MAX6690
2°C Accurate Remote/Local Temperature
Sensor with SMBus Serial Interface
14 ______________________________________________________________________________________
The MAX6690 incorporates collision avoidance so that
completely asynchronous operation is allowed between
SMBus operations and temperature conversions.
When autoconverting, if the T
HIGH
and T
LOW
limits are
close together, it’s possible for both high-temp and low-
temp status bits to be set, depending on the amount of
time between status read operations (especially when
converting at the fastest rate). In these circumstances,
it is best not to rely on the status bits to indicate rever-
sals in long-term temperature changes. Instead, use a
current temperature reading to establish the trend
direction.
Conversion Rate Byte
The conversion rate register (Table 8) programs the
time interval between conversions in free-running auto-
convert mode. This variable rate control can be used to
reduce the supply current in portable-equipment appli-
cations. The conversion rate byte’s POR state is 02h
(0.25Hz). The MAX6690 looks only at the 3LSB bits of
this register, so the upper 5 bits are “don’t care” bits,
which should be set to zero. The conversion rate toler-
ance is ±25% at any rate setting.
Valid A/D conversion results for both channels are
available one total conversion time (125ms nominal,
156ms maximum) after initiating a conversion, whether
conversion is initiated through the RUN/STOP bit, hard-
ware STBY/pin, one-shot command, or initial power-up.
Extended resolution and the parasitic resistance can-
cellation mode are available at conversion rates of 1Hz
or lower.
Slave Addresses
The MAX6690’s device address can be set to one of
nine different values by pin strapping ADD0 and ADD1
so that more than one MAX6690 can reside on the
same bus without address conflicts (Table 9).
The address pin states are checked at POR only, and
the address data stays latched to reduce quiescent
supply current due to the bias current needed for high-
Z state detection.
The MAX6690 also responds to the SMBus Alert
Response slave address (see the
Alert Response
Address
section).
POR and UVLO
The MAX6690 has a volatile memory. 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 2V (typ, see
Electrical
Characteristics
). When power is first applied and V
CC
rises above 2.0V (typ), the logic blocks begin operat-
ing, although reads and writes at V
CC
levels below 3V
are not recommended. A second V
CC
comparator, the
ADC undervoltage lockout (UVLO) comparator, pre-
vents the ADC from converting until there is sufficient
headroom (V
CC
= 2.8V typ).
of the entire status byte if the fault condition no longer exists.
Internal low-temperature alarm has tripped when high; cleared by POR or readout of
the entire status byte if the fault condition no longer exists.
of the entire status byte if the fault condition no longer exists.
of the entire status byte if the fault condition no longer exists.
A high indicates an external diode is open; cleared by POR or readout of the entire
status byte if the fault condition no longer exists.
