ADT7485A D

ADT7485A
Temperature Sensor and
Voltage Monitor with
Simple Serial Transport
The ADT7485A is a digital temperature sensor and voltage monitor
for use in PC applications with Simple Serial Transport (SST)
interface. It can monitor its own temperature as well as the
temperature of a remote sensor diode. It can also monitor four external
voltage channels and its own supply voltage. The ADT7485A is
controlled by a single SST bidirectional data line. This device is a
fixed-address SST client where the target address is chosen by the
state of the address pin, ADD.
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MSOP−10
CASE 846AC
Features





PIN ASSIGNMENT
1 On-Chip Temperature Sensor
1 Remote Temperature Sensor
Monitors Up to 5.0 Voltages
SST Interface
This Device is Pb-Free, Halogen Free and is RoHS Compliant
Applications
 Personal Computers
 Portable Personal Devices
 Industrial Sensor Nets
VCC
1
GND
2
D1+
3
D1−
12 V
10 SST
9
ADD
8
2.5 V
4
7
VCCP
5
6
5.0 V
ADT7485A
(Top View)
MARKING DIAGRAM
10
ON-CHIP
TEMPERATURE
SENSOR
T21
AYWG
G
OFFSET
REGISTERS
1
12 V
5.0 V
VCCP
2.5 V
D1+
INPUT
ATTENUATORS
AND
ANALOG
MULTIPLEXER
DIGITAL MUX
TEMPERATURE
VALUE REGISTERS
VCC
A/D
CONVERTER
VOLTAGE
VALUE REGISTERS
D1−
T21
A
Y
W
G
SST
INTERFACE
= Specific Device Code
= Assembly Location
= Year
= Work Week
= Pb-Free Package
(Note: Microdot may be in either location)
ADDRESS
SELECTION
ORDERING INFORMATION
ADT7485A
GND
ADD
SST
See detailed ordering and shipping information in the package
dimensions section on page 11 of this data sheet.
Figure 1. Functional Block Diagram
 Semiconductor Components Industries, LLC, 2012
July, 2012 − Rev. 4
1
Publication Order Number:
ADT7485A/D
ADT7485A
Table 1. PIN ASSIGNMENT
Pin No.
Mnemonic
Type
Description
1
VCC
Power Supply
2
GND
Ground
3
D1+
Analog Input
Positive Connection to Remote 1 Temperature Sensor
4
D1−
Analog Input
Negative Connection to Remote 1 Temperature Sensor
5
12 V
Analog Input
12 V Supply Monitor
6
5.0 V
Analog Input
5.0 V Supply Monitor
7
VCCP
Analog Input
Processor Core Voltage Monitor
8
2.5 V
Analog Input
2.5 V Supply Monitor
9
ADD
Digital Input
SST Address Select
10
SST
Digital Input/Output
3.3 V 10%. VCC is also Monitored through this Pin
Ground Pin
SST Bidirectional Data Line
Table 2. ABSOLUTE MAXIMUM RATINGS
Parameter
Rating
Unit
4.0
V
Voltage on 12 V Pin
16
V
Voltage on 5.0 V Pin
7.0
V
Supply Voltage (VCC)
Voltage on 2.5 V and VCCP Pins
3.6
V
−0.3 to +3.6
V
Input Current at Any Pin
5.0
mA
Package Input Current
20
mA
Maximum Junction Temperature (TJ MAX)
150
C
−65 to +150
C
Voltage on Any Other Pin (Including SST Pin)
Storage Temperature Range
Lead Temperature, Soldering
IR Peak Re-flow Temperature
Lead Temperature (10 sec)
C
260
300
ESD Rating
1,500
V
Stresses exceeding Maximum Ratings may damage the device. Maximum Ratings are stress ratings only. Functional operation above the
Recommended Operating Conditions is not implied. Extended exposure to stresses above the Recommended Operating Conditions may affect
device reliability.
NOTE: This device is ESD sensitive. Use standard ESD precautions when handling.
Table 3. THERMAL CHARACTERISTICS (Note 1)
Package Type
10-lead MSOP
qJA
qJC
Unit
206
44
C/W
1. qJA is specified for the worst-case conditions, that is, a device soldered in a circuit board for surface-mount packages.
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ADT7485A
Table 4. ELECTRICAL CHARACTERISTICS
(TA = TMIN to TMAX, VCC = VMIN to VMAX, unless otherwise noted)
Parameter
Test Conditions/Comments
Min
Typ
Max
Unit
3.0
3.3
3.6
V
−
2.8
−
V
Continuous Conversions
−
3.8
5.0
mA
Local Sensor Accuracy
40C  TA  70C; VCC = 3.3 V 5%
−40C  TA  +100C
−
−
+1.0
−
1.75
4.0
C
Remote Sensor Accuracy
−40C  TD  +125C; TA = 25C; VCC = 3.3 V
−40C  TD  +125C; −40  TA  70C;
VCC = 3.3 V 5%
−40C  TD  +125C; −40  TA  +100C
−
−
+1.0
1.0
1.75
C
−
−
4.0
Low Level
Mid Level
High Level
−
−
−
12
80
204
−
−
−
mA
−
0.016
−
C
−
1.5
−
kW
2.3
−
−
V
−
−
0.8
V
−1.0
−
−
mA
−
−
1.0
mA
−
5.0
−
pF
Power Supply
Supply Voltage, VCC
Undervoltage Lockout Threshold
Average Operating Supply
Current, IDD
Temperature-to-Digital Converter
Remote Sensor Source Current
Resolution
Series Resistance Cancellation
The ADT7485A Cancels 1.5 kW in Series
with the Remote Thermal Diode
Digital Input (ADD)
Input High Voltage, VIH
Input Low Voltage, VIL
Input High Current, IIH
VIN = VCC
Input Low Current, IIL
VIN = 0
Pin Capacitance
Analog-to-Digital Converter (Including Multiplexer and Attenuators)
Total Unadjusted Error (TUE)
12 V and 5.0 V Channels
For All Other Channels
−
−
−
−
2.0
1.5
%
Differential Non-linearity (DNL)
10 Bits
−
−
1.0
LSB
Power Supply Sensitivity
−
0.1
−
%/V
Conversion Time (Voltage Input)
(Note 1)
Averaging Enabled
−
−
11
ms
Conversion Time
(Local Temperature) (Note 1)
Averaging Enabled
−
−
12
ms
Conversion Time
(Remote Temperature) (Note 1)
Averaging Enabled
−
−
38
ms
Total Monitoring Cycle Time
(Note 1)
Averaging Enabled
−
145
−
ms
80
95
180
110
120
230
140
150
280
kW
Input Resistances
VCCP and 2.5 V Channels
5.0 V Channel
12 V Channel
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ADT7485A
Table 4. ELECTRICAL CHARACTERISTICS (continued)
(TA = TMIN to TMAX, VCC = VMIN to VMAX, unless otherwise noted)
Parameter
Test Conditions/Comments
Min
Typ
Max
Unit
1.1
−
−
V
−
−
0.4
V
−
150
−
mV
Digital I/O (SST Pin)
Input High Voltage , VIH
Input Low Voltage, VIL
Hysteresis (Note 1)
Between Input Switching Levels
Output High Voltage, VOH
ISOURCE = 6 mA (maximum)
1.1
−
1.9
V
High Impedance State Leakage,
ILEAK
Device Powered On SST Bus;
VSST = 1.1 V, VCC = 3.3 V
−
−
1.0
mA
High Impedance State Leakage,
ILEAK
Device Non-powered On SST Bus;
VSST = 1.1 V, VCC = 0 V
−
−
10
mA
Signal Noise Immunity, VNOISE
Noise Glitches from 10 MHz to 100 MHz;
Width Up to 50 ns
300
−
−
mV
p-p
SST Timing
Bitwise Period, tBIT
High Level Time for Logic 1, tH1
(Note 2)
tBIT Defined in Speed Negotiation
High Level Time for Logic 0, tH0
(Note 2)
Time to Assert SST High for
Logic 1, tSU, HIGH
Hold Time, tHOLD (Note 3)
See SST Specification Rev 1.0
Stop Time, tSTOP
Device Responding to a Constant Low Level
Driven by Originator
Time to Respond After a Reset,
tRESET
Response Time to Speed
Negotiation After Powerup
Time after Powerup when Device Can
Participate in Speed Negotiation
0.495
−
500
ms
0.6  tBIT
0.75  tBIT
0.8  tBIT
ms
0.2  tBIT
0.25  tBIT
0.4  tBIT
ms
−
−
0.2  tBIT
ms
−
−
0.5  tBIT−M
ms
1.25  tBIT
2  tBIT
2  tBIT
ms
−
−
0.4
ms
−
500
−
ms
1. Guaranteed by design, not production tested.
2. Minimum and maximum bit times are relative to tBIT defined in the timing negotiation pulse.
3. Device is compatible with hold time specification as driven by SST originator.
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ADT7485A
TYPICAL PERFORMANCE CHARACTERISTICS
1.55
3.56
3.54
750 W (~2 mA)
1.45
3.53
1.40
IDD (mA)
SST O/P (V)
DEV 3
3.55
1.50
270 W (~5.2 mA)
1.35
1.30
DEV 2
3.52
3.51
3.50
3.49
3.48
120 W (~10.6 mA)
DEV 1
3.47
1.25
3.46
1.20
2.6
2.8
3.0
3.2
3.4
3.45
−45 −25
3.6
−5
VCC (V)
7
1.55
6
1.50
5
HI SPEC (VCC = 3.0 V)
2
MEAN (VCC = 3.3 V)
0
0
20
95
115
1.35
120 W (~10.6 mA)
1.25
40
60
1.20
−50
80 100 120 140
0
50
100
150
TEMPERATURE (C)
TEMPERATURE (C)
Figure 4. Local Temperature Error
Figure 5. SST O/P Level vs. Temperature
3.9
TEMPERATURE ERROR (C)
7
3.7
DEV2
DEV3
IDD (mA)
75
270 W (~5.2 mA)
1.40
1.30
LO SPEC (VCC = 3.6 V)
−1
−60 −40 −20
55
750 W (~2 mA)
1.45
4
3
35
Figure 3. Supply Current vs. Temperature
SST O/P (V)
TEMPERATURE ERROR (C)
Figure 2. SST O/P Level vs. Supply Voltage
1
15
TEMPERATURE (C)
3.5
DEV1
3.3
3.1
2.9
2.65
2.85
3.05
3.25
3.45
6
5
4
3
2
1
0
−1
HI SPEC (VCC = 3.0 V)
MEAN (VCC = 3.3 V)
LO SPEC (VCC = 3.6 V)
−2
−60 −40 −20
3.65
VCC (V)
0
20
40
60
80 100 120 140
TEMPERATURE (C)
Figure 6. Supply Current vs. Voltage
Figure 7. Remote Temperature Error
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ADT7485A
TYPICAL PERFORMANCE CHARACTERISTICS (Cont’d)
30
15
D+ TO GND
5
DEV2_EXT2
DEV3_EXT1
DEV3_EXT2
ERROR (C)
0
−5
−10
−15
DEV1_EXT1
DEV1_EXT2
DEV2_EXT1
D+ TO VCC
−20
DEV2_EXT2
DEV3_EXT1
DEV3_EXT2
−25
−30
20
15
0
20
40
60
80
60 mV
10
5
40 mV
0
−35
−40
100 mV
25
TEMPERATURE ERROR (C)
10
DEV1_EXT1
DEV1_EXT2
DEV2_EXT1
−5
10k
100
100k
Figure 8. Remote Temperature Error vs. PCB
Resistance
−10
15
−20
10
5
125 mV
0
−30
ERROR (C)
TEMPERATURE ERROR (C)
1G
0
EXT2
−40
EXT1
−50
−60
50 mV
−70
−5
−80
100k
1M
10M
100M
−90
1G
0
10
POWER SUPPLY NOISE FREQUENCY (Hz)
20
30
40
50
CAPACITANCE (nF)
Figure 10. Local Temperature Error vs. Power
Supply Noise
Figure 11. Remote Temperature Error vs.
Capacitance Between D1+ and D1−
7
5
40 mV
6
TEMPERATURE ERROR (C)
TEMPERATURE ERROR (C)
100M
Figure 9. Temperature Error vs. Common-Mode
Noise Frequency
20
5
4
3
20 mV
2
1
0
10k
10M
NOISE FREQUENCY (Hz)
RESISTANCE (MW)
−10
10k
1M
10 mV
100k
1M
10M
100M
4
3
2
1
0
50 mV
−1
−2
−3
10k
1G
125 mV
100k
1M
10M
100M
1G
POWER SUPPLY NOISE FREQUENCY (Hz)
NOISE FREQUENCY (Hz)
Figure 12. Temperature Error vs. Differential-Mode
Noise Frequency
Figure 13. Remote Temperature Error vs. Power
Supply Noise
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ADT7485A
Product Description
ADT7485A Client Address
The ADT7485A is a temperature- and voltage-monitoring
device. The ADT7485A can monitor the temperature of one
remote sensor diode, plus its own internal temperature. It can
also monitor up to five voltage channels, including its own
supply voltage.
The client address for the ADT7485A is selected using the
address pin. The address pin is connected to a float detection
circuit, which allows the ADT7485A to distinguish between
three input states: high, low (GND), and floating. The
address range for the fixed address, discoverable device is
0x48 to 0x4A.
SST Interface
SST is a one-wire serial bus and a communications
protocol between components intended for use in personal
computers, personal hand-held devices, or other industrial
sensor nets. The ADT7485A supports SST Rev 1.0.
SST is a licensable bus technology from Analog Devices,
Inc., and Intel Corporation. To inquire about obtaining a
copy of the Simple Serial Transport Specification or an SST
technology license, please email Analog Devices at
[email protected] or write to Analog Devices,
3550 North First Street, San Jose, CA 95134, Attention: SST
Licensing, M/S B7−24.
Table 5. ADT7485A SELECTABLE ADDRESSES
ADD
Address Selected
Low (GND)
0x48
Float
0x49
High
0x4A
Command Summary
Table 6 summarizes the commands supported by the
ADT7485A device when directed at the target address
selected by the fixed address pin. It contains the command
name, command code (CC), write data length (WL), read
data length (RL), and a brief description.
Table 6. COMMAND CODE SUMMARY
Command
Code, CC
Write
Length, WL
Read
Length, RL
Ping()
0x00
0x00
0x00
Shows a nonzero FCS over the header if present.
GetIntTemp()
0x00
0x01
0x02
Shows the temperature of the device’s internal thermal diode.
GetExtTemp()
0x01
0x01
0x02
Shows the temperature of External Thermal Diode.
GetAllTemps()
0x00
0x01
0x04
Returns a 4-byte block of data (GetIntTemp, GetExt1Temp).
GetVolt12V()
0x10
0x01
0x02
Shows the voltage attached to 12 V input.
GetVolt5V()
0x11
0x01
0x02
Shows the voltage attached to 5.0 V input.
GetVoltVCC()
0x12
0x01
0x02
Shows the voltage attached to VCC input.
GetVolt2.5V()
0x13
0x01
0x02
Shows the voltage attached to 2.5 V input.
GetVoltVCCP()
0x14
0x01
0x02
Shows the voltage attached to VCCP input.
GetAllVolts()
0x10
0x01
0x10
Shows all voltage measurement values.
SetExtOffset()
0xe0
0x02
0x00
Sets the offset used to correct errors in External Diode.
GetExtOffset()
0xe0
0x01
0x01
Shows the offset that the device is using to correct errors in
External Diode.
ResetDevice()
0xf6
0x01
0x00
Functional reset. The ADT7485A also responds to this
command when directed to the Target Address 0x00.
GetDIB()
0xf7
0xf7
0x01
0x01
0x08
0x10
Shows information used by SW to identify the device’s
capabilities. Can be in 8- or 16-byte format.
Command
Command Code Details
Description
Table 7. The 8-byte format involves the first eight bytes
described in this table. Byte-sized data is returned in the
respective fields as it appears in Table 7. Word-sized data,
including vendor ID, device ID, and data values use little
endian format, that is, the LSB is returned first, followed by
the MSB.
ADT7485A Device Identifier Block
The GetDIB() command retrieves the device identifier
block (DIB), which provides information to identify the
capabilities of the ADT7485A. The data returned can be in
8- or 16-byte format. The full 16 bytes of DIB is detailed in
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ADT7485A
16-bit, twos complement format. The ADT7485A shows
0x8000 in response to this command if the external diode is
an open or short circuit.
Table 7. 16-BYTE DIB DETAILS
Byte
Name
Value
Description
0
Device
Capabilities
0xc0
Fixed Address
Device
1
Version/Revision
0x10
Meets Version 1 of
SST Specification
GetAllTemps()
2, 3
Vendor ID
00x11d4
Contains Company
ID Number in Little
Endian Format
4, 5
Device ID
0x7485
Contains Device ID
Number in Little
Endian Format
The ADT7485A shows the local and remote temperatures
in a 4-byte block of data (internal temperature first, followed
by external temperature) in response to a GetAllTemps()
command.
SetExtOffset()
6
Device Interface
0x01
SST Device
7
Function
Interface
0x00
Reserved
This command sets the offset that the ADT7485A will use
to correct errors in the external diode. The offset is set in little
endian, 16-bit, twos complement format. The maximum
offset is 128C with +0.25C resolution.
8
Reserved
0x00
Reserved
GetExtOffset()
9
Reserved
0x00
Reserved
10
Reserved
0x00
Reserved
11
Reserved
0x00
Reserved
12
Reserved
0x00
Reserved
13
Reserved
0x00
Reserved
14
Revision ID
0x05
Contains Revision ID
15
Client Device
Address
0x48 to
0x4a
This command causes the ADT7485A to show the offset
that it is using to correct errors in the external diode. The
offset value is returned in little endian format, that is, LSB
before MSB.
ADT7485A Response to Unsupported Commands
A full list of command codes supported by the
ADT7485A is given in Table 6. The offset registers
(Command Code 0xe0) are the only registers that the user
can write to. The other defined registers are read only.
Writing to Register Addresses 0x02, 0x09, and 0x15 to 0xdf
shows a valid FSC, but no action is taken by the ADT7485A.
The ADT7485A shows an invalid FSC if the user attempts
to write to the device between Command Codes 0xe2 to
0xee. These registers are reserved for the manufacturer’s use
only, and no data can be written to the device via these
addresses.
Dependent on the
State of Address
Pin
Ping()
The Ping() command verifies if a device is responding at
a particular address. The ADT7485A shows a valid non-zero
FCS in response to the Ping() command when correctly
addressed.
Table 8. PING() COMMAND
Voltage Measurement
Target Address
Write Length
Read Length
(Not Necessary)
0x00
0x00
FCS
The ADT7485A has four external voltage measurement
channels. It can also measure its own supply voltage, VCC.
Pins 5 and 8 measure the supplies of the 12 V, 5.0 V,
processor core voltage (VCCP), and 2.5 V pins, respectively.
The VCC supply voltage measurement is carried out through
the VCC pin (Pin 1). The 2.5 V pin can be used to monitor a
chip-set supply voltage in a computer system.
ResetDevice()
This command resets the register map and conversion
controller. The reset command can be global or directed at
the client address of the ADT7485A.
Analog-to-Digital Converter
Table 9. RESETDEVICE() COMMAND
Target Address
Write
Length
Read
Length
Reset
Command
Device Address
0x01
0x00
0xf6
All analog inputs are multiplexed into the on-chip,
successive approximation, analog-to-digital converter
(ADC). This has a resolution of 10 bits. The basic input
range is 0 V to 2.25 V, but the inputs have built-in
attenuators to allow measurement of 2.5 V, 3.3 V, 5.0 V,
12 V, and the processor core voltage (VCCP) without any
external components.
To allow for the tolerance of these supply voltages, the
ADC produces a specific output for each nominal input
voltage and therefore has adequate headroom to cope with
overvoltage. The full-scale voltage that can be recorded for
each channel is shown in Table 10.
FCS
GetIntTemp()
The ADT7485A shows the local temperature of the device
in response to the GetIntTemp() command. The data has a
little endian, 16-bit, twos complement format.
GetExtTemp()
Prompted by the GetExtTemp() command, the ADT7485A
shows the temperature of the remote diode in little endian,
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ADT7485A
Voltage Data Format
Table 10. MAXIMUM REPORTED INPUT VOLTAGES
Voltage Channel
Full-scale Voltage
12 V
16 V
5.0 V
8.0 V
VCC
4.0 V
2.5 V
4.0 V
VCCP
4.0 V
The returned voltage value is in twos complement, 16-bit,
binary format. The format is structured so that voltages in
the range of 32 V can be reported. In this way, the reported
value represents the number of 1/1024 V in the actual
reading, allowing a resolution of approximately 1 mV.
Table 12. ANALOG-TO-DIGITAL OUTPUT VS. VIN
Twos Complement
Voltage
Input Circuitry
The internal structure for the analog inputs is shown in
Figure 14. The input circuit consists of an input protection
diode and an attenuator, plus a capacitor that forms a
first-order, low-pass filter to provide input immunity to high
frequency noise.
120 kW
12VIN
20 kW
30 pF
47 kW
71 kW
30 pF
MUX
45 kW
2.5VIN
94 kW
30 pF
0011 0000
0000 0000
0001 0100
0000 0000
3.3
0000 1101
0011 0011
3.0
0000 1100
0000 0000
2.5
0000 1010
0000 0000
1.0
0000 0100
0000 0000
0
0000 0000
0000 0000
Table 13. TEMPERATURE MONITORING SEQUENCE
Channel
Number
17.5 kW
VCCP
12
5.0
The ADT7485A has two dedicated temperature
measurement channels: one for measuring the temperature
of an on-chip band gap temperature sensor, and one for
measuring the temperature of a remote diode, usually
located in the CPU or GPU.
The ADT7485A monitors one local and one remote
temperature channel. Monitoring of each of the channels is
done in a round-robin sequence. The monitoring sequence
is in the order shown in Table 13.
30 pF
68 kW
3.3VIN
LSB
Temperature Measurement
93 kW
5VIN
MSB
52.5 kW
35 pF
The voltage measurement command codes are detailed in
Table 11. Each voltage measurement has a read length of
two bytes in little endian format (LSB followed by MSB).
All voltages can be read together by addressing Command
Code 0x10 with a read length of 0x10. The data is retrieved
in the order listed in Table 11.
Table 11. VOLTAGE MEASUREMENT COMMAND
CODE
Command Code
Returned Data
0x10
LSB, MSB
5.0 V
0x11
LSB, MSB
VCC
0x12
LSB, MSB
2.5 V
0x13
LSB, MSB
VCCP
0x14
LSB, MSB
0
Local Temperature
12
1
Remote 1 Temperature
38
A simple method for measuring temperature is to exploit
the negative temperature coefficient of a diode by measuring
the base-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 ADT7485A measures the
change in VBE when the device is operated at three 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,
which is provided for temperature monitoring on some
microprocessors, but it could also 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 from
interfering with the measurement, the more negative
terminal of the sensor is not referenced to ground, but is
Voltage Measurement Command Codes
12 V
Conversion
Time (ms)
Temperature Measurement Method
Figure 14. Internal Structure of Analog Inputs
Voltage Channel
Measurement
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9
ADT7485A
biased above ground by an internal diode at the D1− input.
If the sensor is operating in an extremely noisy environment,
I
REMOTE
SENSING
TRANSISTOR
N1  I
N2  I
C1 can be added as a noise filter. Its value should not exceed
1,000 pF.
IBIAS
VCC
D1+
VOUT+
C1*
To ADC
D1−
VOUT−
BIAS
DIODE
LOW-PASS FILTER
fC = 65 kHz
*CAPACITOR C1 IS OPTIONAL. IT SHOULD ONLY BE USED IN NOISY ENVIRONMENTS.
Figure 15. Signal Conditioning for Remote Diode Temperature Sensors
To measure DVBE, the operating current through the
sensor is switched between three related currents. Figure 15
shows N1  I and N2  I as different multiples of the
current I. The currents through the temperature diode are
switched between I and N1  I, giving DVBE1, and then
between I and N2  I, giving DVBE2. The temperature can
then be calculated using the two DVBE measurements. This
method can also cancel the effect of series resistance on the
temperature measurement. The resulting DVBE waveforms
are passed through a 65 kHz low-pass filter to remove noise
and then through a chopper-stabilized amplifier to amplify
and rectify the waveform, producing a dc voltage
proportional to DVBE. The ADC digitizes this voltage, and
a temperature measurement is produced. To reduce the
effects of noise, digital filtering is performed by averaging
the results of 16 measurement cycles for low conversion
rates. Signal conditioning and measurement of the internal
temperature sensor is performed in the same manner.
sensor format uses a twos complement, 16-bit binary value
to represent values in this range. This format allows
temperatures to be represented with approximately a
0.016C resolution.
Table 15. SST TEMPERATURE DATA FORMAT
Twos Complement
Temperature (5C)
MSB
LSB
−125
1110 0000
1100 0000
−80
1110 1100
0000 0000
−40
1111 0110
0000 0000
−20
1111 1011
0011 1110
−5
1111 1110
1100 0000
Reading Temperature Measurements
The temperature data returned is two bytes in little endian
format, that is, LSB before MSB. All temperatures can be
read together by using Command Code 0x00 with a read
length of 0x04. The command codes and returned data are
described in Table 14.
Command
Code
Internal
0x00
LSB, MSB
External
0x01
LSB, MSB
All Temps
0x00
Internal LSB, Internal MSB;
External LSB, External MSB
1111 1111
1100 0000
0
0000 0000
0000 0000
+1
0000 0000
0100 0000
+5
0000 0001
0100 0000
+20
0000 0100
1100 0010
+40
0000 1010
0000 0000
+80
0001 0100
0000 0000
+125
0001 1111
0100 0000
Using Discrete Transistors
Table 14. TEMPERATURE CHANNEL COMMAND
CODES
Temp
Channel
−1
If a discrete transistor is used, the collector is not grounded
and should be linked to the base. If a PNP transistor is used,
the base is connected to the D− input and the emitter is
connected to the D+ input. If an NPN transistor is used, the
emitter is connected to the D− input and the base is
connected to the D+ input.
Figure 16 shows how to connect the ADT7485A to an NPN
or PNP transistor for temperature measurement. To prevent
ground noise from 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
D1− input.
Returned Data
SST Temperature Sensor Data Format
The data for temperature is structured to allow values in
the range of 512C to be reported. Thus, the temperature
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10
ADT7485A
5. Thermocouple effects should not be a major
problem because 1C corresponds to about
240 mV, and thermocouple voltages are about
3 mV/C of the temperature difference. Unless
there are two thermocouples with a big
temperature differential between them,
thermocouple voltages should be much less than
200 mV.
6. Place a 0.1 mF bypass capacitor close to the
ADT7485A.
7. If the distance to the remote sensor is more than
eight inches, the use of a twisted pair cable is
recommended. This works for distances of about
6 feet to 12 feet.
8. For very long distances (up to 100 feet), use
shielded twisted pair cables, such as Belden #8451
microphone cables. Connect the twisted pair cable
to D+ and D− and the shield to GND, close to the
ADT7485A. Leave the remote end of the shield
unconnected to avoid ground loops.
ADT7485A
2N3904
NPN
2N3906
PNP
D1+
D1−
ADT7485A
D1+
D1−
Figure 16. Connections for NPN and PNP Transistors
The ADT7485A shows an external temperature value of
0x8000 if the external diode is an open or short circuit.
Layout Considerations
Digital boards can be electrically noisy environments.
Take the following precautions to protect the analog inputs
from noise, particularly when measuring the very small
voltages from a remote diode sensor:
1. Place the ADT7485A 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 four to eight inches.
2. Route the D1+ and D1− tracks close together in
parallel with grounded guard tracks on each side.
Provide a ground plane under the tracks if
possible.
3. Use wide tracks to minimize inductance and
reduce noise pickup. A 5 mil track minimum width
and spacing is recommended.
GND
Because the measurement technique uses switched
current sources, excessive cable and/or filter capacitance
can affect the measurement. When using long cables, the
filter capacitor can be reduced or removed. Cable resistance
can also introduce errors. A 1 W series resistance introduces
about 0.5C error.
Temperature Offset
As CPUs run faster, it is more difficult to avoid high
frequency clocks when routing the D+ and D− tracks around
a system board. Even when the recommended layout
guidelines are followed, there may still be temperature
errors, attributed to noise being coupled onto the D+ and D−
lines. High frequency noise generally has the effect of
producing temperature measurements that are consistently
too high by a specific amount. The ADT7485A has
temperature offset command code of 0xe0 through which a
desired offset can be set. By doing a one-time calibration of
the system, the offset caused by system board noise can be
calculated and nulled by specifying it in the ADT7485A.
The offset is automatically added to every temperature
measurement. The maximum offset is 128C with 0.25C
resolution. The offset format is the same as the temperature
data format; 16-bit, twos complement notation, as shown in
Table 15. The offset should be programmed in little endian
format, that is, LSB before MSB. The offset value is also
returned in little endian format when read.
5 MIL
5 MIL
D1+
5 MIL
5 MIL
5 MIL
D1−
5 MIL
GND
5 MIL
Figure 17. Arrangement of Signal Tracks
4. Try to minimize the number of copper/solder
joints, which can cause thermocouple effects.
Where copper/solder joints are used, make sure
that they are in both the D1+ and D1− paths and
are at the same temperature.
Table 16. ORDERING INFORMATION
Device Order Number*
ADT7485AARMZ−R
Package Type
Package Option
Shipping†
10-lead MSOP
RM−10
3,000 Tape & Reel
†For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging
Specifications Brochure, BRD8011/D.
*This is Pb-Free package.
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11
ADT7485A
PACKAGE DIMENSIONS
MSOP−10
CASE 846AC−01
ISSUE O
NOTES:
1. DIMENSIONING AND TOLERANCING PER
ANSI Y14.5M, 1982.
2. CONTROLLING DIMENSION: MILLIMETER.
3. DIMENSION “A” DOES NOT INCLUDE MOLD
FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE
BURRS SHALL NOT EXCEED 0.15 (0.006)
PER SIDE.
4. DIMENSION “B” DOES NOT INCLUDE
INTERLEAD FLASH OR PROTRUSION.
INTERLEAD FLASH OR PROTRUSION
SHALL NOT EXCEED 0.25 (0.010) PER SIDE.
5. 846B−01 OBSOLETE. NEW STANDARD
846B−02
−A−
−B−
K
D 8 PL
0.08 (0.003)
PIN 1 ID
G
0.038 (0.0015)
−T− SEATING
PLANE
M
T B
S
A
S
C
H
L
J
MILLIMETERS
MIN
MAX
2.90
3.10
2.90
3.10
0.95
1.10
0.20
0.30
0.50 BSC
0.05
0.15
0.10
0.21
4.75
5.05
0.40
0.70
DIM
A
B
C
D
G
H
J
K
L
INCHES
MIN
MAX
0.114
0.122
0.114
0.122
0.037
0.043
0.008
0.012
0.020 BSC
0.002
0.006
0.004
0.008
0.187
0.199
0.016
0.028
SOLDERING FOOTPRINT*
10X
1.04
0.041
0.32
0.0126
3.20
0.126
8X
10X
4.24
0.167
0.50
0.0196
SCALE 8:1
5.28
0.208
mm Ǔ
ǒinches
*For additional information on our Pb-Free strategy and soldering
details, please download the ON Semiconductor Soldering and
Mounting Techniques Reference Manual, SOLDERRM/D.
SST is a licensable bus technology from Analog Devices, Inc., and Intel Corporation.
ON Semiconductor and
are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC owns the rights to a number of patents, trademarks,
copyrights, trade secrets, and other intellectual property. A listing of SCILLC’s product/patent coverage may be accessed at www.onsemi.com/site/pdf/Patent−Marking.pdf. SCILLC
reserves the right to make changes without further notice to any products herein. SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for any
particular purpose, nor does SCILLC assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without
limitation special, consequential or incidental damages. “Typical” parameters which may be provided in SCILLC data sheets and/or specifications can and do vary in different applications
and actual performance may vary over time. All operating parameters, including “Typicals” must be validated for each customer application by customer’s technical experts. SCILLC
does not convey any license under its patent rights nor the rights of others. SCILLC products are not designed, intended, or authorized for use as components in systems intended for
surgical implant into the body, or other applications intended to support or sustain life, or for any other application in which the failure of the SCILLC product could create a situation where
personal injury or death may occur. Should Buyer purchase or use SCILLC products for any such unintended or unauthorized application, Buyer shall indemnify and hold SCILLC and
its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly,
any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that SCILLC was negligent regarding the design or manufacture
of the part. SCILLC is an Equal Opportunity/Affirmative Action Employer. This literature is subject to all applicable copyright laws and is not for resale in any manner.
PUBLICATION ORDERING INFORMATION
LITERATURE FULFILLMENT:
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Phone: 303−675−2175 or 800−344−3860 Toll Free USA/Canada
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ADT7485A/D
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