7.3.3 Rail Configuration

A rail includes voltage, a power-supply enable and a margining output. At least one must be included in a rail definition. Once the user has defined how the power-supply rails should operate in a particular system, analog input pins and GPIOs can be selected to monitor and enable each supply (Figure 6).

Figure 6. Fusion GUI Pin-Assignment Tab

After the pins have been configured, other key monitoring and sequencing criteria are selected for each rail from the Vout Config tab (Figure 7):

• Nominal operating voltage (Vout)
• Undervoltage (UV) and overvoltage (OV) warning and fault limits
• Margin-low and margin-high values
• Power-good on and power-good off limits
• PMBus or pin-based sequencing control (On/Off Config)
• Rails and GPIs for Sequence On dependencies
• Rails and GPIs for Sequence Off dependencies
• Turn-on and turn-off delay timing
• Maximum time allowed for a rail to reach POWER_GOOD_ON or POWER_GOOD_OFF after being enabled or disabled
• Other rails to turn off in case of a fault on a rail (fault-shutdown slaves)

Figure 7. Fusion GUI V_OUT-Config Tab

The Synchronize Margins/Limits/PG to Vout checkbox is an easy way to change the nominal operating voltage of a rail and also update all of the other limits associated with that rail according to the percentages shown to the right of each entry.

The plot in the upper left section of Figure 7 shows a simulation of the overall sequence-on and sequence-off configuration, including the nominal voltage, the turnon and turnoff delay times, the power-good on and power-good off voltages and any timing dependencies between the rails.

After a rail voltage has reached its POWER_GOOD_ON voltage and is considered to be in regulation, it is compared against two UV and two OV thresholds in order to determine if a warning or fault limit has been exceeded. If a fault is detected, the UCD90120A responds based on a variety of flexible, user-configured options. Faults can cause rails to restart, shut down immediately, sequence off using turnoff delay times or shut down a group of rails and sequence them back on. Different types of faults can result in different responses.

Fault responses, along with a number of other parameters including user-specific manufacturing information and external scaling and offset values, are selected in the different tabs within the Configure function of the Fusion GUI. Once the configuration satisfies the user requirements, it can be written to device SRAM if Fusion GUI is connected to a UCD90120A using an I²C/PMBus. SRAM contents can then be stored to data flash memory so that the configuration remains in the device after a reset or power cycle.

The Fusion GUI Monitor page has a number of options, including a device dashboard and a system dashboard, for viewing and controlling device and system status.

Figure 8. Fusion GUI Monitor Page

The UCD90120A also has status registers for each rail and the capability to log faults to flash memory for use in system troubleshooting. This is helpful in the event of a power-supply or system failure. The status registers (Figure 9) and the fault log (Figure 10) are available in the Fusion GUI. See the UCD90xxx Sequencer and System Health Controller PMBus Command Reference (SLVU352) and the PMBus Specification for detailed descriptions of each status register and supported PMBus commands.

Figure 9. Fusion GUI Rail-Status Register

Figure 10. Fusion GUI Flash-Error Log (Logged Faults)