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.
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.
This pin is asserted to indicate a valid source-to-sink connection.
The POWER_OK2 / POWER_OK3 Pins
These two pins work with VBUS_EN_SNK to deliver power after USB PD negotiations. POWER_OK2 is a high voltage drain output through an external PMOS transistor. POWER_OK3 is a low voltage open drain output.
If the PD profile of the sink number (2 or 3) matches that of the source, POWER_OKx activates the power path of this sink device. Figure 3 shows how these two pins can be used. In this figure, the two sink devices PDO2 and PDO3 can be activated via the POWER_OK2 and POWER_OK3 pins, respectively.
POWER_OK2 is a high voltage open drain output and is capable of directly driving a PMOS transistor to enable the PDO2 power path. However, POWER_OK3 is a low voltage open drain output. I think that’s why the PDO2 power path is controlled by a PMOS connected directly to the POWER_OK2 pin, while the circuits related to the PDO3 power path are a bit more complicated. If you have any ideas about the circuits connected to the POWER_OK3 pin, please share them with us in the comments below.
The GPIO Pin
This is a general purpose pin. It could be configured to indicate a hardware failure detection or to specify how much current is advertised by the USB Type-C source. There are other configuration options for this pin. Please see the data sheet for more information.
The VBUS_EN_SNK Pin
This pin enables the VBUS power line when a source is connected. Figure 3 shows how this pin can be used. Note that to enable the power path of any of the VSNK, PDO2 or PDO3 sink devices in Figure 3, we must activate the VBUS_EN_SNK pin.
The A_B_SIDE Pin
This output pin indicates the orientation of the wire.
The VBUS_VS_DISCH Pin
This is an input pin that can be used to monitor the VBUS voltage and discharge it when needed. Unlike the DISCH pin, the VBUS_VS_DISCH pin is connected to the receptacle side of the layout (see Figure 3). The maximum discharge current of this pin is 50 mA and the datasheet recommends a current limiting series resistor.
The VREG_1V2 and VREG_2V7 pins
These pins are included to connect an external decoupling capacitor to the chip’s internal 1.2V and 2.7V regulators.
The I²C interface pins
The STUSB4500 supports I2C connectivity via the SCL, SDA, ALERT, ADDR0 and ADDR1 pins.
In this article, we try to provide you with a basic understanding of the STUSB4500 functionality. We examine the pinout of the device by referring to the example schematic given in the device datasheet. Now, you should be able to more easily understand the details provided by the datasheet. Remember that you also need to fully understand the decision algorithm that the STUSB4500 uses to determine which sink device should be powered. Details can be found on page 11 of the data sheet.
If you have experience with this PD controller or other similar parts please let us know in the comments below.