LTC4449 datasheet(36/108 Pages) LINER

36 / 108 page

LTC3882-1

Rev A

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OPERATION

Serial Bus Timeout

The LTC3882-1 implements a timeout feature to avoid

hanging the serial interface. The data packet timer be-

gins running at the first START event before the SLAVE

ADDRESS write byte and ends with the STOP bit. Packet

transmission must be completed before the timer expires,

or the LTC3882-1 will tri-state the bus and ignore all mes-

sage data. The data packet includes the SLAVE ADDRESS

byte, COMMAND CODE byte, repeated START and SLAVE

ADDRESS byte (if a read operation), all ACKNOWLEDGE

and flow control bits (R/W) and all data bytes.

The packet timer is typically set to 30ms. If bit 3 of MFR_

CONFIG_ALL_LTC3882-1 is set, this period is extended

to 255ms. The LTC3882-1 automatically allows a packet

transmission time of 255ms for MFR_FAULT_LOG block

reads regardless of the setting of this bit. In no circum-

stances will the timeout period be less than the tTIMEOUT

specification (25ms minimum).

The LTC3882-1 supports the full PMBus frequency range

of 10kHz to 400kHz.

Serial Communication Errors

The LTC3882-1 supports the optional PMBus packet error

checking protocol. This protocol appends a packet error

code (PEC) to the end of applicable message transfers to

improve communication reliability. The PEC is a CRC-8

error-checking byte calculated by the bus device sending

the last data byte. Refer to SMBus specification 1.2 or

higherforadditionalimplementationdetails.AllLTC3882-1

read operations will return a valid PEC if the bus master

requests it. If bit 2 in the MFR_CONFIG_ALL_LTC3882-1

command is set, the IC will not act in response to a bus

write operation unless a valid PEC is also received from

the host.

PEC errors on command writes, attempts to access un-

supported commands, or writing invalid data to supported

commands all cause the LTC3882-1 to generate a CML

fault. The CML bit is then set in the STATUS_BYTE and

STATUS_WORD commands, and the appropriate bit is set

in the STATUS_CML command.

LTC4449 Datasheet(PDF) 36 Page - Linear Technology

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