By Stephen evanczuk
Larger display screen, stronger performance and higher data throughput are the development trend of 5g smart phones, which promotes the demand for larger battery capacity and fast charging capacity. How to break through the traditional charging method is a challenge for designers. Because the traditional charging method is inefficient and consumers have higher and higher expectations for fast charging, it may lead to excessive heating at the power level to meet this demand.
On USB type-C ® The programmable power supply (PPS) feature introduced in (usb-c) power transfer (PD) 3.0 helps to achieve an effective solution, but the required firmware development still delays product delivery.
This paper will introduce the problems related to fast charging of 5g mobile phones and how usb-c PD 3.0 PPS can help designers efficiently meet the requirements of faster charging of larger capacity batteries. Then, it will also introduce and show how developers can use the highly integrated on semiconductor usb-c controller, which can implement usb-c PD 3.0 PPS in finite state machine (FSM). In this way, there is no need to develop firmware, which can speed up the fast charging function of the next generation charger.
According to market analysts, 5g smartphones are expected to account for more than 50% of the total smartphone shipments by 2023. However, in the process of using these phones to obtain 5g services, users will find that the existing mobile phone charger and charging station can no longer meet the fast charging needs of this new generation of smart phones.
As we have seen in 5g mobile phones such as Samsung S20 ultra 5g, these mobile phones have advanced technology, larger screen and stronger processing capacity, and the data throughput is much higher than that of early smart phones. In order to match its larger screen and corresponding higher power consumption, the existing 5g mobile phones have used larger batteries. For example, the Samsung S20 ultra 5g has a screen size of 6.9 inches and uses a 5000 milliampere hour (MAH) battery with a capacity 25% higher than that of the previous generation.
While consumers expect high-capacity batteries to have longer battery life, they also hope that the charging time will become shorter rather than 25% longer. For manufacturers who want to meet the growing demand for charging stations in cars, homes and offices, facing the bottleneck of the battery itself, how to shorten the charging time of high-capacity battery has become a major problem.
Lithium ion battery manufacturers set strict thresholds for charging current and voltage. A conventional lithium-ion battery with a rated capacity of 1000 MAH generally has a rated charging rate of 0.7 C, that is, the charging current is 700 ma. For a fully depleted 5000mAh battery, it takes about 45 minutes to charge 50% at a 0.7 C charging rate (or 3500 Ma charging current).
More advanced battery technology can support charging rates greater than 1 C, but both chargers and charged devices need to adapt to significantly increased power levels. For example, a 5000 MAH battery charged at a higher rate of 1.5 C takes only about 22 minutes to charge from 0% to 50%, but a charging current of 7.5 amps (a) will put pressure on components and produce excessive thermal load even in an efficient charging system. In fact, as usb-c has been widely accepted as an industry standard interface for power supply and other functions, the maximum current that compatible chargers can provide on usb-c cable will be limited. The maximum current of the usb-c cable is 5 A, which contains the emaker IC that provides cable information for the connected devices. (for non eMarker cables, the maximum current is 3 A).
Of course, mobile device manufacturers can overcome this limitation by inserting a charging pump between the power input and the battery charging circuit. For example, in order to support a 7.5 a charging system, the travel adapter can provide a voltage of 10 V at 4 A. therefore, relying on a typical split charging pump, it can output a voltage of 5 V to the charging circuit at a current of about 8 a. This method enables the travel adapter to increase the usb-c voltage (VBUS) while maintaining the current level compatible with usb-c.
Increasing charging power requires more effective control
It can support VBUS greater than 5 V, so that this high voltage and low current method can be used. The USB PD 2.0 specification defines a series of fixed power transmission objects (PDOS) that specify a fixed combination of voltage levels (5, 9, 15, and 20 V) and current (3 or 5 a).
Although USB PD 2.0 fixed PDO can achieve higher charging power, setting the charging voltage and current too high or too low will lead to low charging efficiency, unacceptable thermal load and pressure on components. In fact, when the input voltage of the charging circuit (provided by usb-c VBUS) is slightly higher than its output voltage (battery voltage), the charging circuit achieves the best working efficiency. However, because the battery voltage will change constantly during normal operation, how to maintain the best charging efficiency has become a big challenge. When the battery is discharged, the difference between the battery voltage and the usb-c charging voltage (VBUS) will become larger, which will reduce the charging efficiency. On the contrary, when the battery is full, the charging circuit needs to reduce the charging current to protect the battery.
If the charging level provided by the travel adapter cannot be directly reduced, the power dissipation will increase, resulting in reduced efficiency and heat generation. Therefore, the optimal charging level will change constantly, often in an incremental way, which requires the corresponding incremental control of charging voltage and current to achieve the highest efficiency.
How can usb-c PD 3.0 PPS improve efficiency?
The usb-c PD 3.0 PPS function is designed to meet the growing demand for higher charging efficiency at higher charging power, allowing the charged device (current injection device) to request the charger (current pull-out device) to increase or decrease the charging voltage and current with the MV and Ma step values published in the enhanced PDO. With this function, the charging device can adjust the voltage and current of its pulling device to optimize the charging efficiency.
The introduction of PPS has greatly changed the working mode of charging process. In the past, chargers controlled and executed charging algorithms at the same time. After the PPS is adopted, the control of the charging algorithm is transferred to the filling equipment, and the charger is required to execute the algorithm according to the instructions of the filling equipment.
Through PPS, smart phones or other filling devices, communicate with the charger to optimize power transmission, so as to reach a mutually agreed PD "contract" through a negotiation agreement including the following brief interaction.
The charger broadcasts its charger voltage and current capabilities described in up to seven PDOS
The incoming device requests one of the broadcast PDOS
The charger accepts the requested PDO
The charger delivers power at agreed voltage and current levels
Advanced mobile devices such as the previously mentioned Samsung 5g mobile phone use this function to provide fast charging with a compatible charger. For manufacturers who design fast charging travel adapters and build charging stations in other products, to implement such charging protocols, it is usually necessary to develop controller firmware that can execute the protocol and operate the relevant power supply devices. However, for mature standards such as usb-c PD PPS, FSM solution provides an effective alternative to eliminate firmware development requirements that may lead to delayed final product delivery. The fusb3307 adaptive charger controller of on semiconductor adopts the implementation of usb-c PD 3.0 FSM including PPS, which speeds up the development of charger to meet the fast charging requirements of the next generation of smart phones and other high-capacity battery mobile devices.
Integrated controller for usb-c PD 3.0 compliant fast charger
Fusb3307 of on semiconductor is an integrated power controller, which can realize usb-c PD 3.0 PPS without external processor. In addition to cable detection, load grid driver, multiple protection functions and constant voltage (CV) and constant current (CC) regulation, the device also integrates a complete PD 3.0 device policy manager, policy engine, protocol and PHY layer in hardware.
Fusb3307 is designed to support AC / DC and DC / DC chargers and can provide a full set of responses suitable for PD power supply. Therefore, designers can use fusb3307 and relatively few other devices and components to realize a power supply compatible with usb-c PD 3.0.
When connected to the filling device, fusb3307 will automatically detect the capacity of the filling device and connecting cable, and broadcast its capacity according to the usb-c specification. When the filling device responds that it can optionally support PDO, fusb3307 will enable VBUS and control the power circuit to ensure that the requested charging voltage and current level are transmitted to the filling device.
When connected to the filling device, fusb3307 will automatically detect the capacity of the filling device and connecting cable, and broadcast its capacity according to the usb-c specification. When the filling device responds that it can optionally support PDO, fusb3307 will enable VBUS and control the power circuit to ensure that the requested charging voltage and current level are transmitted to the filling device.
Because fusb3307 integrates a full set of control functions, its basic working principle remains consistent in the design of AC / DC and DC / DC chargers. In response to the command from the filling device, the fusb3307 in the charger uses its cath output pin to drive the feedback control signal to the charger power level. During charging, fusb3307 uses VFB pin to monitor charging voltage and is + / is - pin to monitor charging current flowing through detection resistor. These monitored levels are fed back to the internal voltage and current loop error circuit connected to the voltage (VFB) and current (IFB) pins. These signals in turn control the CATH pin for CV and CC control. Other pins in the 14 pin small integrated circuit (SOIC) package of fusb3307 support load gate driver, usb-c connector interface and protection functions.
Fusb3307 charger controller simplifies charger design
Of course, the design of each type of charger will use different configurations for the primary cath output, VFB input and other pins. In the AC / DC wall charger or AC / DC adapter, fusb3307 will monitor the voltage and current on the secondary side and drive the control feedback to the primary side (Figure 1).
Figure 1: in the AC / DC design of the wall charger or adapter, fusb3307 controls the PWM controller by isolating the optocoupler to respond to different charging voltage commands from the filling equipment. (image source: on semiconductor)
In this charging design, the output pin of fusb3307 cath is usually connected to the optocoupler cathode on the secondary side to provide feedback control signal (ncp1568 of on semiconductor) to the pulse width modulation (PWM) controller on the primary side. On the secondary side, the voltage and current detection input of fusb3307 will monitor the output from the synchronous rectifier controller, such as ncp4308 of on semiconductor.
For example, in the design of DC / DC charger used in automotive applications, fusb3307 directly controls the DC / DC controller. Here, the fusb3307 cath feedback signal is connected to the DC / DC controller, such as the ncv81599 compensation (COMP) pin of the on semiconductor (Fig. 2).
Figure 2: in the design of DC / DC charger of vehicle charger, fusb3307 directly controls the voltage output of DC / DC controller, and increases or decreases the output according to the instructions of infusion equipment such as 5g mobile phone or other mobile devices. (image source: on semiconductor)
On semiconductor implements this special DC / DC charger design for fusb3307 in its fusb3307mx-pps-gevb evaluation board. The PD uses a single DC power supply from 3.0 V to 3.5 V, which meets the requirements of the VBS standard, and the DC power supply of the PD meets the maximum 3.5 v.
Using this evaluation board, developers can explore the interaction between fusb3307 and USB PD 3.0 compliant devices and traditional USB PD 2.0 devices. By monitoring the VBUS voltage and current delivered by the evaluation board to devices supporting usb-c PD function, developers can immediately start exploring the fast charging process. Similar devices such as laptops or smartphones.
This method provides a special connotation for the ability of fusb3307 to interact with ready-made USB PD 3.0 5g mobile phones, and the mobile phone uses USB PD 3.0 PPS protocol to optimize its charging voltage and current. In a demonstration of this capability [1], it was found that a ready-made Samsung S20 ultra 5g mobile phone sent a series of instructions to the fusb3307mx-pps-gevb evaluation board to modify the charging voltage and current with large step value and small step value (Fig. 3).
Figure 3: the fusb3307mx-pps-gevb evaluation board of on semiconductor shows the ability of fusb3307 to respond to ready-made 5g mobile phone instructions to fine tune its charging voltage and current. (image source: on semiconductor)
In this demonstration, after the evaluation board is connected with the mobile phone, 5g mobile phone selects the benchmark PDO (5.00 V, maximum 5.00 a), as shown in the first 10 seconds in the figure. At this stage, the charging voltage (VBUS) is 5 V and the charging current (IBus) of 5g mobile phone is about 2 A. Then, the 5g mobile phone requests a higher PDO, stating that the charger can provide 8 V voltage at 4 a. Fusb3307 responded to the request and immediately changed: VBUS jumped to 8 V as required, and IBus showed a gradual increase, because 5g mobile phone increased IBus current.
After the sharp jump of VBUS, the possible charging power increment brought by PPS becomes obvious. 5g mobile phones ask VBUS to increase by 40 millivolts (MV) about every 210 milliseconds (MS), gradually raising VBUS to a higher level. When the IBus reaches 4 a (dotted line and green line in the figure), fusb3307 sends an alarm message using the standard PPS protocol to notify the 5g mobile phone that the requested current limit has been reached. 5g mobile phones continue to send requests, further improve VBUS in 40 mV increments, and finally reach 9.8 v. In daily use, the charging capacity of this adaptive charger can achieve the maximum charging efficiency required for fast charging without overheating or other conditions affecting the filling equipment.
Using the fusb3307mx-pps-gevb evaluation board of on semiconductor, developers can immediately explore the application of usb-c PD in existing devices and expand the relevant reference design of the board, so as to realize fast charge customization in devices conforming to USB PD 3.0 specification. Most importantly, there is no need to develop firmware for specific implementation. Through fusb3307 device, developers use familiar power technology to build an adapter that can give full play to the fast charging advantages of the next generation 5g mobile phones and other compatible devices.
epilogue
Although 5g mobile phones have brought users a rich experience of new features and functions, the larger capacity battery required to support these devices has become a challenge for designers. In particular, they need to ensure that travel adapters and charging stations provide fast charging without overheating the phone.
The fusb3307 adaptive charging controller of on semiconductor has the function of fully conforming to USB PD 3.0 PPS - it can provide a direct design solution without firmware development. By combining the controller with common power supply devices and components, developers can quickly implement an adapter to support rapidly expanding 5g mobile phones and other mobile devices with USB PD 3.0 function.
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