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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.
Features
1
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10 T21 RYWG G 1
* * * * *
1 On-Chip Temperature Sensor 1 Remote Temperature Sensor Monitors Up to 5.0 Voltages SST Interface This is a Pb-Free Device
MSOP-10 CASE 846AC T21 R Y W G
= Device Code = Assembly Location = Year = Work Week = Pb-Free Package
Applications
(Note: Microdot may be in either location)
* Personal Computers * Portable Personal Devices * Industrial Sensor Nets
PIN ASSIGNMENT
VCC 1 GND 2 D1+ 3 D1- 4 12 V 5
10 9
SST ADD 2.5 V VCCP 5.0 V
ADT7485A
8 7 6
(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
ADT7485A
OFFSET REGISTERS
VCC 12 V 5.0 V VCCP 2.5 V D1+ D1- INPUT ATTENUATORS AND ANALOG MULTIPLEXER
TEMPERATURE VALUE REGISTERS DIGITAL MUX SST INTERFACE SST
A/D CONVERTER
VOLTAGE VALUE REGISTERS
ADDRESS SELECTION
ADD
GND
Figure 1. Functional Block Diagram
(c) Semiconductor Components Industries, LLC, 2010
April, 2010 - Rev. 3
1
Publication Order Number: ADT7485A/D
ADT7485A
ABSOLUTE MAXIMUM RATINGS
Parameter Supply Voltage (VCC) Voltage on 12 V Pin Voltage on 5.0 V Pin Voltage on 2.5 V and VCCP Pins Voltage on Any Other Pin (Including SST Pin) Input Current at Any Pin Package Input Current Maximum Junction Temperature (TJ Max) Storage Temperature Range Lead Temperature, Soldering IR Peak Re-flow Temperature Lead Temperature (10 sec) ESD Rating Rating 4.0 16 7.0 3.6 -0.3 to +3.6 5.0 20 150 -65 to +150 260 300 1500 Unit V V V V V mA mA C C 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 206 qJC 44 Unit C/W
qJA is specified for the worst-case conditions, that is, a device soldered in a circuit board for surface-mount packages.
PIN ASSIGNMENT
Pin No. 1 2 3 4 5 6 7 8 9 10 Mnemonic VCC GND D1+ D1- 12 V 5.0 V VCCP 2.5 V ADD SST Type Power supply Ground Analog input Analog input Analog input Analog input Analog input Analog input Digital input Digital input/output Description 3.3 V 10%. VCC is also monitored through this pin. Ground Pin. Positive Connection to Remote 1 Temperature Sensor. Negative Connection to Remote 1 Temperature Sensor. 12 V Supply Monitor. 5.0 V Supply Monitor. Processor Core Voltage Monitor. 2.5 V Supply Monitor. SST Address Select. SST Bidirectional Data Line.
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ADT7485A
ELECTRICAL CHARACTERISTICS TA = TMIN to TMAX, VCC = VMIN to VMAX, unless otherwise noted.
Parameter Power Supply Supply Voltage, VCC Undervoltage Lockout Threshold Average Operating Supply Current, IDD Temperature-to-Digital Converter Local Sensor Accuracy Remote Sensor Accuracy 40C TA 70C; VCC = 3.3 V 5% -40C TA +100C -40C TD +125C; TA = 25C; VCC = 3.3 V -40C TD +125C; -40 TA 70C; VCC = 3.3 V 5% -40C TD +125C; -40 TA +100C Low level Mid level High level +1.0 1.75 4.0 1.0 1.75 4.0 12 80 204 0.016 The ADT7485A cancels 1.5 kW in series with the remote thermal diode 1.5 mA C C Continuous conversions 3.0 3.3 2.8 3.8 5.0 3.6 V V mA Test Conditions/Comments Min Typ Max Unit
+1.0
Remote Sensor Source Current
Resolution Series Resistance Cancellation Digital Input (ADD) Input High Voltage, VIH Input Low Voltage, VIL Input High Current, IIH Input Low Current, IIL Pin Capacitance Analog-to-Digital Converter (Including Multiplexer and Attenuators) Total Unadjusted Error (TUE) Differential Non-linearity (DNL) Power Supply Sensitivity Conversion Time (Voltage Input) (Note 1) Conversion Time (Local Temperature) (Note 1) Conversion Time (Remote Temperature) (Note 1) Total Monitoring Cycle Time (Note 1) Input Resistances VCCP and 2.5V Channels 5.0 V Channel 12 V Channel Digital I/O (SST Pin) Input High Voltage , VIH Input Low Voltage, VIL Hysteresis (Note 1) Output High Voltage, VOH Between input switching levels ISOURCE = 6 mA (maximum) 1.1 1.1 Averaging enabled Averaging enabled Averaging enabled Averaging enabled 80 95 180 12 V and 5.0 V channels For all other channels 10 bits VIN = VCC VIN = 0 -1.0 2.3
C kW
V 0.8 V mA 1.0 5.0 mA pF
2.0 1.5 1.0 0.1 11 12 38 145 110 120 230 140 150 280
% LSB %/V ms ms ms ms kW
V 0.4 150 1.9 V mV 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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ADT7485A
ELECTRICAL CHARACTERISTICS TA = TMIN to TMAX, VCC = VMIN to VMAX, unless otherwise noted.
Parameter Digital I/O (SST Pin) High Impedance State Leakage, ILEAK High Impedance State Leakage, ILEAK Signal Noise Immunity, VNOISE SST Timing Bitwise Period, tBIT High Level Time for Logic 1, tH1 (Note 2) High Level Time for Logic 0, tH0 (Note 2) Time to Assert SST High for Logic 1, tSU, HIGH Hold Time, tHOLD (Note 3) Stop Time, tSTOP 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 See SST Specification Rev 1.0 Device responding to a constant low level driven by originator 1.25 x tBIT 2 x tBIT tBIT defined in speed negotiation 0.495 0.6 x tBIT 0.2 x tBIT 0.75 x tBIT 0.25 x tBIT 500 0.8 x tBIT 0.4 x tBIT 0.2 x tBIT 0.5 x tBIT-M 2 x tBIT 0.4 ms ms ms ms ms ms ms ms Device powered on SST bus; VSST = 1.1 V, VCC = 3.3 V Device non-powered on SST bus; VSST = 1.1 V, VCC = 0 V Noise glitches from 10 MHz to 100 MHz; width up to 50 ns 300 1.0 10 mA mA mV p-p Test Conditions/Comments Min Typ Max Unit
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 CHARACTERISTICS
1.55 1.50 750 (~2mA) 1.45 SST O/P (V) 1.40 270 (~5.2mA) 1.35 1.30 1.25 1.20 2.6 3.56 3.55 3.54 3.53 3.52 IDD (mA) 3.51 3.50 3.49 120 (~10.6mA) 3.48 3.47 3.46 2.8 3.0 3.2 VCC (V) 3.4 3.6 3.45 -45 -25 -5 15 35 55 75 95 115 DEV1 DEV2 DEV3
TEMPERATURE (5C)
Figure 2. SST O/P Level vs. Supply Voltage
Figure 3. Supply Current vs. Temperature
7 6 TEMPERATURE ERROR (5C) 5 4 3 2 1 0 -1 -60 LO SPEC (VCC = 3.6 V) -40 -20 0 20 40 60 80 100 120 140 TEMPERATURE (5C) HI SPEC (VCC = 3.0 V) MEAN (VCC = 3.3 V)
1.55 1.50 1.45 SST O/P (V) 270 (~5.2mA) 1.40 1.35 1.30 1.25 1.20 -50 120 (~10.6mA) 750 (~2mA)
0
50 TEMPERATURE (5C)
100
150
Figure 4. Local Temperature Error
Figure 5. SST O/P Level vs. Temperature
3.9
7 6 TEMPERATURE ERROR (5C)
3.7 DEV2 3.5 DEV3 DEV1 3.3
5 4 3 2 1 0 -1 MEAN (VCC = 3.3 V) HI SPEC (VCC = 3.0 V)
IDD (mA)
3.1
2.9 2.65
LO SPEC (VCC = 3.6 V) -40 -20 0 20 40 60 80 100 120 140
2.85
3.05 VCC (V)
3.25
3.45
3.65
-2 -60
TEMPERATURE (5C)
Figure 6. Supply Current vs. Voltage http://onsemi.com
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Figure 7. Remote Temperature Error
ADT7485A
TYPICAL CHARACTERISTICS
15 10 5 0 ERROR (C) -5 -10 -15 -20 -25 -30 -35 -40 0 20 40 60 80 100 -5 10k 100k 1M 10M 100M 1G D+ TO VCC DEV1_EXT1 DEV1_EXT2 DEV2_EXT1 DEV2_EXT2 DEV3_EXT1 DEV3_EXT2 D+ TO GND DEV1_EXT1 DEV1_EXT2 DEV2_EXT1 DEV2_EXT2 DEV3_EXT1 DEV3_EXT2 TEMPERATURE ERROR (5C) 30 25 20 15 60mV 10 5 0 100mV
40mV
RESISTANCE (M)
NOISE FREQUENCY (Hz)
Figure 8. Remote Temperature Error vs. PCB Resistance
20
Figure 9. Temperature Error vs. Common-Mode Noise Frequency
0 -10
15 TEMPERATURE ERROR (5C) -20 10 ERROR (5C) -30 -40 -50 -60 50mV -70 -5 -80 -10 10k 100k 1M 10M 100M 1G -90 0 10 20 30 40 50 EXT1 EXT2
5 125mV 0
POWER SUPPLY NOISE FREQUENCY (Hz)
CAPACITANCE (nF)
Figure 10. Local Temperature Error vs. Power Supply Noise
7 6 TEMPERATURE ERROR (5C) 5 4 3 2 1 10mV 0 10k 100k 1M 10M 100M 1G 20mV 40mV TEMPERATURE ERROR (5C)
Figure 11. Remote Temperature Error vs. Capacitance Between D1+ and D1-
5 4 3 2 5 4 50mV -1 -2 -3 10k
125mV
100k
1M
10M
100M
1G
NOISE FREQUENCY (Hz)
POWER SUPPLY NOISE FREQUENCY (Hz)
Figure 12. Temperature Error vs. Differential-Mode Noise Frequency
Figure 13. Remote Temperature Error vs. Power Supply Noise http://onsemi.com
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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.
SST Interface
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.
Table 1. ADT7485A Selectable Addresses
ADD Low (GND) Float High 0x48 0x49 0x4A Address Selected
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 sst_licensing@analog.com or write to Analog Devices, 3550 North First Street, San Jose, CA 95134, Attention: SST Licensing, M/S B7-24.
Table 2. Command Code Summary
Command Ping() GetIntTemp() GetExtTemp() GetAllTemps() GetVolt12V() GetVolt5V() GetVoltVCC() GetVolt2.5V() GetVoltVCCP() GetAllVolts() SetExtOffset() GetExtOffset() ResetDevice() GetDIB() Command Code, CC 0x00 0x00 0x01 0x00 0x10 0x11 0x12 0x13 0x14 0x10 0xe0 0xe0 0xf6 0xf7 0xf7 Write Length, WL 0x00 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x02 0x01 0x01 0x01 0x01 Read Length, RL 0x00 0x02 0x02 0x04 0x02 0x02 0x02 0x02 0x02 0x10 0x00 0x01 0x00 0x08 0x10
Command Summary
Table 2 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.
Description Shows a nonzero FCS over the header if present. Shows the temperature of the device's internal thermal diode. Shows the temperature of External Thermal Diode. Returns a 4-byte block of data (GetIntTemp, GetExt1Temp). Shows the voltage attached to 12 V input. Shows the voltage attached to 5.0 V input. Shows the voltage attached to VCC input. Shows the voltage attached to 2.5 V input. Shows the voltage attached to VCCP input. Shows all voltage measurement values. Sets the offset used to correct errors in External Diode. Shows the offset that the device is using to correct errors in External Diode. Functional reset. The ADT7485A also responds to this command when directed to the Target Address 0x00. Shows information used by SW to identify the device's capabilities. Can be in 8- or 16-byte format.
Command Code Details
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
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.
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ADT7485A
Table 3. 16-Byte DIB Details
Byte 0 1 2, 3 Name Device Capabilities Version/Revision Vendor ID Value 0xc0 0x10 00x11d 4 0x7485 Description Fixed address device Meets Version 1 of SST specification Contains company ID number in little endian format Contains device ID number in little endian format SST device Reserved Reserved Reserved Reserved Reserved Reserved Reserved Contains revision ID Dependent on the state of address pin
GetAllTemps()
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()
4, 5
Device ID
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 128C with +0.25C resolution.
GetExtOffset()
6 7 8 9 10 11 12 13 14 15
Device Interface Function Interface Reserved Reserved Reserved Reserved Reserved Reserved Revision ID Client Device Address
0x01 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x05 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
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 4. Ping() Command
Target Address (Not necessary) Write Length 0x00 Read Length 0x00 FCS
A full list of command codes supported by the ADT7485A 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 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.
Voltage Measurement
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.
Table 5. ResetDevice() Command
Target Address Device Address Write Length 0x01 Read Length 0x00 Reset Command 0xf6 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.
Analog-to-Digital Converter
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, 16-bit, twos complement format. The ADT7485A shows 0x8000 in response to this command if the external diode is an open or short circuit.
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 6.
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ADT7485A
Table 6. Maximum Reported Input Voltages
Voltage Channel 12 V 5.0 V VCC 2.5 V VCCP Full-Scale Voltage 16 V 8.0 V 4.0 V 4.0 V 4.0 V
Table 8. Analog-to-Digital Output vs. VIN
Voltage 12 5.0 3.3 3.0 2.5 1.0 0 Twos Complement MSB 0011 0000 0001 0100 0000 1101 0000 1100 0000 1010 0000 0100 0000 0000 LSB 0000 0000 0000 0000 0011 0011 0000 0000 0000 0000 0000 0000 0000 0000
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.
12VIN 120k W 20k W 93k W 47k W 68k W 71k W 45k W 94k W 17.5k W 52.5k W 35pF 30pF 30pF MUX 30pF 30pF
Temperature Measurement
5VIN
3.3VIN
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 9.
Table 9. Temperature Monitoring Sequence
Channel Number 0 1 Measurement Local temperature Remote 1 temperature Conversion Time (ms) 12 38
2.5VIN
VCCP
Temperature Measurement Method
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 0x10 with a read length of 0x10. The data is retrieved in the order listed in Table 7.
Table 7. Voltage Measurement Command Code
Voltage Channel 12 V 5.0 V VCC 2.5 V VCCP Command Code 0x10 0x11 0x12 0x13 0x14 Returned Data LSB, MSB LSB, MSB LSB, MSB LSB, MSB 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.
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 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.
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ADT7485A
N1 x I I REMOTE SENSING TRANSISTOR C1* D1- BIAS DIODE N2 x I VDD IBIAS
Table 11. SST Temperature Data Format
Temperature (5C)
VOUT+
Twos Complement MSB 1110 0000 1110 1100 1111 0110 1111 1011 1111 1110 1111 1111 0000 0000 0000 0000 0000 0001 0000 0100 0000 1010 0001 0100 0001 1111 LSB 1100 0000 0000 0000 0000 0000 0011 1110 1100 0000 1100 0000 0000 0000 0100 0000 0100 0000 1100 0010 0000 0000 0000 0000 0100 0000
D1+ TO ADC LOW-PASS FILTER fC = 65kHz VOUT-
-125 -80 -40 -20 -5 -1 0 +1 +5 +20 +40 +80 +125
*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 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 rates. Signal conditioning and measurement of the internal temperature sensor is performed in the same manner.
Reading Temperature Measurements
Using Discrete Transistors
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.
2N3904 NPN
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 10.
Table 10. Temperature Channel Command Codes
Temp Channel Internal External All Temps Command Code 0x00 0x01 0x00 Returned Data LSB, MSB LSB, MSB Internal LSB, Internal MSB; External LSB, External MSB
ADT7485A
D1+ D1- 2N3906 PNP
D1+ D1-
ADT7485A
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
SST Temperature Sensor Data Format
The data for temperature is structured to allow values in the range of 512C 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 0.016C resolution.
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 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. * 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.
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ADT7485A * Use wide tracks to minimize inductance and reduce
noise pickup. A 5 mil track minimum width and spacing is recommended.
GND
5mil 5mil
D1+
5mil 5mil
D1-
5mil 5mil
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. 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 0.5C error.
Temperature Offset
GND
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 1C 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. Place a 0.1 mF bypass capacitor close to the ADT7485A. 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
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 128C with 0.25C 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.
ORDERING INFORMATION
Device Order Number* ADT7485AARMZ-R ADT7485AARMZ-R7 Package Type 10-Lead MSOP Package Option 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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ADT7485A
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 S DIM A B C D G H J K L 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 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
-A-
K
-B-
PIN 1 ID
G
D 8 PL 0.08 (0.003)
M
TB
S
A
0.038 (0.0015) -T- SEATING
PLANE
C H J L
SOLDERING FOOTPRINT*
10X
1.04 0.041
0.32 0.0126
10X
3.20 0.126
4.24 0.167
5.28 0.208
8X
0.50 0.0196
SCALE 8:1
mm inches
*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.
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ADT7485A/D

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