MAX1617 Datasheet, PDF (13/20 Pages) ON Semiconductor – SMBus Temperature Sensor with Internal and External Diode Input

Remote/Local Temperature Sensor
with SMBus Serial Interface
Table 5. Configuration-Byte Bit
Assignments
BIT
7 (MSB)
6
5–0
NAME
MASK
RUN/
STOP
RFU
POR
STATE
0
0
0
FUNCTION
Masks all ALERT inter-
rupts when high.
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.
Reserved for future use
Table 6. Status-Byte Bit Assignments
BIT
7
(MSB)
6
5
4
3
2
1
0
(LSB)
NAME
BUSY
LHIGH*
LLOW*
RHIGH*
RLOW*
OPEN*
RFU
RFU
FUNCTION
A high indicates that the ADC is busy
converting.
A high indicates that the local high-
temperature alarm has activated.
A high indicates that the local low-
temperature alarm has activated.
A high indicates that the remote high-
temperature alarm has activated.
A high indicates that the remote low-
temperature alarm has activated.
A high indicates a remote-diode conti-
nuity (open-circuit) fault.
Reserved for future use (returns 0)
Reserved for future use (returns 0)
*These flags stay high until cleared by POR, or until the status
byte register is read.
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
Table 7. Conversion-Rate Control Byte
DATA
00h
01h
02h
03h
04h
05h
06h
07h
08h to
FFh
CONVERSION
RATE
(Hz)
0.0625
0.125
0.25
0.5
1
2
4
8
RFU
AVERAGE SUPPLY
CURRENT
(µA typ, at V_CC = 3.3V)
30
33
35
48
70
128
225
425
—
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.
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