Silicon Laboratories Si3482 SMART PSE-24 KIT, User Manual, Page: 7 / 22

S i 3 4 8 2 S m a r t P S E - 2 4 U G
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Connect the Class 4 PD with three resistors (19.5 W) to Port 1. Port 1 is granted power, and a system-level
overload is created with approximately 45.5 W. Either Port 3 or Ports 2 and 3 will be turned off depending on
whether the Si3480 reported a severe overload (>44 W). Because the PDs have a soft start circuit, it is possible
that only Port 3 is turned off when the power exceeds 40 W. The ports that are turned off will not turn back on until
the load on Port 1 is reduced. This is because there is not enough power available to grant 15.4 W from the Class
3 PD.
Figure 8. Status Screen Showing Port 3 Denied Power Due to Insufficient Power Available
The Si3482 will manage power on all Si3452 devices to which it is connected. The number of Si3452 devices
connected is discovered upon power up. This means that the Si3482 can manage power on up to 48 ports.
Once configured, the Si3482 will continue to manage the power even when the host is disconnected. To
demonstrate this, exit the GUI, disconnect the PoE USB adapter, and repeat the above tests. While there is no
visual display, the behavior is the same. The PD status can be seen by looking at the LEDs on the Si3402
evaluation boards located on the RJ-45 connector. These LEDs glow steadily if power is supplied.
Note that, in the schematics shown in Figure 6, the Reset and Pgood2 signals are routed through an Si8423
isolator. The Si8423 default state is high so that, when the USB connector is removed, the Si3482 is not held in
reset, and Power Supply 2 is still configured as inserted. This is why Power Supply 2 was chosen to be inserted in
the above examples.
4.1. Easing Software Development with the Serial Packet Protocol SDK
A host MCU uses the Serial Packet Protocol (SPP) to communicate with an Si3482 Power Management Controller.
A Serial Packet Client in the host MCU implements the client side of the Serial Packet Protocol. The SPP Software
Development Kit (SDK) provides the source code for the Serial Packet Client, greatly reducing the software
development effort needed to use an Si3482.
The software included with this SMARTPSE24-KIT includes the SPP SDK and related documentation. Please refer
to that software as well as the Si3482 data sheet for further details on taking the next step in development with the
Si3482 power management controller.