How does mobile phone fast charging work?

have you ever wondered how these modern cell phones with big batteries can charge so fast in this video I will explain you the technology behind cell phone charging from the very basic phones to the state-of-the-art systems [Music] [Music] [Music] in the old days the cellphones in the batteries were small so the charging systems were relatively simple but with new smartphones getting more and more powerful their batteries are getting bigger as well and to quickly charge these batteries requires very complex charging systems the battery chemistry the charging electronics in the cell phone the power adapter and the charging cable all have changed a lot over the years let's start with the battery smartphones normally use lithium-ion batteries the size of the battery is determined by its capacity which is expressed in unpair hours a battery capacity of one ampere hour means that the battery can deliver one amp of current during one hour before the battery is empty you have to charge these batteries with a constant current mode and a constant voltage mode for deeply discharged batteries there will also be a pre charge cycle the majority of charge around 80% is delivered during the constant current mode normal lithium-ion batteries are charged with 0.8 C to 1 C which means you would charge a one ampere hour battery with around 0.8 to 1 amp during the constant current mode due to the battery efficiency and the constant voltage mode it will take around 2 hours to fully charge a battery when it is charged with 1c while these smaller phones used lithium-ion batteries the modern smartphones like this galaxy note template Riis with capacity of more than 4 ampere hours these are often lithium polymer batteries instead of lithium-ion they can be made lighter Flattr can deliver more current and can also be charged with higher currents you can see that as the battery capacity increases you also need to increase the charging current to avoid very long charging times the newer lithium polymer batteries can be charged at higher parents like 1.5 C or 2 C so a 3 ampere hour battery could be charged with 6 amps this will reduce the charging time significantly charging currents of 6 amps or higher inside a phone are quite a challenge and require a very special charging circuits the charger adapter the charger cable current rating and the charger IC inside the cell phone will determine how much battery charging current can be provided but the cell phone must ensure that its input current will not overload the charging cable or the charging adapter also the temperature inside the phone cannot be too high during charging because this affects battery life this small cell phone uses a small 0.6 ampere hour battery and the microUSB cable for charging it uses a linear charger IC which regulates the battery current by dissipating the excess energy the input current therefore equals the battery current a standard USB port can only deliver 5 volts and 0.5 amps which is 2.5 watts so when you plug this phone into the USB port it will charge with less than 0.5 amp battery current which is fine for small batteries the maximum power dissipation in the charger IC is around 0.6 watts which does not heat up the phone too much the slightly bigger cell phones use larger batteries around 1 point 5 ampair hours they use switching charges to regulate the battery current and voltage because linear charges would become too hot input current to output current ratio is determined by the battery voltage to input voltage ratio a one point 5 ampair battery current would give around 1.2 ampere input current at 5 volt input since normal USB ports can only deliver 0.5 amps these USB charger adapters are a bit special they are DC piece dedicated charger ports and can deliver more current up to 1.5 amps the two USB data wires deep and d- are connected together at the adapter output port this is defined in the USB battery charger standard BC 1.2 so the cellphone checks the data wires and when it sees that the D plus and D - wires are connected together it will increase the battery charging current but it will keep the input current below 1.5 amps so the maximum power can be 7.5 watts let's use one of the rich tech 5 ampere switching charges to show how this works the RT 94 67 has this D plus D - detection built in the charger has input current control and battery current control loops you can configure these via I Square C bus and you can set it to automatic DCP port detection here you can see the charger in operation when no DCP port is detected the IC adjusts the battery charge current to keep the input current below 0.5 amps for normal USB bus operation when I now short the D plus and D minus lines and restart charger you can see that the charger increases the battery current but keeps the maximum input current below 1.5 amp to match the DCP port current limit some cell phone makers like Apple and Samsung defined their own system they're charging adaptors manipulate the D plus and D minus data lines in special ways and a Samsung smartphone will recognize a samsung adapter and then can draw even more current but the maximum current is now limited by the maximum current rating of the microUSB cable which is around 2 amps so five or 10 two amps is a maximum power of 10 watts by increasing the input voltage you can increase the power level without exceeding the input current limit let's use the RT 94 67 switching charger again in DCP mode I also set a maximum 2.5 amp battery charge limit watch what happens when I increase the input voltage of the charger above 5 volts because the charger input current regulation loop is active the charger will increase the battery charge current while keeping the input current below 1.5 amps when we reach the 2.5 amps battery charge current limit the charger IC will switch from input current regulation to battery current regulation Samsung's AFC and Qualcomm quick charge QC 2.0 and 3.0 are examples of systems that charge at higher voltages often nine volts instead of five volts these adapters and phones will have a communication link via the D plus and D - wires before the adapter increases the voltage here we have a QC 2.0 adapter let's look at the output voltage and the D plus D - wires I connect this adapter to a phone that supports QC 2.0 you can see that the phone sets different DC voltages on the USB data lines the adapter recognizes this and increases the voltage from 5 volt to 9 volts the charging power increases to around 12 watts but these systems are not compatible with all phones so you end up with a lot of different adapters one for each phone that you owned the newer smartphones use the new USB type-c cable it can carry more current up to 3 amps special cables even up to 5 amps the plug is reversible so you don't need to check which side goes up most important the USB type-c standard defines the way the devices communicate with each other which improved compatibility standard USB type-c only will deliver up to 5 volt 3 amps but the USB type-c with power delivery can provide higher voltages up to 20 volt with currents up to 5 amps so maximum 100 watts the type-c cable includes a CC communication line and 2 CC pins at each connector since the plug can be reversed USB power delivery controllers in the adapter and the phone will talk to each other via their CC line let's check the signals of this galaxy note template for I hope the scope to the V bus and the CC line you can see that the adapter initially provides 5 volt then the voltage changes to around 8 point 6 volts and draws 2.7 amps here you can see the communication on the city line each communication package consists of a request from one side and an answer from the other side the adapter will first tell the phone what voltages and currents it is able to deliver we call these the source capabilities and then the phone tells the adapter which voltage and current it wants to use based on its battery and charging system we call these sync capability then the source will apply the new voltage to the V bus and the sync the phone will then control the battery charger and draw the current based on the power that was agreed upon here is an example of a USB type-c power delivery travel adapter it can provide five volt and nine volt fixed voltages and three volt to 11 volt variable voltage with a maximum power of 25 watts the CC line communication is done via RT 7206 a PD controller which also senses the adapter output voltage and current based on the communicated output voltage and current it will control the primary side USB PD flyback controller to increase the total efficiency this design also incorporates synchronous rectification for an efficiency up to 89% this adapter supports the programmable power supply PPS function this is a special feature that allows the adapter to control its output voltage and current very precisely in small steps the adapter has two PPS ranges from three point three to five point nine volt and from three point three to eleven volts the PPS function is used for phones that support direct charge normal fixed voltage charging systems with a switching charger IC will give relatively high power loss when charging and higher battery currents like four amps for example the RT 94 sixty seven will have an efficiency of 89% when charging from nine volts input at four amp battery current resulting in almost two watts of power dissipation in the phone there are systems that add a slave switching charger in parallel but the efficiency at best can be boosted to around 91% which at 4 point 5 ampair charging current still gives around 1.8 watt of power loss since the temperature inside the phone is critical during fast charging power loss in the phone during fast charging must be minimized to reduce the power loss in the phone charging system the direct charge function was introduced the switching charger is now bypassed by a smart load switch which connects the battery directly to the V bus input as you can see the rich techsmartt load switch itself is quite small in this configuration we can use a lower current switching charger for pre charge and constant voltage mode the smart load switch will be active in the constant current mode of the charge cycle all charge control communication now goes via the CC line the battery voltage current and temperature are monitored by the smart load switch and adapter power supply operates in programmable power supply PPS 3.3 volt to 5.9 volt range and adjust the voltage and current in small steps the big advantage of this system is the minimal power loss in the cell phone this section runs at around 98% efficiency with only 0.3 watt power loss here we have some thermal images of a smart phone with direct charge label a and a switching charger label B you can see that after 10 minutes the direct charge phone is overall cool only the connector shows a hotspot because of the high current in the cable the switching charger shows a big hot area where the charger is located after 20 minutes the direct charge phone is still cool but the switching charger phone has heated up even more after 40 minutes the direct charge phone is finished charging and very cool the switching charger is still charging and quite hot at the top the disadvantage of direct charge is that the high battery current also flows through the cable currents higher than three amps need the special high current cables these cables include a cable ID IC that tells the adapter about the cable properties how much current the cable can handle here you can see an example of such a 5 amp cable and a cable ID IC rt1 731 which can be programmed by the cable manufacturer of course these cables are thicker and more expensive than the standard 3 amp cables to reduce the cable current and increase the power even more the latest smartphones use a technology called direct charge / - these use a capacitive divider circuit to step down the input voltage exactly 50% so now the input voltage is twice the battery voltage the rich tech I see solutions shown here includes a dual phase capacitive divider circuit for reducing ripple and improving efficiency it also includes many sensing functions and can deliver up to 8 amps of battery charging current the big advantage of this circuit over the standard switching charger is high efficiency at five point five amp charging current it can reach 96 point five percent efficiency and the power loss is only 0.77 watts which still keeps the phone cool and the input current is only half the battery charging current similar to previous direct charge the battery voltage current and temperature are monitored by the capacitive divider IC and the adaptive power supply operates in PBS mode and adjusts its voltage and current in small steps the capacitive divider will be active in the constant current mode of the charge cycle but it can also do part of the constant voltage mode cycle due to the higher bus voltage the adapter PPS voltage range will now be 3.3 to 11 volts this system can the ever up to six amps of battery current with a normal three amp USB type-c cable the total charging power is around 27 watts let's use the RT 97 59 capacitive divider evaluation board and the rich tech USB PD PPS adapter application to see the whole system in operation I will use the rich tech USB PD host board to emulate the cellphone USB PD controller interface I will control these two boards via my PC I will also measure the V bus voltage the battery voltage the input current and the output current here you see the rich tech host bored menu showing that the cable is connected in the power request menu you can see the 25 watt adapter source capabilities the fixed 5 and nine-fold power profiles and the two adjustable voltage profiles it starts default at 5 volts first I configure some of the RT in 97 59 settings and protections like maximum bus voltage and maximum battery current in this example I will use a 4.2 volt battery over voltage alarm setting to start the capacitive divider application we need to set the bus voltage slightly higher than two times the battery voltage so in the host board menu I selected the three point three to 11 volt profile and set the V bus start voltage at seven point eight volt and two point seven five ampere current now we can enable the capacitive divider you can see some bus current and battery current we are operating in PPS voltage control mode we now need to increase the bus voltage in small steps to reach the 2.75 and bus current you as you can see requesting higher than nine point zero volt bus voltage will not increase the bus current anymore so now we are operating in PPS 2.75 amp current control mode the battery charge current is now two times two point seven five amps which equals five point five amps as the battery is charging we need to keep increasing the V bus voltage to keep the system in constant current control mode after charging some time we will reach the four point two volt battery voltage and our teen 90 7:59 will show the battery ovp alarm we now need to enter the constant voltage mode of the charge cycle we reduce the PPS bus current which will cause a drop in battery voltage and remove the battery of EP alarm after charging a while the battery ovp alarm will appear again and we reduce the bus current even more and so on so in this way we keep the battery voltage at four point two vote value while charging current is slowly reduced at low charging currents we will switch off the capacitive divider the previous measurements on the galaxy note 10 to divide by two mode to be sure let's hook up a USB PD protocol analyzer it will translate the CC line communication between the adapter and the phone the lower window shows the bus current and voltage it starts at five volt and then rises to around nine volts let's take a closer look at the communication here you can see the adapter sending its source capabilities to the phone the phone will first select the fixed 5 volt profile and then the phone will select the profile for which indeed is the PPS power profile for direct charge divided by 2 mode in PBS mode the phone will keep requesting new voltages and currents I have recorded the full charge cycle here you can see the battery charging constant current mode where the phone requests fixed PPS currents with increasing voltage to keep the system in PPS constant current not here the system enters the battery charging constant voltage mode and the phone slowly reduces the PPS current while keeping the battery voltage constant here the capacitive divider circuit is switched off and the phone requests profile - which is the fixed nine fault profile the switching charger in the phone takes over for the final portion of the constant voltage mode as the rich tech 25 watt adapter also supports USB PD PPS mode it should also work with this phone as you can see the phone charges with almost the same power level so the compatibility is quite good the Galaxy Note 10.1 Levin volt at 4 amps so this adapter must be using the high current cable with cable ID we can check this via the protocol analyzer here you can see the adapter talking to the cable IDIC which shows that it can handle 5 amps you can see that the adapter now shows PPS source capabilities of 11 volt 5 amps here you can see the phone selecting the 11 volt PBS profile with 3.7 5 amps current so the battery will be charging with 7.5 amps so what kind of charging circuits will be used in future phones we know some new smartphones will use a divided by four system which basically consists of two capacitive divider circuits placed in series this would divide the input voltage by four and multiply the input current by four so with the three amp cable you could charge up to 12 amps other smartphone makers implement two batteries in series for a higher total battery voltage and charge these with a single stage capacitive divider in PBS mode another capacitive divider stage is then used to step down the dual cell voltage to a lower voltage more suitable for cell phone electronics in both cases you will need an adapter that supports a PBS range up to 20 volts here is an example of a 60 watt adapter that supports this in the future you will not only see high power USB PD travel adapters but also the new generation cars will have high power USB PD ports which are powered from the car battery like this RT q 7 88 0 car charger board that includes a 60 watt buck boost converter 60 watt systems can be used not only to charge your phone but also the newer tablets and notebook PCs that include a USB type-c port I hope you liked this video please stay tuned for more interesting videos at rich Tec your power partner

Channel: Richtek Technology 立錡科技

Views: 182,859

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Length: 24min 43sec (1483 seconds)

Published: Tue Apr 28 2020