ADT7485AARMZ-R7_技术文档

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.

http://onsemi.com

MARKING

DIAGRAM

10

T21

RYWG

G

Features

1

MSOP−10

CASE 846AC

1

• 1 On−Chip Temperature Sensor

• 1 Remote Temperature Sensor

• Monitors Up to 5.0 Voltages

• SST Interface

T21 = Device Code

R

Y

W

G

= Assembly Location

= Year

= Work Week

= Pb−Free Package

• This is a Pb−Free Device

(Note: Microdot may be in either location)

Applications

• Personal Computers

• Portable Personal Devices

• Industrial Sensor Nets

PIN ASSIGNMENT

V

1

2

3

4

5

10 SST

CC

GND

D1+

D1–

12 V

9

8

7

6

ADD

2.5 V

ADT7485A

V

CCP

5.0 V

(Top View)

ORDERING INFORMATION

See detailed ordering and shipping information in the package

dimensions section on page 11 of this data sheet.

ADT7485A

ON−CHIP

TEMPERATURE

SENSOR

OFFSET REGISTERS

TEMPERATURE

VALUE REGISTERS

V

CC

12 V

INPUT

ATTENUATORS

AND

SST INTERFACE

SST

5.0 V

A/D

CONVERTER

V

CCP

ANALOG

MULTIPLEXER

2.5 V

D1+

D1−

VOLTAGE

VALUE REGISTERS

ADDRESS

SELECTION

ADD

GND

Figure 1. Functional Block Diagram

1

Publication Order Number:

April, 2010 − Rev. 3

ADT7485A/D

ADT7485A

ABSOLUTE MAXIMUM RATINGS

Parameter

Rating

Unit

Supply Voltage (V

)

4.0

V

CC

Voltage on 12 V Pin

Voltage on 5.0 V Pin

16

7.0

V

Voltage on 2.5 V and V

Pins

3.6

V

CCP

Voltage on Any Other Pin (Including SST Pin)

Input Current at Any Pin

−0.3 to +3.6

5.0

V

mA

°C

Package Input Current

20

Maximum Junction Temperature (T Max)

150

J

Storage Temperature Range

−65 to +150

Lead Temperature, Soldering

IR Peak Re−flow Temperature

Lead Temperature (10 sec)

260

300

ESD Rating

1500

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

q

JA

q

JC

Unit

10−Lead MSOP

206

44

°C/W

NOTE: is specified for the worst−case conditions, that is, a device soldered in a circuit board for surface−mount packages.

q

JA

PIN ASSIGNMENT

Pin No.

Mnemonic

Type

Power supply

Ground

Description

1

2

V

CC

3.3 V 10%. V is also monitored through this pin.

CC

GND

D1+

Ground Pin.

3

Analog input

Digital input

Digital input/output

Positive Connection to Remote 1 Temperature Sensor.

Negative Connection to Remote 1 Temperature Sensor.

12 V Supply Monitor.

4

D1−

5

12 V

5.0 V

6

5.0 V Supply Monitor.

7

V

CCP

Processor Core Voltage Monitor.

2.5 V Supply Monitor.

8

2.5 V

ADD

SST

9

SST Address Select.

10

SST Bidirectional Data Line.

http://onsemi.com

2

ADT7485A

ELECTRICAL CHARACTERISTICS T = T

to T

, V = V

to V , unless otherwise noted.

MAX

A

MIN

MAX

CC

MIN

Parameter

Test Conditions/Comments

Min

Typ

Max

3.6

Unit

Power Supply

Supply Voltage, V

3.0

3.3

2.8

3.8

V

CC

Undervoltage Lockout Threshold

Average Operating Supply Current, I

Continuous conversions

5.0

mA

DD

Temperature−to−Digital Converter

Local Sensor Accuracy

40°C ≤ T ≤ 70°C; V = 3.3 V 5%

+1.0

1.75

4.0

°C

A

CC

−40°C ≤ T ≤ +100°C

A

Remote Sensor Accuracy

−40°C ≤ T ≤ +125°C; T = 25°C; V = 3.3 V

1.0

1.75

D

A

CC

−40°C ≤ T ≤ +125°C; −40 ≤ T ≤ 70°C;

D

A

V

CC

= 3.3 V 5%

−40°C ≤ T ≤ +125°C; −40 ≤ T ≤ +100°C

4.0

D

A

Remote Sensor Source Current

Low level

Mid level

High level

12

80

204

mA

Resolution

0.016

1.5

°C

Series Resistance Cancellation

The ADT7485A cancels 1.5 kW in series with

the remote thermal diode

kW

Digital Input (ADD)

Input High Voltage, V

2.3

V

IH

Input Low Voltage, V

0.8

1.0

V

IL

Input High Current, I

V

= V

= 0

−1.0

mA

pF

IH

IN

CC

Input Low Current, I

IL

IN

Pin Capacitance

5.0

0.1

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

%/V

ms

Power Supply Sensitivity

Conversion Time (Voltage Input)

(Note 1)

Averaging enabled

11

12

38

Conversion Time

(Local Temperature) (Note 1)

ms

kW

Conversion Time

(Remote Temperature) (Note 1)

Total Monitoring Cycle Time (Note 1)

Input Resistances

145

V

CCP

and 2.5V Channels

80

95

180

110

120

230

140

150

280

5.0 V Channel

12 V Channel

Digital I/O (SST Pin)

Input High Voltage , V

1.1

V

IH

Input Low Voltage, V

Hysteresis (Note 1)

0.4

1.9

IL

Between input switching levels

150

mV

V

Output High Voltage, V

I

= 6 mA (maximum)

OH

SOURCE

1. Guaranteed by design, not production tested.

2. Minimum and maximum bit times are relative to t

defined in the timing negotiation pulse.

BIT

3. Device is compatible with hold time specification as driven by SST originator.

http://onsemi.com

3

ADT7485A

ELECTRICAL CHARACTERISTICS T = T

to T

, V = V

to V , unless otherwise noted.

MAX

A

MIN

MAX

CC

MIN

Parameter

Test Conditions/Comments

Min

Typ

Max

Unit

Digital I/O (SST Pin)

High Impedance State Leakage, I

Device powered on SST bus;

= 1.1 V, V = 3.3 V

1.0

10

mA

LEAK

V

SST

CC

High Impedance State Leakage, I

Device non−powered on SST bus;

= 1.1 V, V = 0 V

V

SST

CC

Signal Noise Immunity, V

Noise glitches from 10 MHz to 100 MHz;

width up to 50 ns

300

mV

p−p

NOISE

SST Timing

Bitwise Period, t

0.495

0.6 x

500

ms

BIT

High Level Time for Logic 1, t

(Note 2)

t

defined in speed negotiation

0.75 x

BIT

0.8 x

H1

BIT

t

BIT

High Level Time for Logic 0, t

(Note 2)

0.2 x

BIT

0.25 x

BIT

0.4 x

BIT

ms

H0

t

Time to Assert SST High for Logic 1,

0.2 x

t

SU, HIGH

BIT

Hold Time, t

(Note 3)

See SST Specification Rev 1.0

0.5 x

HOLD

STOP

t

BIT−M

Stop Time, t

Device responding to a constant low level

driven by originator

1.25 x

2 x t

BIT

t

BIT

Time to Respond After a Reset, t

0.4

ms

RESET

Response Time to Speed Negotiation

After Powerup

Time after powerup when device can participate

in speed negotiation

500

ms

1. Guaranteed by design, not production tested.

2. Minimum and maximum bit times are relative to t

defined in the timing negotiation pulse.

BIT

3. Device is compatible with hold time specification as driven by SST originator.

http://onsemi.com

4

ADT7485A

TYPICAL CHARACTERISTICS

1.55

1.50

1.45

1.40

1.35

1.30

1.25

1.20

3.56

3.55

3.54

3.53

3.52

3.51

3.50

3.49

3.48

3.47

3.46

3.45

DEV3

DEV2

750Ω (~2mA)

270Ω (~5.2mA)

120Ω (~10.6mA)

DEV1

95

2.6

2.8

3.0

3.2

3.4

3.6

–45

–25

–5

15

35

55

75

115

V

(V)

TEMPERATURE (5C)

CC

Figure 2. SST O/P Level vs. Supply Voltage

Figure 3. Supply Current vs. Temperature

7

6

5

4

1.55

1.50

1.45

1.40

1.35

1.30

1.25

1.20

750Ω (~2mA)

270Ω (~5.2mA)

3

2

HI SPEC (V = 3.0 V)

CC

MEAN (V = 3.3 V)

CC

1

120Ω (~10.6mA)

0

LO SPEC (V = 3.6 V)

CC

–1

–60 –40 –20

0

20

40

60

80

100 120 140

–50

0

50

100

150

TEMPERATURE (5C)

Figure 4. Local Temperature Error

Figure 5. SST O/P Level vs. Temperature

3.9

3.7

3.5

3.3

3.1

2.9

7

6

5

4

3

2

DEV2

DEV3

DEV1

HI SPEC (V = 3.0 V)

CC

1

MEAN (V = 3.3 V)

CC

0

–1

–2

LO SPEC (V = 3.6 V)

CC

2.65

2.85

3.05

3.25

3.45

3.65

–60 –40 –20

0

20

40

60

80

100 120 140

V

(V)

TEMPERATURE (5C)

CC

Figure 6. Supply Current vs. Voltage

Figure 7. Remote Temperature Error

http://onsemi.com

5

ADT7485A

TYPICAL CHARACTERISTICS

15

10

5

30

DEV1_EXT1

DEV1_EXT2

DEV2_EXT1

DEV2_EXT2

DEV3_EXT1

DEV3_EXT2

D+ TO GND

25

20

0

100mV

60mV

–5

–10

–15

–20

–25

–30

–35

–40

15

10

5

DEV1_EXT1

DEV1_EXT2

DEV2_EXT1

DEV2_EXT2

DEV3_EXT1

DEV3_EXT2

D+ TO V

CC

40mV

1M

0

–5

10k

100k

10M

100M

1G

0

20

40

60

80

100

NOISE FREQUENCY (Hz)

RESISTANCE (MΩ)

Figure 8. Remote Temperature Error vs. PCB

Resistance

Figure 9. Temperature Error vs. Common−Mode

Noise Frequency

20

15

10

5

0

–10

–20

–30

EXT2

–40

–50

EXT1

125mV

0

–60

–70

–80

–90

50mV

−5

–10

10k

100k

1M

10M

100M

1G

0

10

20

30

40

50

POWER SUPPLY NOISE FREQUENCY (Hz)

CAPACITANCE (nF)

Figure 10. Local Temperature Error vs. Power

Supply Noise

Figure 11. Remote Temperature Error vs.

Capacitance Between D1+ and D1−

7

5

4

3

2

40mV

6

5

4

3

5

125mV

4

50mV

20mV

2

–1

1

–2

–3

10mV

0

10k

100k

1M

10M

100M

1G

10k

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

6

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

Table 1. ADT7485A Selectable Addresses

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.

ADD

Low (GND)

Address Selected

0x48

0x49

0x4A

Float

High

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.

Table 2. Command Code Summary

Command

Code, CC

Write

Length, WL

Read

Length, RL

Command

Ping()

Description

0x00

0x01

0x00

0x10

0x11

0x12

0x13

0x14

0x10

0xe0

0x00

0x01

0x02

0x01

0x00

0x02

0x04

0x02

0x10

0x00

0x01

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.

GetIntTemp()

GetExtTemp()

GetAllTemps()

GetVolt12V()

GetVolt5V()

Shows the voltage attached to 5.0 V input.

GetVoltVCC()

GetVolt2.5V()

GetVoltVCCP()

GetAllVolts()

SetExtOffset()

GetExtOffset()

Shows the voltage attached to V input.

CC

Shows the voltage attached to 2.5 V input.

Shows the voltage attached to V

input.

CCP

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.

ResetDevice()

GetDIB()

0xf6

0x01

0x00

Functional reset. The ADT7485A also responds to this

command when directed to the Target Address 0x00.

0xf7

0x01

0x08

0x10

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.

http://onsemi.com

7

ADT7485A

GetAllTemps()

Table 3. 16−Byte DIB Details

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.

Byte

Name

Value

Description

0

Device

Capabilities

0xc0

Fixed address

device

1

Version/Revision

0x10

Meets Version 1 of

SST specification

SetExtOffset()

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.

2, 3

Vendor ID

00x11d

4

Contains company

ID number in little

endian format

4, 5

Device ID

0x7485

Contains device ID

number in little

endian format

GetExtOffset()

6

7

Device Interface

0x01

0x00

SST device

Reserved

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.

Function

Interface

8

Reserved

Revision ID

0x00

0x05

Reserved

9

Reserved

ADT7485A Response to Unsupported Commands

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.

10

11

12

13

14

15

Reserved

Contains revision ID

Client Device

Address

0x48 to

0x4a

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.

Voltage Measurement

The ADT7485A has four external voltage measurement

Table 4. Ping() Command

channels. It can also measure its own supply voltage, V

.

CC

Target Address

Write Length

Read Length

FCS

Pins 5 and 8 measure the supplies of the 12 V, 5.0 V,

processor core voltage (V ), and 2.5 V pins, respectively.

(Not necessary)

0x00

CCP

The V supply voltage measurement is carried out through

CC

ResetDevice()

the V pin (Pin 1). The 2.5 V pin can be used to monitor a

CC

This command resets the register map and conversion

controller. The reset command can be global or directed at

the client address of the ADT7485A.

chip−set supply voltage in a computer system.

Analog−to−Digital Converter

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,

Table 5. ResetDevice() Command

Write

Length

Read

Length Command

Reset

Target Address

FCS

Device Address

0x01

0x00 0xf6

12 V, and the processor core voltage (V

external components.

) without any

CCP

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.

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.

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.

http://onsemi.com

8

ADT7485A

Table 6. Maximum Reported Input Voltages

Table 8. Analog−to−Digital Output vs. V_IN

Twos Complement

Voltage Channel

Full−Scale Voltage

Voltage

MSB

LSB

12 V

16 V

8.0 V

4.0 V

12

5.0

3.3

3.0

2.5

1.0

0

0011 0000

0001 0100

0000 1101

0000 1100

0000 1010

0000 0100

0000 0000

0011 0011

0000 0000

5.0 V

V

CC

2.5 V

V

CCP

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.

Temperature Measurement

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.

120kW

12V

IN

20kW

47kW

71kW

94kW

30pF

35pF

93kW

68kW

45kW

5V

IN

3.3V

2.5V

IN

MUX

Table 9. Temperature Monitoring Sequence

Channel

Number

Conversion

Time (ms)

Measurement

IN

0

1

Local temperature

12

38

Remote 1 temperature

17.5kW

52.5kW

V

CCP

Temperature Measurement Method

A simple method for measuring temperature is to exploit

the negative temperature coefficient of a diode by measuring

Figure 14. Internal Structure of Analog Inputs

the base−emitter voltage (V ) of a transistor operated at

BE

constant current. Unfortunately, this technique requires

Voltage Measurement Command Codes

calibration to null the effect of the absolute value of V

which varies from device to device.

,

BE

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.

The technique used in the ADT7485A measures the

change in V when the device is operated at three different

BE

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.

Table 7. Voltage Measurement Command Code

Voltage Channel

Command Code

Returned Data

LSB, MSB

12 V

0x10

0x11

0x12

0x13

0x14

5.0 V

V

CC

2.5 V

V

CCP

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.

http://onsemi.com

9

ADT7485A

N1× I N2× I

V

Table 11. SST Temperature Data Format

DD

I

BIAS

Twos Complement

Temperature (5C)

REMOTE

SENSING

MSB

LSB

V

OUT+

TRANSISTOR

−125

−80

−40

−20

−5

1110 0000

1110 1100

1111 0110

1111 1011

1111 1110

1111 1111

0000 0000

0000 0001

0000 0100

0000 1010

0001 0100

0001 1111

1100 0000

0000 0000

0011 1110

1100 0000

0000 0000

0100 0000

1100 0010

0000 0000

0100 0000

D1+

D1–

C1*

TO

ADC

BIAS

DIODE

LOW−PASS FILTER

OUT–

f_C= 65kHz

*CAPACITOR C1 IS OPTIONAL.

IT SHOULD ONLY BE USED

IN NOISY ENVIRONMENTS.

−1

0

Figure 15. Signal Conditioning for Remote Diode

Temperature Sensors

+1

+5

To measure DV , the operating current through the

BE

+20

+40

+80

+125

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 DV , and then

BE1

between I and N2 x I, giving DV . The temperature can

BE2

Using Discrete Transistors

then be calculated using the two DV measurements. This

BE

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.

method can also cancel the effect of series resistance on the

temperature measurement. The resulting DV waveforms

BE

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 . The ADC digitizes this voltage, and

BE

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.

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

2N3904

NPN

ADT7485A

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.

D1+

2N3906

PNP

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.

Table 10. Temperature Channel Command Codes

Temp

Command

Code

Returned Data

Layout Considerations

Channel

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:

Internal

External

All Temps

0x00

0x01

0x00

LSB, MSB

Internal LSB, Internal MSB;

External LSB, External MSB

• 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.

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

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.

http://onsemi.com

10

ADT7485A

cables. Connect the twisted pair cable to D+ and D−

• Use wide tracks to minimize inductance and reduce

noise pickup. A 5 mil track minimum width and

spacing is recommended.

and the shield to GND, close to the ADT7485A. Leave

the remote end of the shield unconnected to avoid

ground loops.

5mil

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.

D1+

D1–

GND

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 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.

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

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

ORDERING INFORMATION

†

Device Order Number*

ADT7485AARMZ−R

ADT7485AARMZ−R7

Package Type

Package Option

Shipping

3000 Tape & Reel

1000 Tape & Reel

10−Lead MSOP

RM−10

†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.

http://onsemi.com

11

ADT7485A

PACKAGE DIMENSIONS

MSOP−10

CASE 486AC−01

ISSUE O

NOTES:

1. DIMENSIONING AND TOLERANCING PER

ANSI Y14.5M, 1982.

−A−

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

−B−

K

G

PIN 1 ID

D 8 PL

M

S

A

0.08 (0.003)

T B

MILLIMETERS

INCHES

DIM MIN

MAX

3.10

MIN

MAX

0.122

0.043

0.012

A

B

C

D

G

H

J

2.90

0.95

0.20

0.114

1.10 0.037

0.30 0.008

0.50 BSC

0.020 BSC

0.05

0.10

4.75

0.40

0.15 0.002

0.21 0.004

5.05 0.187

0.70 0.016

0.006

0.008

0.199

0.028

C

0.038 (0.0015)

K

L

−T−

SEATING

PLANE

L

H

J

SOLDERING FOOTPRINT*

1.04

0.041

0.32

0.0126

10X

3.20

4.24

5.28

0.126

0.167 0.208

0.50

mm

inches

ǒ

Ǔ

^8X0.0196

SCALE 8:1

*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:

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

ON Semiconductor Website: www.onsemi.com

Order Literature: http://www.onsemi.com/orderlit

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: orderlit@onsemi.com

For additional information, please contact your local

Sales Representative

ADT7485A/D

http://onsemi.com

12


型号：	ADT7485AARMZ-R7
厂家：	ONSEMI
描述：	Temperature Sensor and Voltage Monitor with Simple Serial Transport 温度传感器和电压监视器用简单串行传输传感器换能器温度传感器监视器输出元件
文件：	总12页 (文件大小：330K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

ADT7485AARMZ-R7 [ONSEMI]

相关型号：

ADT7485AARMZ-REEL

ADT7485AARMZ-REEL7

ADT7486A

ADT7486AARMZ-R7

ADT7486AARMZ-REEL

ADT7486AARMZ-REEL7

ADT7486AARMZ-RL

ADT7486AARMZ-U5

ADT7486ARMZ

ADT7486ARMZ-REEL

ADT7488A

ADT7488A