ON ADT7488AARMZ-RL Sst digital temperature sensor and voltage monitor Datasheet

ADT7488A
SST Digital Temperature
Sensor and Voltage Monitor
The ADT7488A is a simple digital temperature sensor for use in PC
applications with Simple Serial Transport (SST) interface. It can
monitor its own temperature as well as the temperature of two remote
sensor diodes. It also measures the processor core voltage, VCCP; a
2.5 V supply voltage; and its own supply voltage, VCC. The
ADT7488A is controlled by an SST single 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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MARKING
DIAGRAM
10
Features
•
•
•
•
•
1 On−Chip Temperature Sensor
2 Remote Temperature Sensors
Monitors 3 Voltage Inputs, Including VCC
Simple Serial Transport (SST) Interface
These are Pb−Free Devices
1
T24
AYWG
G
MSOP−10
CASE 846AC
1
T24 = Device Code
A
= Assembly Location
Y
= Year
W = Work Week
G
= Pb−Free Package
(Note: Microdot may be in either location)
Applications
• Personal Computers
• Portable Personal Devices
• Industrial Sensor Nets
PIN ASSIGNMENT
VCC 1
10
SST
GND 2
9
ADD
8
2.5 V
D1– 4
7
VCCP
D2+ 5
6
D2–
D1+ 3
ADT7488A
(Top View)
ORDERING INFORMATION
See detailed ordering and shipping information in the package
dimensions section on page 11 of this data sheet.
ON−CHIP
TEMPERATURE
SENSOR
ADT7488A
OFFSET REGISTERS
D1+
D1–
D2+
D2–
INPUT
ATTENUATORS
AND
ANALOG
MULTIPLEXER
VCCP
2.5 V
DIGITAL MUX
TEMPERATURE
VALUE REGISTERS
VCC
A/D
CONVERTER
VOLTAGE
VALUE REGISTERS
SST INTERFACE
ADDRESS
SELECTION
SST
ADD
GND
Figure 1. Functional Block Diagram
© Semiconductor Components Industries, LLC, 2009
December, 2009 − Rev. 4
1
Publication Order Number:
ADT7488A/D
ADT7488A
ABSOLUTE MAXIMUM RATINGS
Parameter
Supply Voltage (VCC)
Voltage on 2.5 V and VCCP Pins
Rating
Unit
4.0
V
3.6
V
−0.3 to +3.6
V
±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)
Input Current at Any Pin
Storage Temperature Range
Lead Temperature, Soldering
IR Peak Re−flow Temperature
Lead Temperature (10 sec)
260
300
ESD Rating
1500
°C
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.
THERMAL CHARACTERISTICS
Package Type
10−Lead MSOP
NOTE:
qJA
qJC
Unit
206
44
°C/W
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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ADT7488A
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
Power Supply
Supply Voltage, VCC
Undervoltage Lockout Threshold
Average Operating Supply Current, IDD
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
±1.75
°C
Temperature−to−Digital Converter
Remote Sensor Source Current
+1.0
±4.0
Low level
Mid level
High level
Resolution
Series Resistance Cancellation
The ADT7488A cancels 1.5 kW in series with
the remote thermal diode
12
80
204
mA
0.016
°C
1.5
kW
Digital Input (ADD)
2.3
Input High Voltage, VIH
V
Input Low Voltage, VIL
0.8
Input High Current, IIH
VIN = VCC
Input Low Current, IIL
VIN = 0
−1.0
mA
1.0
Pin Capacitance
V
5.0
mA
pF
Analog−to−Digital Converter (Including Multiplexer and Attenuators)
Total Unadjusted Error (TUE)
Differential Non−linearity (DNL)
10 bits
Power Supply Sensitivity
±1.5
%
±1.0
LSB
%/V
±0.1
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
121
Input Resistances
VCCP and 2.5V Channels
80
110
ms
140
kW
Digital I/O (SST Pin)
1.1
Input High Voltage , VIH
V
Input Low Voltage, VIL
0.4
Hysteresis (Note 1)
Between input switching levels
Output High Voltage, VOH
ISOURCE = 6 mA (maximum)
High Impedance State Leakage, ILEAK
Device powered on SST bus;
VSST = 1.1 V, VCC = 3.3 V
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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3
150
1.1
V
mV
1.9
V
±1.0
mA
ADT7488A
ELECTRICAL CHARACTERISTICS TA = TMIN to TMAX, VCC = VMIN to VMAX, unless otherwise noted.
Parameter
Test Conditions/Comments
Min
Typ
Max
Unit
±10
mA
Digital I/O (SST Pin)
High Impedance State Leakage, ILEAK
Device non−powered on SST bus;
VSST = 1.1 V, VCC = 0 V
Signal Noise Immunity, VNOISE
Noise glitches from 10 MHz to 100 MHz;
width up to 50 ns
300
mV
p−p
SST Timing
0.495
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)
See SST Specification Rev 1.0
Stop Time, tSTOP
Device responding to a constant low level
driven by originator
0.75 x
tBIT
0.8 x
tBIT
ms
0.2 x
tBIT
0.25 x
tBIT
0.4 x
tBIT
ms
0.2 x
tBIT
ms
0.5 x
tBIT−M
ms
2 x tBIT
ms
0.4
ms
1.25 x
tBIT
2 x tBIT
Time to Respond After a Reset, tRESET
Response Time to Speed Negotiation
After Powerup
Time after powerup when device can participate
in speed negotiation
500
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.
PIN ASSIGNMENT
Type
Pin No.
Mnemonic
Description
1
VCC
Power supply
3.3 V ±10%. VCC is also monitored through this pin.
2
GND
Ground
Ground Pin.
3
D1+
Analog input
Positive Connection to Remote 1 Temperature Sensor.
4
D1−
Analog input
Negative Connection to Remote 1 Temperature Sensor.
5
D2+
Analog input
Positive Connection to Remote 2 Temperature Sensor.
6
D2−
Analog input
Negative Connection to Remote 2 Temperature Sensor.
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
SST Bidirectional Data Line.
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4
ms
0.6 x
tBIT
Time to Assert SST High for Logic 1,
tSU, HIGH
Hold Time, tHOLD (Note 3)
500
ms
ADT7488A
TYPICAL CHARACTERISTICS
1.55
3.56
3.55
1.50
3.53
1.45
DEV2
3.52
1.40
IDD (mA)
SST O/P (V)
DEV3
3.54
750Ω (~2mA)
270Ω (~5.2mA)
1.35
3.51
3.50
3.49
1.30
3.48
120Ω (~10.6mA)
DEV1
3.47
1.25
3.46
1.20
2.6
2.8
3.0
3.2
3.4
3.45
–45
3.6
–25
–5
15
VCC (V)
Figure 2. SST O/P Level vs. Supply Voltage
55
75
95
115
Figure 3. Supply Current vs. Temperature
7
1.55
6
1.50
5
750Ω (~2mA)
1.45
4
SST O/P (V)
TEMPERATURE ERROR (5C)
35
TEMPERATURE (5C)
HI SPEC (VCC = 3.0 V)
3
2
MEAN (VCC = 3.3 V)
270Ω (~5.2mA)
1.40
1.35
1.30
1
1.25
0
–1
–60
LO SPEC (VCC = 3.6 V)
–40
–20
0
20
40
60
80
100
120
120Ω (~10.6mA)
1.20
–50
140
0
50
100
150
TEMPERATURE (5C)
TEMPERATURE (5C)
Figure 4. Local Temperature Error
Figure 5. SST O/P Level vs. Temperature
3.9
7
6
TEMPERATURE ERROR (5C)
3.7
IDD (mA)
DEV2
DEV3
3.5
DEV1
3.3
3.1
5
4
3
2
HI SPEC (VCC = 3.0 V)
1
0
MEAN (VCC = 3.3 V)
–1
2.9
2.65
2.85
3.05
3.25
3.45
LO SPEC (VCC = 3.6 V)
–2
–60
3.65
VCC (V)
–40
–20
0
20
40
60
80
100
120
TEMPERATURE (5C)
Figure 6. Supply Current vs. Voltage
Figure 7. Remote Temperature Error
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5
140
ADT7488A
TYPICAL CHARACTERISTICS
30
15
D+ TO GND
5
DEV2_EXT2
DEV3_EXT1
DEV3_EXT2
25
TEMPERATURE ERROR (5C)
10
DEV1_EXT1
DEV1_EXT2
DEV2_EXT1
–5
–10
D+ TO VCC
–15
–20
DEV1_EXT1
DEV1_EXT2
DEV2_EXT1
DEV2_EXT2
DEV3_EXT1
DEV3_EXT2
–25
–30
20
100mV
15
60mV
10
5
40mV
0
–35
–40
0
20
40
60
–5
10k
100
80
100k
1M
10M
100M
1G
NOISE FREQUENCY (Hz)
RESISTANCE (MΩ)
Figure 8. Remote Temperature Error vs. PCB
Resistance
Figure 9. Temperature Error vs. Common−Mode
Noise Frequency
0
20
–10
15
TEMPERATURE ERROR (5C)
–20
10
ERROR (5C)
–30
5
125mV
0
EXT2
ć40
EXT1
ć50
–60
50mV
ć70
−5
ć80
–10
10k
100k
1M
10M
100M
–90
1G
0
10
20
30
50
40
CAPACITANCE (nF)
POWER SUPPLY NOISE FREQUENCY (Hz)
Figure 10. Local Temperature Error vs. Power
Supply Noise
Figure 11. Remote Temperature Error vs.
Capacitance Between D1+ and D1−
7
5
40mV
4
TEMPERATURE ERROR (5C)
6
TEMPERATURE ERROR (5C)
ERROR (°C)
0
5
4
3
20mV
2
1
3
2
5
125mV
4
50mV
–1
–2
10mV
0
10k
100k
1M
10M
100M
–3
10k
1G
NOISE FREQUENCY (Hz)
100k
1M
10M
100M
1G
POWER SUPPLY 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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ADT7488A
Product Description
ADT7488A Client Address
The ADT7488A is a temperature− and voltage−monitoring
device. The ADT7488A can monitor the temperature of two
remote sensor diodes, plus its own internal temperature. It can
also monitor up to three voltage channels, including its own
supply voltage.
The client address for the ADT7488A is selected using the
address pin. The address pin is connected to a float detection
circuit, which allows the ADT7488A 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
Simple Serial Transport (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 ADT7488A 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 1. ADT7488A Selectable Addresses
ADD
Address Selected
Low (GND)
0x48
Float
0x49
High
0x4A
Command Summary
Table 2 summarizes the commands supported by the
ADT7488A 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 2. 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.
GetExt1Temp()
0x01
0x01
0x02
Shows the temperature of External Thermal Diode 1.
GetExt2Temp()
0x02
0x01
0x02
Shows the temperature of External Thermal Diode 2.
GetAllTemps()
0x00
0x01
0x06
Returns a 6−byte block of data (GetIntTemp, GetExt1Temp,
GetExt2Temp).
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()
0x12
0x01
0x06
Shows all voltage measurements in a 6−byte block of data
(GetVoltVcc, GetVolt2.5, GetVoltVccp).
SetExt1Offset()
0xe0
0x03
0x00
Sets the offset used to correct errors in External Diode 1.
GetExt1Offset()
0xe0
0x01
0x02
Shows the offset that the device is using to correct errors in
External Diode 1.
SetExt2Offset()
0xe1
0x03
0x00
Sets the offset used to correct errors in External Diode 2.
GetExt2Offset()
0xe1
0x01
0x02
Returns the offset the device is using to correct errors in
External Diode 2.
ResetDevice()
0xf6
0x01
0x00
Functional reset. The ADT7488A 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 3. 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 3. 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.
ADT7488A Device Identifier Block
The GetDIB() command retrieves the device identifier
block (DIB), which provides information to identify the
capabilities of the ADT7488A. The data returned can be in
8− or 16−byte format. The full 16 bytes of DIB is detailed in
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ADT7488A
GetExt2Temp()
Table 3. 16−Byte DIB Details
Byte
Name
Value
Prompted by the GetExt2Temp() command, ADT7488A
shows the temperature of Remote Diode 2 in little endian,
16−bit, twos complement format. The ADT7488A shows
0x8000 in response to this command if the external diode is
an open or short circuit.
Description
0
Device
Capabilities
0xc0
Fixed address
device
1
Version/Revision
0x10
Meets Version 1 of
SST specification
2, 3
Vendor ID
00x11d4
Contains company
ID number in little
endian format
4, 5
Device ID
0x7488
Contains device ID
number in little
endian format
The ADT7488A shows the local and remote temperatures
in a 6−byte block of data (internal temperature first,
followed by External 1 temperature, followed by External 2
temperature) in response to a GetAllTemps() command.
6
Device Interface
0x01
SST device
SetExtOffset()
7
Function
Interface
0x00
Reserved
8
Reserved
0x00
Reserved
9
Reserved
0x00
Reserved
This command sets the offset that the ADT7488A 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.
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
Dependent on the
state of address pin
GetAllTemps()
GetExtOffset()
This command causes the ADT7488A 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.
ADT7488A Response to Unsupported Commands
A full list of command codes supported by the
ADT7488A is given in Table 2. 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 ADT7488A.
The ADT7488A 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.
Ping()
The Ping() command verifies if a device is responding at
a particular address. The ADT7488A shows a valid
non−zero FCS in response to the Ping() command when
correctly addressed.
Table 4. Ping() Command
Target Address
Write Length
Read Length
(Not necessary)
0x00
0x00
FCS
ResetDevice()
This command resets the register map and conversion
controller. The reset command can be global or directed at
the client address of the ADT7488A.
Voltage Measurement
The ADT7488A has two external voltage measurement
channels. It can also measure its own supply voltage, VCC.
Pins 7 and 8 measure the supplies of the 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.
Table 5. ResetDevice() Command
Target Address
Write
Length
Read
Length
Reset
Command
Device Address
0x01
0x00
0xf6
FCS
GetIntTemp()
Analog−to−Digital Converter
The ADT7488A shows the local temperature of the device
in response to the GetIntTemp() command. The data has a
little endian, 16−bit, twos complement format.
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
GetExt1Temp()
Prompted by the GetExt1Temp() command, the
ADT7488A shows the temperature of Remote Diode 1 in
little endian, 16−bit, twos complement format. The
ADT7488A shows 0x8000 in response to this command if
the external diode is an open or short circuit.
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ADT7488A
Temperature Measurement
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 6.
The ADT7488A has three dedicated temperature
measurement channels: one for measuring the temperature
of an on−chip band gap temperature sensor, and two for
measuring the temperature of a remote diode, usually
located in the CPU or GPU.
The ADT7488A monitors one local and two remote
temperature channels. Monitoring of each of the channels is
done in a round−robin sequence. The monitoring sequence
is in the order shown in Table 9.
Table 6. Maximum Reported Input Voltages
Voltage Channel
Full−Scale Voltage
VCC
4.0 V
2.5 V
4.0 V
VCCP
4.0 V
Input Circuitry
Table 9. Temperature Monitoring Sequence
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.
3.3VIN
68kΩ
71kΩ
2.5VIN
30pF
30pF
MUX
35pF
Figure 14. Internal Structure of Analog Inputs
Voltage Measurement Command Codes
The voltage measurement command codes are detailed in
Table 7. 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
0x12 with a read length of 0x06. The data is retrieved in the
order listed in Table 7.
Table 7. Voltage Measurement Command Code
Voltage Channel
Command Code
Returned Data
VCC
0x12
LSB, MSB
2.5 V
0x13
LSB, MSB
VCCP
0x14
LSB, MSB
Voltage Data Format
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 8. Analog−to−Digital Output vs. VIN
Voltage
Conversion
Time (ms)
0
Local temperature
12
1
Remote 1 temperature
38
2
Remote 2 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 ADT7488A 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 biased above
ground by an internal diode at the D1− input. If the sensor is
operating in an extremely noisy environment, C1 can be
added as a noise filter. Its value should not exceed 1000 pF.
To measure DVBE, the operating current through the
sensor is switched between three related currents. Figure 15
shows N1 x I and N2 x I as different multiples of the
current I. The currents through the temperature diode are
switched between I and N1 x I, giving DVBE1, and then
between I and N2 x 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
17.5kΩ
52.5kΩ
Measurement
Temperature Measurement Method
45kΩ
94kΩ
VCCP
Channel
Number
Twos Complement
LSB
MSB
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
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9
ADT7488A
Using Discrete Transistors
rates. Signal conditioning and measurement of the internal
temperature sensor is performed in the same manner.
N1 × I
N2 × I
VDD
IBIAS
I
REMOTE
SENSING
TRANSISTOR
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 ADT7488A 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
D− input.
VOUT+
D1+
C1*
D1–
TO
ADC
BIAS
DIODE
VOUT–
LOW−PASS FILTER
fC = 65kHz
*CAPACITOR C1 IS OPTIONAL.
IT SHOULD ONLY BE USED
IN NOISY ENVIRONMENTS.
Figure 15. Signal Conditioning for Remote Diode
Temperature Sensors
2N3904
NPN
Reading Temperature Measurements
D1–
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 0x06. The command codes and returned data are
described in Table 10.
Command
Code
Internal
0x00
LSB, MSB
External 1
0x01
LSB, MSB
External 2
0x02
LSB, MSB
All Temps
0x00
Internal LSB, internal MSB;
External 1 LSB, External 1 MSB,
External 2 LSB, External 2 MSB
D1–
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:
• Place the ADT7488A 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.
• 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.
• Use wide tracks to minimize inductance and reduce
noise pickup. A 5 mil track minimum width and
spacing is recommended.
Returned Data
The data for temperature is structured to allow values in
the range of ±512°C to be reported. Thus, the temperature
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.
GND
5mil
5mil
Table 11. SST Temperature Data Format
D1+
Twos Complement
LSB
D1+
The ADT7488A shows an external temperature value of
0x8000 if the external diode is an open or short circuit.
SST Temperature Sensor Data Format
Temperature (5C)
ADT7488A
2N3906
PNP
Figure 16. Connections for NPN and PNP Transistors
Table 10. Temperature Channel Command Codes
Temp
Channel
ADT7488A
D1+
5mil
5mil
MSB
−125
1110 0000
1100 0000
−80
1110 1100
0000 0000
−40
1111 0110
−20
1111 1011
0011 1110
−5
1111 1110
1100 0000
D1–
5mil
GND
0000 0000
−1
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
5mil
5mil
Figure 17. Arrangements of Signal Tracks
• 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.
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
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10
ADT7488A
temperature difference. Unless there are two
thermocouples with a big temperature differential
between them, thermocouple voltages should be much
less than 200 mV.
• Place a 0.1 mF bypass capacitor close to the
ADT7488A.
• 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.
• 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 ADT7488A. Leave
the remote end of the shield unconnected to avoid
ground loops.
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.
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 ADT7488A has
temperature offset command codes of 0xe0 and 0xe1
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 ADT7488A. 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 11. 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.
Application Schematic
A typical application circuit for the ADT7488A is shown
in Figure 18. The ADT7488A can be used in conjunction
with the ADP3192 controller to monitor the CPU power.
The result is a complete thermal and power monitor for the
CPU.
Temperature Offset
As CPUs run faster, it is more difficult to avoid high
frequency clocks when routing the D+ and D− tracks around
VCC
2N3905
NPN
ADT7488A
1
VCC
SST 10
2
GND
ADD
9
3
D1+
2.5 V
8
4
D1–
VCCP
7
5
D2+
D2–
6
SST
POWER
MONITORING
R = 1k W
ADP3192 CPU POWER
CONTROLLER
IMON
C = 10nF
VCCP
CPU
DRIVERS
ADP3120A
THERMAL DIODE
Figure 18. ADT7488A Application Schematic: CPU Thermal− and Power−Supply Monitoring
ORDERING INFORMATION
Device Order Number*
ADT7488AARMZ−RL
ADT7488AARMZ−RL7
Package Type
Package Option
10−Lead MSOP
RM−10
Shipping†
3000 Tape & Reel
1000 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.
*These are Pb−Free packages.
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11
ADT7488A
PACKAGE DIMENSIONS
MSOP−10
CASE 486AC−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 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:
Literature Distribution Center for ON Semiconductor
P.O. Box 5163, Denver, Colorado 80217 USA
Phone: 303−675−2175 or 800−344−3860 Toll Free USA/Canada
Fax: 303−675−2176 or 800−344−3867 Toll Free USA/Canada
Email: [email protected]
N. American Technical Support: 800−282−9855 Toll Free
USA/Canada
Europe, Middle East and Africa Technical Support:
Phone: 421 33 790 2910
Japan Customer Focus Center
Phone: 81−3−5773−3850
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12
ON Semiconductor Website: www.onsemi.com
Order Literature: http://www.onsemi.com/orderlit
For additional information, please contact your local
Sales Representative
ADT7488A/D
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