ltc2978 Linear Technology Corporation, ltc2978 Datasheet - Page 16

• Manufacturer Part Number: ltc2978
• Description: Octal Pmbus Power Supply Monitor And Controller With Eeprom
• Manufacturer: Linear Technology Corporation

PMBus SERIAL DIGITAL INTERFACE
The LTC2978 communicates with a host (master) using
the standard PMBus serial bus interface. The Timing
Diagram 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 LTC2978 is a slave device. The master can communicate
with the LTC2978 using the following formats:
n
n
The following SMBus protocols are supported:
n
n
n
Table 1. LTC2978 Address Look-Up Table
H = Tie to V
*MFR_I2C_BASE_ADDRESS = 7’h5C (Factory Default)
LTC2978
operaTion

Alert Response
DESCRIPTION
Master transmitter, slave receiver
Master receiver, slave transmitter
Write Byte, Write Word, Send Byte
Read Byte, Read Word, Block Read
Alert Response Address
Global
0*
1
2
3
4
5
6
7
8
DD33
, NC = No Connect, Open or Float, L = Tie to GND, X = Don’t Care
7’h
0C
5B
5C
5D
5E
5F
60
61
62
63
64
HEX DEVICE
ADDRESS
8’h
BA
BC
19
B6
B8
BE
C0
C2
C4
C6
C8
6
0
1
1
1
1
1
1
1
1
1
1
5
0
0
0
0
0
0
1
1
1
1
1
4
0
1
1
1
1
1
0
0
0
0
0
BINARY DEVICE ADDRESS
Figures 1-10 illustrate the aforementioned SMBus pro-
tocols. All transactions support PEC (parity error check)
and GCP (group command protocol). The Block Read
supports 256 bytes of returned data. For this reason, the
PMBus timeout may be extended using the Mfr_config_all_
longer_pmbus_timeout setting.
The LTC2978 will not acknowledge any PMBus command if
it is still busy with a STORE_USER_ALL, RESTORE_USER_
ALL, MFR_CONFIG or if fault log data is being written to
the EEPROM. Status_word_busy will also be set.
Slave Address
The LTC2978 can be configured to respond to one of nine
addresses for a given MFR_I2C_BASE_ADDRESS value
(the factory default value for this register is 7’h5C). In
addition, the LTC2978 will always respond to its global
address and the PMBus Alert Response address regard-
less of the state of the address select pins.
By connecting each of the address inputs to V
or by floating them, the user determines the slave address
as shown in Table 1.
3
1
1
1
1
1
1
0
0
0
0
0
2
1
0
1
1
1
1
0
0
0
0
1
1
0
1
0
0
1
1
0
0
1
1
0
0
0
1
0
1
0
1
0
1
0
1
0
R/W
1
0
0
0
0
0
0
0
0
0
0
ASEL1
ADDRESS PINS
NC
NC
NC
X
X
H
H
H
L
L
L
DD33
ASEL0
, GND,
NC
NC
NC
X
X
L
H
L
H
L
H
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