Figure 1: Intersil battery charger architecture–dual USB Type-C ports with 2x BB regulator + buck charger
The USB-C interface is revolutionizing the way we charge our electronic devices. Physically, the Type-C connector is both bidirectional (either end of the cable can be inserted into either device) and non-polarized (connector can go in either right side up or upside down). The connecting systems electrically figure out polarity as part of the connection process. In addition to data transfer, USB-C also supports bidirectional power flow at a much higher level. With a default 5V voltage, the USB-C port is capable of negotiating with a plugged-in device to raise the port voltage up to 20V, or another mutually agreed on voltage, and at an agreed to current level. The USB-C port’s maximum power delivery is 100W (20V at 5A), which is more than adequate to charge most devices. With such appeal, it is easy to understand why electronics manufacturers are flocking to USB-C for their next generation products.
Compared to conventional USB Type-A and USB Type-B fixed voltages, USB Type-C is a bidirectional port featuring a variable input and 5V to 20V output voltage range. Its adjustable output voltage allows portable devices to use USB Type-C to replace the conventional AC/DC power adapter and USB Type-A and B terminals. Considering these advantages, some customers are designing in dual or multiple USB Type-C ports into their systems.
The current system architecture for dual or multiple USB Type-C ports is complicated and cannot meet many customer requirements. A new system architecture is now available using Intersil’s ISL95338 buck-boost voltage regulator and ISL95521A combo battery charger. This architecture simplifies design and fully supports all USB-C functions.
A New Architecture for USB Type-C
Figure 1 shows a new USB Type-C architecture that consists of the ISL95338 bidirectional buckboost (BB) voltage regulator and ISL95521A combo battery charger or ISL9238 BB battery charger. It allows a system to charge its battery through USB Type-C ports, and it supports the fast charge function when two PD chargers are plugged into USB-C_1 and USB-C_2. This new architecture also supports full USB 3.1 On-The-Go (OTG) for both ports without additional complex port-control logic circuits or ICs.
Comparing Figure 1 and Figure 2, it’s easy to see that the current battery charger architecture requires more devices and complicated external circuitry to implement the same functions and performance level as Intersil’s battery charger architecture. Obviously, with the current battery charger system, every individual charger path requires a USB-PD controller to control two ASGATE and perform the charge function, which increases the design’s system cost. To implement 5V buck OTG, the OTG gate also needs a PD controller. Note that the current buck converter can only output a single fixed voltage. Figure 2 shows that if the 5V buck is adapted, designers can only output a fixed 5V, which doesn’t match the adjustable 5V up to 20V OTG output voltage required by many USB Type-C applications.
Intersil product architecture overcomes all of these disadvantages. Figure 1 shows that two ISL95338 are in parallel to interface two USB Type-C ports to the ISL95521A battery charger. The system architecture is simplified, saving significant costs for customers because several components are eliminated, including individual PD controllers, ASGATE and OTG GATE. Most important, using fewer components does not degrade performance.
Figure 2: Current battery charger architecture–single BB charger + complicated external logic
Programmable Power Supply Solution
In conventional USB Type-A and USB Type-B applications, the input voltage is a fixed value, which brings new challenges to USB Type-C because USB-C can also accept variable input voltages. The solution is the programmable power supply (PPS) function, which allows the power supply’s output voltage and current to be programmed and adjusted in 20mV/50mA steps to optimize the power path. As shown in Figure 3, the ISL95338 buck-boost voltage regulator works well with PPS because it outputs an adjustable, bidirectional voltage using SMBus communication from the USB-PD controller.
Figure 3: New Intersil PPS architecture
Applying the ISL95338 in a multiport USB Type-C battery charging system enables a new, easy to use charging architecture. Compared to today’s currently available charging architecture, the Intersil product’s new architecture can be implemented at much lower cost, and achieve higher performance, faster charging and longer battery life. Furthermore, all USB Type-C requirements are in full compliance, including the ability to address PPS, one of the key USB additions required for future applications.