LT3757 datasheet(40/48 Pages) AD

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LTC7841

Rev. 0

For more information www.analog.com

PMBus COMMAND DETAILS

MFR_RESET

This command provides a means by which the user can

perform a reset of the LTC7841. All latched faults (ALERT

and status register) and register (telemetry, margin, con-

fig etc) contents will be reset to a power-on condition by

this command. ASEL config resistor is re-measured.

Since the power-on condition for OPERATION ON bit and

MFR_VOUT_COMMAND are zero, VOUT will be turned off

by MFR_RESET and require writing to these registers

again to turn VOUT back on.

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 communi-

cation using the MFR_RAIL_ADDRESS address. Setting

this bit disables this address. The default setting of this

Figure 20.

7841 F20

7-BIT ADDRESS

CLEAR B7 TO ENABLE RAIL ADDRESS

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 LTC7841 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.

Clearing the ON bit turns off the output voltage with

PMBus interface still active and telemetry data refreshed

at a slower 1Hz rate to minimize supply current. The

ON bit is automatically reset to OFF after a master shut-

down (RUN pin < 1.28V), power cycle, or MFR_RESET

command.

The MARGIN_HIGH/LOW bits command the VOUT ref-

erence to the value stored in either the MFR_VOUT_

MARGIN_HIGH or MFR_VOUT_MARGIN_LOW, resp. at

the slew rate set by the CSLEW capacitor. Cycling the ON

bit has no affect on the margin registers and thus when

re-asserting ON, VOUT 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 LTC7841.

This command has one data byte. It will accept one or two

but ignore the second byte.

Table 6. Supported OPERATION Command Register Values

ACTION

VALUE

Turn off immediately

0x00 (default)

Turn on

0x80

Margin Low

0x98

Margin High

0xA8

VOUT_MODE

VOUT_MODE command specifies the formatting for read-

ing output voltage. The data byte always reads 0x3F 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.

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