LTC3815_15 Datasheet, PDF (18/42 Pages) Linear Technology – 6A Monolithic Synchronous DC/DC Step-Down Converter with Digital Power System Management

LTC3815
Operation
For a description of the minor extensions and exceptions
PMBus makes to SMBus, refer to PMBus Specification
Part 1 Revision 1.1: Paragraph 5: Transport.
For a description of the differences between SMBus and
I²C, refer to System Management Bus (SMBus) Speci-
fication Version 2.0: Appendix B—Differences Between
SMBus and I²C.
PMBus Serial Interface
The LTC3815 communicates with a host (master) using the
standard PMBus serial bus interface. The Timing Diagram,
Figure 1, shows the timing relationship of the signals on
the bus. The two bus lines, SDA and SCL, must be high
when the bus is not in use. External pull-up resistors or
current sources are required on these lines.
The LTC3815 is a slave device. The master can com-
municate with the LTC3815 using the following formats:
n _{Master transmitter, slave receiver}
n _{Master receiver, slave transmitter}
The following PMBus protocols are supported:
n _{Write Byte, Write Word, Send Byte}
n _{Read Byte, Read Word}
n _{Alert Response Address}
Figures 3 through 6 illustrate the aforementioned PMBus
protocols. All transactions support GCP (group command
protocol).
Figure 2 is a key to the protocol diagrams in this section.
SDA
t_f
t_LOW
SCL
t_HD(STA)
START
CONDITION
t_r
t_SU(DAT)
t_f
t_HD(DAT)
t_HIGH
t_HD(SDA)
t_SU(STA)
REPEATED START
CONDITION
Figure 1. Timing Diagram
t_SP
t_r
t_BUF
t_SU(STO)
STOP
CONDITION
3815 F01
START
CONDITION
18
1
7
11
8
11
S SLAVE ADDRESS Wr A DATA BYTE A P
x
x
S START CONDITION
Sr REPEATED START CONDITION
Rd READ (BIT VALUE OF 1)
Wr WRITE (BIT VALUE OF 0)
x SHOWN UNDER A FIELD INDICATES THAT THAT
FIELD IS REQUIRED TO HAVE THE VALUE OF x
A ACKNOWLEDGE (THIS BIT POSITION MAY BE 0
FOR AN ACK OR 1 FOR A NACK)
P STOP CONDITION
PEC PACKET ERROR CODE
MASTER TO SLAVE
SLAVE TO MASTER
... _{CONTINUATION OF PROTOCOL}
3815 F02
Figure 2. PMBus Packet Protocol Diagram Element Key
For more information www.linear.com/LTC3815
3815p