[introduction] USB charges the main component that port already made system of entertainment of contemporary car information. Passenger more and more the electrical system that is used to passing car will be a smartphone (or other portable equipment) charge, use these equipment to abound car information and recreational function conversely. To support power source and data ability at the same time, and get used to the portable equipment market of ceaseless and rapid change, USB charges port must be satisfied transmit all sorts of systems related to rash club sex to ask with power source, data, although face a variety of dangerous situations in reality.

Portable equipment batteries charges — include to support extensive facilities to charge consultative ability, for example USB BC 1.2 charges port of be issued to lower levels (CDP) , special charge port (port of be issued to lower levels of DCP) , standard (SDP) and all sorts of common have an agreement only — it is right merely USB charges the one part in the numerous requirement of port. Other requirement includes to safeguard the signal integrality that data of high speed USB transmits, and protective USB lead plane avoids the effect of common and hazardous condition in sufferring car environment. In addition, small size solution and low electromagnetism radiate are the significant demand that satisfies increasingly complex car electron requirement. The article demonstrated a kind of contented car contemporary USB charges in the environment the solution that port asks, include to design give typical examples.

System of car USB power source is summarized

Graph the 1 block diagram that showed system of charger of typical car USB, among them switch transformer is VBUS power supply from voltage of batteries generation 5 V. The USB that shows here charges port emulator and power switch IC have 3 main functions. Above all, USB charges the optimal charging current that port emulator fixes a join equipment, pass thereby charge port mode (if USB BC 1.2 CDP, DCP and supplier have charger only,emulate an agreement to wait) implementation charges quickly. Next, USB power switch uses as current limliting implement with switch, can detect and restrict bus line electric current. Finally, place of port controller support undertakes data of USB 2.0 high speed is transmitted between join equipment and USB lead plane.

In be in harsh car environment as a result of USB port, because this must try to protect to sensitive USB circuit, make its avoid the effect that suffers all sorts of real harms, for example the electrostatic discharge of socket (ESD) incident and incident of wire cable breakdown, it is normal that these incidents may make the line that gets an effect suffers Yuan Chao to cross its the voltage that the job is worth.

Graph 1. Block diagram of car USB charger

Graph 2 showed system of power source of USB of a car simplify block diagram, this system goes to a lot of power source, port and protective function union in an IC. In this exemple, LT8698S mixes switch transformer the function of power switch is compositive to 4mm × 6mm in enclosing, offer at the same time can resist the protection of powerful data line of ESD incident and wire cable breakdown.

The compositive charger solution of graphic representation included independent between USB port and portable equipment executive USB BC 1.2 CDP to negotiate all and necessary hardware of alignment, make CDP compatible the electric current that equipment can be as high as 1.5 A from VBUS derive, can undertake with lead plane high speed corresponds at the same time.

Wire cable is pressed fall compensation

When the physical distance when USB electrical outlet and controller is further, for example USB electrical outlet is located in car hind, and USB lead plane is located in in dashboard, so wire cable is pressed fall the condition of 5 V stabilized voltage that compensation can make VBUS course keeps accurate. LT8698S is had but cable of process designing wire is pressed fall compensation function, outstanding adjustment can be carried out on USB electrical outlet, and need not open way of line of Er article check additionally.

Graph 3 showed wire cable is pressed fall compensatory job principle. OUT/ISP and BUS/ISN are brought join one detects between the foot resistor RSEN, this resistor series connection is between manostat output and load. LT8698S brings a foot to go up to produce 46 × through resistor of RCBL ground connection in its RCBL (the current source of VBUS/ISN)/RCBL of VOUT/ISP –. This electric current and the electricity that make a base through joining in manostat output and USB 5V bring the RCDC resistor between the foot to flow into USB5V are identical. This meeting the voltage deflection that in RCDC resistor two end produce feedback of 5 V USB5V of a prep above to cite a base, its and RCDC/RCBL resistor compare scale. Result, the point that LT8698S makes BUS/ISN crural adjustment to 5V of target of load of a prep above according to load current (the biggest be restricted to be worth for 6.05V) , adjust accurately what VBUS cites a base in order to maintain socket.

Wire cable is pressed fall compensation was eliminated join from manostat additional run from opposite directions means of line of Er article check needs ladenly to far end, but personnel of requirement system design knows RCABLE of wire cable resistor, LT8698S won’t detect this value. Setting wire cable presses fall compensatory component can use option leaving type: RCDC/RCABLE of × of RSEN of × of RCBL = 46. Wire cable resistor can follow temperature and change, want to obtain better whole to output voltage precision inside very wide temperature range, can add a negative temperature coefficient (the one part that NTC) resistor regards RCBL as, make wire cable is pressed fall to compensation follows temperature and change.

Graph 2. Of the system of car USB power source that builds around compose of solution of controller of odd IC USB simplify block diagram

Graph 3. Wire cable is pressed fall compensation job principle

The powerful protection function of graph 4.LT8698S/LT8698S-1

Provide powerful protection in the light of car environment

Car environment is put in a variety of harms, it is this to must protect USB leader. Breakdown of these cable of harm bag vinculum bring about data line to bear batteries voltage or ground connection, and the big ESD concussion that USB electrical outlet is in. Graph 4 showed how to protect USB lead plane to avoid suffer these to endanger an effect.

The HD+ of LT8698S and HD – bring a foot to be able to bear be as high as 20 VDC, prevent the incident of air discharge IEC 61000-4-2 ESD of the osculatory discharge that is as high as 8 KV and 15 KV, also can protect lead plane to avoid the effect that suffers these abominable states at the same time. In addition, USB5V, OUT/ISP and BUS/ISN bring a foot to be able to bear output voltage breakdown, include to be as high as the volts d.c. of 42 V. When producing output breakdown, latch and try a function automatically to be able to restrict average output electric current accurately again.

Although a lot of USB port controller have exterior clamp on line of IC need data diode or capacitance will offer ESD to protect (this meeting increases cost and material, at the same time the likelihood reduces signal integrality) , but LT8698S does not need.

Data line switch can bear not only in front says dc breakdown and ESD incident, and conduce to the signal integrality with outstanding implementation. Specific say, the bandwidth of – 3 DB that HD+ and HD – cite a base is 480 MHz (typical cost) , this already checked through production. Graph 5 showed according to USB 2.0 the standard is checking plane of 2 demonstrate board on measures high speed transmits a graph. This graph shows its accord with USB pattern plate 1, the test is planar 2 be restricted to be worth, and have adequate abundant amount.

Graph 5. Demonstrating board on plan of surveys eye of high speed USB 2.0. Be shown for pattern plate 1 requirement.

Compatible support extensive charger character

The controller IC that uses in this exemple and character of a variety of USB connector types and charger are compatible, if express,1 is shown. Individual controller is in in light of us solution of USB Type-C 5 V, 3 A (how to work in 15 W) .

Graph 6 showed a wired cable to press fall the principle graph of manostat of compensatory USB 5 V, 3 A VBUS. This circuit chooses the RSEN resistance of 8 M Ω to support the output electric current that is as high as 3 A, SYNC/MODE brings crural ground connection to be able to jump in order to make pulse job mode, reduce the switch frequency when carrying electricity gently and static electric current.

LT8698S still supports pattern of USB BC 1.2 DCP, this mode can offer the charging current that is as high as 1.5 A, support chargeability of big electric current. Should use as when DCP port, d+ and D – circuit are short receive, be defeated as it is said without number.

Manufacturer developed a lot of portable equipment to have charger agreement only. Same, agreements of these manufacturer proprietary charger and corresponding the biggest charging current (like 2.0 A, 2.4 A, 2.1 A and 1.0 A) also get support. Lead plane small controller can bring a foot to achieve these charger agreements through controlling 3 SEL.

Graph the 7 principles that showed charger of 2.4 A/1.5 A USB pursue. In applying here, small controller uses LT8698S STATUS to bring the information that foot and monitor of IMON electric current provide, the charger agreement that will choose to need through controlling SEL1-3 input to cite a base. Such, small controller charges with respect to what can optimize portable equipment characteristic, thereby with as far as possible big voltaic safety charges.

Express the compatibility of 1.LT8698S/LT8698S-1 and interface of a variety of USB connector types, charger agreement and data

Graph 6.5 V, 3 A, USB Type-C applies

Graph 7. The 2.4 A/1.5 A that takes voltaic monitor is automatic the agreement detects charger

EMI solution

A crucial requirement of power source of car electron system is low EMI, normally need satisfies CISPR 25 5 kind discharge a standard. LT8698S uses technology of Silent Switcher 2 to undertake designing, make USB power source can satisfy these rigid car EMI standards, and won’t sacrifice the dimension of the solution, efficiency and rash club sex.

Framework of Silent Switcher 2 encloses interior in LQFN compositive bypass capacitance, come with falling EMI lowest. Of bypass capacitance compositive simplified circuit board design, reduced the size of integral solution, reduced the PCB layout effect to EMI function as far as possible at the same time. LT8698S-1 does not contain these in-house bypass capacitance, other side and LT8698S are identical. Bring to bear on through citing a base to SYNC/MODE the volts d.c. of prep above 3.0 V, these two parts of an apparatus can offer the optional modulation that exhibit frequency. Graph the 8 radiation EMI performance that showed LT8698S falls in representative application condition.

LT8698S and LT8698S-1 can come with 300 KHz of 3 MHz but form is changed and but synchro switch frequency works. Taller switch frequency allows to use lesser inductance and capacitance value, in order to reduce the size of integral solution. Graph 9 show, although be below the taller switch frequency of 2 MHz, this kind of 12 V also can achieve the efficiency of 93% to solution of 5 V USB.

Graph 8. Radiation EMI function (interference of radiate of CISPR 25 electromagnetism, radiodetector of use peak value, 5 kinds of peak value are restricted)

The efficiency of solution of graph 9.5 V USB and power loss curve.

Conclusion

USB charges the main component that port is system of entertainment of contemporary car information, all sorts of actual and dangerous incident in facing car environment, support and respect of rash club sex must be transmitted to answer all sorts of systems to challenge in power source, data. The adoption of article introduction the give typical examples of LT8698S USB charger IC settled these challenges. They support agreements of all sorts of portable equipment charger, can charge for USB Type-C application provides the output power that is as high as 15 W. In addition, they still can protect USB lead plane to avoid suffer potential hazardous condition effect, for example wire cable breakdown and serious ESD incident. While LT8698S is providing this kind of protection, still can maintain the signal integrality that transmission place of data of high speed USB needs between USB lead plane and portable equipment.

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