EVAL-ADM1275EBZ Datasheet, PDF (30/48 Pages) Analog Devices – Hot-Swap Controller and Digital Power

ADM1275
Data Sheet
HOT-SWAP CONTROL COMMANDS
OPERATION Command
The GATE pin that drives the FET is controlled by a dedicated
hot-swap state machine. The UV and OV input pins, along with
the TIMER and SS pins and the current sense, all feed into the
state machine and control when and how strongly the gate is
turned off.
It is also possible to control the hot-swap GATE output using
commands over the PMBus interface. The OPERATION com-
mand can be used to request the hot-swap output to turn on.
However, if the UV pin indicates that the input supply is less
than required, the hot-swap output is not turned on, even if the
OPERATION command indicates that the output should be
enabled.
If the OPERATION command is used to disable the hot-swap
output, the GATE pin is held low, even if all hot-swap state
machine control inputs indicate that it can be enabled.
The default state of the OPERATION command ON bit is 1,
so the hot-swap output is always enabled when the ADM1275
comes out of UVLO. If the ON bit is never changed, the UV
input (or the ENABLE input on the ADM1275-3) is the hot-
swap master on/off control signal.
By default at power-up, the OPERATION command is disabled
and must be enabled using the DEVICE_CONFIG command.
This prevents inadvertent shutdowns of the hot-swap controller
by software.
If the ON bit is set to 0 while the UV signal is high, the hot-swap
output is turned off. If the UV signal is low or if the OV signal
is high, the hot-swap output will already be off and the status
of the ON bit has no effect.
If the ON bit is set to 1, the hot-swap output is requested to turn
on. If the UV signal is low or if the OV signal is high, setting the
ON bit to 1 has no effect, and the hot-swap output remains off.
It is possible to determine at any time whether the hot-swap output
is enabled using the STATUS_BYTE or the STATUS_WORD
command (see the Status Commands section).
The OPERATION command can also be used to clear any latched
faults in the status registers. To clear latched faults, set the ON
bit to 0 and then reset it to 1.
DEVICE_CONFIG Command
The DEVICE_CONFIG command is used to configure certain
settings within the ADM1275, for example, to enable or disable
foldback in the hot-swap controller or to modify the duration of
the severe overcurrent glitch filter. This command is also used
to configure the polarity of the second IOUT current warnings.
At power-up, the OPERATION command is disabled and
the ADM1275 responds with a NACK if the OPERATION
command is received. To allow use of the OPERATION
command, the OPERATION_CMD_EN bit must be set
using the DEVICE_CONFIG command.
POWER_CYCLE Command
The POWER_CYCLE command can be used to request that the
ADM1275 be turned off for ~4 seconds and then back on. This
command can be useful if the processor that controls the
ADM1275 is also powered off when the ADM1275 is turned off.
This command allows the processor to request that the ADM1275
turn off and back on again as part of a single command.
ADM1275 INFORMATION COMMANDS
CAPABILITY Command
The CAPABILITY command can be used by host processors
to determine the I²C bus features supported by the ADM1275.
The features reported are the maximum bus speed and whether
the device supports the packet error checking (PEC) byte and
the SMBAlert reporting function.
PMBUS_REVISION Command
The PMBUS_REVISION command reports the version of Part I
and Part II of the PMBus standard.
MFR_ID, MFR_MODEL, and MFR_REVISION Commands
The MFR_ID, MFR_MODEL, and MFR_REVISION
commands return ASCII strings that can be used to facilitate
detection and identification of the ADM1275 on the bus.
These commands are read using the SMBus block read message
type. This message type requires that the ADM1275 return a
byte count corresponding to the length of the string data that is
to be read back.
STATUS COMMANDS
The ADM1275 provides a number of status bits that are used
to report faults and warnings from the hot-swap controller and
the power monitor. These status bits are located in six different
registers that are arranged in a hierarchy. The STATUS_BYTE
and STATUS_WORD commands provide 8 bits and 16 bits of
high level information, respectively. The STATUS_BYTE and
STATUS_WORD commands contain the most important status
bits, as well as pointer bits that indicate whether any of the four
other status registers need to be read for more detailed status
information.
In the ADM1275, a particular distinction is made between
faults and warnings. A fault is always generated by the hot-swap
controller and is defined by hardware component values. Three
events can generate a fault:
• Overcurrent condition that causes the hot-swap timer to
time out
• Overvoltage condition on the OV pin
• Undervoltage condition on the UV pin
When a fault occurs, the hot-swap controller always takes some
action, usually to turn off the GATE pin, which is driving the
FET. A fault can also generate an SMBAlert on one or both of
the GPOx/ALERTx pins.
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