LTC3815_15 Datasheet, PDF (34/42 Pages) Linear Technology – 6A Monolithic Synchronous DC/DC Step-Down Converter with Digital Power System Management

LTC3815
PMBus Command Details
MFR_RESET
This command provides a means by which the user can
perform a reset of the LTC3815. All latched faults (ALERT
and status register) and register (telemetry, margin, etc)
contents will be reset to a power-on condition by this
command. V_OUT will remain in regulation but may change
due to the reset of the margin registers. ASEL and PGFD
config resistors are re-measured.
This write-only command accepts zero, one, or two data
bytes but ignores them.
MFR_RAIL_ADDRESS
The MFR_RAIL_ADDRESS command allows all devices
to share a common address, such as all devices attached
to a single power supply rail. The desired 7-bit address
value is written to the 7 bits of the data byte.
The MSB (bit B7) must be set low to enable communication
using the MFR_RAIL_ADDRESS address. Setting this bit
disables this address.
7-BIT ADDRESS
B7
B0
CLEAR B7 TO ENABLE RAIL ADDRESS
3815 F14
Figure 16. MFR_RAIL_ADDRESS Data Byte
The user should only perform command writes to this
address. If a read is performed from this address and
the rail devices do not respond with EXACTLY the same
value, the LTC3815 will detect bus contention and set a
CML communications fault.
This command accepts one or two data bytes but the
second is ignored.
OPERATION
The OPERATION command is used to turn the unit on/off
and for margining the output voltage.
The ON bit has the same function as the RUN_STBY pin,
i.e. clearing it turns off the output voltage with PMBus
interface still active and telemetry data refreshed at a slower
1Hz rate to minimize supply current. Either RUN_STBY pin
or ON bit can be cleared/deasserted to put the LTC3815
into this standy mode. The ON bit is automatically reset
to ON after a master shutdown (RUN_MSTR = 0V), power
cycle, or MFR_RESET command.
The MARGIN_LOW/HIGH bits command the V_OUT reference
to the offset value stored in either the MFR_VOUT_
MARGIN_HIGH or MFR_VOUT_MARGIN_LOW, resp. at
the slew rate set by the C_SLEW capacitor. These bits are
identical in function to margin high/low from the MARGIN
pin. However, the MARGIN pin has precedence over the
MARGIN_LOW/HIGH bits when there is a conflict. Cycling
the RUN_STBY pin has no affect on the margin bits and
thus when re-asserting RUN_STBY, V_OUT will return to
the state it was in prior to the shutdown.
Margin high (ignore faults) and margin low (ignore faults)
operations are not supported by the LTC3815.
This command has one data byte. It will accept one or two
but ignore the second byte.
Table 7. Supported OPERATION Command Register Values
ACTION
VALUE
Turn off immediately
0x00
Turn on
0x80
Margin Low
0x98
Margin High
0xA8
VOUT_MODE
VOUT_MODE command specifies the formatting for
reading output voltage. The data byte always reads 0x3E
for VID data format and cannot be changed. Attempts to
write to VOUT_MODE will set a CML fault.
This read-only command has one data byte.
MFR_VOUT_COMMAND
The MFR_VOUT_COMMAND consists of a value (%) used
to offset the output reference voltage at the REF pin. The
C_SLEW capacitor sets the slew rate limit of the output volt-
age if this command is modified while the output is active
and in a steady-state condition.
3815p
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