ADM1275-1ACPZ-R7 datasheet(30/48 Pages) AD

30 / 48 page

ADM1275

Data Sheet

Rev. D | Page 30 of 48

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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