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zxsc100 single cell dc-dc converter solution zxsc100 document number: ds33613 rev. 6 - 2 1 of 13 www.diodes.com january 2012 ? diodes incorporated zxsc100x8 obsolete closest a lternative is ZXSC100N8 description the zxsc100 series is designed for dc-dc applications where step-up voltage conversion from very low input voltages is required. these applications mainly operate from single nickel cadmium or nickel metal hydride battery cells. the circuit can start up under full load with regulation maintained down to an input voltage of only 0.926 volts. the solution configuration ensures optimum efficiency over a wide range of load currents. severa l circuit configurations are possible with loads up to 2w. the step up output voltage is easily programmed with external resistors. with its non- synchronous architecture an out put voltage down to the input voltage level can be achieved. for best performance the zxsc100 quiescent current is a small 150 a ensuring minimum battery drain in no load conditions. the ic and discrete combination offers the ultimate cost vs. performance solution for single cell dc-dc conversion. pin assignments so-8 features ? efficiency maintained over a wide range of input voltages and load currents 82% efficiency @ v batt = 1v ? startup under full load ? minimum operating input voltage v batt = 0.926v ? adjustable output voltage down to v batt ? quiescent current typically 150 a referred to input voltage ? so-8 package in ?green? molding compound (no br, sb) with lead free finish/rohs compliant (note 1) notes: 1. eu directive 2002/95/ec (rohs). all applicable rohs exemptions applied. please visit our website at: http://www.diodes.com /products/lead_free.html applications ? cordless telephones ? mp3 players ? pda ? pagers ? battery backup supplies ? electronic toothbrush ? gps receivers ? digital camera ? palmtop computers ? hand held instruments ? portable medical equipment ? solar powered equipment typical application circuit
zxsc100 single cell dc-dc converter solution zxsc100 document number: ds33613 rev. 6 - 2 2 of 13 www.diodes.com january 2012 ? diodes incorporated zxsc100x8 obsolete closest a lternative is ZXSC100N8 pin descriptions pin no. name description 1 em emitter of internal drive transistor. connect to re in lower power applications. must be unconnected in higher power applications. 2 bas only used if increased drive current to the main external npn switching transistor is required. (see note 2). 3 re drive current sense input. internal threshold voltage set 25mv below v cc . connected external sense resistor. (note 2) 4 v cc supply voltage, generally nimh, nicd single cell. 5 i sense inductor current sense input. internal threshold voltage set to 25mv. connect external sense resistor. 6 fb feedback sense. internal threshold set to 730mv. connect external resistive divider to output voltage. 7 gnd ground 8 v drive drive output for external switching transistor. connect to base of external bipolar transistor. for increased drive current see note 2 note: 2. in higher load current applications an additional pnp can be used to increase the drive current of the main external n pn switching transistor. the pnp base should be connected to bas pin, its emitter to the re pin and its collector connected to v drive pin. functional block diagram absolute maximum ratings description rating unit supply voltage 0.3 to 3.5 v maximum voltage other pins 0.3 to v cc +0.3 v power dissipation (25c) so-8 780 mw operating temperature 0 to 70 c storage temperature -55 to +150 c junction temperature 150 c
zxsc100 single cell dc-dc converter solution zxsc100 document number: ds33613 rev. 6 - 2 3 of 13 www.diodes.com january 2012 ? diodes incorporated zxsc100x8 obsolete closest a lternative is ZXSC100N8 operating conditions symbol parameter min typ. max unit f osc recommended operating frequency (note 3) 200 khz note: 3. operating frequency is applicatio n circuit dependent. see application section. electrical characteristics (t a = 25 c, v cc = 1.2v; unless otherwise specified) symbol parameter conditions min typ max units i cc quiescent current not switching 150 200 a i drive base drive current v re = v cc 5 10 ma v drive v drive o/p voltage v re = v cc , i drive = 5ma v cc ? 0.17 v v fb feedback voltage 708 730 752 mv v isense output current reference voltage 12 17.5 24 mv t cvisense i sense voltage temp co. 0.4 %/c v dref drive current refernce voltage measured with respect to v cc 20 30 40 mv t cvdref v dref temp co. 1 %/c v cc(srt) startup voltage any output load 1.01 1.06 1.1 v v cc(min) minimum operating input voltage 0.926 0.98 1 v v cc(hys) supply start up to shutdown hysteresis 80 mv i fb feedback input current 100 200 na i sense isense input current v isense = 0v 3 4 5.5 a v o(min) minimum output voltage v cc v v o(max) maximum output voltage fmmt617 as pass element (note 4) 20 v t off discharge pulse width 1.7 3 s note: 4. depends on breakdown volt age of pass device. see fmmt617 datasheet
zxsc100 single cell dc-dc converter solution zxsc100 document number: ds33613 rev. 6 - 2 4 of 13 www.diodes.com january 2012 ? diodes incorporated zxsc100x8 obsolete closest a lternative is ZXSC100N8 typical characteristics
zxsc100 single cell dc-dc converter solution zxsc100 document number: ds33613 rev. 6 - 2 5 of 13 www.diodes.com january 2012 ? diodes incorporated zxsc100x8 obsolete closest a lternative is ZXSC100N8 device description the zxsc100 is non-synchronous pfm, dc-dc controller ic which, when combined with a high performance external transistor, enables the production of a high efficiency boost conv erter for use in single cell applications. a block diagram is shown for the zxsc100 on page 2. a shutdown circuit turns the device on or off at v cc = 1v with a hysteresis of typically 80mv. at start up, comparator comp1 turns the driver circuit and therefore the ex ternal switching transistor on. this circ uit will remain active until the feedback voltage at the pin fb rises above v ref , which is set to 730mv. an external resistive divider on the fb pin sets the output voltage level. comparator comp2 forces the driver circuit and the external switching transistor off, if the voltage at i sense exceeds 25mv. the voltage at i sense is taken from a current sense resistor connected in series with the emitter of the switching transistor. a monostable following the output of comp2 extends the turn-off time of the output stage by a minimum of 2s. this ensures that there is sufficient time to dischar ge the inductor coil before the next on period. the and gate between the monostable and comp1 output ensures that the switching transistor always remains on until the i sense threshold is reached and that the minimum discharge period is always asserted. the pulse width is constant, the pulse frequency varies with the output load. the driver circuit supplies the external switching transistor with a defined current, which is programmed by an external resistor connected between the re pin and v cc . the internal reference voltage for the circuit is 25mv below v cc . to maximise efficiency the external transistor is switched quickly, typically being forced off within 20ns. in higher power applications more current can be supplied to the switching transistor by using a further external component. the driver transistor in the ic can be bypassed with the addi tion of a discrete pnp. more information on this circuit configuration can be found in the applications section.
zxsc100 single cell dc-dc converter solution zxsc100 document number: ds33613 rev. 6 - 2 6 of 13 www.diodes.com january 2012 ? diodes incorporated zxsc100x8 obsolete closest a lternative is ZXSC100N8 application information the following section is a design guide for optimum converter performance. switching transistor selection the choice of switching transistor has a major impact on the dc- dc converter efficiency. for optimum performance, a bipolar transistor with low v ce(sat) and high gain is required. the majority of losse s in the transistor are, ?on-state? and can be calculated by using the formula below: from the calculations above the impact on converter efficiency can be seen. external drive transistor selection for higher power applications an external transistor is requir ed to provide the additional base drive current to the main switching transistor. for this, any small signal pnp transisto r is sufficient. please see reference designs for recommended part numbers. schottky diode selection as with the switching transistor the sc hottky rectifier diode has a major impact on the dc-dc converter efficiency. a schottky diode with a low forward voltage and fast recovery time should be used for this application. the majority of losses in the diod e are, ?on-state? and can be calculated by using the formula below: the diode should be selected so that the maximum forward curr ent is greater or equal to t he maximum peak current in the inductor, and the maximum reverse voltage is greater or equal to the output vo ltage. the diodes zhcs1000 meets these needs. a data sheet for the zhcs1000 is available on the diodes web site or through your local diodes sales office. outline information is included in the characte ristics section of this data sheet. the inductor value must be chosen to satisfy performance, cost and size requirements of the overall solution. for the reference designs we recommend an inductor value of 22 h with a core saturation current rating greater than the converter peak current value. inductor selection has a significant impact on the converter efficiency. for applications where efficiency is critical, a 5% improvement can be achieved with a high pe rformance inductor. this should be selected with a core saturation current rating much higher than the peak current of the converter, say 3 times greater. the result ant reduction in core losses brings about the efficiency improvement. peak current definition the peak current rating is a design parameter whose value is dependent upon the overall application. for the reference designs, a peak current of 1.2a was chosen to ensure t hat the converter could provide the required output power. in general, the i pk value must be chosen to ensure that the switching transistor, q1, is in full saturation with maximum output power conditions, assuming worse-case input voltage and tr ansistor gain under all operating temperature extremes. once ipk is decided the value of r sense can be determined by:
zxsc100 single cell dc-dc converter solution zxsc100 document number: ds33613 rev. 6 - 2 7 of 13 www.diodes.com january 2012 ? diodes incorporated zxsc100x8 obsolete closest a lternative is ZXSC100N8 application information (cont.) output power definition by making the above assumptions for the inductor and i pk the output power can be determined by: note: v out = output voltage + rectifier diode vf figure 1 shows the discontinuous inductor current and the relationship between output power, t on , t dis and t off . fig. 1 discontinuous inductor current output capacitors output capacitors are a critical choice in the overall performance of the soluti on. they are required to filter the output and supply load transient currents. there are three parameters wh ich are paramount in the select ion of the output capacitors; their capacitance value, i ripple and esr. the capacitance value is selected to meet the load transient requirements. the capacitors i ripple rating must meet or exceed t he current ripple of the solution. the esr of the output capacitor can also affect loop stability and transient perfo rmance. the capacitors selected for the solution, and indicated in the reference designs, ar e optimised to provide the best overall performance. input capacitors the input capacitor is chosen for its voltage and rms current rati ng. the use of low esr electrol ytic or tantalum capacitors is recommended. capacitor values for optimum performanc e are suggested in the reference design section. also note that the esr of the i nput capacitor is effectively in series with the input and hence contributes to efficiency losse s in the order of i rms 2 x esr.
zxsc100 single cell dc-dc converter solution zxsc100 document number: ds33613 rev. 6 - 2 8 of 13 www.diodes.com january 2012 ? diodes incorporated zxsc100x8 obsolete closest a lternative is ZXSC100N8 application information (cont.) output voltage adjustment the zxsc100 is an adjustable converter allowing the end user the maximum flexibility in output voltage selection. for adjustable operation a potential divider network is connected as indicated in the diagram. the output voltage is determined by the equation: v out = v fb (1 + ra / rb), where v fb =730mv the resistor values, ra and rb, should be maximised to impr ove efficiency and decrease battery drain. optimisation can be achieved by providing a minimum current of i fb(max) = 200na to the v batt pin. the output is adjustable from v fb to the (br)v ceo of the switching transistor, q1. note: for the reference designs, ra is assigned the label r3 and rb the label r4. external transistor base drive selection optimisation of the external switching transistor base dr ive may be necessary for improved efficiency in low power applications. this can be achieved by introducing an external re sistor between the supply and the re pin of the zxsc100. the resistor value can be determined by: layout issues layout is critical for the circuit to func tion optimally in terms of electrical effi ciency, thermal consid erations and noise. for ?step-up converters? there are four main current loops, the input loop, po wer-switch loop, rectifier loop and output loop. the supply charging the input capacitor forms the input loop. the power-switch loop is defined when q1 is ?on?, current flows from the input through the inductor, q1, r sense and to ground. when q1 is ?off?, the energy stored in the inductor is transferred to the output capacitor and load via d1, forming the rectifier loop. the output loop is formed by the output capacitor supplying the load when q1 is switched back off. to optimise for best performance each of these loops should be kept separate from each other and interconnections made with short, thick traces thus minimising parasitic inductance, capacitance and resistance. also the sense resistor r2 should be connected, with minimum trace length, between emitter lead of q1 and ground, again minimising stray parasitics.
zxsc100 single cell dc-dc converter solution zxsc100 document number: ds33613 rev. 6 - 2 9 of 13 www.diodes.com january 2012 ? diodes incorporated zxsc100x8 obsolete closest a lternative is ZXSC100N8 designing with the zxsc100 introduction this section refers to the zxsc100, 3.3v/100ma output re ference design and demonstrates the dynamic performance of the solution. fig. 2 zxsc100 low power solution, 3.3v/100ma output efficiency efficiency is often quoted as one of the key parameters of a dc-dc converter. not onl y does it give an instantaneous idea of heat dissipation, but also an idea as to the extent battery life can be extended. figure 3. shows the efficiency of the zxsc100 low power solution. efficiency v output current is shown for a 3.3v output at various input voltages. fig. 3 zxsc100 efficiency vs. output current
zxsc100 single cell dc-dc converter solution zxsc100 document number: ds33613 rev. 6 - 2 10 of 13 www.diodes.com january 2012 ? diodes incorporated zxsc100x8 obsolete closest a lternative is ZXSC100N8 designing with the zxsc100 (cont.) main switching waveforms steady state operation under constant load gives an excellent indication of zxsc100 performance. represented in figure 4. is the main switching waveform, measur ed at the collector of q1, indicating t he transistor on-state and the diode energy transfer to the output. fig. 4 switching waveform fig. 5 i sense threshold the peak switching current is deriv ed from the threshold of the i sense pin and the sense resistor value (see applications section for calculations). figure 5. shows t he switching waveform associated with the i sense pin. shown in figure 6. is the discontinuous inductor current. the ramp-up current stor es energy in the inductor. the switching transistor,q1, is on during this time and has an equivalent cu rrent ramp-up, shown in figure 7. the ramp-down current is associated with the energy being delivered to the output via the schottky diode, d1. th e diode current is equivalent to this ramp-down current and is shown in figure 8. fig. 6 inductor current (200ma/div) fig. 7 transistor current (200ma/div)
zxsc100 single cell dc-dc converter solution zxsc100 document number: ds33613 rev. 6 - 2 11 of 13 www.diodes.com january 2012 ? diodes incorporated zxsc100x8 obsolete closest a lternative is ZXSC100N8 designing with the zxsc100 (cont.) main switching waveforms (cont.) fig. 8 diode current (200ma/div) fig. 9 output voltage ripple for 3.3v/100ma output output voltage ripple output voltage ripple is shown in figure 9. the circuit is operated with a 1.2v input voltage, 3.3v output voltage and 100ma load current. output voltage ripple will be dependent, to a large extent, on the output capacitor esr. (see applications sectio n for recommended capacitors). transient response transient response to step changes in load is a critical feature in many converter circuits. the zxsc100 operates a pulse by pulse regulation scheme and therefore corrects for changes in the output every pulse cycl e, giving excellent response characteristic. measurement with a power supply when measuring with a power supply it is important to realise that the impedance is much greate r than that of a secondary battery (nicd or nimh). to simulate the lower impedance of the battery x10 low esr 1000f capacitors where placed in parallel at the input of the converter. all the dynamic performance measurements were taken using this technique.
zxsc100 single cell dc-dc converter solution zxsc100 document number: ds33613 rev. 6 - 2 12 of 13 www.diodes.com january 2012 ? diodes incorporated zxsc100x8 obsolete closest a lternative is ZXSC100N8 ordering information device package part marking status 7? tape and reel quantity part number suffix ZXSC100N8ta so-8 zxsc100 active 500/tape & reel ta zxsc100x8ta msop-8 zxsc100 obsolete 1000/tape & reel ta package outline dimensions (all dimensions in mm) so-8 so-8 dim min max a - 1.75 a 1 0.10 0.20 a 2 1.30 1.50 a 3 0.15 0.25 b 0.3 0.5 d 4.85 4.95 e 5.90 6.10 e1 3.85 3.95 e 1.27 typ h - 0.35 l 0.62 0.82 0 8 all dimensions in mm gauge plane seating plane detail ?a? detail ?a? e e1 h l d e b a2 a1 a 45 7 ~ 9 a3 0.254
zxsc100 single cell dc-dc converter solution zxsc100 document number: ds33613 rev. 6 - 2 13 of 13 www.diodes.com january 2012 ? diodes incorporated zxsc100x8 obsolete closest a lternative is ZXSC100N8 important notice diodes incorporated makes no warranty of any kind, express or implied, with regards to this document, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose (and their equivalents under the laws of any jurisdiction). diodes incorporated and its subsidiaries reserve the right to make modifications, enhancements, improvements, corrections or ot her changes without further notice to this document and any product described herein. diodes incorporated does not assume any liabi lity arising out of the application or use of this document or any product described herein; neither does diodes incorporated convey any license under its patent or trademark rights, nor the rights of others. any customer or user of this document or products desc ribed herein in such applications shall assume all risks of such use and will agree to hold diodes incorporated and all the companies whose products are represented on diodes incorporated website, harmless against all damages. diodes incorporated does not warrant or accept any liability whatsoever in respect of any products purchased through unauthoriz ed sales channel. should customers purchase or use diodes incorporated products for any unintended or unauthorized application, customers shall indemnify and hold diodes incorporated and its representatives harmless against all claims, damages, expenses, and attorney fee s arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized a pplication. products described herein may be covered by one or more united states, international or foreign patents pending. product names and markings noted herein may also be covered by one or more united states, international or foreign trademarks. life support diodes incorporated products are specifically not authorized for use as critical components in life support devices or systems without the express written approval of the chief executive officer of diodes incorporated. as used herein: a. life support devices or systems are devices or systems which: 1. are intended to implant into the body, or 2. support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided in the labeling can be reasonably expected to result in significant injury to the user. b. a critical component is any component in a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or to affect its safety or effectiveness. customers represent that they have all necessary expertise in the safety and regulatory ramifications of their life support dev ices or systems, and acknowledge and agree that they are solely responsible for all legal, regulatory and safety-related requirements concerning their products and any use of diodes incorporated products in such safety-critical, life support devices or systems, notwithstanding any devices- or systems-related information or support that may be provided by diodes incorporated. further, customers must fully indemnify diodes incorporated and its representatives against any damages arising out of the use of diodes incorporated products in such safety-critical, life support devices or systems. copyright ? 2012, diodes incorporated www.diodes.com

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