Datasheet

MAX6694
5-Channel Precision Temperature Monitor
with Beta Compensation
8 _______________________________________________________________________________________
Figure 2. SMBus Protocols
S ADDRESS WR ACK ACK PDATA ACKCOMMAND
7 BITS 18 BITS8 BITS
SLAVE ADDRESS: EQUIVA-
LENT TO CHIP-SELECT LINE OF
A 3-WIRE INTERFACE
DATA BYTE: DATA GOES INTO THE REGISTER
SET BY THE COMMAND BYTE (TO SET
THRESHOLDS, CONFIGURATION MASKS, AND
SAMPLING RATE)
WRITE BYTE FORMAT
S ADDRESSADDRESS WR ACK ACK PS RD ACK ///DATACOMMAND
7 BITS 7 BITS 8 BITS8 BITS
READ BYTE FORMAT
SLAVE ADDRESS: EQUIVA-
LENT TO CHIP SELECT LINE
COMMAND BYTE: SELECTS
FROM WHICH REGISTER YOU
ARE READING
COMMAND BYTE: SELECTS
TO WHICH REGISTER YOU
ARE WRITING
SPADDRESS WR ACK ACKCOMMAND
7 BITS 8 BITS
SEND BYTE FORMAT
COMMAND BYTE: SENDS COM-
MAND WITH NO DATA, USUALLY
USED FOR ONE-SHOT COMMAND
SPADDRESS RD ACK ///DATA
7 BITS 8 BITS
RECEIVE BYTE FORMAT
DATA BYTE: READS DATA FROM
THE REGISTER COMMANDED
BY THE LAST READ BYTE OR
WRITE BYTE TRANSMISSION;
ALSO USED FOR SMBus ALERT
RESPONSE RETURN ADDRESS
SLAVE ADDRESS: REPEATED
DUE TO CHANGE IN DATA-
FLOW DIRECTION
DATA BYTE: READS FROM
THE REGISTER SET BY THE
COMMAND BYTE
S = START CONDITION.
P = STOP CONDITION.
SHADED = SLAVE TRANSMISSION.
/// = NOT ACKNOWLEDGED.
350µA. During either software or hardware standby,
data is retained in memory. During hardware standby,
the SMBus interface is inactive. During software stand-
by, the SMBus interface is active and listening for
SMBus commands. The timeout is enabled if a start
condition is recognized on SMBus. Activity on the
SMBus causes the supply current to increase. If a
standby command is received while a conversion is in
progress, the conversion cycle is interrupted, and the
temperature registers are not updated. The previous
data is not changed and remains available.
Operating-Current Calculation
The MAX6694 operates at different operating-current
levels depending on how many external channels are in
use. Assume that I
CC1
is the operating current when
the MAX6694 is converting the remote channel 1 and
I
CC2
is the operating current when the MAX6694 is con-
verting the other channels. For the MAX6694 with
remote channel 1 and n other remote channels con-
nected, the operating current is:
I
CC
= (2 x I
CC1
+ I
CC2
+ n x I
CC2
)/(n + 3)
SMBus Digital Interface
From a software perspective, the MAX6694 appears as
a series of 8-bit registers that contain temperature mea-
surement data, alarm threshold values, and control bits.
A standard SMBus-compatible, 2-wire serial interface is
used to read temperature data and write control bits
and alarm threshold data. The same SMBus slave
address also provides access to all functions.
The MAX6694 employs four standard SMBus protocols:
write byte, read byte, send byte, and receive byte
(Figure 2). The shorter receive byte protocol allows
quicker transfers, provided that the correct data regis-
ter was previously selected by a read byte instruction.
Use caution with the shorter protocols in multimaster
systems, since a second master could overwrite the
command byte without informing the first master. Figure
3 is the SMBus write-timing diagram and Figure 4 is the
SMBus read-timing diagram.
The remote diode 1 measurement channel provides 11
bits of data (1 LSB = +0.125°C). All other temperature-
measurement channels provide 8 bits of temperature
data (1 LSB = +1°C). The 8 most significant bits (MSBs)