UCD9246: Proper Reset Process

Best option moving forward is to provide the configuration file for the UCD9246 and the power schematic.  nRESET should be tied to 3V3 by resistor 10K pull-up, including a 10nF capacitor wouldn't hurt either.  Prefer nRESET is not actively used to control power circuit, PMBus_CTRL pin or OPERATION command to enable/disable rails.  Some customers like to include the ability to cycle this pin as a last ditch option but it has never been shown to be needed.

1) STATUS_MFR_SPECIFIC: 0x80

This is a CLF (Current Limit Flag) which is triggered by the internal overcurrent comparator (vs. FLT which is often an OC triggered by the driver circuitry).  It is a paged fault so it would be specific to a particular rail.  Probable older logged fault as MFR bit in STATUS_WORD not set.

2) STATUS_WORD: 0x00c8

Multiple items - Can be Error or Current State (sent Little Endian so bytes need to be reversed to 0xc800)

VOUT (There should be corresponding STATUS_VOUT register value that provides additional info)

IOUT (There should be corresponding STATUS_IOUT register value that provides additional info)  Likely bit 7 (IOUT_OC_FAULT)

POWER_GOOD# - Rail is OFF

3) STATUS_CML: 0x97

A few items here shown below, appear to be old logged faults as the CML bit is not set in the STATUS_WORD.  Likely from attempting to write while part is initializing or shutting down.

Hi Brad,

From your response, I take that using nRESET would not cause any problem, but it should not be needed to control the devices. Is this interpretation correct?

Furthermore, the main problem that I am having is that the voltage rails on the devices fail to turn on. These are what I observed:

• When I follow this sequence: Configure Dev1 > Soft Reset Dev1 > 2sec delay > Configure Dev2 > Soft Reset Dev2 > PMBus_CTRL pin ON, and OPERATION command ON, the rail on Dev2 turns on OK.
• When I follow this sequence: Configure Dev1 > Configure Dev2 > Soft Reset Dev1 > Soft Reset Dev2 > 2sec delay > PMBus_CTRL pin ON, and OPERATION command ON, both both devices fail to turn on.
• When the rails failed to turn on, I attempted toggling PMBus_CTRL pin, and OPERATION command two more times, without any luck.
• I tried sending CLEAR_FAULT before PMBus_CTRL pin ON, and OPERATION command ON, still not any luck.

These are the questions I have:

1. Does this mean that there is some timing constrains between the time the configuration is complete and the rails to be able to turn on?
2. Is the soft reset required to turn on the rails?

Regards,

Ryan B.

Hi Brad,
Just wanted to check in for any updates.
Thank you!
Ryan B.

Exercising nRESET shouldn't cause any problems but there should be no need to use it during normal operation (power conversion) of the device.

As for programming, the PMBus script that can be exported from the Fusion Digital Power Designer contains all the operations needed to properly configure a device. The Soft Reset should only be needed after completing the base configuration commands, PHASE_INFO, GPIO_SEQ_CONFIG, FREQ_SWITCH (each rail) and SYNC_OFFSET have been written followed by a STORE_DEFAULT_ALL command, as these are required to define which rails/phases are to be used. There should be a delay after this STORE_DEFAULT_ALL before the SOFT_ RESET to allow the device to complete the update of the flash memory. Then another delay for the device to re-initialize after the SOFT_RESET before continuing on with the rest of the configuration commands and the final STORE_DEFAULT_ALL required to store these configuration commands to the flash memory. Another SOFT_RESET can be applied after the flash completes the write process but should not be needed. If the SOFT_RESET is applied before the write process finishes then the config flash data would be corrupted and it would not have a valid checksum so I believe the device reverts to the default configuration. Is it possible this is occurring?

Do they have a copy of the Configuration Programming for UCD Devices document?

/cfs-file/__key/communityserver-discussions-components-files/196/6102.1007.Configuration-Programming-of-UCD-Devices.pdf

Link should work now.

Thank you so much for the feedback.
Is it possible for you guys to help me take a look at the sequence that we are using to see if there is anything amiss?

I have sent you the PMBus scripts that were generated by Fusion, as well as the modified scripts that I am using.

We are using this sequence to configure and turn on the voltage rails:
1. Configure device 1 using script
2. Configure device 2 using script
3. Enable device 1, device 2 using PMBUS_CTRL pin
4. Send PMBUS command to turn on device 1, device 2

Currently with this sequence, the rails are not turning on after step 4.
If we insert a step to toggle nRESET line after step 3, both devices output correctly on the rails.