ADT7483AARQZ-REEL7 [ADI]
Dual Channel Temperature Sensor and Over Temperature Alarm; 双通道温度传感器和超温报警
| 型号： | ADT7483AARQZ-REEL7 |
| 厂家： | 
ADI |
| 描述： | Dual Channel Temperature Sensor and Over Temperature Alarm |
| 文件： | 总24页 (文件大小：502K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
Dual Channel Temperature Sensor
and Over Temperature Alarm
ADT7483A
FEATURES
GENERAL DESCRIPTION
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/under temperature limits
Offset registers for system calibration
Up to 2 overtemperature fail-safe THERM outputs
Small 16-lead QSOP package
The ADT7483A1 is a three-channel digital thermometer and
under/over temperature alarm, intended for use in PCs and
thermal management systems. It can measure the temperature
in two remote locations, for example, the remote thermal diode
in a CPU or GPU, or a discrete diode connected transistor. It can
also measure its own ambient temperature. The temperature of the
remote thermal diode and ambient temperature can be accurately
measured to 1ꢀC. The temperature measurement range defaults to
0ꢀC to 127ꢀC, compatible with ADM1032, but can be switched
to a wider measurement range, from −64ꢀC to +191ꢀC.
240 μA operating current, 5 μA standby current
The ADT7483A communicates over a 2-wire serial interface
compatible with system management bus (SMBus) standards.
The SMBus address is set by the ADD0 and ADD1 pins. As
many as nine different SMBus addresses are possible.
APPLICATIONS
Desktop and notebook computers
Industrial controllers
Smart batteries
ALERT
An
temperature is outside the programmed limits. The
output is a comparator output that allows, for example, on/off
ALERT
output signals when the on-chip or remote
THERM
Automotive
Embedded systems
Burn-in applications
Instrumentation
control of a cooling fan. The
as a second
output can be reconfigured
output, if required.
THERM
FUNCTIONAL BLOCK DIAGRAM
ADDRESS POINTER
REGISTER
ONE-SHOT
REGISTER
CONVERSION RATE
LOCAL TEMPERATURE
THERM LIMIT REGISTER
REGISTER
ON-CHIP TEMP
SENSOR
LOCAL TEMPERATURE
VALUE REGISTER
LOCAL TEMPERATURE
LOW LIMIT REGISTER
3
4
D1+
D1–
LOCAL TEMPERATURE
HIGH LIMIT REGISTER
ANALOG
MUX
11-BIT A-TO-D
CONVERTER
D2+ 12
REMOTE 1 AND 2 TEMP
THERM LIMIT REGISTER
BUSY RUN/STANDBY
11
D2–
REMOTE 1 AND 2 TEMP
VALUE REGISTERS
REMOTE 1 AND 2 TEMP
LOW LIMIT REGISTERS
REMOTE 1 AND 2 TEMP
HIGH LIMIT REGISTERS
REMOTE 1 AND 2 TEMP
OFFSET REGISTERS
CONFIGURATION
REGISTERS
EXTERNAL DIODES OPEN-CIRCUIT
INTERRUPT
MASKING
13
ALERT/THERM2
STATUS REGISTERS
ADT7483A
SMBus INTERFACE
2
6
14
15
5
16
1
V
GND
SDATA SCLK
ADD0 ADD1
DD
THERM
Figure 1.
1 Protected by U.S. Patents 5,195,827, 5,867,012, 5,982,221, 6,097,239, 6,133,753, 6,169,442, other patents pending.
Rev. 0
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rights of third parties that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarks and registeredtrademarks arethe property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
Fax: 781.461.3113
www.analog.com
©2005 Analog Devices, Inc. All rights reserved.
ADT7483A
TABLE OF CONTENTS
Features .............................................................................................. 1
Registers....................................................................................... 11
Serial Bus Interface..................................................................... 16
Addressing the Device............................................................... 16
Applications....................................................................................... 1
General Description......................................................................... 1
Functional Block Diagram .............................................................. 1
Revision History ............................................................................... 2
Specifications..................................................................................... 3
SMBus Timing Specifications..................................................... 4
Absolute Maximum Ratings............................................................ 5
Thermal Characteristics .............................................................. 5
ESD Caution.................................................................................. 5
Pin Configuration and Function Descriptions............................. 6
Typical Performance Characteristics ............................................. 7
Theory of Operation ........................................................................ 9
Temperature Measurement Method .......................................... 9
Temperature Measurement Results.......................................... 10
Temperature Measurement Range ........................................... 10
Temperature Data Format......................................................... 10
ALERT
Output............................................................................ 18
ALERT
Masking the
Output..................................................... 19
Low Power Standby Mode......................................................... 19
Sensor Fault Detection .............................................................. 19
Interrupt System......................................................................... 19
Applications..................................................................................... 21
Noise Filtering............................................................................. 21
Factors Affecting Diode Accuracy........................................... 21
Thermal Inertia and Self-Heating............................................ 21
Layout Considerations............................................................... 22
Application Circuit..................................................................... 22
Outline Dimensions....................................................................... 23
Ordering Guide .......................................................................... 23
REVISION HISTORY
7/05—Revision 0: Initial Version
Rev. 0 | Page 2 of 24
ADT7483A
SPECIFICATIONS
TA = −40ꢀC to +125ꢀC, VDD = 3 V to 3.6 V, unless otherwise noted.
Table 1.
Parameter
Min Typ Max Unit Test Conditions
POWER SUPPLY
Supply Voltage, VDD
Average Operating Supply Current, IDD
3.0
3.30 3.6
240 350
V
μA
μA
V
0.0625 conversions/sec rate1
Standby mode
VDD input, disables ADC, rising edge
5
2.55
30
2.5
1
Undervoltage Lockout Threshold
Power-On-Reset Threshold
TEMPERATURE-TO-DIGITAL CONVERTER2
1
V
Local Sensor Accuracy
°C
0°C ≤ TA ≤ 70°C
0°C ≤ TA ≤ 85°C
−40 ≤ TA ≤ 100°C
1.5 °C
2.5 °C
°C
Resolution
Remote Diode Sensor Accuracy
1
3
1
°C
0°C ≤ TA ≤ 70°C, −55°C ≤ TD ≤ 150°C
1.5 °C
2.5 °C
°C
0°C ≤ TA ≤ 85°C, −55°C ≤ TD3 ≤ 150°C
−40 ≤ TA ≤ 100°C, −55°C ≤ TD3 ≤ +150°C
Resolution
Remote Sensor Source Current3
0.25
233
14
μA
μA
High level
Low level
Conversion Time
73
94
ms
From stop bit to conversion complete (all channels),
one-shot mode with averaging switched on
11
14
ms
One-shot mode with averaging off,
(conversion rate = 16, 32, or 64 conversions/sec)
OPEN-DRAIN DIGITAL OUTPUTS (THERM, ALERT/THERM2)
Output Low Voltage, VOL
High Level Output Leakage Current, IOH
SMBus INTERFACE3, 4
Logic Input High Voltage, VIH, SCLK, SDATA
Logic Input Low Voltage, VIL, SCLK, SDATA
Hysteresis
SDA Output Low Voltage, VOL
Logic Input Current, IIH, IIL
0.4
1
V
μA
IOUT = −6.0 mA
VOUT = VDD
0.1
500
2.1
−1
V
V
mV
V
μA
pF
kHz
ms
μs
0.8
0.4
+1
IOUT = −6.0 mA
SMBus Input Capacitance, SCLK, SDATA
SMBus Clock Frequency
SMBus Timeout5
5
400
32
1
25
User programmable
Master clocking in data
SCLK Falling Edge to SDATA Valid Time
1 See Table 11 for information on other conversion rates.
2 Temperature accuracy guaranteed with averaging enabled.
3 Guaranteed by design, but not production tested.
4 See the SMBus Timing Specifications section for more information.
5 Disabled by default. Instructions to enable it are in the Serial Bus Interface section.
Rev. 0 | Page 3 of 24
ADT7483A
SMBUS TIMING SPECIFICATIONS
Table 2.
Parameter1
Limit at TMIN, TMAX
Unit
Description
fSCLK
tLOW
tHIGH
tR
tF
tSU; STA
tHD; STA
tSU; DAT
tSU; STO
tBUF
400
4.7
4
kHz max
μs min
μs min
μs max
ns max
μs min
μs min
ns min
μs min
μs min
Clock low period, between 10% points
Clock high period, between 90% points
Clock/data rise time
Clock/data fall time
Start condition setup time
Start condition hold time
Data setup time
Stop condition setup time
Bus free time between stop and start conditions
1
300
4.7
4
250
4
2
3
4
4.7
1 Guaranteed by design, but not production tested.
2 Time from 10% of SDATA to 90% of SCLK.
3 Time for 10% or 90% of SDATA to 10% of SCLK.
4 Time for 90% of SCLK to 10% of SDATA.
tR
tF
tHD;STA
tLOW
SCLK
tHIGH
tSU;STA
tHD;STA
tSU;STO
tHD;DAT
tSU;DAT
SDATA
tBUF
STOP START
START
STOP
Figure 2. Serial Bus Timing
Rev. 0 | Page 4 of 24
ADT7483A
ABSOLUTE MAXIMUM RATINGS
Table 3.
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
Parameter
Rating
Positive Supply Voltage (VDD) to GND
D+
D− to GND
SCLK, SDATA, ALERT, THERM
Input Current, SDATA, THERM
Input Current, D−
−0.3 V, +3.6 V
−0.3 V to VDD + 0.3 V
−0.3 V to +0.6 V
−0.3 V to +3.6 V
−1 mA, +50 mA
1 mA
THERMAL CHARACTERISTICS
ESD Rating, All Pins (Human Body Model)
1,500 V
16-lead QSOP package:
θJA = 150ꢀC/W
Maximum Junction Temperature (TJ MAX
Storage Temperature Range
IR Reflow Peak Temperature
)
150°C
−65°C to +150°C
220°C
θJC = 38.8ꢀC/W
IR Reflow Peak Temperature Pb-Free
Lead Temperature (Soldering 10 sec)
260°C
300°C
ESD CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on
the human body and test equipment and can discharge without detection. Although this product features
proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy
electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance
degradation or loss of functionality.
Rev. 0 | Page 5 of 24
ADT7483A
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
ADD1
ADD0
SCLK
SDATA
V
DD
ADT7483A
TOP VIEW
(Not to Scale)
D1+
D1–
ALERT/THERM2
D2+
THERM
GND
D2–
NC
NC
NC
NC
NC = NO CONNECT
Figure 3.16-Lead QSOP Pin Configuration
Table 4. Pin Function Descriptions
Pin No.
Mnemonic
ADD1
VDD
D1+
D1−
Description
1
2
3
4
5
Address 1 Pin. Tri-state input to set the SMBus address.
Positive Supply, 3 V to 3.6 V.
Positive Connection. Connects to the first remote temperature sensor.
Negative Connection. Connects to the first remote temperature sensor.
Open-Drain Output. Turns a fan on/off, or throttles a CPU clock in the event of an overtemperature
condition.
THERM
6
7
GND
NC
Supply Ground Connection.
No Connect.
8
NC
No Connect.
9
NC
No Connect.
10
11
12
13
NC
D2−
D2+
No Connect.
Negative Connection. Connects to the second remote temperature sensor.
Positive Connection. Connects to the second remote temperature sensor.
Open-Drain Logic Output. Used as interrupt or SMBus alert. This may also be configured as a second THERM
output. Requires a pull-up resistor.
ALERT THERM2
/
14
15
16
SDATA
SCLK
ADD0
Logic Input/Output, SMBus Serial Data. Open-drain output. Requires a pull-up resistor.
Logic Input, SMBus Serial Clock. Requires a pull-up resistor.
Address 0 Pin. Tri-state input to set the SMBus address.
Rev. 0 | Page 6 of 24
ADT7483A
TYPICAL PERFORMANCE CHARACTERISTICS
3.5
10
5
DEV 1
DEV 2
DEV 3
DEV 4
DEV 5
DEV 6
DEV 7
DEV 8
DEV 9
DEV 15
DEV 16
MEAN
HIGH 4Σ
LOW 4Σ
3.0
2.5
2.0
1.5
1.0
0.5
0
DEV 10
DEV 11
DEV 12
DEV 13
DEV 14
D+ TO GND
0
–5
D+ TO V
CC
–10
–15
–20
–25
–0.5
–1.0
–50
0
50
100
150
1
10
LEAKAGE RESISTANCE (MΩ)
100
TEMPERATURE (°C)
Figure 4. Local Temperature Error vs. Temperature
Figure 7. Temperature Error vs. D+/D− Leakage Resistance
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
0
–2
–4
–6
–8
DEV 1
DEV 2
DEV 3
DEV 4
DEV 5
DEV 6
DEV 7
DEV 8
DEV 9
DEV 15
DEV 16
HIGH 4Σ
LOW 4Σ
DEV 10
DEV 11
DEV 12
DEV 13
DEV 14
–10
DEV 3
–12
–14
–16
–18
DEV 2
DEV 4
–0.5
–1.0
–50
0
50
100
150
0
5
10
15
20
25
TEMPERATURE (°C)
CAPACITANCE (nF)
Figure 5. Remote 1 Temperature Error vs. Temperature
Figure 8. Temperature Error vs. D+/D− Capacitance
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
1000
900
800
700
600
500
400
300
200
100
0
DEV 8
DEV 9
DEV 15
DEV 16
MEAN
HIGH 4Σ
LOW 4Σ
DEV 1
DEV 2
DEV 3
DEV 4
DEV 5
DEV 6
DEV 7
DEV 2BC
DEV 10
DEV 11
DEV 12
DEV 13
DEV 14
DEV 4BC
DEV 3BC
–0.5
–1.0
–50
0
50
100
150
0.01
0.1
1
10
100
TEMPERATURE (°C)
CONVERTION RATE (Hz)
Figure 6. Remote 2 Temperature Error vs. Temperature
Figure 9. Operating Supply Current vs. Conversion Rate
Rev. 0 | Page 7 of 24
ADT7483A
422
420
418
416
414
412
410
25
20
15
10
5
DEV 2BC
100mV
DEV 3BC
DEV 4BC
50mV
20mV
408
3.0
0
3.1
3.2
3.3
(V)
3.4
3.5
3.6
0
100
200
300
400
500
600
NOISE FREQUENCY (MHz)
V
DD
Figure 13. Temperature Error vs. Common-Mode Noise Frequency
Figure 10. Operating Supply Current vs. Voltage
4.4
4.2
4.0
3.8
3.6
3.4
3.2
3.0
80
70
DEV 2
60
100mV
50
40
30
DEV 3
DEV 4
50mV
20
10
20mV
0
–10
3.0
3.1
3.2
3.3
(V)
3.4
3.5
3.6
0
100
200
300
400
500
600
V
NOISE FREQUENCY (MHz)
DD
Figure 11. Standby Supply Current vs. Voltage
Figure 14. Temperature Error vs. Differential Mode Noise Frequency
35
30
25
20
15
10
5
DEV 2BC
DEV 3BC
DEV 4BC
0
1
10
100
1000
FSCL (kHz)
Figure 12. Standby Supply Current vs. SCLK Frequency
Rev. 0 | Page 8 of 24
ADT7483A
THEORY OF OPERATION
The ADT7483A is a local and 2x remote temperature sensor
and over/under temperature alarm. When the ADT7483A is
operating normally, the on-board ADC operates in a free-
running mode. The analog input multiplexer alternately selects
either the on-chip temperature sensor or one of the remote
temperature sensors to measure its local temperature. The ADC
digitizes these signals, and the results are stored in the local,
Remote 1, and Remote 2 temperature value registers.
emitter voltage (VBE) of a transistor, operated at constant
current. Unfortunately, this technique requires calibration to
null the effect of the absolute value of VBE, which varies from
device to device. The technique used in the ADT7483A is to
measure the change in VBE when the device is operated at two
different currents.
Figure 15 shows the input signal conditioning used to measure
the output of a remote temperature sensor. This figure shows
the remote sensor as a substrate transistor, but it could equally
be a discrete transistor. If a discrete transistor is used, the
collector is not grounded and should be linked to the base. To
prevent ground noise interfering with the measurement, the
more negative terminal of the sensor is not referenced to ground
but is biased above ground by an internal diode at the D− input.
C1 can be optionally added as a noise filter (recommended
maximum value 1,000 pF).
The local and remote measurement results are compared with
THERM
the corresponding high, low, and
temperature limits
stored in on-chip registers. Out-of-limit comparisons generate
flags that are stored in the status register. A result that exceeds
the high temperature limit, the low temperature limit, or a
ALERT
remote diode open circuit causes the
output to assert
temperature limits causes the
ALERT
THERM
output to assert low. The
low. Likewise, exceeding
THERM
output can be
output.
THERM
reprogrammed as a second
To measure ΔVBE, the operating current through the sensor is
switched among two related currents, I and N × I. The currents
through the temperature diode are switched between I and N × I,
giving ΔVBE. The temperature is then calculated using the ΔVBE
measurement.
The limit registers can be programmed, and the device
controlled and configured, via the serial SMBus. The contents
of any register can also be read back via the SMBus.
Control and configuration functions consist of:
The resulting ΔVBE waveforms pass through a 65 kHz low-pass
filter to remove noise and then to a chopper-stabilized
amplifier. This amplifies and rectifies the waveform to produce
a dc voltage proportional to ΔVBE. The ADC digitizes this
voltage and produces a temperature measurement. To reduce
the effects of noise, digital filtering is performed by averaging
the results of 16 measurement cycles for low conversion rates.
At rates of 16, 32, and 64 conversions/second, no digital
averaging takes place.
•
Switching the device between normal operation and
standby mode.
•
•
•
•
Selecting the temperature measurement scale.
ALERT
Masking or enabling the
Switching Pin 13 between
output.
ALERT THERM2
and
.
Selecting the conversion rate.
TEMPERATURE MEASUREMENT METHOD
Signal conditioning and measurement of the local temperature
sensor is performed in the same manner.
A simple method of measuring temperature is to exploit the
negative temperature coefficient of a diode, measuring the base-
V
DD
I
BIAS
I
N × I
V
OUT+
D+
1
TO ADC
C1
REMOTE
SENSING
TRANSISTOR
LPF
fC = 65kHz
D–
V
OUT–
BIAS
DIODE
1
CAPACITOR C1 IS OPTIONAL. IT IS ONLY NECESSARY IN NOISY ENVIRONMENTS. C1 = 1000pF MAX.
Figure 15. Input Signal Conditioning
Rev. 0 | Page 9 of 24
ADT7483A
When reading the full remote temperature value, both the high
and low byte, the two registers should be read LSB first and then
the MSB. This is because reading the LSB will cause the MSB to
be locked until it is read, guaranteeing that the two values read
are a result of the same temperature measurement.
TEMPERATURE MEASUREMENT RESULTS
The results of the local and remote temperature measurements
are stored in the local and remote temperature value registers
and are compared with limits programmed into the local and
remote high and low limit registers.
TEMPERATURE MEASUREMENT RANGE
The local temperature measurement is an 8-bit measurement
with 1ꢀC resolution. The remote temperature measurements are
10-bit measurements, with eight MSBs stored in one register
and two LSBs stored in another register. Table 5 lists the
temperature measurement registers.
The temperature measurement range for both local and remote
measurements is, by default, 0ꢀC to 127ꢀC. However, the
ADT7483A can be operated using an extended temperature
range from −64ꢀC to +191ꢀC. This means, the ADT7483A can
measure the full temperature range of a remote thermal diode,
from −55ꢀC to +150ꢀC. The user can switch between these two
temperature ranges by setting or clearing Bit 2 in the Configura-
tion 1 register. A valid result is available in the next measurement
cycle after changing the temperature range.
Table 5. Register Address for the Temperature Values
Temperature
Channel
MSB Register
Address
LSB Register
Address
Local
Remote 1
Remote 2
0x00
0x01
0x30
N/A
0x10 (2 MSBs)
0x33 (2 MSBs)
In extended temperature mode, the upper and lower temperatures
that can be measured by the ADT7483A are limited by the remote
diode selection. The temperature registers themselves can have
values from −64ꢀC to +191ꢀC. However, most temperature sensing
diodes have a maximum temperature range of −55ꢀC to +150ꢀC.
By setting Bit 3 of the Configuration 1 Register to 1, the
Remote 2 temperature values can be read from the following
register addresses:
Remote 2, MSBs = 0x01
Remote 2, LSBs = 0x10
Note that although both local and remote temperature measure-
ments can be made while the part is in extended temperature
mode, the ADT7483A should not be exposed to temperatures
greater than those specified in theAbsolute Maximum Ratings
section. Further, the device is only guaranteed to operate as
specified at ambient temperatures from −40ꢀC to +120ꢀC.
The above is true only when Bit 3 of the Configuration 1
register is set. To read the Remote 1 temperatures, this bit needs
to be switched back to 0.
Only the two MSBs in the remote temperature low byte are
used. This gives the remote temperature measurement a
resolution of 0.25ꢀC. Table 6 shows the data format for the
remote temperature low byte.
TEMPERATURE DATA FORMAT
The ADT7483A has two temperature data formats. When the
temperature measurement range is from 0ꢀC to 127ꢀC (default),
the temperature data format for both local and remote temperature
results is binary. When the measurement range is in extended
mode, an offset binary data format is used for both local and
remote results. Temperature values in the offset binary data
format are offset by +64. Examples of temperatures in both data
formats are shown in Table 7.
Table 6. Extended Temperature Resolution
(Remote Temperature Low Byte)
Extended Resolution
Remote Temperature Low Byte
0.00°C
0.25°C
0.50°C
0.75°C
0 000 0000
0 100 0000
1 000 0000
1 100 0000
Rev. 0 | Page 10 of 24
ADT7483A
Table 7. Temperature Data Format (Local and Remote Temperature High Byte)
Temperature
Binary
Offset Binary1
0 000 1001
0 100 0000
0 100 0001
0 100 1010
0 101 1001
0 111 0010
1 000 1011
1 010 0100
1 011 1101
1 011 1111
1 101 0110
–55°C
0°C
+1°C
+10°C
0 000 00002
0 000 0000
0 000 0001
0 000 1010
0 001 1001
0 011 0010
0 100 1011
0 110 0100
0 111 1101
0 111 1111
0 111 11113
+25°C
+50°C
+75°C
+100°C
+125°C
+127°C
+150°C
1 Offset binary scale temperature values are offset by +64.
2 Binary scale temperature measurement returns 0 for all temperatures <0°C.
3 Binary scale temperature measurement returns 127 for all temperatures >127°C.
The user may switch between measurement ranges at any time.
Switching the range also switches the data format. The next
temperature result following the switching is reported back to
the register in the new format. However, the contents of the
limit registers do not change. It is up to the user to ensure that
when the data format changes, the limit registers are
reprogrammed as necessary (for more information, see the
Limit Registers section).
power-on without first writing to the address pointer, the value
of the local temperature will be returned, since its register
address is 0x00.
Temperature Value Registers
The ADT7483A has five registers to store the results of local
and remote temperature measurements. These registers can
only be written to by the ADC and can be read by the user over
the SMBus.
REGISTERS
•
•
The local temperature value register is at Address 0x00.
The registers in the ADT7483A are eight bits wide. These
registers are used to store the results of remote and local
temperature measurements, and high and low temperature
limits, and to configure and control the device. A description of
these registers is provided in this section.
The Remote 1 temperature value high byte register is
at Address 0x01, with the Remote 1 low byte register at
Address 0x10.
•
•
The Remote 2 temperature value high byte register is
at Address 0x30, with the Remote 2 low byte register
at Address 0x33.
Address Pointer Register
The address pointer register does not have, nor does it require,
an address because the first byte of every write operation is
automatically written to this register. The data in this first byte
always contains the address of another register on the ADT7483A,
which is stored in the address pointer register. It is to this other
register address that the second byte of a write operation is
written, or to which a subsequent read operation is performed.
The Remote 2 temperature values can be read from
Address 0x01 for the high byte and Address 0x10 for
the low byte if Bit 3 of Configuration Register 1 is set to 1.
•
•
To read the Remote 1 temperature values, Bit 3 of
Configuration Register 1 should be set to 0.
The power-on default value of the address pointer register is
0x00, so if a read operation is performed immediately after
The power-on default for all five registers is 0x00.
Rev. 0 | Page 11 of 24
ADT7483A
Configuration 1 Register
Table 8. Configuration 1 Register (Read Address = 0x03, Write Address = 0x09)
Bit Mnemonic
Function
7
Mask
Setting this bit to 1 masks all ALERTs on the ALERT pin. Default = 0 = ALERT enabled. This applies only if Pin 13
is configured as ALERT, otherwise it has no effect.
6
Mon/STBY
Setting this bit to 1 places the ADT7483A in standby mode, that is, suspends all temperature measurements
ALERT
(ADC). The SMBus remains active and values can be written to, and read from, the registers. THERM and
are also active in standby mode. Changes made to the limit registers in standby mode that affect the THERM or
ALERT outputs will cause these signals to be updated. Default = 0 = temperature monitoring enabled.
5
AL/TH
This bit selects the function of Pin 13. Default = 0 = ALERT. Setting this bit to 1 configures Pin 13 as the
THERM2 pin.
4
3
Reserved
Reserved for future use.
Remote 1/Remote 2 Setting this bit to 1 enables the user to read the Remote 2 values from the Remote 1 registers.
Default = 0 = Remote 1 temperature values and limits are read from these registers. This bit is not lockable.
2
1
0
Temp Range
Setting this bit to 1 enables the extended temperature measurement range (−50°C to +150°C).
Default = 0 = 0°C to +127°C.
Setting this bit to 1 masks ALERTs due to the Remote 1 temperature exceeding a programmed limit.
Mask R1
Default = 0.
Mask R2
Setting this bit to 1 masks ALERTs due to the Remote 2 temperature exceeding a programmed limit.
Default = 0.
Configuration 2 Register
Table 9. Configuration 2 Register (Address = 0x24)
Bit
Mnemonic
Function
7
Lock Bit
Setting this bit to 1 locks all lockable registers to their current values. This prevents settings being
tampered with until the device is powered down. Default = 0.
<6:0>
Reserved
Reserved for future use.
Conversion Rate/Channel Selector Register
This register can be written to and read back over the SMBus.
The default value of this register is 0x07, giving a rate of
8 conversions/second.
The conversion rate/channel selector register is at Address 0x04
for reads, and Address 0x0A for writes. The four LSBs of this
register are used to program the conversion times from 15.5 ms
(Code 0x0A) to 16 seconds (Code 0x00). To program the
ADT7483A to perform continuous measurements, set the
conversion rate register to 0x0B. For example, a conversion rate
of 8 conversions/second means that beginning at 125 ms
intervals, the device performs a conversion on the local and the
remote temperature channels.
Bit 7 in this register can be used to disable averaging of the
temperature measurements. The ADT7483A can be configured
to take temperature measurements of either a single temperature
channel or all temperature channels. Bit 5 and Bit 4 can be used
to specify which temperature channel or channels are measured.
Rev. 0 | Page 12 of 24
ADT7483A
Table 10. Conversion Rate/Channel Selector Register
Bit
Mnemonic
Function
7
Averaging
Setting this bit to 1 disables averaging of the temperature measurements at the slower conversion rates
(averaging cannot take place at the three faster rates, hence, setting this bit has no effect).
Default = 0 = averaging enabled.
6
Reserved
Reserved for future use. Do not write to this bit.
<5:4> Channel
Selector
These bits are used to select the temperature measurement channels.
00 = round robin = default = all channels.
01 = local temperature.
10 = Remote 1 temperature.
11 = Remote 2 temperature.
<3:0> Conversion
Rates
These bits set how often the ADT7483A measures each temperature channel.
Conversions/second
0000 = 0.0625
0001 = 0.125
0010 = 0.25
Time (seconds)
16
8
4
0011 = 0.5
2
0100 = 1
1
0101 = 2
0110 = 4
0111 = 8 = default
1000 = 16
1001 = 32
500 m
250 m
125 m
62.5 m
31.25 m
1010 = continuous measurements
Limit Registers
exceeding either the local limit or remote high limit asserts
THERM2
that applies to both
low. A default hysteresis value of 10ꢀC is provided
THERM
The ADT7483A has three limits for each temperature channel:
THERM
channels. This hysteresis value may
high, low, and
temperature limits for local, Remote 1,
be reprogrammed to any value after power-up using Register
Address 0x21.
and Remote 2 temperature measurements. The remote temperature
high and low limits span two registers each to contain an upper
THERM
and lower byte for each limit. There is also a
hysteresis
It is important to remember that the data format for temperature
limits is the same as the temperature measurement data format.
Thus, if the temperature measurement uses the default (binary),
then the temperature limits also use the binary scale. If the
temperature measurement scale is switched, however, the
temperature limits do not automatically switch. The user must
reprogram the limit registers to the desired value in the correct
data format. For example, if the remote low limit is set at 10ꢀC
and the default binary scale is being used, the limit register
value should be 0000 1010b. If the scale is switched to offset
binary, the value in the low temperature limit register should be
reprogrammed to be 0100 1010b.
register. All limit registers can be written to and read back over
the SMBus. See Table 8 for details of the limit registers’ addresses
and their power-on default values.
ALERT
When Pin 13 is configured as an
output, the high limit
registers perform a > comparison while the low limit registers
perform a ≤ comparison. For example, if the high limit register
is programmed with 80ꢀC, then measuring 81ꢀC will result in
an out-of-limit condition, setting a flag in the status register. If
the low limit register is programmed with 0ꢀC, measuring 0ꢀC
or lower will result in an out-of-limit condition.
THERM
Exceeding either the local or remote
THERM
limit asserts
THERM2
low. When Pin 13 is configured as
,
Rev. 0 | Page 13 of 24
ADT7483A
Status Registers
the master reading the device address, provided the error
condition has gone away and the status register flag bits have
been reset.
The status registers are read-only registers, at Address 0x02
(Status Register 1) and Address 0x23 (Status Register 2). They
contain status information for the ADT7483A.
When Flag 1 and/or Flag 0 of Status Register 1, or Flag 1 of
Table 11. Status Register 1 Bit Assignments
Bit Mnemonic Function
THERM
Status Register 2 are set, the
indicate that the temperature measurements are outside the
THERM
output goes low to
ALERT
7
6
BUSY
LHIGH1
Bit set to 1 when ADC converting
Bit set to 1 when local high
temperature limit tripped
Bit set to 1 when local low
temperature limit tripped
Bit set to 1 when remote 1 high
temperature limit tripped
Bit set to 1 when remote 1 low
temperature limit tripped
Bit set to 1 when remote 1 sensor
open circuit
No
Yes
programmed limits. The
output does not need to be
output. Once the measurements are
within the limits, the corresponding status register bits are
THERM
ALERT
reset, unlike the
5
4
3
2
1
0
LLOW1
Yes
Yes
Yes
Yes
No
No
automatically reset and the
output goes high. The user
may add hysteresis by programming Register 0x21. The
R1HIGH1
R1LOW1
D1 OPEN1
R1THRM1
LTHRM1
THERM
below the
output will be reset only when the temperature falls
THERM
limit minus hysteresis.
THERM2
When Pin 13 is configured as
, only the high
temperature limits are relevant. If Flag 6, Flag 4 of Status
THERM2
THERM
Register 1, or Flag 4 of Status Register 2 are set, the
Bit set to 1 when remote1
limit tripped
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
THERM
Bit set to 1 when local
tripped
limit
1 These flags stay high until the status register is read, or they are reset by POR.
THERM2
THERM2
. The behavior of
is otherwise the same as
THERM
.
Table 12. Status Register 2 Bit Assignments
ALERT
Bit Mnemonic Function
ALERT
output of
Bit 0 of Status Register 2 is set whenever the
7
6
5
4
Res
Res
Res
R2HIGH1
Reserved for future use
Reserved for future use
Reserved for future use
Bit set to 1 when Remote 2 high
temperature limit tripped
Bit set to 1 when Remote 2 low
temperature limit tripped
Bit set to 1 when Remote 2 sensor
open circuit
No
No
No
Yes
the ADT7483A is asserted low. This means that the user need
only read Status Register 2 to determine if the ADT7483A is
ALERT
output is reset. If the
responsible for the
ALERT
. Bit 0 of Status Register 2 is reset
ALERT
output is
when the
masked, then this bit is not set.
3
2
1
0
R2LOW1
D2 OPEN1
R2THRM1
ALERT
Yes
Yes
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.
THERM No
Bit set to 1 when Remote2
limit tripped
ALERT
No
Bit set to 1 when
exists
condition
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 0x12 (low byte, left justified). The Remote 2
offset MSBs are stored in Register 0x34, and the LSBs are stored
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.
1 These flags stay high until the status register is read, or they are reset by POR.
ALERT
interrupt latch is set and
output goes low (provided they are not masked out).
The eight flags that can generate an
ALERT
are NOR’d together,
so if any of them are high, the
ALERT
the
Reading the Status 1 register will clear the five flags, Bit 6 to
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 to 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.
Only the upper 2 bits of the LSB registers are used. The MSB of
the MSB offset registers is the sign bit. The minimum offset that
can be programmed is −128ꢀC, and the maximum is +127.75ꢀC.
The value in the offset register is added or subtracted to the
measured value of the remote temperature.
The offset register powers up with a default value of 0ꢀC and
will have no effect unless the user writes a different value to it.
ALERT
register. It is reset when the
The
interrupt latch is not reset by reading the status
ALERT
output has been serviced by
Rev. 0 | Page 14 of 24
ADT7483A
Table 13. Sample Offset Register Codes
ALERT
Consecutive
The value written to this register determines how many out-of-
ALERT
Register
Offset Value
−128°C
−4°C
0x11/0x34
1000 0000
1111 1100
1111 1111
1111 1111
0000 0000
0000 0000
0000 0001
0000 0100
0111 1111
0x12/0x35
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
limit measurements must occur before an
The default value is that one out-of-limit measurement generates
ALERT
is generated.
−1°C
an
. The maximum value that can be chosen is 4. The
−0.25°C
0°C
purpose of this register is to allow the user to perform some
filtering of the output. This is particularly useful at the fastest
three conversion rates, where no averaging takes place. This
register is at Address 0x22.
+0.25°C
+1°C
+4°C
ALERT
Table 14. Consecutive
Register Bit
+127.75°C
Register
Value
Number of Out-of-Limit
Measurements Required
One-Shot Register
yzax 000x
yzax 001x
yzax 011x
yzax 111x
x = don’t care bit.
1
2
3
4
The one-shot register is used to initiate a conversion and
comparison cycle when the ADT7483A is in standby mode,
after which the device returns to standby. Writing to the one-
shot register address (0x0F) causes the ADT7483A 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.
y = SMBus SCL timeout bit. Default = 0. See the SMBus section for more
information.
z = SMBus SDA timeout bit. Default = 0. See the SMBus section for more
information.
ALERT
a = mask internal
s
Table 15. List of ADT7483A Registers
Read
Write
Address
(Hex)
Address
(Hex)
Mnemonic
Power-On Default
Undefined
0000 0000 (0x00)
0000 0000 (0x00)
0000 0000 (0x00)
Undefined
0000 0000 (0x00)
0000 0111 (0x07)
0101 0101 (0x55) (85°C)
0000 0000 (0x00) (0°C)
0101 0101 (0x55) (85°C)
0101 0101 (0x55) (85°C)
0000 0000 (0x00) (0°C)
0000 0000 (0x00) (0°C)
Comment
Lock
No
No
No
No
N/A
00
01
01
02
03
04
05
06
07
07
08
08
N/A
10
10
11
11
12
12
13
13
14
14
19
19
20
N/A
N/A
N/A
N/A
N/A
09
0A
0B
0C
Address Pointer
Local Temperature Value
Remote 1 Temperature Value High Byte
Remote 2 Temperature Value High Byte
Status Register 1
Bit 3 Conf Reg = 0
Bit 3 Conf Reg = 1
No
Configuration Register 1
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
N/A
No
Conversion Rate/Channel Selector
Local Temperature High Limit
Local Temperature Low Limit
Remote 1 Temp High Limit High Byte
Remote 2 Temp High Limit High Byte
Remote 1 Temp Low Limit High Byte
Remote 2 Temp Low Limit High Byte
One-Shot
Remote 1 Temperature Value Low Byte
Remote 2 Temperature Value Low Byte
Remote 1 Temperature Offset High Byte
Remote 2 Temperature Offset High Byte
Remote 1 Temperature Offset Low Byte
Remote 2 Temperature Offset Low Byte
Remote 1 Temp High Limit Low Byte
Remote 2 Temp High Limit Low Byte
Remote 1 Temp Low Limit Low Byte
Remote 2 Temp Low Limit Low Byte
0D
0D
0E
Bit 3 Conf Reg = 0
Bit 3 Conf Reg = 1
Bit 3 Conf Reg = 0
Bit 3 Conf Reg = 1
0E
0F1
N/A
N/A
11
0000 0000
0000 0000
0000 0000
0000 0000
0000 0000
0000 0000
0000 0000
0000 0000
0000 0000
0000 0000
0101 0101 (0x55) (85°C)
0101 0101 (0x55) (85°C)
0101 0101 (0x55) (85°C)
Bit 3 Conf Reg = 0
Bit 3 Conf Reg = 1
Bit 3 Conf Reg = 0
Bit 3 Conf Reg = 1
Bit 3 Conf Reg = 0
Bit 3 Conf Reg = 1
Bit 3 Conf Reg = 0
Bit 3 Conf Reg = 1
Bit 3 Conf Reg = 0
Bit 3 Conf Reg = 1
Bit 3 Conf Reg = 0
Bit 3 Conf Reg = 1
No
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
11
12
12
13
13
14
14
19
THERM
THERM
Remote 1
Remote 2
Local
Limit
Limit
19
20
THERM
Limit
Rev. 0 | Page 15 of 24
ADT7483A
Read
Write
Address
(Hex)
Address
(Hex)
Mnemonic
Power-On Default
0000 1010 (0x0A) (10°C)
0000 0001 (0x01)
Comment
Lock
Yes
Yes
No
Yes
No
Yes
Yes
No
Yes
Yes
Yes
Yes
Yes
N/A
N/A
21
22
23
24
30
31
32
33
34
35
36
37
39
FE
FF
21
THERM Hysteresis
22
Consecutive ALERT
N/A
24
N/A
31
32
N/A
34
35
36
37
39
Status Register 2
Configuration 2 Register
0000 0000 (0x00)
0000 0000 (0x00)
0000 0000 (0x00)
0101 0101 (0x55) (85°C)
0000 0000 (0x00) (0°C)
0000 0000 (0x00)
0000 0000 (0x00)
0000 0000 (0x00)
0000 0000 (0x00) (0°C)
0000 0000 (0x00) (0°C)
0101 0101 (0x55) (85°C)
0100 0001 (0x41)
Remote 2 Temperature Value High Byte
Remote 2 Temp High Limit High Byte
Remote 2 Temp Low Limit High Byte
Remote 2 Temperature Value Low Byte
Remote 2 Temperature Offset High Byte
Remote 2 Temperature Offset Low Byte
Remote 2 Temp High Limit Low Byte
Remote 2 Temp Low Limit Low Byte
Remote 2 THERM limit
N/A
N/A
Manufacturer ID
Die Revision Code
1001 0100 (0x94)
1 Writing to Address 0F causes the ADT7483A to perform a single measurement. It is not a data register, as such, and it does not matter what data is written to it.
SERIAL BUS INTERFACE
Although only two address pins are provided, these are three-
Control of the ADT7483A is carried out via the serial bus. The
ADT7483A is connected to the serial bus as a slave device,
under the control of a master device.
state, and can be grounded, left unconnected, or tied to VDD, so
that a total of nine different addresses are possible, as shown in
Table 16. It should be noted that the state of the address pins is
only sampled at power-up, so changing them after power-up
has no effect.
The ADT7483A has an SMBus timeout feature. When this is
enabled, the SMBus typically times out after 25 ms of no activity.
However, this feature is not enabled by default. Bit 7 (SCL
Table 16. Device Addresses
timeout bit) of the consecutive
register (Address = 0x22)
ALERT
should be set to enable the SCL timeout. Bit 6 (SDA timeout bit)
of the consecutive register (Address = 0x22) should be set
ADD1
ADD0
Device Address
0011 000
0011 001
0011 010
0101 001
0101 010
0101 011
1001 100
1001 101
1001 110
0
0
0
NC
NC
NC
1
1
1
0
NC
1
0
NC
1
0
NC
1
ALERT
to enable the SDA timeout.
The ADT7483A supports packet error checking (PEC) and its
use is optional. It is triggered by supplying the extra clock for
the PEC byte. The PEC byte is calculated using CRC-8. The
frame check sequence (FCS) conforms to CRC-8 by the
polynomial
C
(
x
= x8 + x2 + x1 +1
)
The serial bus protocol operates as follows:
Consult the SMBus 1.1 specification for more information
(www.smbus.org).
1. The master initiates data transfer by establishing a start
condition, defined as a high-to-low transition on the serial
data line (SDATA), while the serial clock line (SCLK)
remains high. This indicates that an address/data stream
follows. All slave peripherals connected to the serial bus
respond to the start condition and shift in the next eight
ADDRESSING THE DEVICE
Address Pins
In general, every SMBus device has a 7-bit device address
(except for some devices that have extended, 10-bit addresses).
When the master device sends a device address over the bus,
the slave device with that address will respond. The ADT7483A
has two address pins, ADD0 and ADD1, to allow selection of
the device address, so that several ADT7483As can be used on
the same bus, and/or to avoid conflict with other devices.
W
bits, consisting of a 7-bit address (MSB first) plus an R/
bit, which determines the direction of the data transfer,
that is, whether data will be written to, or read from, the
slave device. The peripheral whose address corresponds to
the transmitted address responds by pulling the data line
low during the low period before the ninth clock pulse,
known as the acknowledge bit. All other devices on the bus
Rev. 0 | Page 16 of 24
ADT7483A
pulse, then high during the tenth clock pulse to assert a
stop condition.
now remain idle while the selected device waits for data
W
to be read from or written to it. If the R/ bit is a 0, the
W
master writes to the slave device. If the R/ bit is a 1, the
master reads from the slave device.
Any number of bytes of data may be transferred over the serial
bus in one operation, but it is not possible to mix read and write
in one operation because the type of operation is determined at
the beginning and cannot subsequently be changed without
starting a new operation. For the ADT7483A, write operations
contain either one or two bytes, while read operations contain
one byte.
2. Data is sent over the serial bus in a sequence of nine clock
pulses, eight bits of data followed by an acknowledge bit
from the slave device. Transitions on the data line must
occur during the low period of the clock signal and remain
stable during the high period, since a low-to-high transition
when the clock is high may be interpreted as a stop signal.
The number of data bytes that can be transmitted over the
serial bus in a single read or write operation is limited only
by what the master and slave devices can handle.
To write data to one of the device data registers, or to read data
from it, the address pointer register must be set so that the
correct data register is addressed. The first byte of a write
operation always contains a valid address that is stored in the
address pointer register. If data is to be written to the device, the
write operation contains a second data byte that is written to the
register selected by the address pointer register (see Figure 16).
3. When all data bytes have been read or written, stop
conditions are established. In write mode, the master will
pull the data line high during the tenth clock pulse to assert
a stop condition. In read mode, the master device will
override the acknowledge bit by pulling the data line high
during the low period before the ninth clock pulse. This is
known as no acknowledge. The master will then take the
data line low during the low period before the tenth clock
W
The device address is sent over the bus followed by R/ set
to 0. This is followed by two data bytes. The first data byte is
the address of the internal data register to be written to, which
is stored in the address pointer register. The second data byte is
the data to be written to the internal data register.
1
9
1
9
SCL
D7
D6
D5
D4
D3
D2
D1
D0
0
1
R/W
0
0
1
1
1
SDA
ACK. BY
ADT7483A
ACK. BY
ADT7483A
START BY
MASTER
FRAME 1
FRAME 2
SERIAL BUS ADDRESS BYTE
ADDRESS POINTER REGISTER BYTE
1
9
SCL (CONTINUED)
SDA (CONTINUED)
D7
D6
D5
D4
D3
D2
D1
D0
ACK. BY
ADT7483A
STOP BY
MASTER
FRAME 3
DATA
BYTE
Figure 16. Writing a Register Address to the Address Pointer Register, then Writing Data to the Selected Register
1
9
1
9
SCL
SDA
1
0
0
1
1
0
1
R/W
D7
D6
D5
D4
D3
D2
D1
D0
ACK. BY
ADT7483A
ACK. BY STOP BY
ADT7483A MASTER
START BY
MASTER
FRAME 2
FRAME 1
SERIAL BUS ADDRESS BYTE
ADDRESS POINTER REGISTER BYTE
Figure 17. Writing to the Address Pointer Register Only
Rev. 0 | Page 17 of 24
ADT7483A
1
9
1
9
SCL
1
0
0
1
1
0
1
R/W
D7
D6
D5
D4
D3
D2
D1
D0
SDA
ACK. BY
ADT7483A
ACK. BY STOP BY
MASTER MASTER
START BY
MASTER
FRAME 2
DATA BYTE FROM ADT7483A
FRAME 1
SERIAL BUS ADDRESS BYTE
Figure 18. Reading from a Previously Selected Register
When reading data from a register there are two possibilities:
ALERT
The
processor, or it can be used as an
the SMBus cannot normally signal to the bus master that they
SMBALERT
output can be used as an interrupt signal to a
SMBALERT
. Slave devices on
•
If the address pointer register value of the ADT7483A is
unknown or not the desired value, it is first necessary to set
it to the correct value before data can be read from the
desired data register. This is done by performing a write to
the ADT7483A as before, but only the data byte containing
the register read address is sent, as data is not to be written
to the register (see Figure 17).
want to talk, but the
function allows them to do so.
outputs can be connected to a common
ALERT
One or more
SMBALERT
SMBALERT
line connected to the master. When the
line is pulled low by one of the devices, the
following procedure occurs, as shown in Figure 19.
A read operation is then performed consisting of the serial
MASTER
RECEIVES
SMBALERT
W
bus address, R/ bit set to 1, followed by the data byte
read from the data register (see Figure 18).
ALERT RESPONSE
ADDRESS
DEVICE
ADDRESS
NO
ACK
START
RD ACK
STOP
MASTER SENDS
ARA AND READ
COMMAND
•
If the address pointer register is known to be already at the
desired address, data can be read from the corresponding
data register without first writing to the address pointer
register and the bus transaction shown in Figure 17 can
be omitted.
DEVICE SENDS
ITS ADDRESS
SMBALERT
Figure 19. Use of
SMBALERT
1.
is pulled low.
Notes
2. Master initiates a read operation and sends the alert
response address (ARA = 0001 100). This is a general call
address that must not be used as a specific device address.
•
It is possible to read a data byte from a data register
without first writing to the address pointer register.
However, if the address pointer register is already at the
correct value, it is not possible to write data to a register
without writing to the address pointer register because the
first data byte of a write is always written to the address
pointer register.
ALERT
3. The device whose
output is low responds to the
alert response address, and the master reads its device
address. The device address is seven bits, so an LSB of 1 is
added. The address of the device is now known and it can
be interrogated in the usual way.
•
Remember that some of the ADT7483A registers have
different addresses for read and write operations. The write
address of a register must be written to the address pointer
if data is to be written to that register, but it may not be
possible to read data from that address. The read address
of a register must be written to the address pointer before
data can be read from that register.
ALERT
4. If more than one device’s
output is low, the one
with the lowest device address will have priority, in
accordance with normal SMBus arbitration.
5. Once the ADT7483A has responded to the alert response
address, it will reset its
output, provided that the
ALERT
error condition that caused the
no longer exists. If
ALERT
the
line remains low, the master will send the
SMBALERT
ALERT
OUTPUT
ARA again, and so on, until all devices whose
were low have responded.
outputs
ALERT
ALERT
This is applicable when Pin 13 is configured as an
output. The
ALERT
output goes low whenever an out-of-limit
measurement is detected, or if the remote temperature sensor is
open circuit. It is an open-drain output and requires a pull-up
ALERT
to VDD. Several
outputs can be wire-OR’ed together, so
ALERT
that the common line will go low if one or more of the
outputs goes low.
Rev. 0 | Page 18 of 24
ADT7483A
If a remote sensor is not used with the ADT7483A, then the D+
and D− inputs of the ADT7483A need to be tied together to
prevent the OPEN flag from being continuously set.
MASKING THE ALERT OUTPUT
ALERT
The
output can be masked for local, Remote 1,
Remote 2, or all three channels. This is done by setting the
appropriate mask bits in either the Configuration 1 register
(read address = 0x03, write address = 0x09) or in the
Most temperature sensing diodes have an operating temperature
range of −55ꢀC to +150ꢀC. Above 150ꢀC, they lose their
ALERT
consecutive
register (address = 0x22)
semiconductor characteristics and approximate conductors
instead. This results in a diode short, setting the OPEN flag. The
remote diode in this case no longer gives an accurate temperature
measurement. A read of the temperature result register will give
the last good temperature measurement. The user should be
aware that, while the diode fault is triggered, the temperature
measurement on the remote channels may not be accurate.
ALERT
To mask
s due to local temperature, set Bit 5 of the
ALERT
consecutive
register to 1. Default = 0.
ALERT
To mask
s due to Remote 1 temperature, set Bit 1 of the
Configuration 1 register to 1. Default = 0.
INTERRUPT SYSTEM
ALERT
To mask
s due to Remote 2 temperature, set Bit 0 of the
ALERT
The ADT7483A has two interrupt outputs,
and
Configuration 1 register to 1. Default = 0.
THERM
. Both outputs have different functions and behavior.
ALERT
is maskable and responds to violations of software
ALERT
To mask
s due to any channel, set Bit 7 of the
programmed temperature limits or an open-circuit fault on the
THERM
output that cannot be masked.
Configuration 1 register to 1. Default = 0.
remote diode.
is intended as a fail-safe interrupt
LOW POWER STANDBY MODE
The ADT7483A can be put into low power standby mode by
setting Bit 6 (Mon/STBY bit) of the Configuration 1 register
(read address = 0x03, write address = 0x09) to 1. When Bit 6 is
0, the ADT7483A operates normally. When Bit 6 is 1, the ADC
is inhibited, and any conversion in progress is terminated
without writing the result to the corresponding value register.
If the Remote 1, Remote 2, or local temperature exceeds the
programmed high temperature limits, or equals or exceeds the
ALERT
low temperature limits, the
open-circuit fault on the remote diode also causes
ALERT
output is asserted low. An
ALERT
to
is reset when serviced by a master reading its
assert.
device address, provided the error condition has gone away and
the status register has been reset.
The SMBus is still enabled. Power consumption in the standby
mode is reduced to less than 5 μA.
THERM
Similarly, the
Remote 2, or local temperature exceeds the programmed
THERM THERM
output asserts low if the Remote 1,
When the device is in standby mode, it is still possible to initiate
a one-shot conversion of both channels by writing to the one-
shot register (Address 0x0F), after which the device will return
to standby. It does not matter what is written to the one-shot
register, all data written to it is ignored.
limits. The
normally be equal to or greater than the high temperature
THERM
temperature limits should
limits.
falls back within the (
THERM
is automatically reset when the temperature
THERM
− Hysteresis) limit. The local and
limits are set by default to 85ꢀC. An hysteresis
THERM
It is also possible to write new values to the limit register while
in standby mode. If the values stored in the temperature value
remote
value can be programmed, in which case,
resets when
ALERT
registers are now outside the new limits, an
is
the temperature falls to the limit value minus the hysteresis
value. This applies to both local and remote measurement
channels. The power-on hysteresis default value is 10ꢀC, but this
may be reprogrammed to any value after power-up.
generated, even though the ADT7483A is still in standby.
SENSOR FAULT DETECTION
The ADT7483A has internal sensor fault detection circuitry
located at its D+ input. This circuit can detect situations where
a remote diode is not connected, or is incorrectly connected, to
the ADT7483A. A simple voltage comparator trips if the voltage
at D+ exceeds VDD − 1 V (typical), signifying an open circuit
between D+ and D−. The output of this comparator is checked
when a conversion is initiated. Bit 2 (D1 OPEN flag) of the
Status Register 1 (Address 0x02) is set if a fault is detected on
the Remote 1 channel. Bit 2 (D2 OPEN flag) of the Status
Register 2 (Address 0x23) is set if a fault is detected on the
THERM
The hysteresis loop on the
THERM
can be set up so that when
outputs is useful when
is used for on/off control of a fan. The user’s system
THERM
asserts, a fan can be
THERM
switched on to cool the system. When
the fan can be switched off. Programming an hysteresis value
protects from fan jitter, wherein the temperature hovers around
goes high again,
THERM
the
limit and the fan is constantly being switched.
ALERT
Remote 2 channel. If the
pin is enabled, setting this flag
ALERT
will cause
to assert low.
Rev. 0 | Page 19 of 24
ADT7483A
THERM
THERM Hysteresis
Table 17.
Hysteresis
Pin 13 on the ADT7483A can be configured as either an
ALERT THERM THERM2
will assert low when the temperature exceeds the programmed
local and/or remote high temperature limits. It is reset in the
Binary Representation
0 000 0000
0 000 0001
output or as an additional
output.
0°C
1°C
10°C
0 000 1010
THERM
same manner as
hysteresis value also applies to
THERM THERM2
, and it is not maskable. The programmed
THERM2
. Figure 21 shows how
THERM
ALERT
Figure 20 shows how the
and
outputs operate.
and
methods of cooling the system. In this example, the
THERM THERM2
output
might operate together to implement two
ALERT
SMBALERT
The
output can be used as an
to signal to
THERM2
the host via the SMBus that the temperature has risen. If the
THERM
limits are set lower than the
limits. The
temperature continues to increase, the
output can be
can be used to turn on a fan. If the temperature continues to
used to turn on a fan to cool the system. This method ensures
that there is a fail-safe mechanism to cool the system, without
the need for host intervention.
THERM
THERM
output can
rise and exceeds the
limits, the
provide additional cooling by throttling the CPU.
TEMPERATURE
TEMPERATURE
90°C
100°C
90°C
80°C
70°C
60°C
50°C
40°C
30°C
THERM LIMIT
THERM2 LIMIT
80°C
70°C
60°C
50°C
40°C
THERM LIMIT
THERM LIMIT-HYSTERESIS
HIGH TEMP LIMIT
RESET BY MASTER
1
4
ALERT
THERM
1
4
THERM2
THERM
2
3
3
2
ALERT
THERM
Outputs
Figure 20. Operation of the
and
THERM
THERM2
Figure 21. Operation of the
and
Interrupts
•
•
If the measured temperature exceeds the high temperature
ALERT
THERM2
THERM2
signal
•
•
•
When the
asserts low.
limit is exceeded, the
limit, the
output asserts low.
If the temperature continues to increase and exceeds the
If the temperature continues to increase and exceeds the
THERM THERM
THERM THERM
limit, the
output asserts low. This can
limit, the
output asserts low.
output deasserts (goes high) when the
be used to throttle the CPU clock or switch on a fan.
THERM
The
THERM
•
•
The
temperature falls to
Figure 20, the default hysteresis value of 10ꢀC is shown.
output deasserts (goes high) when the
THERM
temperature falls to
limit minus hysteresis. In
THERM
limit minus hysteresis. In
Figure 21, there is no hysteresis value shown.
•
As the system cools further, and the temperature falls
THERM2
Again, no hysteresis value is shown for
ALERT
The
output deasserts only when the temperature
THERM2
below the
limit, the
signal resets.
THERM2
has fallen below the high temperature limit, and the master
has read the device address and cleared the status register.
.
The temperature measurement can be either the local or the
remote temperature measurement.
Rev. 0 | Page 20 of 24
ADT7483A
APPLICATIONS
NOISE FILTERING
If a discrete transistor is used with the ADT7483A, the best
accuracy is obtained by choosing devices according to the
following criteria:
For temperature sensors operating in noisy environments,
previous practice was to place a capacitor across the D+ and D−
pins to help combat the effects of noise. However, large capacitances
affect the accuracy of the temperature measurement, leading to a
recommended maximum capacitor value of 1,000 pF.
•
Base-emitter voltage greater than 0.25 V at 6 μA, at the
highest operating temperature.
•
Base-emitter voltage less than 0.95 V at 100 μA, at the
lowest operating temperature.
FACTORS AFFECTING DIODE ACCURACY
Remote Sensing Diode
•
•
Base resistance less than 100 Ω.
The ADT7483A is designed to work with substrate transistors
built into processors or with discrete transistors. Substrate
transistors will generally be PNP types with the collector
connected to the substrate. Discrete types can be either a PNP
or NPN transistor connected as a diode (base shorted to
collector). If an NPN transistor is used, the collector and base
are connected to D+ and the emitter to D−. If a PNP transistor
is used, the collector and base are connected to D− and the
emitter to D+.
Small variation in hFE (50 to 150) that indicates tight
control of VBE characteristics.
Transistors such as 2N3904, 2N3906, or equivalents in SOT-23
packages, are suitable devices to use.
THERMAL INERTIA AND SELF-HEATING
Accuracy depends on the temperature of the remote sensing
diode and/or the local temperature sensor being at the same
temperature as that being measured. A number of factors can
affect this. Ideally, the sensor should be in good thermal contact
with the part of the system being measured. If it is not, the
thermal inertia caused by the sensor’s mass causes a lag in the
response of the sensor to a temperature change. In the case of
the remote sensor, this should not be a problem, since it will
either be a substrate transistor in the processor or a small
package device, such as SOT-23, placed in close proximity to it.
To reduce the error due to variations in both substrate and
discrete transistors, the following factors should be taken into
consideration:
•
The ideality factor, nf, of the transistor is a measure of the
deviation of the thermal diode from ideal behavior. The
ADT7483A is trimmed for an nf value of 1.008. Use the
following equation to calculate the error introduced at a
temperature,T (ꢀC) when using a transistor whose nf does
not equal 1.008. Consult the processor data sheet for the nf
values.
The on-chip sensor, however, is often remote from the
processor and only monitors the general ambient temperature
around the package. In practice, the ADT7483A package will be
in electrical, and hence thermal, contact with a PCB and may
also be in a forced airflow. How accurately the temperature of
the board and/or the forced airflow reflects the temperature to
be measured will also affect the accuracy. Self-heating, due to
the power dissipated in the ADT7483A or the remote sensor,
causes the chip temperature of the device or remote sensor to
rise above ambient. However, the current forced through the
remote sensor is so small that self-heating is negligible. In the
case of the ADT7483A, the worst-case condition occurs when
the device is converting at 64 conversions per second while
ΔT =
nf –1.008
/1.008×
273.15 Kelvin+T
To factor this in, write the ΔT value to the offset register. It
is then automatically added to, or subtracted from, the
temperature measurement by the ADT7483A.
•
Some CPU manufacturers specify the high and low current
levels of the substrate transistors. The high current level of
the ADT7483A, IHIGH, is 200 μA, and the low level current,
I
LOW, is 12 μA. If the ADT7483A current levels do not match
the current levels specified by the CPU manufacturer, it may
be necessary to remove an offset. Refer to the CPU data
sheet to determine whether this offset needs to be removed
and how to calculate it. This offset is programmed to the
offset register. It is important to note that if more than one
offset must be considered, program the algebraic sum of
these offsets to the offset register.
ALERT
sinking the maximum current of 1 mA at the
THERM
device is about 4.5 mW. The thermal resistance, θJA, of the
QSOP-16 package is about 150ꢀC/W.
and
output. In this case, the total power dissipation in the
Rev. 0 | Page 21 of 24
ADT7483A
•
Place a 0.1 μF bypass capacitor close to the VDD pin. In
extremely noisy environments, place an input filter
capacitor across D+ and D− close to the ADT7483A. This
capacitance can effect the temperature measurement, so
care must be taken to ensure that any capacitance seen at
D+ and D− is a maximum of 1,000 pF. This maximum
value includes the filter capacitance, plus any cable or stray
capacitance between the pins and the sensor diode.
LAYOUT CONSIDERATIONS
Digital boards can be electrically noisy environments, and the
ADT7483A measures very small voltages from the remote
sensor, so care must be taken to minimize noise induced at the
sensor inputs. Follow these precautions:
•
Place the ADT7483A as close as possible to the remote
sensing diode. Provided that the worst noise sources such
as clock generators, data/address buses, and CRTs are
avoided, this distance can be 4 inches to 8 inches.
•
•
If the distance to the remote sensor is more than 8 inches,
the use of twisted pair cable is recommended. A total of
6 feet to 12 feet is needed.
•
Route the D+ and D– tracks close together, in parallel,
with grounded guard tracks on each side. To minimize
inductance and reduce noise pickup, a 5 mil track width
and spacing is recommended. Provide a ground plane
under the tracks, if possible.
For very long distances (up to 100 feet), use shielded
twisted pair, such as Belden No. 8451 microphone cable.
Connect the twisted pair to D+ and D−, and the shield to
GND close to the ADT7483A. Leave the remote end of the
shield unconnected to avoid ground loops.
5MIL
5MIL
5MIL
5MIL
5MIL
5MIL
5MIL
GND
Because the measurement technique uses switched current
sources, excessive cable or filter capacitance can affect the
measurement. When using long cables, the filter capacitance
can be reduced or removed.
D+
D–
APPLICATION CIRCUIT
Figure 23 shows a typical application circuit for the ADT7483A,
using discrete sensor transistors. The pull-ups on SCLK,
SDATA, and
GND
Figure 22. Typical Arrangement of Signal Tracks
ALERT
are required only if they are not already
provided elsewhere in the system.
•
Minimize the number of copper/solder joints that can cause
thermocouple effects. Where copper/solder joints are used,
make sure that they are in both the D+ and D− path and at
the same temperature.
The SCLK and SDATA pins of the ADT7483A can be interfaced
directly to the SMBus of an I/O controller, such as the Intel® 820
chipset.
Thermocouple effects should not be a major problem as
1ꢀC corresponds to approximately 200 mV, and thermo-
couple voltages are about 3 mV/ꢀC of temperature difference.
Unless there are two thermocouples with a large temperature
differential between them, thermocouple voltages should
be much less than 200 mV.
V
3V TO 3.6V
DD
ADT7483A
D1+
0.1μF
TYP 10kΩ
SCLK
2N3904/06
OR
CPU THERMAL
DIODE
5V OR 12V
SMBUS
CONTROLLER
D1–
SDATA
D2+
ALERT
V
THERM
D2–
DD
ADD0
TYP 10kΩ
FAN ENABLE
ADD1
GND
FAN CONTROL
CIRCUIT
Figure 23. Typical Application Circuit
Rev. 0 | Page 22 of 24
ADT7483A
OUTLINE DIMENSIONS
0.193
BSC
16
1
9
8
0.154
BSC
0.236
BSC
PIN 1
0.069
0.053
0.065
0.049
8°
0°
0.010
0.004
0.025
BSC
0.012
0.008
0.050
0.016
SEATING
PLANE
0.010
0.006
COPLANARITY
0.004
COMPLIANT TO JEDEC STANDARDS MO-137-AB
Figure 24. 16-Lead Shrink Small Outline Package [QSOP]
(RQ-16)
Dimensions shown in inches
ORDERING GUIDE
Model
ADT7483AARQZ1
ADT7483AARQZ-REEL1
ADT7483AARQZ-REEL71
EVAL-ADT7483EB
Operating Temperature Range
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
Package Description
16-Lead QSOP Package
16-Lead QSOP Package
16-Lead QSOP Package
Evaluation Board
Package Option
RQ-16
RQ-16
RQ-16
1Z = Pb-free part.
Rev. 0 | Page 23 of 24
ADT7483A
NOTES
Preliminary Technical Data
©2005 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D05570-0-7/05(0)
Rev. 0 | Page 24 of 24
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