sx8744emstrt Semtech Corporation, sx8744emstrt Datasheet - Page 13

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

1. Offset binary scale temperature values are offset by 64ºC
2. Binary scale returns 0ºC for all temperatures <0ºC
3. Binary scale returns 127ºC for all temperatures >127ºC
4. A diode fault is detected when the temperature ADC hard limits at 0% or 100% pulse density
3.9. Continuous Time Vs. Single Shot
The chip can be operated in 2 distinct modes: continuous time or one-shot.
The one-shot mode performs one temperature measurement of all sensors selected in RegSensor. After completion, it
returns to standby.
In continuous temperature sampling, temperature measurements are taken at regular intervals and the result held in
internal registers accessible by SMBUS. The RegADCRate register controls the sampling time period.
4. Application Note
4.1. Typical Temperature Sensing System With A SX8743
When the remote-sensing diode is a discrete transistor, its collector and base should be connected together. An external
capacitor of 100pF across the PN junction smoothes out external noise interference. The capacitor must be located very
close to the pins.
The ideality factor is a measure of the deviation of the thermal diode from ideal behavior. The chips are trimmed for the
PNP device described in Table 5.
ACS Revision 2.91/February 2010
©2010 Semtech Corp.
ADVANCED COMMUNICATIONS & SENSING
Temperature (ºC)
140 or more
Diode fault
-40 or less
100
127
50
64
0
1
Figure 9. SX8743 Performs Remote Temperature Measurement In Mode 8
HOST
Interface
SMBus
Temperature High Byte
GPIO
0000 0000
0000 0000
0000 0001
0011 0010
0100 0000
0110 0100
0111 1111
0111 1111
1111 1111
Binary
10k
VBUS
ALARM1
ALARM2
10k
2
3
4
10k
10k
7
8
2
6
SMBDAT
SMBCLK
P3
P4
Offset Binary
0001 1000
0100 0000
0100 0001
0111 0010
0000 0000
1010 0100
1011 1111
1100 1100
1111 1111
SX8743
Page 13
VSS
3.3V
VDD
VSS
5
1
4
1
SX8733/SX8743/SX8744
Precision Diode Digital Temperature
P2
P1
3
4
For Up To 3 External Sensors
Temperature (ºC)
100nF
100pF
x.000
x.125
x.250
x.375
x.500
x.625
x.750
x.875
Temperature Low Byte
MMBT3906
www.semtech.com
DATASHEET
Offset Binary
Binary or
0000 0000
0000 0001
0000 0010
0000 0011
0000 0100
0000 0101
0000 0110
0000 0111