1/4 rev. a structure silicon monol ithic integrated circuit product name synchronous rectification with built-in fet type dc/dc converter ic model name b d 8 6 4 3 f v features ?synchronous rectification with built-in fet type dc /dc converter ?output current 3a ?reference voltage accuracy fb 0.8v1% ?switching frequency 100khz600khz ?over current pro tection circuit ?thermal shutdown ?input low volta ge detection uvlo ?soft start / start delay circuit ?programmable offlatch time absolute maximum rating ta=25 parameter symbol limits unit input supply voltage v in 20 v boot terminal voltage v boot 28 v en terminal voltage v en gnd-0.3 v in +0.3 v input terminal voltage v in p *1 gnd-0.3 7 v sw terminal voltage v sw gnd-0.3 v in +0.3 v output switch current i out 3.5 *2 a power dissipation pd 2.06 *3 operating temperature topr -20 85 storage temperature tstg -55 150 maximum junction temperature tjmax 150 1 v inp application terminal ss/d elay, fb, fc, rt, pset 2 do not however exceed pd. 3 70mm70mm, thickness 1.6mm, and four layer glass epoxy subs trateswhen mounting substrate and the package back exposure part are connected with solder. operating at higher than ta=25, 9.5mw shall be reduced per 1 operation condition parameter symbol min typ max unit input supply voltage v in 4.5 - 18.0 output switch current i out - - 3.0 a this product is not designed for protection against radioactive rays.
2/4 rev. a electrical characteristic (unless otherwise noted ta=25, vin=12v, v en = 3v) parameter symbol specification value unit condition min typ max vin supply current (operating) i qactive - 1.5 2.5 ma v fb = 0.75v vin supply current (standby) i q - 0.8 1.2 ma v en = 0v reference voltage v fb 0.792 0.8 0.808 v fb-fc short oscillation frequency os c 270 300 330 khz r rt = 56k high side fet on resistance r hfet - 110 160 m i sw = -1a low side fet on resistance r lfet - 110 160 m i sw = 1a uvlo voltage v uvl o 3.8 4.0 4.2 v vin sweep sw leak current i lsw - 0 5 a v en = 0v en terminal h threshold voltage v enh 1.6 - - v en terminal l threshold voltage v enl - - 0.4 v ss/delay terminal source current i sss o 2.8 4 5.2 a v s s = 1v ss/delay C fb offset voltage v ssfbost 450 600 750 mv v s s = 1v pset terminal source current i pset 3 5 7 a v pset = 2v pset terminal threshold voltage v pset 0.8 1.0 1.2 v v fb :fb terminal voltagev en :en terminal voltagev ss :ss/delay terminal voltage, v pset :pset terminal voltage, r rt :rt resistor current capability should not exceed pd.
3/4 rev. a block diagram 11 12 13 14 15 16 17 en pwm control 10 9 8 7 6 5 4 current det fc rt pset en nc nc gnd nc boot sw sw sw vout 5v ss fb softstart/delay 18 19 20 3 2 1 vin vin vin pgnd pgnd pgnd osc protect time pin assignment no. symbol description no. symbol description 1 pgnd power gnd terminal 11 fb feedback terminal 2 pgnd power gnd terminal 12 fc phase amends terminal 3 pgnd power gnd terminal 13 rt frequency adjustment resistance connection terminal 4 sw switching output terminal 14 pset adjust off latch time ter minal 5 sw switching output terminal 15 en enable input 6 sw switching output terminal 16 nc - 7 boot boot strap terminal 17 nc - 8 nc - 18 vin power supply input terminal 9 ss/delay soft start adjustment capacity connection terminal 19 vin power supply input terminal 10 gnd signal gnd terminal 20 vin power supply input terminal package outline product number lo no. 1pin mark ssop-b20w (unitmm) bd8643
4/4 rev. a note on use 1about the absolute maximum rating attention is brushed off enough to the quality control, it is l ikely to destroy when the absolute maximum rating such as impre ssed voltages (vcc_in,dcin) and ranges (topr) of the operating temperature as it is exceeded, the mode of breakings of the short or the open ing, etc. cannot be specified, and examine it in this ic to give physical measures for safety such as fuses when a special mode that exceeds the a bsolute maximum rating is assumed. 2gnd pin voltage gnd terminal should be connected the lowest voltage, under all conditions. and all terminals ex cept sw should be under gnd ter minal voltage under all conditions including transient situations. if a terminal exists under gnd,it should be inserting a bypass route. 3power dissipation if ic is used on condition that the power loss is over the powe r dissipation, the reliability will become worse by heat up, su ch as reduced output current capability. also, be sure to use this ic within a power dissipa tion range allowing enough of margin. 4input supply voltage input supply pattern layout should be as short as possible. 5about the short and the miss-installation between terminals note the direction and the miss-registration of ic enough when you install it in the set substr ate. ic might destroy it as wel l as reversely connecting the power supply connector when installing it by mistake. moreo ver, there is fear of destruction when the foreign body enters between terminals, the terminal, the power supply, and grandeur and it is short-ci rcuited. 6about operation in strong electromagnetic field in use in strong electromagnetic field, note that there is a po ssibility of malfunctioning. 7about the inspection by the set substrate it is likely to suffer stress to ic and discharge electricity e very one process when you connect the capacitor with the pin wi th low impedance when inspecting it in the set substrate. moreover, detach it after c onnecting after the power supply is turned off without fail whe n detaching it to g in the inspection process, inspecting, and turning off the power suppl y. n addition, be give the earth to the assembly process as a s tatic electricity measures, and careful enough when it transports and you preserv e it. 8about each input terminal this ic is a monolithic ic which has a p + isolations and p substrate to isolate elements each other. this p layer and an n layer in each element form a pn junction to construct various parasitic elements. for instance, the potential difference operates in resistance a s shown in the figure below when resistance and the transistor connect it with the terminal and the playground (gnd) >(terminal b) joint of pn ope rates as a parasitic diode in playground (gnd) >(terminal a) tr ansistor (npn). in addition, the npn transistor of parasitism works with n layer o f the element of the above-mentioned parasitic diode and the ne ighborhood and others in transistor (npn). a parasitic element in ic compositi on is inevitably formed because of the potential relation. a parasitic element can operate, the interference with the circ uit operation be caused, it malfunction, and, consequently, it cause destruction. therefore, do not do the usage that a parasitic element operate s as a voltage that is lower than the playground (gnd;p substra te) is impressed to the input terminal enough. moreover, do not impress the voltage to the input terminal when you do not impress the power-supply voltage to ic. give each input terminal to me the voltage below the power-supp ly voltage or in the guarantee value of an electric characteris tic when you similarly impress the power-supply voltage. example of ic of simple structure 9earth wiring pattern if small signal gnd and large current gnd exist, disperse their pattern. in addition, for voltage change by pattern wiring imp edance and large current not to change voltage of small signal gnd, each ground terminal of ic must be connected at the one point on the set circuit bo ard. as for gnd of external parts, it is similar to the above-mentioned. 10. sw terminal a counter-electromotive force may generate a negative potential at the sw terminal during connection to the particular applica tion. therefore, it should be inserting a bypass route between sw to gnd. 11. about each output terminal we recommend to put diode for protection purpose in case of out put pin connected with large load of impedance or reserve curre nt occurred at initial and output off. 12. thermal shut down circuit a temperature control is built in the ic to prevent the damage due to overheat. therefore, the outputs are turned off when the thermal circuit works. 13. over output current protection sw output terminal has over current protection circuit of 5a, with prevents ic from being damage by short circuit at over curre nt. however, it is recommend not to use that continuously operates the protection circ uit (for instance, always the load that greatly exceeds the output current ability is connected or the output is short-circuited, etc.) in these protection circuits by an effective one to the destructio n prevention due to broken accident.
appendix-rev4.0 thank you for your accessing to rohm product informations. more detail product informations and catalogs are available, please contact your nearest sales office. rohm customer support system the americas / europe / asia / japan contact us : webmaster@ rohm.co. jp www.rohm.com copyright ? 2009 rohm co.,ltd. 21 saiin mizosaki- cho, ukyo-ku, kyoto 615-8585, japan tel : +81-75-311-2121 fax : +81-75-315-0172 appendix notes no copying or reproduction of this document, in part or in whole, is permitted without the consent of rohm co.,ltd. the content specified herein is subject to change for improvement without notice. the content specified herein is for the purpose of introducing rohm's products (hereinafter "products"). if you wish to use any such product, please be sure to refer to the specifications, which can be obtained from rohm upon request. examples of application circuits, circuit constants and any other information contained herein illustrate the standard usage and operations of the products. the peripheral conditions must be taken into account when de signing circuits for mass production. great care was taken in ensuring the accuracy of the information specified in this document. however, should you incur any damage arising from any inaccuracy or misprint of such information, rohm shall bear no re- sponsibility for such damage. the technical information specified herein is intended only to show the typical functions of and examples of application circuits for the products. rohm does not grant you, explicitly or implicitly, any license to use or exer cise intellectual property or other rights held by rohm and other parties. rohm shall bear no re- sponsibility whatsoever for any dispute arising from the use of such technical information. the products specified in this document are intended to be used with general-use electronic equipment or devices (such as audio visual equipment, office-automation equipment, communication devices, elec- tronic ap pliances and amusement devices). the products are not designed to be radiation tolerant. while rohm always makes efforts to enhance the quality and reliability of its products, a product may fail or malfunction for a variety of reasons. please be sure to implement in your equipment using the products safety measures to guard against the possi bility of physical injury, fire or any other damage caused in the event of the failure of any product, such as derating, redundancy, fire control and fail-safe designs. rohm shall bear no responsibility whatsoever for your use of any product outside of the prescribed scope or not in accordance with the instruction manual. the products are not designed or manufactured to be used with any equipment, device or system which re quires an extremely high level of reliability the failure or malfunction of which may result in a direct threat to human life or create a risk of human injury (such as a medical instrument, transportation equipment, aerospace machinery, nuclear-reactor controller, fuel-controller or other safety device). rohm shall bear no responsibility in any way for use of any of the products for the above special purposes. if a product is intend- ed to be used for any such special purpose, please contact a rohm sales representative before purchasing. if you intend to export or ship overseas any product or technology specified herein that may be controlled under the foreign exchange and the foreign trade law, you will be required to obtain a license or permit under the law.
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