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ADT7484AARMZ-R7

P1-P3P4-P6P7-P9P10-P12P13-P14
ADT7484A/ADT7486A
http://onsemi.com
7
Product Description
The ADT7484A is a single remote temperature sensor,
and the ADT7486A is a dual temperature sensor for use in
PC applications. The ADT7484A/ADT7486A accurately
measure local and remote temperature and communicate
over a one-wire Simple Serial Transport (SST) bus interface.
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 handheld devices, or
other industrial sensor nets. The ADT7484A/ADT7486A
support SST specification Rev 1.
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
sst_licensing@analog.com or write to Analog Devices,
3550 North First Street, San Jose, CA 95134, Attention:
SST Licensing, M/S B7-24.
ADT7484A/ADT7486A Client Address
The client address for the ADT7484A/ADT7486A is
selected using the address pin. The address pin is connected
to a float detection circuit, which allows the ADT7484A/
ADT7486A to distinguish between three input states: high,
low (GND), and floating. The address range for fixed
address, discoverable devices is 0x48 to 0x50.
Table 6. ADT7484A/ADT7486A SELECTABLE
ADDRESSES
ADD1 ADD0
Address
Selected
Low (GND) Low (GND) 0x48
Low (GND) Float 0x49
Low (GND) High 0x4A
Float Low (GND) 0x4B
Float Float 0x4C
Float High 0x4D
High Low (GND) 0x4E
High Float 0x4F
High High 0x50
Command Summary
Table 7 summarizes the commands supported by the
ADT7484A/ADT7486A devices when directed at the target
address selected by the fixed address pins. It contains the
command name, command code (CC), write data length
(WL), read data length (RL), and a brief description.
Table 7. COMMAND CODE SUMMARY
Command
Command
Code, CC
Write Length,
WL
Read Length, RL Description
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
(ADT7486A only).
GetAllTemps() 0x00 0x01 0x04 (ADT7484A)
0x06 (ADT7486A)
Shows a 4- or 6-byte block of data (ADT7484A:
GetIntTemp, GetExt1Temp; ADT7486A: GetIntTemp,
GetExt1Temp, GetExt2Temp).
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
(ADT7486A only).
GetExt2Offset() 0xe1 0x01 0x02 Shows the offset that the device is using to correct errors
in External Diode 2 (ADT7486A only).
ResetDevice() 0xf6 0x01 0x00 Functional reset. The ADT7484A/ADT7486A also
respond 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.
ADT7484A/ADT7486A
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8
Command Code Details
ADT7484A/ADT7486A Device Identifier Block
The GetDIB() command retrieves the device identifier
block (DIB), which provides information to identify the
capabilities of the ADP7484A/ADT7486A. The data
returned can be in 8- or 16-byte format. The full 16-bytes of
DIB is detailed in Table 8. 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 8.
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.
Table 8. DIB BYTE DETAILS
Byte Name Value Description
0
Device
Capabilities
0xc0 Fixed Address Device
1
Version/
Revision
0x10 Meets Version 1 of
the SST Specification
2, 3 Vendor ID 00x11d4 Contains Company ID
Number in Little
Endian Format
4, 5 Device ID 0x7484
or
0x7486
Contains Device ID
Number in Little
Endian Format
6 Device
Interface
0x01 SST Device
7 Function
Interface
0x00 Reserved
8 Reserved 0x00 Reserved
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
0x50
Dependent on the
State of the Address
Pins
Ping()
The Ping() command verifies if a device is responding at
a particular address. The ADT7484A/ADT7486A show a
valid nonzero FCS in response to the Ping() command when
correctly addressed.
Table 9. PING() COMMAND
Target Address Write Length Read Length FCS
Device Address 0x00 0x00
ResetDevice()
This command resets the register map and conversion
controller. The reset command can be global or directed at
the client address of the ADT7484A/ADT7486A.
Table 10. RESET DEVICE() COMMAND
Target Address
Write
Length
Read
Length
Reset
Command
FCS
Device Address 0x01 0x00 0xf6
GetIntTemp()
The ADT7484A/ADT7486A show 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
ADT7484A/ADT7486A show the temperature of the
remote diode in little endian, 16-bit, twos complement
format. The ADT7484A/ADT7486A show 0x8000 in
response to this command if the external diode is an open or
short circuit.
GetAllTemps()
The ADT7484A shows the local and remote temperatures
in a 4-byte block of data (internal temperature first, followed
by External Temperature 1) in response to a GetAllTemps()
command. The ADT7486A shows the local and remote
temperatures in a 6-byte block of data (internal temperature
first, followed by External Temperature 1 and External
Temperature 2) in response to this command.
SetExtOffset()
This command sets the offset that the ADT7484A/
ADT7486A 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 128C with +0.25C
resolution.
GetExtOffset()
This command causes the ADT7484A/ADT7486A to
show the offset that they are using to correct errors in the
external diode. The offset value is returned in little endian
format, that is, LSB before MSB.
ADT7484A/ADT7486A Response to Unsupported
Commands
A full list of command codes supported by the
ADT7484A/ADT7486A is given in Table 7. The offset
registers (Command Codes 0xe0 and 0xe1) are the only
registers that the user can write to. The other defined
registers are read only. Writing to Register Addresses 0x03
to 0xdf shows a valid FSC, but no action is taken by the
ADT7484A/ADT7486A. The ADT7484A/ADT7486A
show an invalid FSC if the user attempts to write to the
devices between Command Codes 0xe2 to 0xee and no data
is written to the device. These registers are reserved for the
manufacturer’s use only, and no data can be written to the
device via these addresses.
ADT7484A/ADT7486A
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9
Temperature Measurement
The ADT7484A/ADT7486A each have 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 ADT7484A monitors one local and one remote
temperature channel, whereas the ADT7486A 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 11.
Table 11. TEMPERATURE MONITORING SEQUENCE
Channel
Number
Measurement
Conversion
Time (ms)
0 Local Temperature 12
1 Remote Temperature 1 38
2 Remote Temperature 2
(ADT7486A Only)
38
Temperature Measurement Method
A simple method for measuring temperature is to exploit
the negative temperature coefficient of a diode by measuring
the base-emitter voltage (V
BE
) of a transistor operated at
constant current. Unfortunately, this technique requires
calibration to null the effect of the absolute value of V
BE
,
which varies from device to device.
The technique used in the ADT7484A/ADT7486A
measures the change in V
BE
when the device is operated at
three different currents.
Figure 14 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
1,000 pF.
To measure DV
BE
, the operating current through the
sensor is switched between three related currents. Figure 14
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 DV
BE1
, and then between I and
N2 I, giving DV
BE2
. The temperature can then be
calculated using the two DV
BE
measurements. This method
can also cancel the effect of series resistance on the
temperature measurement. The resulting DV
BE
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 DV
BE
. 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.
Figure 14. Signal Conditioning for Remote Diode Temperature Sensors
LOW-PASS FILTER
f
C
= 65 kHz
REMOTE
SENSING
TRANSISTOR
BIAS
DIODE
D+
D−
V
CC
I
BIAS
I N2 I
V
OUT+
V
OUT−
To ADC
C1*
*CAPACITOR C1 IS OPTIONAL. IT SHOULD ONLY BE USED IN NOISY ENVIRONMENTS.
N1 I
P1-P3P4-P6P7-P9P10-P12P13-P14

ADT7484AARMZ-R7

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Manufacturer:
ON Semiconductor
Description:
Board Mount Temperature Sensors DIGITAL TEMP SENSOR W/SST INTERFACE
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