LT3045 datasheet(45/62 Pages) AD

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Data Sheet

LT3074

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Rev 0.

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the LT3074 are not violated in the application setup. Faults that are detrimental to the device operation (such as

thermal shutdown) are always reported and acted upon. See the STATUS_BYTE and STATUS_WORD commands and

the related fault reporting commands for details on the faults supported by the LT3074.

Bus Timeout

The LT3074 implements a timeout feature to avoid hanging the serial interface. The SMBus specification includes

three clock stretching specifications related to timeout conditions. The timeout conditions are described as

following.

TTIMEOUT

A timeout condition occurs if any single SCL clock pulse is held low for longer than TTIMEOUT_MIN of 25ms. Upon detecting

the timeout condition, the LT3074 aborts the transfer, releases the bus lines, and readies to accept a new start

condition. The device initiating the timeout is required to hold the SCL clock line low for at least TTIMEOUT_MAX of 35ms,

guaranteeing that the LT3074 device has enough time to reset its communication protocol.

TLOW:SEXT

The TLOW:SEXT of 25ms specification is defined as the cumulative time that the SCL line is held low by the target device

in any one message from the start to stop condition. The LT3074 is guaranteed by design not to violate this

specification.

TLOW:MEXT

The TLOW:MEXT of 10ms specification is defined as the cumulative time that the SCL line is held low by the host device

in any one byte of a message between the start-to-acknowledge, acknowledge-to-acknowledge, or acknowledge-to-

stop. This check is not implemented in the LT3074.

PMBus Command Details

PAGE

The PAGE command is included to provide integration with multipage devices. The LT3074 accepts all data values

for the PAGE register, ACKs the data, and discards it. Reading the PAGE register always returns 8’hFF.

OPERATION

The OPERATION command is used to turn the unit on or off in conjunction with the status of the EN pin. It is also used

to program the output voltage to a high or low margin state. The unit stays in the commanded operating mode until

a subsequent OPERATION command or a reset operation (either using the EN pin or the MRF_RESET command).

Table 11. OPERATION Command Bit Field Descriptions

Bit

Access Mode

Description

Read/Write

On/Off State

Value

Output Status

‘b0 1

Off

‘b1

Read Only

Turn Off Behavior (hardwired to turn off immediately)

5:4

Read/Write

Voltage Command Source

Value

Output Status

‘b00

Nominal Output

‘b01

Output Margin Low (margin value set by MFR_MARGIN register)

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