = 0.3v/0.1 =3a. to program a lower overcurrent use a resistor rs as shown in figure 1. calculate rs from: ( ) ua on rds iout rs 30 ) ( 15.1 3.0 ? = ?..?? (5) the overcurrent circuit triggers at peak current through q1 which is usually about 15% higher than average output current. hence the multiplier 1.15 is used in (5). example: a switching mosfet used with sp6126 has rds(on) of 0.1 . program the over- current circuit so that maximum output is 2a. ( ) ua ohm a rs 30 1.0 1 15.1 3.0 ? = rs = 2333 using the above equation there is good agreement between calculated and test results when an rs in the range of 0.5k to 3k is used. for rs larger than 3k test results are lower than those predicted by (5), due to circuit parasitics. using the on/off function feedback pin serves a dual role of on/off control. the mosfet driver is disabled when a voltage greater than 1v is applied at fb pin. maximum voltage rating of this pin is 5.5v. the controlling signal should be applied through a small signal diode as shown on page 1. please note that an optional 10k bleeding resistor across the output helps keep the output capacitor discharged under no load condition. programming the output voltage to program the output voltage, calculate r2 using the following equation: ? ?? ? ? ?? ? ? = 1 1 2 vref vout r r where: vref=0.6 is the reference voltage of the sp6126 r1=200k is a fixed-value resistor that, in addition to being a voltage divider, it is part of the compensation network. in order to simplify compensation calculations, r1 is fixed at 200k . soft start soft start is preset internally to 5ms (nominal). internal soft start eliminates the need for the external capacitor css that is commonly used to program this function. mosfet gate drive p-channel drive is derived through an internal regulator that generates v in -5v. this pin (vdr) has to be connected to v in with a 0.1uf decoupling capacitor. the gate drive circuit swings between v in and v in -5 and employs powerful drivers for efficient switching of the p- channel mosfet. general overview
mar 29-07 revd sp6126 : tsot-6 pfet buck controller ? 2007 sipex corporation 7 power mosfet selection select the power mosfet for voltage rating bv dss , on resistance r ds(on) , and thermal resistance rthja. bv dss should be about twice as high as v in in order to guard against switching transients. recommended mosfet voltage rating for v in of 5v, 12v and 24v is 12v, 30v and 40v respectively. r ds(on) has to be selected such that when operating at peak current and junction temperature the overcurrent threshold of the sp6126 is not exceeded. allowing 50% for temperature coefficient of r ds(on) and 15% for inductor current ripple, the following expression can be used: ?? ? ?? ? iout mv on rds 15.1 5.1 300 ) ( within this constraint, selecting mosfets with lower r ds(on) will reduce conduction losses at the expense of increased switching losses. as a rule of thumb select the highest r ds(on) mosfet that meets the above criteria. switching losses can be assumed to roughly equal the conduction losses. a simplified expression for conduction losses is given by: ?? ? ?? ? = vin vout on rds iout pcond ) ( mosfet?s junction temperature can be estimated from: ( ) tambient rthja pc t + = 2 schottky rectifier selection select the schottky for voltage rating v r , forward voltage v f , and thermal resistance rthja. voltage rating should be selected using the same guidelines outlined for mosfet voltage selection. for a low duty cycle application such as the circuit shown on first page, the schottky is conducting most of the time and its conduction losses are the largest component of losses in the converter. conduction losses can be estimated from: ?? ? ?? ? ? = vin vout iout vf pc 1 where: vf is diode forward voltage at i out schottky?s ac losses due to its switching capacitance are negligible. inductor selection select the inductor for inductance l and saturation current i sat . select an inductor with i sat higher than the programmed overcurrent. calculate inductance from: ( ) ? ?? ? ? ?? ? ? ?? ? ? ?? ? ?? ? ?? ? ? = irip f vin vout vout vin l 1 1 where: v in is converter input voltage v out is converter output voltage f is switching frequency i rip is inductor peak-to-peak current ripple (nominally set to 30% of i out ) keep in mind that a higher i rip results in a smaller inductor which has the advantages of small size, low dc equivalent resistance dcr, high saturation current i sat and allows the use of a lower output capacitance to meet a given step load transient. a higher i rip , however, increases the output voltage ripple and increases the current at which converter enters discontinuous conduction mode. the output current at which converter enters dcm is ? of i rip . note that a negative current step load that drives the converter into dcm will result in a large output voltage transient. therefore the lowest current for a step load should be larger than ? of i rip . output capacitor selection select the output capacitor for voltage rating, capacitance and equivalent series resistance (esr). nominally the voltage rating is selected to be twice as large as the output voltage. select the capacitance to satisfy the specification for output voltage overshoot/undershoot caused by current step load. a steady-state output current i out corresponds to inductor stored energy of ? l i out 2 . general overview
mar 29-07 revd sp6126 : tsot-6 pfet buck controller ? 2007 sipex corporation 8 a sudden decrease in i out forces the energy surplus in l to be absorbed by c out . this causes an overshoot in output voltage that is corrected by power switch reduced duty cycle. use the following equation to calculate c out : ?? ? ?? ? ? = 2 2 vout - vos 1 2 i i l cout where: l is the output inductance i 2 is the step load high current i 1 is the step load low current vos is output voltage including overshoot v out is steady state output voltage output voltage undershoot calculation is more complicated. test results for sp6126 buck circuits show that undershoot is approximately equal to overshoot. therefore above equation provides a satisfactory method for calculating c out . select esr such that output voltage ripple (v rip ) specification is met. there are two components to v rip : first component arises from charge transferred to and from c out during each cycle. the second component of v rip is due to inductor ripple current flowing through output capacitor?s esr. it can be calculated from: 2 2 8 1 ? ?? ? ? ?? ? + = fs cout esr irip vrip where: i rip is inductor ripple current f s is switching frequency c out is output capacitor calculated above note that a smaller inductor results in a higher i rip , therefore requiring a larger c out and/or lower esr in order to meet v rip . input capacitor selection select the input capacitor for voltage, capacitance, ripple current, esr and esl. voltage rating is nominally selected to be twice the input voltage. the rms value of input capacitor current, assuming a low inductor ripple current ( i rip ), can be calculated from: ( ) d d iout icin ? = 1 in general total input voltage ripple should be kept below 1.5% of v in (not to exceed 180mv). input voltage ripple has three components: esr and esl cause a step voltage drop upon turn on of the mosfet. during on time capacitor discharges linearly as it supplies i out -iin. the contribution to input voltage ripple by each term can be calculated from: ( ) 2 , vin cin fs vout vin vout iout cin v ? = ? ( ) irip iout esr esr v 5.0 , ? = ? ( ) trise irip iout esl esl v 5.0 , ? = ? where trise is the rise time of current through capacitor total input voltage ripple is sum of the above: esl v esr v cin v tot v , , , , ? + ? + ? = ? general overview
mar 29-07 revd sp6126 : tsot-6 pfet buck controller ? 2007 sipex corporation 9 high=of f l1, ihlp-2525cz 6.8uh, 60mohm, 4.5a c4 22uf ds mbra340t3g r1 200k, 1% rz 2k r2 44.2k, 1% q1 si2343ds cz 62pf c7 0.1uf c1 10uf rs=1k d1 1n4148 12v shdn vin gnd gnd vout vin gnd vdr vfb gate lx sp6126 3.3v 0-2.0a 5 3 1 26 4 figure 4- application circuit for v in =12v c2 2.2uf c1, c2 ceramic, 50v l1, vishay ihlp-2525cz 6.8uh, 4.5a, 60mohm ds, mbra340t3 3a, 40v r1 200k, 1% rz 2k r2 44.2k, 1% m1, si4447dy 72mohm, 40v cz 62pf c7 0.1uf rs 1k c4, ceramic 22uf, 6.3v d1 1n4148 24-29v shdn gnd vin gnd vout vdr vfb vin gate lx gnd sp6126 3.3v 0-2.0a 1 5 3 26 4 c1 2.2uf figure 5- application circuit for v in = 24-29v application circuits
mar 29-07 revd sp6126 : tsot-6 pfet buck controller ? 2007 sipex corporation 10 typical performance characteristics figure 7- efficiency at v in = 12 v figure 6- application circuit for v out = 4.5-5.5 v high=of f l1, vishay ihlp-2525cz 3.3uh, 6a, 30mohm ds, mbra340t3 3a, 40v r1 200k, 1% rz 2k r2 44.2k, 1% m1, si2335ds 51mohm, 12v cz 33pf c7 0.1uf rs 1k c4, ceramic 22uf, 6.3v d1 1n4148 4.5-5.5 v shdn gnd vin gnd vout vin vdr vfb gate lx gnd sp6126 3.3v 0-3a 1 5 3 26 4 c1 10uf c2 10uf c3 10uf sp6126 efficiency versus iout, vin=12v,ta=25c 60 70 80 90 100 0.0 0.5 1.0 1.5 2.0 2.5 iout (a) efficiency (%) vout=3.3v vout=5v vout=2.5v
mar 29-07 revd sp6126 : tsot-6 pfet buck controller ? 2007 sipex corporation 11 typical performance characteristics sp6126 efficiency versus iout, vin=24v,ta=25c 50 60 70 80 90 0.0 0.5 1.0 1.5 2.0 2.5 iout (a) efficiency (%) vout=3.3v vout=5v figure 8- efficiency at v in = 24 v sp6126 efficiency versus iout, vin=5v,ta=25c 70 75 80 85 90 95 100 0.0 0.5 1.0 1.5 2.0 2.5 3.0 iout (a) efficiency (%) vout=2.5v vout=3.3v figure 9- efficiency at v in = 5 v
mar 29-07 revd sp6126 : tsot-6 pfet buck controller ? 2007 sipex corporation 12 typical performance characteristics figure 10- step load 1-2a, figure 11- step loa d 0.3-2a, ch1: v in ; ch2: v out ; ch3: i out ch1: v in ; ch2: v out ; ch3: i out figure 12- startup no load, f igure 13- start up 2a, ch1: v in ch2: v out , ch3: i out ch1: v in ; ch2: v out ; ch3: i out figure 14- output ripple at 0a is 11mv, figure 15- output ripple at 2a is 18mv, ch1: v in ; ch2: v out ; ch3: i out ch1: v in ; ch2: v out ; ch3: i out
mar 29-07 revd sp6126 : tsot-6 pfet buck controller ? 2007 sipex corporation 13 package: 6pin tsot
mar 29-07 revd sp6126 : tsot-6 pfet buck controller ? 2007 sipex corporation 14 ordering information part number temperature range package sp6126ek1-l????????????? .-40 c to +85 c?????? .?(lead free) 6 pin tsot sp6126ek1-l/tr..?????????? ....-40 c to +85 c?????? ?.(lead free) 6 pin tsot /tr = tape and reel pack quantity for tape and reel is 2500 for further assistance: email: sipexsupport@sipex.com www support page: http://www.sipex.com/content.aspx?p=support sipex application notes: http://www.sipex.com/applicationnotes.aspx sipex corporation headquarters and sales office 233 south hillview drive milpitas, ca95035 tel: (408) 934-7500 fax: (408) 935-7600 sipex corporation reserves the right to make change s to any products described herein. sipex does not assume any liability arising out of the application or use of any product or circuit described herein; neither do es it convey any license under its patent rights no r the rights of others. solved by tm

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