The new USB 3.1 type-C standard greatly simplifies the way we interconnect and power our electronics. The standard uses a USB type-C connector to transfer up to 100W of data and power between any two devices. Therefore, the battery charging system needs more functions. For each new portable device, the battery charging system tends to be smaller and lighter. This paper reviews the typical USB type-C charging system and shows how to simplify the design while providing more power and more functions in a smaller space.
USB 3.1 type-C standard
USB 3.1 type-C (also known as usb-c) is a new standard, which supports high data rate and increases power transmission between electronic products. USB 3.1 can provide 10Gbps throughput, and provide up to 3A current through standard cables and up to 5A current through enhanced cables. The bus voltage can be adjusted up to 20V (60W when the standard cable is 3a and 100W when the enhanced cable is 5a). Today, many notebook computers need less than 100W power, so the new type-C connector can be charged through the USB port, just like the charging method of today‘s small devices.
The complexity of the USB 3.1 type-C standard requires that devices be negotiated as power suppliers (power supplies) or power users (receivers) before power transmission. The connectors at both ends of the type-C cable are the same, allowing reversible insertion. Each connector is also reversible, which allows it to be inserted with either side up. Type-C USB also allows two-way power supply, so it can charge peripheral devices, and the same device can also charge host devices. This is expected to eliminate many proprietary power adapters and various types of USB cables, and ultimately reduce the maze of wires around today‘s desktops.
Configure channel detection
A new feature of USB type-C is configuration channel (CC) detection. Configure channel logic to detect the presence, direction and current carrying capacity of cables. Cable detection occurs when one of the two CC lines is pulled down. Which line (CC1 and CC2) to pull down determines the direction of the cable. The current carrying capacity is determined by the value of the terminal resistance. Another new feature of USB type-C is cold plug, that is, 5V is provided only after end-to-end detection is successful. This feature forces CC detection in USB type-C applications.
USB 3.1 typical system
We showed a typical portable power management front end with a USB type-C cable connected and powered by a lithium ion (li+) battery.
When VBUS voltage is present, it supplies power to the charger, system and other modules. At this stage, the battery is charged through Q batt as a current source. When VBUS is disconnected, the battery supplies power to the system through Q batt, which operates as an "on" switch.
Through USB type-C protocol, CC1 and CC2 pins determine port connection, cable direction, role detection and port control. The charger in Figure 2 also supports the traditional protocol battery charger 1.2 (bc1.2).
Typical solutions
A typical implementation of a battery system can be very expensive in terms of bill of materials (BOM) and PCB space. Shows the PCB size of the charger and the detection part, using two ICs, one for the charger and one for the two detection blocks.
The two chip scheme plus passive components occupy 61mm2.
Highly integrated solutions
Through a higher degree of integration, the BOM is greatly simplified. The blue highlighted box shows all modules that can ideally be integrated into a single power management IC (PMIC).
With this integration, the complexity of the system is greatly reduced.
Integrated USB type-C charger
The max77860 is more integrated. It is a high-performance, single input switching mode charger with USB type-C configuration channel detection function for a single li+ battery (Figure 6). The IC supports applications up to 15W, including reverse boost function, high voltage LDO and 6-channel ADC. The switch charger is designed with powerful constant current, constant voltage and chip temperature regulation algorithms and input power regulation, as well as I 2 C programmable settings to adapt to various battery sizes and system loads. It fits in a compact 3.9mm x 4.0mm WLP package.
In a typical system, the microcontroller or host microprocessor configures the input current limit of the charger according to the current level detected by the port controller IC. The max77860 independently sets the input current limit of the charger, allowing the charger to charge the battery with the full capacity of the power supply, thus accelerating the charging speed. This also simplifies host software development.
Design flexibility
Backward compatibility support is available for USB type-C and legacy adapter designs. The integrated ADC frees up resources in the microcontroller while providing accurate voltage, current and temperature measurements for complex power management.
Reverse boost of OTG power supply
USB on the go (OTG) is a specification that allows USB devices such as handheld computers and terminals, portable game consoles, and battery powered health monitoring devices to act as hosts. This allows other USB devices or accessories, such as a USB flash drive, digital camera, mouse, or keyboard, to be connected to them. The USB type-C specification also allows the device to supply power to other devices through the reverse boost function.
In the charging mode, when s 1 is turned on, the switching regulator (s 2 and S 3 synchronous switches in the step-down mode) depressurizes the chgin voltage to the sys pin. From there, the linear regulator that controls the transfer transistor s 4 charges the battery (s 4 is on).
In the reverse boost mode (OTG) without input power, the battery voltage (s 4 is fully on) is boosted at the chgin pin (s 1 is on) (s 2 and S 3 are switched synchronously in the boost mode).
In this implementation, the reverse boost mode does not require additional inductors. Then use the increased chgin voltage for the USB OTG function.
In battery only mode, switch S1 is off.
Safe output LDO
The safe output LDO is a protected high voltage input linear regulator that provides a programmable output voltage of 3.3v/4.85v/4.9v/4.95v through the I 2C register. It is used to power the low voltage rated USB system. When chgin ≥ 3.2V, the safety output linear regulator is on, and when chgin is greater than the overvoltage threshold, it is disabled.
conclusion
The new USB 3.1 type-C standard requires the battery charging system to provide more functions, even in smaller and lighter portable devices.
We reviewed a typical charging solution with low integration, resulting in the need for a large BOM with a large PCB area.
The highly integrated solution, as shown in the max77860 USB type-C 3A switch mode charger, significantly reduces the system complexity through the integration of charger, power path, safeout LDO, ADC, usb-c configuration channel and BC 1.2 detection, and adopts a small 3.9mm x 4.0mm, 0.4mm spacing and WLP package. OTG functions are seamlessly integrated without additional inductors. This level of integration simplifies the design and provides more power and more functions in the smallest PCB space.
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