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PDF ADT7481 Data sheet ( Hoja de datos )
| Número de pieza | ADT7481 | |
| Descripción | Dual Channel Temperature Sensor and Overtemperature Alarm | |
| Fabricantes | ON Semiconductor | |
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ADT7481
Dual Channel Temperature
Sensor and Overtemperature
Alarm
The ADT7481 is a 3-channel digital thermometer and under/ over
temperature alarm, intended for use in PCs and thermal management
systems. It can measure its own ambient temperature or the
temperature of two remote thermal diodes. These thermal diodes can
be located in a CPU or GPU, or they can be discrete diode connected
transistors. The ambient temperature, or the temperature of the remote
thermal diode, can be accurately measured to ±1°C. The temperature
measurement range defaults to 0°C to +127°C, compatible with
ADM1032, but can be switched to a wider measurement range from
−64°C to +191°C.
The ADT7481 communicates over a 2-wire serial interface
compatible with System Management Bus (SMBus) standards. The
SMBus address of the ADT7481 is 0x4C. An ADT7481−1 with an
SMBus address of 0x4B is also available.
An ALERT output signals when the on-chip or remote temperature
is outside the programmed limits. The THERM output is a comparator
output that allows, for example, on/off control of a cooling fan. The
ALERT output can be reconfigured as a second THERM output if
required.
Features
• 1 Local and 2 Remote Temperature Sensors
• 0.25°C Resolution/1°C Accuracy on Remote Channels
• 1°C Resolution/1°C Accuracy on Local Channel
• Extended, Switchable Temperature Measurement Range
0°C to 127°C (Default) or −64°C to +191°C
• 2-wire SMBus Serial Interface with SMBus ALERT Support
• Programmable Over/Undertemperature Limits
• Offset Registers for System Calibration
• Up to 2 Overtemperature Fail-Safe THERM Outputs
• Small 10-lead MSOP Package
• 240 mA Operating Current, 5 mA Standby Current
• These Devices are Pb-Free, Halogen Free and are RoHS Compliant
Applications
• Desktop and Notebook Computers
• Industrial Controllers
• Smart Batteries
• Automotive
• Embedded Systems
• Burn-In Applications
• Instrumentation
http://onsemi.com
MSOP−10
CASE 846AC
PIN ASSIGNMENT
VDD 1
D1+ 2
D1− 3
THERM 4
GND 5
10 SCLK
9 SDATA
ADT7481 8 ALERT/THERM2
7 D2+
6 D2−
MARKING DIAGRAM
10
T0x
AYWG
G
1
T0x = Refer to Ordering Info Table
A = Assembly Location
Y = Year
W = Work Week
G = Pb-Free Package
(Note: Microdot may be in either location)
ORDERING INFORMATION
See detailed ordering and shipping information in the package
dimensions section on page 19 of this data sheet.
© Semiconductor Components Industries, LLC, 2014
September, 2014 − Rev. 8
1
Publication Order Number:
ADT7481/D
1 page  
ADT7481
TYPICAL PERFORMANCE CHARACTERISTICS
3.5
DEV 1 DEV 8 DEV 15
3.0 DEV 2 DEV 9 DEV 16
DEV 3 DEV 10 MEAN
2.5 DEV 4 DEV 11 HIGH 4S
DEV 5 DEV 12 LOW 4S
2.0
DEV 6
DEV 7
DEV 13
DEV 14
1.5
1.0
0.5
0
−0.5
−1.0
−50
0 50 100
TEMPERATURE (°C)
150
Figure 3. Local Temperature Error vs. Temperature
3.5
DEV 1 DEV 8 DEV 15
3.0 DEV 2 DEV 9 DEV 16
DEV 3 DEV 10 MEAN
2.5
DEV 4
DEV 5
DEV 11 HIGH 4S
DEV 12 LOW 4S
DEV 6 DEV 13
2.0 DEV 7 DEV 14
1.5
1.0
0.5
0
−0.5
−1.0
−50
0 50 100
TEMPERATURE (°C)
Figure 5. Remote 2 Temperature Error
vs. Temperature
150
0
−2
−4
−6
−8
−10
−12
−14
−16
−18
0
DEV 2
DEV 4
DEV 3
5 10 15 20
CAPACITANCE (nF)
25
Figure 7. Temperature Error vs. D+/D− Capacitance
3.5
DEV 1 DEV 8 DEV 15
3.0 DEV 2 DEV 9 DEV 16
DEV 3 DEV 10 HIGH 4S
2.5 DEV 4 DEV 11 LOW 4S
DEV 5 DEV 12
2.0 DEV 6 DEV 13
DEV 7 DEV 14
1.5
1.0
0.5
0
−0.5
−1.0
−50
0 50 100
TEMPERATURE (°C)
Figure 4. Remote 1 Temperature Error
vs. Temperature
150
10
5
D+ To GND
0
−5
−10
D+ To VCC
−15
−20
−25
1
10
LEAKAGE RESISTANCE (MW)
100
Figure 6. Temperature Error vs. D+/D− Leakage
Resistance
1000
900
800
700
600
500
400
300
200
100
0
0.01
DEV 2BC
DEV 4BC
DEV 3BC
0.1 1
10
CONVERTION RATE (Hz)
Figure 8. Operating Supply Current
vs. Conversion Rate
100
http://onsemi.com
5
5 Page 
ADT7481
Table 13. STATUS REGISTER 2 BIT ASSIGNMENTS
Bit Mnemonic
Function
ALERT
7 Res Reserved for Future Use No
6 Res Reserved for Future Use No
5 Res Reserved for Future Use No
4 R2HIGH 1 when Remote 2 High
Yes
(Note 1)
Temperature Limit Tripped
3 R2LOW 1 when Remote 2 Low
Yes
(Note 1)
Temperature Limit Tripped
2 D2 OPEN 1 when Remote 2 Sensor
(Note 1)
Open Circuit
Yes
1 R2THRM1 1 when Remote 2 THERM
Limit Tripped
No
0
ALERT
1 when ALERT Condition
Exists
No
1. These flags stay high until the status register is read, or they are
reset by POR.
The eight flags that can generate an ALERT are NOR’d
together. When any flag is high, the ALERT interrupt latch
is set and the ALERT output goes low (provided that the
flag(s) is/are not masked out).
Reading the Status 1 register will clear the five flags (Bit 6
through Bit 2) in Status Register 1, provided the error
conditions that caused the flags to be set have gone away.
Reading the Status 2 register will clear the three flags (Bit 4
through Bit 2) in Status Register 2, provided the error
conditions that caused the flags to be set have gone away. A
flag bit can only be reset if the corresponding value register
contains an in-limit measurement, or if the sensor is good.
The ALERT interrupt latch is not reset by reading the
status register. It will be reset when the ALERT output has
been serviced by the master reading the device address,
provided the error condition has gone away and the status
register flag bits have been reset.
When Flag 1 and/or Flag 0 of Status Register 1, or Flag 1
of Status Register 2 are set, the THERM output goes low to
indicate that the temperature measurements are outside the
programmed limits. The THERM output does not need to be
reset, unlike the ALERT output. Once the measurements are
within the limits, the corresponding status register bits are
reset automatically, and the THERM output goes high. The
user may add hysteresis by programming Register 0x21.
The THERM output will be reset only when the temperature
falls below the THERM limit minus hysteresis.
When Pin 8 is configured as THERM2, only the high
temperature limits are relevant. If Flag 6 and Flag 4 of Status
Register 1, or Flag 4 of Status Register 2 are set, the
THERM2 output goes low to indicate that the temperature
measurements are outside the programmed limits. Flag 5
and Flag 3 of Status Register 1, and Flag 3 of Status
Register 2 have no effect on THERM2. The behavior of
THERM2 is otherwise the same as THERM.
Bit 0 of Status Register 2 gets set whenever the ALERT
output is asserted low. Thus, the user need only read Status
Register 2 to determine if the ADT7481 is responsible for
the ALERT. This bit gets reset when the ALERT output gets
reset. If the ALERT output is masked, then this bit is not set.
Offset Register
Offset errors may be introduced into the remote
temperature measurement by clock noise or by the thermal
diode being located away from the hot spot. To achieve the
specified accuracy on this channel, these offsets must be
removed.
The offset values are stored as 10-bit, twos complement
values.
• The Remote 1 offset MSBs are stored in Register 0x11
and the LSBs are stored in Register 0x12 (low byte, left
justified).
• The Remote 2 offset MSBs are stored in Register 0x34
and the LSBs are stored in Register 0x35 (low byte, left
justified). The Remote 2 offset can be written to, or
read from, the Remote 1 offset registers if Bit 3 of the
Configuration 1 register is set to 1. This bit should be
set to 0 (default) to read the Remote 1 offset values.
Only the upper two bits of the LSB registers are used. The
MSB of the MSB offset register is the sign bit. The minimum
offset that can be programmed is −128°C, and the maximum
is +127.75°C. The value in the offset register is added to, or
subtracted from, the measured value of the remote
temperature.
The offset register powers up with a default value of 0°C
and will have no effect unless the user writes a different
value to it.
Table 14. SAMPLE OFFSET REGISTER CODES
Offset Value
0x11/0x34
0x12/0x35
−128°C
−4°C
−1°C
−0.25°C
0°C
+0.25°C
+1°C
+4°C
+127.75°C
1000 0000
1111 1100
1111 1111
1111 1111
0000 0000
0000 0000
0000 0001
0000 0100
0111 1111
00 00 0000
00 00 0000
00 000000
10 00 0000
00 00 0000
01 00 0000
00 00 0000
00 00 0000
11 00 0000
One-shot Register
The one-shot register is used to initiate a conversion and
comparison cycle when the ADT7481 is in standby mode,
after which the device returns to standby. Writing to the
one-shot register address (0x0F) causes the ADT7481 to
perform a conversion and comparison on both the local and
the remote temperature channels. This is not a data register
as such, and it is the write operation to Address 0x0F that
causes the one-shot conversion. The data written to this
address is irrelevant and is not stored. However the ALERT
and THERM outputs are not operational in one-shot mode
and should not be used.
http://onsemi.com
11
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