1°C Accurate Remote/Local Temperature
Sensor with SMBus Serial Interface
Table 7. Status Byte Bit Assignments
POR
STATE
BIT
NAME
FUNCTION
7 (MSB)
BUSY
0
ADC is busy converting when high.
Internal high-temperature alarm has tripped when high; cleared by POR or readout
of the entire status byte if the fault condition no longer exists.
6
5
4
3
LHIGH
LLOW
RHIGH
RLOW
0
0
0
0
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.
External high-temperature alarm has tripped when high; cleared by POR or readout
of the entire status byte if the fault condition no longer exists.
External low-temperature alarm has tripped when high; cleared by POR or readout
of the entire status byte if the fault condition no longer exists.
A high indicates an external diode open; cleared by POR or readout of the entire
status byte if the fault condition no longer exists.
2
OPEN
RFU
0
0
1 or 0
Reserved.
The MAX6654 incorporates collision avoidance so that
completely asynchronous operation is allowed between
SMBus operations and temperature conversions.
Extended resolution and the parasitic resistance can-
cellation mode are available at conversion rates of 1Hz
or lower.
When autoconverting, if the T
and T
limits are
HIGH
LOW
Slave Addresses
The MAX6654’s device address can be set to one of
nine different values by pin strapping ADD0 and ADD1
so that more than one MAX6654 can reside on the
same bus without address conflicts (Table 9).
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.
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.
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 MAX6654 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.
The MAX6654 also responds to the SMBus Alert
Response slave address (see the Alert Response
Address section).
POR and UVLO
The MAX6654 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
and clears the
CC
memory if V
falls below 2V (typ, see Electrical
CC
Characteristics). When power is first applied and V
rises above 2.0V (typ), the logic blocks begin operat-
CC
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.
ing, although reads and writes at V
are not recommended. A second V
levels below 3V
comparator, the
CC
CC
ADC undervoltage lockout (UVLO) comparator, pre-
vents the ADC from converting until there is sufficient
headroom (V
= 2.8V typ).
CC
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