The PMBus protocol is an I²C-based communication standard for power-supply management. PMBus contains standard command codes tailored to power supply applications. The DACx3701 implement some PMBus commands such as Turn Off, Turn On, Margin Low, Margin High, Communication Failure Alert Bit (CML), as well as PMBUS revision. Figure 8-2 shows typical PMBus connections. The EN_PMBUS bit (Bit 12, address D1h) must be set to 1 to enable the PMBus protocol.

Figure 8-2 PMBus Connections

Similar to I²C, PMBus is a variable length packet of 8-bit data bytes, each with a receiver acknowledge, wrapped between a start and stop bit. The first byte is always a 7-bit slave address followed by a write bit, sometimes called the even address that identifies the intended receiver of the packet. The second byte is an 8-bit command byte, identifying the PMBus command being transmitted using the respective command code. After the command byte, the transmitter either sends data associated with the command to write to the receiver command register (from most significant byte to least significant byte), or sends a new start bit indicating the desire to read the data associated with the command register from the receiver. Then the receiver transmits the data following the same most significant byte first format (see Table 8-11).