Status Registers And Alert Masking - Analog Devices LTM4683 Manual

LTM4683
OPERATION
microcontroller to poll the fault commands. Alternatively,
the FAULTn pins can be used as inputs to detect external
faults downstream of the controller that require an imme-
diate response.
Any fault or warning event will always cause the ALERT_ nn
pin to assert low unless the fault or warning is masked
by the SMBALERT_MASK. The pin will remain asserted
low until the CLEAR_FAULTS command is issued, the
fault bit is written to a 1 or, bias power is cycled, or an
MFR_RESET command is issued, or the RUNn pins are
toggled Off/On, or the part is commanded Off/On via
PMBus, or an alert response address (ARA) command
operation is performed. The MFR_FAULT_PROPAGATE
command determines if the FAULTn pins are pulled low
when a fault is detected.
Output and input fault event handling is controlled by the
corresponding fault response byte as specified in Table 17
—Table 21. Shutdown recovery from these types of faults
can either be autonomous or latched. For autonomous
recovery, the faults are not latched, so if the fault condi-
tions are not present after the retry interval has elapsed,
a new soft-start is attempted.
If the fault persists, the controller will continue to retry.
The retry interval is specified by the MFR_RETRY_DELAY
command and prevents damage to the regulator com-
ponents by repetitive power cycling, assuming the fault
condition itself is not immediately destructive. The MFR_
RETRY_DELAY must be greater than 120ms. It can not
exceed 83.88 seconds.

Status Registers and ALERT Masking

Figure 5 summarizes the internal LTM4683 status regis-
ters accessible by the PMBus command. These contain
indications of various faults, warnings and other impor-
tant operating conditions. As shown, the STATUS_BYTE
and STATUS_WORD commands also summarize the con-
tents of other status registers. See the PMBus Command
Details for specific information.
NONE OF THE ABOVE in the STATUS_BYTE indicates that
one or more of the bits in the most significant nibble of
STATUS_WORD are also set.
38
Generally, any asserted bit in a STATUS_x register also
pulls the ALERT_nn pin low. Once set, the ALERT_nn pin
will remain low until one of the following occurs.
A CLEAR_FAULTS or MFR_RESET Command
n
Is Issued
The Related Status Bit Is Written to a One
n
The Faulted Channel Is Properly Commanded Off and
n
Back On
The LTM4683 Successfully Transmits Its Address
n
During a PMBus Alert Response Address (ARA)
Bias Power Is Cycled
n
With some exceptions, the SMBALERT_MASK command
can be used to prevent the LTM4683 from asserting
ALERT_nn for bits in these registers on a bit-by-bit basis.
These mask settings are promoted to STATUS_WORD
and STATUS_BYTE in the same fashion as the status
bits themselves. For example, if ALERT_nn is masked
for all bits in Channel n STATUS_VOUT, then ALERT_nn
is effectively masked for the V
for PAGEn. The BUSY bit in STATUS_BYTE also asserts
ALERT_nn low and cannot be masked. This bit can be set
as a result of various internal interactions with the PMBus
communication. This fault occurs when a command is
received that it cannot be safely executed with one or
both channels enabled. As discussed in the Applications
Information section, BUSY faults can be avoided by poll-
ing MFR_COMMON before executing some commands.
If masked faults occur immediately after power up,
ALERT_nn may still be pulled low because there has not
been time to retrieve all of the programmed masking
information from EEPROM.
Status information contained in MFR_COMMON and
MFR_PADS can be used to further debug or clarify the
contents of STATUS_BYTE or STATUS_WORD as shown,
but the contents of these registers do not affect the state
of the ALERT_nn pin and may not directly influence bits
in STATUS_BYTE or STATUS_WORD.
For more information www.analog.com
bit in STATUS_WORD
OUT
Rev. 0