±1°C, SMBus-Compatible Remote/Local Temperature
Sensors with Overtemperature Alarms
MAX6657/MAX6658/MAX6659
Functional Diagram
V
CC
MAX6657
MAX6658
MAX6659
2
DXP
DXN
MUX
REMOTE
ADC
LOCAL
DIODE
FAULT
ALERT
Q
S
R
OVERT1
S
Q
R
REGISTER BANK
COMMAND BYTE
REMOTE TEMPERATURE
LOCAL TEMPERATURE
ALERT THRESHOLD
ALERT RESPONSE
ADDRESS
S
Q
R
MAX6659 ONLY
OVERT1 THRESHOLD
(OVERT2 THRESHOLD)
( ) ARE FOR MAX6659 ONLY
8
8
SMBus
READ
WRITE
7
SMBDATA
SMBCLK
CONTROL
LOGIC
(STBY)
ADDRESS
DECODER
(ADD)
(OVERT2)
Detailed Description
The MAX6657/MAX6658/MAX6659 are temperature
sensors designed to work in conjunction with a micro-
processor or other intelligence in thermostatic,
process-control, or monitoring applications. Com-
munication with the MAX6657/MAX6658/MAX6659
occurs through the SMBus serial interface and dedicat-
ed alert pins. Two independent overtemperature alarms
(OVERT1 and
OVERT2)
are asserted if their software
programmed temperature thresholds are exceeded.
OVERT1
and
OVERT2
can be connected to fans, a sys-
tem shutdown, or other thermal management circuitry.
The MAX6657/MAX6658/MAX6659 convert tempera-
tures to digital data either at a programmed rate or a
single conversion. Conversions have a 0.125°C resolu-
tion (extended resolution) or 1°C resolution (legacy res-
olution). Extended resolution represents temperature as
6
10 bits + sign bit and is available for autonomous con-
versions that are 4Hz and slower and single-shot con-
versions. Legacy resolution represents temperature as
7 bits + sign bit and allows for faster autonomous con-
version rates of 8Hz and 16Hz.
ADC and Multiplexer
The averaging ADC integrates over a 60ms period
(each channel, typically, in the 7-bit + sign legacy
mode). Using an averaging ADC attains excellent noise
rejection.
The multiplexer automatically steers bias currents
through the remote and local diodes. The ADC and
associated circuitry measure each diode’s forward volt-
age and compute the temperature based on this volt-
age. If the remote channel is not used, connect DXP to
DXN. Do not leave DXP and DXN unconnected. When a
conversion is initiated, both channels are converted
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