JAJSIO3A February 2020 – September 2020 TPS546B24A
PRODUCTION DATA
To allow multiple devices with a shared output to communicate through a single PMBus address and single PMBus slave, the TPS546B24A uses a back-channel communication implemented through BCX_CLK and BCX_DAT pins. During POR, all of the devices connected to VSHARE must also be connected to BCX_CLK and BCX_DAT and have appropriate Section 7.6.82 settings. Any programming error among the devices of a stack will result in a POR fault and prevent enabling of conversion.
During POR, the loop master reads the programmed values from the loop slaves to ensure all expected slaves are present and correctly phase-shifted. Then, the Master will load critical operating parameters such as the following to the slave devices to ensure correct operation of the STACK:
During operation, the master device receives and responds to all PMBus communication, and slave devices do not need to be connected to the PMBus. If the master receives commands that require updates to the PMBus registers of the slave, the master relays these commands to the slaves. Additionally, the master periodically polls slave devices for status and telemetry information to maintain an accurate record of the telemetry and STATUS information for the full stack of devices.
Most PMBus communication should be directed to all phases by leaving the Section 7.6.5 PMBus command at its Power On Reset default value of FFh. If a specific device must be communicated with, the Section 7.6.5 command can be changed to address a specific device within the stack, as set by the order value of the Section 7.6.30 command programmed during POR.
When commands are directed to individual slaves, write commands are queued by the master to be sent to the slaves through the BCX if other BCX communication is in progress. Queued write commands are written to the slaves in the order the master receives them. To avoid unnecessary delays on the PMBus and excessive clock stretching, read transactions targeting individual slaves are not queued, and will be processed as soon as the BCX bus is available. As a result, it is possible for a read command targeting an individual slave immediately following a write command can be processed before the preceding write command. To ensure accurate read-back, users must allow a minimum of 4 ms between writing a value to an individual slave and reading that same value back from the same slave.