UCD90120A_15 Datasheet, PDF (46/58 Pages) Texas Instruments – 12-Rail Power Supply Sequencer and Monitor With ACPI Support

UCD90120A
SLVSAN9B – APRIL 2011 – REVISED DECEMBER 2015
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Typical Application (continued)
3. Depending on application environment, the PMBus signal integrity may be compromised at times. This causes
the UCD90120A to receive incorrect PMBus commands. In a particular case, if (D9h) ROM_MODE command is
erroneously received by a UCD90120A device, it causes the device to enter ROM mode; in this mode the device
does not function unless Fusion GUI is connected to the device. To avoid such occurences in a running system,
it is suggested to enable Packet Error Checking (PEC) in the PMBus host. The UCD90120A automatically
detects and works with PMBus hosts, both with and without PEC enabled.
4. The fault log in UCD90120A is checksum protected. After new log entries are written into the fault log, the
checksum is updated accordingly. After each device reset, UCD90120A re-calculates the fault log checksum and
compares it with the existing checksum. If the two checksums are not the same, the device determines the fault
log as corrupted and erases the fault log as a result.
In the event that the V33D power is dropped before the device finishes writing the fault log, the checksum will not
be updated correctly, thus the fault log is erased at the next power-up. The results will be:
• User sees an empty fault log
• The device initialization time is approximately 160 ms longer than normal due to the Flash erasing time.
Such an event usually happens when the main power of the board drops and no standby power can stay alive
for V33D. If such a scenario can be anticipated in an application, it is strongly suggested to use the brown-out
function and circuit as described in the Brownout Function section.
5. Do not use RESET pin to power cycle the rails. Instead, use PMBus_CNTRL pin as described in the Power-
Supply Sequencing section; or, use Pin-Selected Rail States function described in the Pin-Selected Rail States
section.
8.2.2 Detailed Design Procedure
Fusion GUI can be used to design the device configuration online or offline (with or without a UCD90120A device
connected to the computer). In offline mode, Fusion GUI prompts the user to create or open a project file (.xml)
at launch. In online mode, Fusion GUI automatically detects the device on the PMBus and reads the
configuration data from the device. A USB-to-GPIO Adapter EVM (HPA172) from Texas Instruments is required
to connect Fusion GUI to the PMBus.
The general design steps include
1. Rail setup
2. Rail monitoring configuration
3. GPI configuration
4. Rail sequence configuration
5. Fault response configuration
6. GPO configuration
7. Margining configuration
8. Other configurations such as Pin Selected Rail States, Watchdog Timer, System Reset, and so on.
Details of the steps are self-explanatory in Fusion GUI
After configuration changes, the user must click the Write to Hardware button to apply the changes. In online
mode, the user can then click the Store RAM to Flash button to permanently store the new configuration into the
data flash of the device.
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