MAX8688 Datasheet, PDF (21/38 Pages) Maxim Integrated Products – Digital Power-Supply Controller/Monitor with PMBus Interface

Digital Power-Supply Controller/Monitor
with PMBus Interface
PMBus Digital Interface
From a software perspective, the MAX8688 appears as a
PMBus device capable of executing a subset of PMBus
commands. A PMBus 1.0-compliant device uses the
SMBus version 1.1 for transport protocol and responds
to the SMBus slave address. In this data sheet, the term
SMBus is used to refer to the electrical characteristics of
the PMBus communication using the SMBus physical
layer. The term PMBus is used to refer to the PMBus
command protocol.
The MAX8688 employs five standard SMBus protocols
(Write Word, Read Word, Write Byte, Read Byte and Send
Byte (see Figures 12–15)) to program output voltage and
warning/faults thresholds, read monitored data, and pro-
vide access to all manufacturer-specific commands.
The MAX8688 also supports the group command. The
group command is used to send commands to more
than one PMBus device. It is not required that all the
devices receive the same command. However, no more
than one command can be sent to any one device in
one group command packet. The group command
must not be used with commands that require receiving
devices to respond with data, such as the
STATUS_BYTE command. When the MAX8688 receives
a command through this protocol, it immediately begins
execution of the received command after detecting the
STOP condition.
When the data word is transmitted, the lower order byte
is sent first and the higher order byte is sent last. Within
any byte, the most significant bit (MSB) is sent first and
the least significant bit (LSB) is sent last.
WRITE BYTE FORMAT
S
ADDR
7 BITS
SLAVE ADDRESS
READ BYTE FORMAT
S
ADDR
7 BITS
SLAVE ADDRESS
WRITE WORD FORMAT
S
ADDR
7 BITS
SLAVE ADDRESS
READ WORD FORMAT
S
ADDR
7 BITS
SLAVE ADDRESS
SEND BYTE FORMAT
S
ADDR
7 BITS
SLAVE ADDRESS
WA
COMMAND
A
8 BITS
DATA
8 BITS
AP
COMMAND BYTE:
SELECTS WHICH
COMMAND PARAMETER
TO WRITE TO
DATA BYTE: DATA FOR THE COMMAND
SET BY THE COMMAND BYTE
WA
COMMAND
A
8 BITS
COMMAND BYTE:
SELECTS WHICH
COMMAND PARAMETER
TO READ FROM
SR
ADDR
RA
DATA
NA P
7 BITS
8 BITS
SLAVE ADDRESS:
REPEATED DUE TO
CHANGE IN DATA-FLOW
DIRECTION
DATA BYTE: DATA FOR THE COMMAND
SET BY THE COMMAND BYTE
WA
COMMAND
A
DATA0
A
DATA1
AP
8 BITS
8 BITS
8 BITS
COMMAND BYTE:
SELECTS WHICH
COMMAND PARAMETER
TO WRITE TO
DATA BYTE: DATA FOR THE COMMAND SET BY THE
COMMAND BYTE
WA
COMMAND
A SR
ADDR
RA
DATA0
A
DATA1
NA P
8 BITS
7 BITS
8 BITS
8 BITS
COMMAND BYTE:
SELECTS WHICH
COMMAND PARAMETER
TO READ FROM
SLAVE ADDRESS:
REPEATED DUE TO
CHANGE IN DATA-FLOW
DIRECTION
DATA BYTE: DATA FOR THE COMMAND SET BY THE
COMMAND BYTE
WA
COMMAND
8 BITS
AP
COMMAND BYTE: SEND
COMMAND WITH NO DATA
S = START CONDITION.
SR = REPEATED START CONDITION.
P = STOP CONDITION.
= SLAVE TRANSMISSION.
Figure 12. SMBus Protocols
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