MAX6698
Detailed Description
The MAX6698 is a precision multichannel temperature
monitor that features one local, three remote thermal
diode temperature-sensing channels, and three ther-
mistor voltage-sensing channels. All channels have a
programmable alert threshold for each temperature
channel and a programmable overtemperature thresh-
old for channels 1, 4, 5, and 6 (see Figure 1).
Communication with the MAX6698 is achieved through
the SMBus serial interface and a dedicated alert
(ALERT) pin. The alarm outputs, OVERT and ALERT,
assert if the software-programmed temperature thresh-
olds are exceeded. ALERT typically serves as an inter-
rupt, while OVERT can be connected to a fan, system
shutdown, or other thermal-management circuitry.
Note that thermistor “temperature data” is really the volt-
age across the fixed resistor, R
EXT
, in series with the
thermistor. This voltage is directly related to temperature,
but the data is expressed in percentage of the reference
voltage not in °C.
ADC Conversion Sequence
In the default conversion mode, the MAX6698 starts the
conversion sequence by measuring the temperature on
the channel 1 remote diode, followed by the channel 2,
remote diode, channel 3 remote diode, and the local
channel. Then it measures thermistor channel 1, ther-
mistor channel 2, and thermistor channel 3. The con-
version result for each active channel is stored in the
corresponding temperature data register.
In some systems, one of the remote thermal diodes may
be monitoring a location that experiences temperature
changes that occur much more rapidly than in the other
channels. If faster temperature changes must be moni-
tored in one of the temperature channels, the MAX6698
allows channel 1 to be monitored at a faster rate than the
other channels. In this mode (set by writing a 1 to bit 4 of
the configuration 1 register), measurements of channel 1
alternate with measurements of the other channels. The
sequence becomes remote-diode channel 1, remote-
diode channel 2, remote-diode channel 1, remote-diode
channel 3, remote-diode channel 1, etc. Note that the
time required to measure all seven channels is consider-
ably greater in this mode than in the default mode.
Low-Power Standby Mode
Standby mode reduces the supply current to less than
15µA by disabling the internal ADC. Enter standby by
setting the STOP bit to 1 in the configuration 1 register.
During standby, data is retained in memory, and the
SMBus interface is active and listening for SMBus com-
mands. The timeout is enabled if a start condition is rec-
ognized on the SMBus. Activity on the SMBus causes
the supply current to increase. If a standby command is
received while a conversion is in progress, the conver-
sion cycle is interrupted, and the temperature registers
are not updated. The previous data is not changed and
remains available.
7-Channel Precision Remote-Diode, Thermistor,
and Local Temperature Monitor
6 _______________________________________________________________________________________
Pin Description (continued)
