MAX6642
±1°C, SMBus-Compatible Remote/
Local Temperature Sensor with
Overtemperature Alarm
Maxim Integrated | 9www.maximintegrated.com
tion rules apply, and the device with the lower address
code wins. The losing device does not generate an
acknowledge and continues to hold the ALERT line low
until cleared. (The conditions for clearing an ALERT
vary depending on the type of slave device.)
Successful completion of the alert response protocol
clears the interrupt latch. If the condition still exists, the
device reasserts the ALERT interrupt at the end of the
next conversion.
Command Byte Functions
The 8-bit command byte register (Table 3) is the master
index that points to the various other registers within the
MAX6642. The register’s POR state is 0000 0000, so a
Receive Byte transmission (a protocol that lacks the
command byte) that occurs immediately after POR
returns the current local temperature data.
Single-Shot
The single-shot command immediately forces a new
conversion cycle to begin. If the single-shot command
is received while the MAX6642 is in standby mode
(RUN bit = 1), a new conversion begins, after which the
device returns to standby mode. If a single-shot con-
version is in progress when a single-shot command is
received, the command is ignored. If a single-shot
command is received in autonomous mode (RUN bit =
0), the command is ignored.
Configuration Byte Functions
The configuration byte register (Table 4) is a read-write
register with several functions. Bit 7 is used to mask
(disable) interrupts. Bit 6 puts the MAX6642 into stand-
by mode (STOP) or autonomous (RUN) mode. Bit 5 dis-
ables local temperature conversions for faster (8Hz)
remote temperature monitoring. Bit 4 prevents setting
the ALERT output until two consecutive measurements
result in fault conditions.
Status Byte Functions
The status byte register (Table 5) indicates which (if
any) temperature thresholds have been exceeded. This
byte also indicates whether the ADC is converting and
whether there is an open-circuit fault detected on the
external sense junction. After POR, the normal state of
all flag bits is zero, assuming no alarm conditions are
present. The status byte is cleared by any successful
read of the status byte after the overtemperature fault
condition no longer exists.
Slave Addresses
The MAX6642 has eight fixed addresses available.
These are shown in Table 6.
The MAX6642 also responds to the SMBus alert
response slave address (see the
Alert Response
Address
section).
POR and UVLO
To prevent ambiguous power-supply conditions from
corrupting the data in memory and causing erratic
behavior, a POR voltage detector monitors V
CC
and
clears the memory if V
CC
falls below 2.1 (typ). When
power is first applied and V
CC
rises above 2.1 (typ),
the logic blocks begin operating, although reads and
writes at V
CC
levels below 3V are not recommended. A
second V
CC
comparator, the ADC undervoltage lockout
(UVLO) comparator prevents the ADC from converting
until there is sufficient headroom (V
CC
= +2.7V typ).
Power-Up Defaults
Power-up defaults include:
• ALERT output is cleared.
• ADC begins autoconverting at a 4Hz rate.
• Command byte is set to 00h to facilitate quick
local Receive Byte queries.
• Local (internal) T
HIGH
limit set to +70°C.
• Remote (external) T
HIGH
limit set to +120°C.
Applications Information
Remote-Diode Selection
The MAX6642 can directly measure the die temperature
of CPUs and other ICs that have on-board temperature-
sensing diodes (see the
Typical Operating Circuit
) or
they can measure the temperature of a discrete diode-
connected transistor.
Effect of Ideality Factor
The accuracy of the remote temperature measurements
depends on the ideality factor (n) of the remote “diode”
(actually a transistor). The MAX6642 is optimized for n
= 1.008, which is the typical value for the Intel Pentium
PART NO. SUFFIX ADDRESS
