Maria Montero

USB Type-C Power Management – A New …

This article discusses STUSB4500, which is a standalone USB power supply controller from STMicroelectronics.

The STUSB4500 is a Power Delivery (PD) controller for sink devices such as printers, cameras, point of sale and healthcare devices. Supports configurable PD profiles for up to three different sink devices. These profiles, referred to as Power Data Objects (PDO) in the datasheet, are stored in non-volatile memory on the chip. This allows the device to function as a standalone solution where PD contracts can be negotiated without necessarily requiring an MCU to be included in the design.

The STUSB4500 includes features intended to simplify the overall circuit design, such as on-chip drivers for PMOS transistors that switch the VBUS power line. You can monitor the VBUS pin and download it via internal or external routes when needed. Additionally, the device withstands high voltages up to 28V on the VBUS pins and has short-to-VBUS protection on the DC pins.

In the rest of the article, we will briefly review some of these features. If you are interested, you can learn more about fixing the USB Type-C standard.

Why USB Type-C?

The USB Type-C standard allows devices to choose the level of power flow through the interface through a protocol called USB Power Delivery.

In the figure below, you can see an example of a USB power supply where the sink is requesting 9V bus voltage (left) and 5V bus voltage (right) from the source. The VBUS voltage is adjusted as necessary.

Figure 1. Image courtesy of Richtek.

The STUSB4500 is designed to detect the connection between two USB Type-C ports as a standalone solution. Determine the orientation of the cable to redirect USB data through the cable accordingly.

When connected to a receiving device that supports PD capability, the STUSB4500 handles USB PD contract negotiations and configures the incoming VBUS power path based on requests from the receiver. As mentioned above, the device incorporates several features to facilitate design.

Functional block diagram

The functional block diagram of the STUSB4500 is shown in Figure 2.

Figure 2. Image courtesy of STMicroelectronics.

The CC1 and CC2 pins

Pins CC1 and CC2 are used to determine cable connection and plug orientation. Also, PD negotiations are performed on these pins. As shown in the example schematic in Figure 3, these two pins are connected to the CC1 and CC2 pins of the USB Type-C standard.

Figure 3. Image courtesy of STMicroelectronics. Click to enlarge.

The CC1DB and CC2DB pins

These two pins are used to enable the “low battery” mode of operation. When low battery mode is supported, pins CC1DB and CC2DB should be connected to pins CC1 and CC2, respectively (see Figure 3). This creates a drop-down path on pins CC1 / CC2 and establishes a source-to-sink connection, even when the heatsink has a dead battery.

Screen pin

There are circumstances that we need to quickly download the VBUS line, for example. when the cable is disconnected or the heatsink requests a lower voltage on the VBUS. The DISCH pin can be configured to implement a discharge path for the VBUS line on the devices side of the sink (see Figure 3).

The DISCH pin can be configured as an input or an output. When used as an input pin, the STUSB4500 creates an internal discharge path. The maximum discharge current through the chip is approximately 500 mA, therefore a series current limiting resistor must be included (R2 in Figure 3). When a higher discharge current is required, we can configure the DISCH pin as an output to control an external discharge path.