SX8743 View Datasheet(PDF) - Semtech Corporation
Part Name
Description
View to exact match
SX8743 Datasheet PDF : 24 Pages
| |||
SX8733/SX8743/SX8744
Digital temperature sensor
ADVANCED COMMUNICATIONS & SENSING
DATASHEET
3.7. Alarm
VDD
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.
ALARM 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
VSS
selected to trigger Alarm1 and Alarm2.
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.
Temperature
Alarm threshold
Remote or local
temperature
Alarm(1 or 2)
Hysteresis
Over-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 limit temperature is reached, 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.
Time
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.
Page 12
www.semtech.com
Share Link: 