MAX1618 Datasheet, PDF (10/20 Pages) Maxim Integrated Products – Remote Temperature Sensor with SMBus Serial Interface

Remote Temperature Sensor
with SMBus Serial Interface
above V_CC - 1V (typ) or below V_DXN + 50mv (typ), a
fault is detected and ALERT is asserted. ADC reads
+127°C. Also, if the ADC has an extremely low differen-
tial input voltage, the diode is assumed to be shorted
and a fault is detected. Note that the diode fault is not
checked until a conversion is initiated, so immediately
after power-on reset, the status byte indicates no fault
is present even if the diode path is broken.
ALERT Interrupts
Normally, the ALERT interrupt output signal is latched
and can be cleared only by reading the Alert Response
address. Interrupts are generated in response to T_HIGH
and T_LOW comparisons and when the remote diode is
faulted. The interrupt does not halt automatic conver-
sions; new temperature data continues to be available
over the SMBus interface after ALERT is asserted. The
interrupt output pin is open-drain so the devices can
share a common interrupt line.
The interface responds to the SMBus Alert Response
address, an interrupt pointer return-address feature
(see Alert Response Address section). Before taking
corrective action, always check to ensure that an inter-
rupt is valid by reading the current temperature.
The alert activates only once per crossing of a given
temperature threshold to prevent any re-entrant inter-
rupts. To enable a new interrupt, rewrite the value of the
violated temperature threshold.
Alert Response Address
The SMBus Alert Response interrupt pointer provides
quick fault identification for simple slave devices that
lack the complex, expensive logic needed to be a bus
master. Upon receiving an ALERT interrupt signal, the
host master can broadcast a Receive Byte transmission
to the Alert Response slave address (0001100). Any
slave device that generated an interrupt then attempts
to identify itself by putting its own address on the bus
(Table 2).
The Alert Response can activate several different slave
devices simultaneously, similar to the I²C General Call.
If more than one slave attempts to respond, bus arbitra-
tion rules apply, and the device with the lower address
code wins. The losing device does not generate an
acknowledgement and continues to hold the ALERT
line low until serviced (implies that the host interrupt
input is level sensitive). Successful reading of the alert
response address clears the interrupt latch.
Command Byte Functions
The 8-bit command byte register (Table 3) is the master
index that points to the other registers within the
MAX1618. The register’s POR state is 0000 0001, so a
I²C is a trademark of Philips Corp.
Table 2. Read Format for Alert Response
Address (0001 100)
BIT
NAME
FUNCTION
7
(MSB)
6
5
4
3
2
1
0
(LSB)
ADD7
ADD6
ADD5
ADD4
ADD3
ADD2
ADD1
ADD0
Provide the current MAX1618
slave address that was latched at
POR (Table 6)
Logic 1
Receive Byte transmission (a protocol that lacks the
command byte) that occurs immediately after POR
returns the current remote temperature data.
The one-shot command immediately forces a new con-
version cycle to begin. A new conversion begins in
software standby mode (RUN/STOP bit = high). The
device returns to standby mode after the conversion. If
a conversion is in progress when a one-shot command
is received, the command is ignored. If a one-shot
command is received in autoconvert mode (RUN/STOP
bit = low) between conversions, a new conversion
begins; the conversion rate timer is reset, and the next
automatic conversion takes place after a full delay
elapses.
Configuration Byte Functions
The configuration byte register (Table 4) is used to
mask (disable) interrupts, to put the device in software
standby or thermostat mode, change the polarity of the
alert output (thermostat mode only), and to change the
diode bias current. The lower three bits are internally
driven low (000), making them “don’t care” bits. Write
zeros to these bits. The serial interface can read back
this register’s contents.
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 a fault in the remote diode DXP-DXN
path. After POR, the normal state of all the flag bits is
zero, assuming none of the alarm conditions is present.
The status byte is cleared by any successful read of
the status byte. Note that the ALERT interrupt latch is
not automatically cleared when the status flag bit is
cleared.
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