13
Remote/Local Temperature Sensor
with SMBus Serial Interface
MAX1617
Maxim Integrated
To check for internal bus collisions, read the status
byte. If the least significant seven bits are ones, discard
the data and read the status byte again. The status bits
LHIGH, LLOW, RHIGH, and RLOW are refreshed on the
SMBus clock edge immediately following the stop con-
dition, so there is no danger of losing temperature-relat-
ed status data as a result of an internal bus collision.
The OPEN status bit (diode continuity fault) is only
refreshed at the beginning of a conversion, so OPEN
data is lost. The ALERT interrupt latch is independent of
the status byte register, so no false alerts are generat-
ed by an internal bus collision.
When auto-converting, if the THIGH and TLOW 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 (espe-
cially when converting at the fastest rate). In these cir-
cumstances, it’s best not to rely on the status bits to
indicate reversals in long-term temperature changes
and instead use a current temperature reading to
establish the trend direction.
Conversion Rate Byte
The conversion rate register (Table 7) programs the
time interval between conversions in free-running auto-
convert mode. This variable rate control reduces the
supply current in portable-equipment applications. The
conversion rate byte’s POR state is 02h (0.25Hz). The
MAX1617 looks only at the 3 LSB bits of this register, so
the upper 5 bits are “don’t care” bits, which should be
set to zero. The conversion rate tolerance 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 via the RUN/STOP bit, hardware
STBY pin, one-shot command, or initial power-up.
Changing the conversion rate can also affect the delay
until new results are available. See Table 8.
RUN/
STOP
6 0
0
POR
STATE
Standby mode control
bit. If high, the device
immediately stops con-
verting and enters stand-
by mode. If low, the
device converts in either
one-shot or timer mode.
Masks all ALERT inter-
rupts when high.
FUNCTION
RFU5–0 0 Reserved for future use
MASK7 (MSB)
BIT NAME
Table 5. Configuration-Byte Bit
Assignments
Table 7. Conversion-Rate Control Byte
Table 6. Status-Byte Bit Assignments
*These flags stay high until cleared by POR, or until the status
byte register is read.
LHIGH*6
A high indicates that the local high-
temperature alarm has activated.
A high indicates that the ADC is busy
converting.
FUNCTION
LLOW*5
A high indicates that the local low-
temperature alarm has activated.
RHIGH*4
A high indicates that the remote high-
temperature alarm has activated.
RLOW*3
A high indicates that the remote low-
temperature alarm has activated.
OPEN*2
A high indicates a remote-diode conti-
nuity (open-circuit) fault.
RFU1
BUSY
7
(MSB)
Reserved for future use (returns 0)
RFU
0
(LSB)
Reserved for future use (returns 0)
BIT NAME
0.12501h 33
30
0.2502h 35
0.503h 48
104h 70
205h 128
406h
0.062500h
225
807h 425
RFU
08h to
FFh
—
DATA
CONVERSION
RATE
(Hz)
AVERAGE SUPPLY
CURRENT
(µA typ, at V
CC
= 3.3V)
