sx8744emstrt Semtech Corporation, sx8744emstrt Datasheet - Page 12

• Manufacturer Part Number: sx8744emstrt
• Description: Precision Diode Digital Temperature For Up To 3 External Sensors
• Manufacturer: Semtech Corporation

3.7. Alarm
Figure 7. Alarm Output Internal Simplified Schematics
The pseudo-open drain output shown in Figure 7 requires a pull-up resistor connected to VDD. It allows connection to a
GPIO, a system shutdown or other thermal management circuitry.
Figure 8. Alarm Output
3.8. Temperature Data Format
Temperature output code from the internal and external sensors are made of 2 bytes. The temperature high byte has an
LSB representing 1ºC and contains the integer part of the temperature while the low byte contains the fractional value with
a resolution of 0.125ºC.
The SX8733 has 2 temperature data formats. By default, the format is binary and the measurement range is from 0ºC to
127ºC. To extend the measurement range to -40ºC to +140ºC, an offset of 64ºC is added to the binary code.
When a conversion is complete, the main temperature register and the extended temperature register are updated
simultaneously. Ensure that no conversions are completed between reading the main register and the extended register,
so that both registers contain the result of the same conversion.
ACS Revision 2.91/February 2010
©2010 Semtech Corp.
ADVANCED COMMUNICATIONS & SENSING
Alarm threshold
Remote or local
temperature
Alarm(1 or 2)
Temperature
VDD
VSS
ALARM
Alarm threshold registers (RegAlarm1 and RegAlarm2) contain the value the user wishes
the alarms to trip on. The alarm data format is the same as the temperature data format
which is set in RegControl (bit TempOffsetMode). In other words, in binary mode alarm
value is set in degree; in offset binary mode alarm is set in with an offset of 64.
The alarm calculation is performed at the end of the temperature sensing cycle.
Therefore, if TempOffsetMode bit or alarm values are changed, a temperature sensor
measurement must be run to update the alarm outputs.
Depending on the selected mode, the chip can have two alarm outputs: Alarm1 and
Alarm2. If the external or internal temperature exceeds or goes under a programmed
temperature threshold, the alarm is activated. Any remote or local sensor may be
selected to trigger Alarm1 and Alarm2.
Over-temperature
Hysteresis
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Time
SX8733/SX8743/SX8744
Precision Diode Digital Temperature
The alarm polarity can be set active low or high
and, the over or under temperature can also be
set with RegAlarmSet register.
To prevent alarm outputs to trig constantly when
the
RegAlarmHyst register holds a hysteresis value.
The alarm remains active while the temperature is
superior to the alarm threshold minus the value
programmed in the RegAlarmHyst register (for a
trig on over-temperature) as described on
Figure 8.
For Up To 3 External Sensors
limit
temperature
is
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