ADT7481ARMZ-1R7中文资料_数据手册_规格书

ADT7481

Dual Channel Temperature

Sensor and Overtemperature

Alarm

The ADT7481 is a 3−channel digital thermometer and under/ over

temperature alarm, intended for use in PCs and thermal management

systems. It can measure its own ambient temperature or the

temperature of two remote thermal diodes. These thermal diodes can

be located in a CPU or GPU, or they can be discrete diode connected

transistors. The ambient temperature, or the temperature of the remote

thermal diode, can be accurately measured to 1°C. The temperature

measurement range defaults to 0°C to +127°C, compatible with

ADM1032, but can be switched to a wider measurement range from

−64°C to +191°C.

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MSOP−10

CASE 846AC

1

The ADT7481 communicates over a 2−wire serial interface

compatible with System Management Bus (SMBus) standards. The

SMBus address of the ADT7481 is 0x4C. An ADT7481−1 with an

SMBus address of 0x4B is also available.

An ALERT output signals when the on−chip or remote temperature

is outside the programmed limits. The THERM output is a comparator

output that allows, for example, on/off control of a cooling fan. The

ALERT output can be reconfigured as a second THERM output if

required.

MARKING DIAGRAM

10

T0x

AYWG

G

1

T0x = Refer to Ordering Info Table

A

Y

W

G

= Assembly Location

= Year

= Work Week

Features

• 1 Local and 2 Remote Temperature Sensors

= Pb−Free Package

• 0.25°C Resolution/1°C Accuracy on Remote Channels

• 1°C Resolution/1°C Accuracy on Local Channel

(Note: Microdot may be in either location)

• Extended, Switchable Temperature Measurement Range

0°C to 127°C (Default) or −64°C to +191°C

PIN ASSIGNMENT

• 2−Wire SMBus Serial Interface with SMBus ALERT Support

• Programmable Over/Undertemperature Limits

• Offset Registers for System Calibration

• Up to 2 Overtemperature Fail−Safe THERM Outputs

• Small 10−Lead MSOP Package

• 240 mA Operating Current, 5 mA Standby Current

• These are Pb−Free Devices

V

1

2

3

4

5

10

9

SCLK

DD

D1+

D1–

SDATA

8

ALERT/THERM2

ADT7481

THERM

GND

7

D2+

6

D2−

Applications

ORDERING INFORMATION

See detailed ordering and shipping information in the package

dimensions section on page 19 of this data sheet.

• Desktop and Notebook Computers

• Industrial Controllers

• Smart Batteries

• Automotive

• Embedded Systems

• Burn−In Applications

• Instrumentation

1

Publication Order Number:

June, 2010 − Rev. 5

ADT7481/D

ADT7481

ADDRESS POINTER

REGISTER

ONE−SHOT

REGISTER

CONVERSION RATE

REGISTER

LOCAL TEMPERATURE

THERM LIMIT REGISTER

ON−CHIP TEMP

SENSOR

LOCAL TEMPERATURE

VALUE REGISTER

LOCAL TEMPERATURE

LOW LIMIT REGISTER

2

3

7

8

D1+

D1–

D2+

LOCAL TEMPERATURE

HIGH LIMIT REGISTER

ANALOG

MUX

11−BIT A−TO−D

CONVERTER

REMOTE 1 AND 2 TEMP

THERM LIMIT REGISTER

BUSY RUN/STANDBY

D2–

REMOTE 1 AND 2 TEMP

VALUE REGISTERS

REMOTE 1 AND 2 TEMP

LOW LIMIT REGISTERS

REMOTE 1 AND 2 TEMP

HIGH LIMIT REGISTERS

REMOTE 1 AND 2 TEMP

OFFSET REGISTERS

CONFIGURATION

REGISTERS

EXTERNAL DIODES OPEN−CIRCUIT

INTERRUPT

MASKING

8

ALERT/THERM2

STATUS REGISTERS

ADT7481

SMBUS INTERFACE

1

6

9

10

4

V

GND

SDATA

SCLK

DD

THERM

Figure 1. Functional Block Diagram

ABSOLUTE MAXIMUM RATINGS

Parameter

Rating

Unit

Positive Supply Voltage (V ) to GND

−0.3 to +3.6

V

DD

D+

−0.3 to V + 0.3

DD

D− to GND

−0.3 to +0.6

−0.3 to +3.6

−1 to +50

1

V

SCLK, SDATA, ALERT, THERM

Input Current, SDATA, THERM

Input Current, D−

V

mA

V

ESD Rating, All Pins (Human Body Model)

1500

Maximum Junction Temperature (T max)

150

°C

J

Storage Temperature Range

−65 to +150

220

IR Reflow Peak Temperature

IR Reflow Peak Temperature for Pb−Free

Lead Temperature, Soldering (10 sec)

260

300

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

142

43.74

°C/W

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2

ADT7481

PIN ASSIGNMENT

Pin No.

Mnemonic

Description

1

2

3

4

V

Positive Supply, 3.0 V to 3.6 V.

DD

D1+

D1−

Positive Connection to the Remote 1 Temperature Sensor.

Negative Connection to the Remote 1 Temperature Sensor.

THERM

Open−Drain Output. Requires pullup resistor. Signals overtemperature events, could be used to turn a

fan on/off, or throttle a CPU clock.

5

6

7

8

GND

D2−

Supply Ground Connection.

Negative Connection to the Remote 2 Temperature Sensor.

Positive Connection to the Remote 2 Temperature Sensor.

D2+

ALERT/THERM2

Open−Drain Logic Output. Used as interrupt or SMBALERT. This may also be configured as a second

THERM output. Requires pullup resistor.

9

SDATA

SCLK

Logic Input/Output, SMBus Serial Data. Open−Drain Output. Requires pullup resistor.

10

Logic Input, SMBus Serial Clock. Requires pullup resistor.

TIMING SPECIFICATIONS (Note 1)

Parameter

Limit at T

and T

Unit

Description

MIN

400

4.7

4.0

1.0

300

4.7

4.0

MAX

f

kHz max

ms min

ms max

ns max

ms min

SCLK

t

Clock low period, between 10% points

Clock high period, between 90% points

Clock/data rise time

LOW

HIGH

t

R

t

F

Clock/data fall time

t

Start condition setup time

Start condition hold time

SU; STA

t

HD; STA

(Note 2)

t

250

4.0

4.7

ns min

ms min

Data setup time

SU; DAT

(Note 3)

t

Stop condition setup time

SU; STO

(Note 4)

t

Bus free time between stop and start conditions

BUF

1. Guaranteed by design, not production tested.

2. Time from 10% of SDATA to 90% of SCLK.

3. Time for 10% or 90% of SDATA to 10% of SCLK.

4. Time for 90% of SCLK to 10% of SDATA.

t_R

t_F

t_HD;STA

t_LOW

SCLK

t_HIGH

t_SU;STA

t_HD;STA

t_HD;DAT

t_SU;STO

t_SU;DAT

SDATA

t_BUF

STOP START

START

STOP

Figure 2. Serial Bus Timing

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3

ADT7481

ELECTRICAL CHARACTERISTICS (T = −40°C to +120°C, V = 3.0 V to 3.6 V, unless otherwise noted)

A

DD

Parameter

Conditions

Min

Typ

Max

Unit

Power Supply

Supply Voltage, V

3.0

3.30

3.0

3.6

4.0

30

V

mA

V

DD

Average Operating Supply Current, I

0.0625 Conversions/Sec Rate (Note 1)

Standby mode

DD

5.0

Undervoltage Lockout Threshold

Power−On−Reset Threshold

V

DD

input, disables ADC, rising edge

2.55

1.0

2.5

V

Temperature−To−Digital Converter

Local Sensor Accuracy (Note 2)

0°C ≤ T ≤ +70°C

1

1.5

2.5

°C

A

0°C ≤ T ≤ +85°C

A

−40 ≤ T ≤ +100°C

A

Resolution

1.0

°C

Remote Diode Sensor Accuracy (Note 2)

0°C ≤ T ≤ +70°C, −55°C ≤ T (Note 3) ≤ +150°C

1

1.5

2.5

A

D

0°C ≤ T ≤ +85°C, −55°C ≤ T (Note 3) ≤ +150°C

A

D

−40°C ≤ T ≤ +100°C, −55°C ≤ T (Note 3) ≤ +150°C

A

D

Resolution

0.25

233

14

°C

mA

ms

Remote Sensor Source Current

High level (Note 4)

Low level (Note 4)

Conversion Time

From stop bit to conversion complete (both channels)

one−shot mode with averaging switched on

73

94

14

One−shot mode with averaging off (conversion

rate = 16, 32, or 64 conversions per second)

11

ms

Open−Drain Digital Outputs (THERM, ALERT/THERM2)

Output Low Voltage, V = −6.0 mA

I

0.4

1.0

V

OL

OUT

High Level Output Leakage Current, I

V

OUT

= V

DD

0.1

mA

OH

SMBus Interface (Notes 4 and 5)

Logic Input High Voltage, V

SCLK, SDATA

2.1

V

IH

Logic Input Low Voltage, V

SCLK, SDATA

0.8

IL

Hysteresis

500

mV

V

SDA Output Low Voltage, V

I

= −6.0 mA

0.4

OL

OUT

Logic Input Current, I , I

−1.0

+1.0

mA

pF

IH IL

SMBus Input Capacitance,

SCLK, SDATA

5.0

25

SMBus Clock Frequency

SMBus Timeout (Note 6)

400

32

kHz

ms

User programmable

SCLK Falling Edge to SDATA Valid Time

Master clocking in data

1.0

1. See Table 6 for information on other conversion rates.

2. Averaging enabled.

3. Guaranteed by characterization, not production tested.

4. Guaranteed by design, not production tested.

5. See Timing Specifications section for more information.

6. Disabled by default. See the Serial Bus Interface section for details to enable it.

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ADT7481

TYPICAL CHARACTERISTICS

3.5

3.0

2.5

2.0

3.5

3.0

2.5

2.0

DEV 1

DEV 2

DEV 3

DEV 4

DEV 5

DEV 6

DEV 7

DEV 8

DEV 9

DEV 1

DEV 2

DEV 3

DEV 4

DEV 5

DEV 6

DEV 7

DEV 8

DEV 9

DEV 10

DEV 11

DEV 12

DEV 13

DEV 14

DEV 15

DEV 16

MEAN

DEV 15

DEV 16

HIGH 4S

LOW 4S

DEV 10

DEV 11

DEV 12

DEV 13

DEV 14

HIGH 4S

LOW 4S

1.5

1.0

1.5

1.0

0.5

0

0.5

–1.0

–50

–1.0

–50

0

50

100

150

0

50

100

150

TEMPERATURE (5C)

Figure 3. Local Temperature Error vs. Temperature

Figure 4. Remote 1 Temperature Error vs.

Temperature

3.5

10

DEV 8

DEV 9

DEV 15

DEV 16

MEAN

HIGH 4S

LOW 4S

DEV 1

DEV 2

DEV 3

DEV 4

DEV 5

DEV 6

DEV 7

3.0

2.5

5

DEV 10

DEV 11

DEV 12

DEV 13

DEV 14

D+ TO GND

2.0

1.5

1.0

D+ TO V

CC

–10

–15

–20

–25

0.5

0

0.5

–1.0

–50

0

50

100

150

1

10

LEAKAGE RESISTANCE (MΩ)

100

TEMPERATURE (5C)

Figure 5. Remote 2 Temperature Error vs.

Temperature

Figure 6. Temperature Error vs. D+/D− Leakage

Resistance

0

1000

DEV 2BC

900

–2

800

700

600

500

–4

–6

DEV 4BC

400

DEV 3

–12

ć14

ć16

–18

DEV 2

300

DEV 3BC

200

100

0

DEV 4

0

5

10

15

20

25

0.01

0.1

1

10

100

CAPACITANCE (nF)

CONVERTION RATE (Hz)

Figure 7. Temperature Error vs. D+/D− Capacitance

Figure 8. Operating Supply Current vs.

Conversion Rate

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ADT7481

TYPICAL CHARACTERISTICS

422

420

418

416

414

412

410

408

4.4

4.2

DEV 2

DEV 2BC

4.0

3.8

3.6

3.4

3.2

3.0

DEV 3

DEV 4

DEV 3BC

DEV 4BC

3.0

3.1

3.2

3.3

(V)

3.4

3.5

3.6

3.0

3.1

3.2

3.3

(V)

3.4

3.5

3.6

V

DD

Figure 9. Operating Supply Current vs. Voltage

Figure 10. Standby Supply Current vs. Voltage

35

25

DEV 2BC

DEV 3BC

30

DEV 4BC

20

25

20

15

10

5

100mV

15

10

50mV

5

20mV

0

1

10

100

1000

0

100

200

300

400

500

600

NOISE FREQUENCY (MHz)

FSCL (kHz)

Figure 11. Standby Supply Current vs. SCLK

Frequency

Figure 12. Temperature Error vs. Common−Mode

Noise Frequency

80

70

60

50

40

30

20

10

0

100mV

50mV

20mV

–10

0

100

200

300

400

500

600

NOISE FREQUENCY (MHz)

Figure 13. Temperature Error vs. Differential Mode Noise Frequency

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6

ADT7481

Theory of Operation

This technique requires calibration to null the effect of the

The ADT7481 is a local and dual remote temperature

sensor and over/under temperature alarm. When the

ADT7481 is operating normally, the on−board ADC

operates in a free−running mode. The analog input

multiplexer alternately selects either the on−chip

temperature sensor to measure its local temperature, or

either of the remote temperature sensors. The ADC digitizes

these signals and the results are stored in the local, Remote 1,

and Remote 2 temperature value registers.

The local and remote measurement results are compared

with the corresponding high, low, and THERM temperature

limits, stored in on−chip registers. Out−of−limit comparisons

generate flags that are stored in the status register. A result that

exceeds the high temperature limit, the low temperature limit,

or remote diode open circuit will cause the ALERT output to

assert low. Exceeding THERM temperature limits causes the

THERM output to assert low. The ALERT output can be

reprogrammed as a second THERM output.

absolute value of V , which varies from device to device.

The technique used in the ADT7481 measures the change

BE

in V when the device is operated at two different currents.

BE

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, but

it could equally be a discrete transistor. If a discrete

transistor is used, the collector is not grounded and is linked

to the base. To prevent ground noise 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. C1 may optionally be added

as a noise filter with a recommended maximum value of

1,000 pF.

To measure DV , the operating current through the

BE

sensor is switched among two related currents. The currents

through the temperature diode are switched between I, and

N x I, giving DV . The temperature can then be calculated

BE

The limit registers can be programmed, and the device

controlled and configured via the serial SMBus. The

contents of any register can also be read back via the SMBus.

Control and configuration functions consist of switching

the device between normal operation and standby mode,

selecting the temperature measurement scale, masking or

enabling the ALERT output, switching Pin 8 between

ALERT and THERM2, and selecting the conversion rate.

using the DV measurement.

BE

The resulting DV waveforms pass through a 65 kHz

BE

low−pass filter to remove noise and then to

chopper−stabilized amplifier. This amplifies and rectifies

the waveform to produce a dc voltage proportional to DV

The ADC digitizes this voltage producing a temperature

measurement. To reduce the effects of noise, digital filtering

is performed by averaging the results of 16 measurement

cycles for low conversion rates. At rates of 16, 32, and 64

conversions/second, no digital averaging takes place.

Signal conditioning and measurement of the local

temperature sensor is performed in the same manner.

a

.

BE

Temperature Measurement Method

A simple method of measuring temperature is to exploit

the negative temperature coefficient of a diode, measuring

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

BE

constant current.

V

DD

I

BIAS

I

N ×I

V

OUT+

D+

TO ADC

C1

D–

REMOTE

SENSING

TRANSISTOR

f_C= 65kHz

V

OUT–

BIAS

DIODE

NOTE:

CAPACITOR C1 IS OPTIONAL. IT IS ONLY NECESSARY IN NOISY ENVIRONMENTS. C1 = 1000pF MAX.

Figure 14. Input Signal Conditioning

Temperature Measurement Results

The local temperature measurement is an 8−bit

measurement with 1°C resolution. The remote temperature

measurements are 10−bit measurements, with the 8 MSBs

stored in one register and the 2 LSBs stored in another

register. Table 1 is a list of the temperature measurement

registers.

The results of the local and remote temperature

measurements are stored in the local and remote temperature

value registers and are compared with limits programmed

into the local and remote high and low limit registers.

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7

ADT7481

In extended temperature mode, the upper and lower

Table 1. Register Address for the Temperature Values

temperatures that can be measured by the ADT7481 are

limited by the remote diode selection. While the temperature

registers can have values from −64°C to +191°C, most

temperature sensing diodes have a maximum temperature

range of −55°C to +150°C.

Note that while both local and remote temperature

measurements can be made while the part is in extended

temperature mode, the ADT7481 should not be exposed to

temperatures greater than those specified in the Absolute

section. Furthermore, the device is only guaranteed to operate

as specified at ambient temperatures from −40°C to +120°C.

Temperature

Channel

Register Address,

MSBs

Register Address,

LSBs

Local

0x00

0x01

0x30

N/A

Remote 1

Remote 2

0x10 (2 MSBs)

0x33 (2 MSBs)

If Bit 3 of the Configuration 1 register is set to 1, then the

Remote 2 temperature values can be read from the following

register addresses:

Remote 2, MSBs = 0x01

Remote 2, LSBs = 0x10

The above is true only when Bit 3 of the Configuration 1

register is set. To read the Remote 1 temperatures, this bit

needs to be switched back to 0.

Only the two MSBs in the remote temperature low byte

are used. This gives the remote temperature measurement a

resolution of 0.25°C. Table 2 shows the data format for the

remote temperature low byte.

Temperature Data Format

The ADT7481 has two temperature data formats. When

the temperature measurement range is from 0°C to +127°C

(default), the temperature data format is binary for both local

and remote temperature results. See the Temperature

Measurement Range section for information on how to

switch between the two data formats.

When the measurement range is in extended mode, an

offset binary data format is used for both local and remote

results. Temperature values in the offset binary data format

are offset by +64. Examples of temperatures in both data

formats are shown in Table 3.

Table 2. Extended Temperature Resolution

(Remote Temperature Low Byte)

Extended Resolution

Remote Temperature Low Byte

0.00°C

0.25°C

0.50°C

0.75°C

0 000 0000

0 100 0000

1 000 0000

1 100 0000

Table 3. Temperature Data Format

(Local and Remote Temperature High Byte)

Temperature

Binary

Offset Binary (Note 1)

When reading the full remote temperature value,

including both the high and low byte, the two registers

should be read LSB first and then the MSB. This is because

reading the LSB will cause the MSB to be locked until it is

read. This is to guarantee that the two values read are derived

from the same temperature measurement. The MSB register

updates only after it has been read. The MSB will not lock

if a SMBus repeat start is used between reading the two

registers. There needs to be a stop between reading the LSB

and MSB.

−55°C

0 000 0000

(Note 2)

0 000 1001

110°C

+1°C

0 000 0000

0 000 0001

0 000 1010

0 001 1001

0 011 0010

0 100 1011

0 110 0100

0 111 1101

0 111 1111

0 100 0000

0 100 0001

0 100 1010

0 101 1001

0 111 0010

1 000 1011

1 010 0100

1 011 1101

1 011 1111

1 101 0110

+10°C

+25°C

+50°C

+75°C

+100°C

+125°C

+127°C

+150°C

If the LSB register is read but not the MSB register, then

fail−safe protection is provided by the THERM and ALERT

signals which update with the latest temperature measurements

rather than the register values.

0 111 1111

(Note 3)

1. Offset binary scale temperature values are offset by +64.

2. Binary scale temperature measurement returns 0 for all

temperatures <0°C.

Temperature Measurement Range

The temperature measurement range for both local and

remote measurements is, by default, 0°C to +127°C.

However, the ADT7481 can be operated using an extended

temperature range. The temperature range in the extended

mode is −64°C to +191°C. The user can switch between these

two temperature ranges by setting or clearing Bit 2 in the

Configuration 1 register. A valid result is available in the next

measurement cycle after changing the temperature range.

3. Binary scale temperature measurement returns 127 for all

temperatures >127°C.

The user may switch between measurement ranges at any

time. Switching the range will also switch the data format.

The next temperature result following the switching will be

reported back to the register in the new format. However, the

contents of the limit registers will not change. It is up to the

user to ensure that when the data format changes, the limit

registers are reprogrammed as necessary. More information

on this can be found in the Limit Registers section.

Bit 2 Configuration Register 2 = 0 = 0°C to +127°C = default

Bit 2 Configuration Register 2 = 1 = −64°C to +191°C

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ADT7481

Registers

Temperature Value Registers

The registers in the ADT7481 are eight bits wide. These

registers are used to store the results of remote and local

temperature measurements, high and low temperature limits,

and to configure and control the device. A description of these

registers follows.

The ADT7481 has five registers to store the results of

local and remote temperature measurements. These

registers can only be written to by the ADC and read by the

user over the SMBus.

• The local temperature value register is at Address 0x00.

• The Remote 1 temperature value high byte register is at

Address 0x01, with the Remote 1 low byte register at

Address 0x10.

• The Remote 2 temperature value high byte register is at

Address 0x30, with the Remote 2 low byte register at

Address 0x33.

• The Remote 2 temperature values can also be read from

Address 0x01 for the high byte, and Address 0x10 for the

low byte if Bit 3 of Configuration Register 1 is set to 1.

Address Pointer Register

The address pointer register does not have, nor does it

require, an address because the first byte of every write

operation is automatically written to this register. The data

in this first byte always contains the address of another

register on the ADT7481, which is stored in the address

pointer register. It is to this register address that the second

byte of a write operation is written to, or to which a

subsequent read operation is performed.

The power−on default value of the address pointer register

is 0x00, so if a read operation is performed immediately after

power−on, without first writing to the address pointer, the

value of the local temperature will be returned since its

register address is 0x00.

• To read the Remote 1 temperature values, set Bit 3 of

Configuration Register 1 to 0.

• The power−on default value for all five registers is 0x00.

Table 4. Configuration 1 Register (Read Address 0x03, Write Address 0x09)

Bit

Mnemonic

Function

7

Mask

Setting this bit to 1 masks all ALERTs on the ALERT pin. Default = 0 = ALERT enabled. This applies only if Pin 8 is

configured as ALERT, otherwise it has no effect.

6

Mon/STBY

Setting this bit to 1 places the ADT7481 in standby mode, that is, it suspends all temperature measurements

(ADC). The SMBus remains active and values can be written to, and read from, the registers. However THERM

and ALERT are not active in standby mode, and their states in standby mode are not reliable.

Default = 0 = temperature monitoring enabled.

5

4

3

AL/TH

This bit selects the function of Pin 8. Default = 0 = ALERT. Setting this bit to 1 configures Pin 8 as the THERM2 pin.

Reserved for future use.

Reserved

Remote

1/2

Setting this bit to 1 enables the user to read the Remote 2 values from the Remote 1 registers. When default = 0,

Remote 1 temperature values and limits are read from these registers.

2

Temp

Range

Setting this bit to 1 enables the extended temperature measurement range of −64°C to +191°C. When using the

default = 0, the temperature range is 0°C to +127°C.

1

0

Mask R1

Mask R2

Setting this bit to 1 masks ALERTs due to the Remote 1 temperature exceeding a programmed limit. Default = 0.

Setting this bit to 1 masks ALERTs due to the Remote 2 temperature exceeding a programmed limit. Default = 0.

Table 5. Configuration 2 Register (Address 0x24)

Bit

Mnemonic

Function

7

Lock Bit

Setting this bit to 1 locks all lockable registers to their current values. This prevents tampering with settings until

the device is powered down. Default = 0.

<6:0>

Res

Reserved for future use.

Conversion Rate/Channel Selector Register

This register can be written to, and read back from, the

SMBus. The default value of this register is 0x08, giving a

rate of 16 conversions per second. Using slower conversion

times greatly reduces the device power consumption.

Bit 7 in this register can be used to disable averaging of the

temperature measurements. All temperature channels are

measured by default. It is possible to configure the

ADT7481 to measure the temperature of one channel only.

This can be configured using Bit 4 and Bit 5 (see Table 6).

The conversion rate/channel selector register for reads is

at Address 0x04, and at Address 0x0A for writes. The four

LSBs of this register are used to program the conversion

times from 15.5 ms (Code 0x0A) to 16 seconds (Code

0x00). To program the ADT7481 to perform continuous

measurements, set the conversion rate register to 0x0B. For

example, a conversion rate of eight conversions/second

means that beginning at 125 ms intervals, the device

performs a conversion on the local and the remote

temperature channels.

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Table 6. Conversion Rate/Channel Selector Register (Read Address 0x04, Write Address 0x0A)

Bit

Mnemonic

Function

7

Averaging

Setting this bit to 1 disables averaging of the temperature measurements at the slower conversion

rates (averaging cannot take place at the three faster rates, so setting this bit has no effect). When

default = 0, averaging is enabled.

6

Reserved

Reserved for future use. Do not write to this bit.

<5:4>

Channel Selector

These bits are used to select the temperature measurement channels:

00 = Round robin = default = all channels measured

01 = Local temperature only measured

10 = Remote 1 temperature only measured

11 = Remote 2 temperature only measured

<3:0>

Conversion Rates

These bits set how often the ADT7481 measures each temperature channel.

Conversion rates are as follows:

Conversions/sec

Time (seconds)

0000 = 0.0625

0001 = 0.125

0010 = 0.25

0011 = 0.5

0100 = 1

16

8

4

2

1

0101 = 2

500 m

250 m

125 m

62.5 m

31.25 m

15.5 m

0110 = 4

0111 = 8 = default

1000 = 16

1001 = 32

1010 = 64

1011 = continuous measurements

73 m (averaging enabled)

Limit Registers

used, the limit register value should be 0000 1010b. If the

scale is switched to offset binary, the value in the low

temperature limit register should be reprogrammed to be

0100 1010b.

The ADT7481 has three limits for each temperature

channel: high, low, and THERM temperature limits for

local, Remote 1, and Remote 2 temperature measurements.

The remote temperature high and low limits span two

registers each to contain an upper and lower byte for each

limit. There is also a THERM hysteresis register. All limit

registers can be written to, and read back from, the SMBus.

See Table 11 for details of the limit register addresses and

power−on default values.

Status Registers

The status registers are read−only registers, at Address

0x02 (Status Register 1) and Address 0x23 (Status

Register 2). They contain status information for the

ADT7481.

C will result in an out−of−limit condition, setting a flag in

the status register.

If the low limit register is programmed with 0°C,

measuring 0°C or lower will result in an out−of−limit

condition.

Table 7. Status Register 1 Bit Assignments

Bit

Mnemonic

Function

ALERT

7

6

BUSY

1 when ADC converting

No

1 when local high

temperature limit tripped

Yes

LHIGH

(Note 1)

Exceeding either the local or remote THERM limit asserts

THERM low. When Pin 8 is configured as THERM2,

exceeding either the local or remote high limit asserts

THERM2 low. A default hysteresis value of 10°C is

provided that applies to both THERM channels. This

hysteresis value may be reprogrammed.

It is important to remember that the temperature limits

data format is the same as the temperature measurement data

format. So if the temperature measurement uses the default

binary scale, then the temperature limits also use the binary

scale. If the temperature measurement scale is switched,

however, the temperature limits do not automatically

switch.

5

1 when local low

temperature limit tripped

Yes

LLOW

(Note 1)

1

4

3

R1HIGH

1 When Remote 1 High

Yes

Temperature Limit Tripped

1 When Remote 1 Low

Temperature Limit Tripped

R1LOW

(Note 1)

2

1 When Remote 1 Sensor

Open Circuit

Yes

D1 OPEN

(Note 1)

1

0

R1THRM1

1 when Remote1 THERM

Limit Tripped

No

LTHRM1

1 when local THERM Limit

Tripped

The user must reprogram the limit registers to the desired

value in the correct data format. For example, if the remote

low limit is set at 10°C and the default binary scale is being

1. These flags stay high until the status register is read, or they

are reset by POR.

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ADT7481

the ALERT. This bit gets reset when the ALERT output gets

reset. If the ALERT output is masked, then this bit is not set.

Table 8. Status Register 2 Bit Assignments

Bit

Mnemonic

Function

ALERT

Offset Register

7

6

5

4

Res

Reserved for Future Use

No

Offset errors may be introduced into the remote

temperature measurement by clock noise or by the thermal

diode being located away from the hot spot. To achieve the

specified accuracy on this channel, these offsets must be

removed.

The offset values are stored as 10−bit, twos complement

values.

• The Remote 1 offset MSBs are stored in Register 0x11

and the LSBs are stored in Register 0x12 (low byte, left

justified).

• The Remote 2 offset MSBs are stored in Register 0x34

and the LSBs are stored in Register 0x35 (low byte, left

justified). The Remote 2 offset can be written to, or

read from, the Remote 1 offset registers if Bit 3 of the

Configuration 1 register is set to 1. This bit should be

set to 0 (default) to read the Remote 1 offset values.

Only the upper two bits of the LSB registers are used. The

MSB of the MSB offset register is the sign bit. The minimum

offset that can be programmed is −128°C, and the maximum

is +127.75°C. The value in the offset register is added to, or

subtracted from, the measured value of the remote

temperature.

No

1 When Remote 2 High

Temperature Limit Tripped

Yes

R2HIGH

(Note 1)

3

2

1 When Remote 2 Low

Temperature Limit Tripped

Yes

R2LOW

(Note 1)

1 When Remote 2 Sensor

Open Circuit

D2 OPEN

(Note 1)

1

0

R2THRM1

1 When Remote 2

THERM Limit Tripped

No

ALERT

1 When ALERT Condition

Exists

1. These flags stay high until the status register is read, or they

are reset by POR.

The eight flags that can generate an ALERT are NOR’d

together. When any flag is high, the ALERT interrupt latch

is set and the ALERT output goes low (provided that the

flag(s) is/are not masked out).

Reading the Status 1 register will clear the five flags (Bit 6

through Bit 2) in Status Register 1, provided the error

conditions that caused the flags to be set have gone away.

Reading the Status 2 register will clear the three flags (Bit 4

through Bit 2) in Status Register 2, provided the error

conditions that caused the flags to be set have gone away. A

flag bit can only be reset if the corresponding value register

contains an in−limit measurement, or if the sensor is good.

The ALERT interrupt latch is not reset by reading the

status register. It will be reset when the ALERT output has

been serviced by the master reading the device address,

provided the error condition has gone away and the status

register flag bits have been reset.

When Flag 1 and/or Flag 0 of Status Register 1, or Flag 1

of Status Register 2 are set, the THERM output goes low to

indicate that the temperature measurements are outside the

programmed limits. The THERM output does not need to be

reset, unlike the ALERT output. Once the measurements are

within the limits, the corresponding status register bits are

reset automatically, and the THERM output goes high. The

user may add hysteresis by programming Register 0x21. The

THERM output will be reset only when the temperature falls

below the THERM limit minus hysteresis.

The offset register powers up with a default value of 0°C

and will have no effect unless the user writes a different

value to it.

Table 9. Sample Offset Register Codes

Offset Value

0x11/0x34

0x12/0x35

−128°C

−4°C

1000 0000

1111 1100

1111 1111

0000 0000

0000 0001

0000 0100

0111 1111

00 00 0000

00 000000

10 00 0000

00 00 0000

01 00 0000

00 00 0000

11 00 0000

−1°C

−0.25°C

0°C

+0.25°C

+1°C

+4°C

+127.75°C

One−Shot Register

The one−shot register is used to initiate a conversion and

comparison cycle when the ADT7481 is in standby mode,

after which the device returns to standby. Writing to the

one−shot register address (0x0F) causes the ADT7481 to

perform a conversion and comparison on both the local and

the remote temperature channels. This is not a data register

as such, and it is the write operation to Address 0x0F that

causes the one−shot conversion. The data written to this

address is irrelevant and is not stored. However the ALERT

and THERM outputs are not operational in one−shot mode

and should not be used.

When Pin 8 is configured as THERM2, only the high

temperature limits are relevant. If Flag 6 and Flag 4 of Status

Register 1, or Flag 4 of Status Register 2 are set, the

THERM2 output goes low to indicate that the temperature

measurements are outside the programmed limits. Flag 5

and Flag 3 of Status Register 1, and Flag 3 of Status

Register 2 have no effect on THERM2. The behavior of

THERM2 is otherwise the same as THERM.

Bit 0 of Status Register 2 gets set whenever the ALERT

output is asserted low. Thus, the user need only read Status

Register 2 to determine if the ADT7481 is responsible for

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ADT7481

Consecutive ALERT Register

Table 10. Consecutive ALERT Register Bit

The value written to this register determines how many

out−of−limitmeasurements must occur before an ALERT is

generated. The default value is that one out−of−limit

measurement generates an ALERT. The maximum value

that can be chosen is 4.

Bit

Name

Description

7

SCL

Timeout

Set to 1, enables the SMBus SCL

timeout bit. Default = 0 = timeout

disabled. See the Serial Bus Interface

section for more information.

The purpose of this register is to allow the user to perform

some filtering of the output. This is particularly useful at the

fastest three conversion rates, where no averaging takes

place. This register is at Address 0x22. This register has

other functions that are listed in Table 10.

6

5

SDA

Set to 1 to enable the SMBus SDA

Timeout Bit. Default = 0 = Timeout

disabled. See the Serial Bus Interface

section for more information.

Timeout

Mask Local

Setting this bit to 1 masks ALERTs

due to the local temperature

exceeding a programmed limit.

Default = 0.

4

Res

Reserved for future use.

<3:0>

Consecutive

ALERT

These bits set the number of

consecutive out−of−limit

measurements that have to occur

before an ALERT is generated.

000x = 1

001x = 2

011x = 3

111x = 4

Table 11. List of Registers

Read

Address

(Hex)

Write

Address

(Hex)

Mnemonic

Power−On Default

Undefined

Comment

Lock

N/A

00

01

02

03

04

05

06

07

08

N/A

09

Address Pointer

No

Local Temperature Value

0000 0000 (0x00)

Remote 1 Temperature Value High Byte

Remote 2 Temperature Value High Byte

Status Register 1

0000 0000 (0x00)

Bit 3 Conf Reg = 0

Bit 3 Conf Reg = 1

No

0000 0000 (0x00)

No

Undefined

No

Configuration Register 1

0000 0000 (0x00)

Yes

N/A

0A

Conversion Rate/Channel Selector

Local Temperature High Limit

Local Temperature Low Limit

Remote 1 Temp High Limit High Byte

Remote 2 Temp High Limit High Byte

Remote 1 Temp Low Limit High Byte

Remote 2 Temp Low Limit High Byte

One−Shot

0000 0111 (0x07)

0B

0101 0101 (0x55) (85°C)

0000 0000 (0x00) (0°C)

0101 0101 (0x55) (85°C)

0000 0000 (0x00) (0°C)

0C

0D

0E

Bit 3 Conf Reg = 0

Bit 3 Conf Reg = 1

Bit 3 Conf Reg = 0

Bit 3 Conf Reg = 1

0E

0F

(Note 1)

10

11

12

13

14

19

20

N/A

11

Remote 1 Temperature Value Low Byte

Remote 2 Temperature Value Low Byte

Remote 1 Temperature Offset High Byte

Remote 2 Temperature Offset High Byte

Remote 1 Temperature Offset Low Byte

Remote 2 Temperature Offset Low Byte

Remote 1 Temp High Limit Low Byte

Remote 2 Temp High Limit Low Byte

Remote 1 Temp Low Limit Low Byte

Remote 2 Temp Low Limit Low Byte

Remote 1 THERM Limit

0000 0000

Bit 3 Conf Reg = 0

Bit 3 Conf Reg = 1

Bit 3 Conf Reg = 0

Bit 3 Conf Reg = 1

Bit 3 Conf Reg = 0

Bit 3 Conf Reg = 1

Bit 3 Conf Reg = 0

Bit 3 Conf Reg = 1

Bit 3 Conf Reg = 0

Bit 3 Conf Reg = 1

Bit 3 Conf Reg = 0

Bit 3 Conf Reg = 1

No

0000 0000

Yes

11

0000 0000

12

13

14

19

20

0000 0000

0101 0101 (0x55) (85°C)

Remote 2 THERM Limit

Local THERM Limit

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ADT7481

Table 11. List of Registers

Read

Address

(Hex)

Write

Address

(Hex)

Mnemonic

Power−On Default

Comment

Lock

21

22

23

24

30

31

32

33

34

35

36

37

39

3D

3E

21

22

THERM Hysteresis

0000 1010 (0x0A) (10°C)

0000 0001 (0x01)

Yes

No

Consecutive ALERT

Status Register 2

N/A

24

0000 0000 (0x00)

Configuration 2 Register

0000 0000 (0x00)

Yes

No

N/A

31

Remote 2 Temperature Value High Byte

Remote 2 Temp High Limit High Byte

Remote 2 Temp Low Limit High Byte

Remote 2 Temperature Value Low Byte

Remote 2 Temperature Offset High Byte

Remote 2 Temperature Offset Low Byte

Remote 2 Temp High Limit Low Byte

Remote 2 Temp Low Limit Low Byte

Remote 2 THERM Limit

0000 0000 (0x00)

0101 0101 (0x55) (85°C)

0000 0000 (0x00) (0°C)

0000 0000 (0x00)

Yes

No

32

N/A

34

0000 0000 (0x00)

Yes

35

0000 0000 (0x00)

36

0000 0000 (0x00) (0°C)

0101 0101 (0x55) (85°C)

1000 0001 (0x81)

37

39

N/A

Device ID

Manufacturer ID

0100 0001 (0x41)

N/A

1. Writing to Address 0F causes the ADT7481 to perform a single measurement. It is not a data register as such, and it does not matter

what data is written to it.

Serial Bus Interface

SMBus addresses, the ADT7481 and the ADT7481−1 are

Control of the ADT7481 is achieved via the serial bus.

The ADT7481 is connected to this bus as a slave device

under the control of a master device.

The ADT7481 has an SMBus timeout feature. When this

is enabled, the SMBus will typically timeout after 25 ms of

no activity. However, this feature is not enabled by default.

Set Bit 7 (SCL timeout bit) of the consecutive alert register

(Address 0x22) to enable the SCL timeout. Set Bit 6 (SDA

timeout bit) of the consecutive alert register (Address 0x22)

to enable the SDA timeout.

The ADT7481 supports packet error checking (PEC) and

its use is optional. It is triggered by supplying the extra clock

for the PEC byte. The PEC byte is calculated using CRC−8.

The frame check sequence (FCS) conforms to CRC−8 by the

polynomial:

functionally identical.

The serial bus protocol operates as follows:

The master initiates data transfer by establishing a start

condition, defined as a high−to−low transition on the serial

data line (SDATA) while the serial clock line (SCLK)

remains high. This indicates that an address/data stream

follows. All slave peripherals connected to the serial bus

respond to the start condition and shift in the next eight bits,

consisting of a 7−bit address (MSB first) plus a R/W bit,

which determines the direction of the data transfer, that is,

whether data will be written to, or read from, the slave

device. The peripheral with the address corresponding to the

transmitted address responds by pulling the data line low

during the low period before the ninth clock pulse, known as

the acknowledge bit. All other devices on the bus remain idle

while the selected device waits for data to be read from or

written to it. If the R/W bit is 0, the master writes to the slave

device. If the R/W bit is 1, the master reads from the slave

device.

C(x) + x⁸) x²) x¹) 1

(eq. 1)

Consult the SMBus 1.1 specification for more

information (www.smbus.org).

Addressing the Device

Data is sent over the serial bus in a sequence of nine clock

pulses, eight bits of data followed by an acknowledge bit

from the slave device. Transitions on the data line must

occur during the low period of the clock signal and remain

stable during the high period, since a low−to−high transition

when the clock is high may be interpreted as a stop signal.

The number of data bytes that can be transmitted over the

serial bus in a single read or write operation is limited only

by what the master and slave devices can handle.

In general, every SMBus device has a 7−bit device

address, except for some devices that have extended, 10−bit

addresses. When the master device sends a device address

over the bus, the slave device with that address responds.

The ADT7481 is available with one device address, 0x4C

(1001 100b). An ADT7481−1 is also available. The only

difference between the ADT7481 and the ADT7481−1 is the

SMBus address. The ADT7481−1 has a fixed SMBus

address of 0x4B (1001 011b). The addresses mentioned in

this datasheet are 7−bit addresses. The R/W bit needs to be

added to arrive at an 8−bit address. Other than the different

When all data bytes have been read or written, stop

conditions are established. In write mode, the master will

pull the data line high during the tenth clock pulse to assert

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ADT7481

a stop condition. In read mode, the master device will

To write data to one of the device data registers or to read

data from it, the address pointer register must be set so that

the correct data register is addressed. The first byte of a write

operation always contains a valid address that is stored in the

address pointer register. If data is to be written to the device,

the write operation contains a second data byte that is written

to the register selected by the address pointer register.

This procedure is illustrated in Figure 15. The device

address is sent over the bus followed by R/W set to 0 and

followed by two data bytes. The first data byte is the address

of the internal data register to be written to, which is stored

in the address pointer register. The second data byte is the

data to be written to the internal data register.

override the acknowledge bit by pulling the data line high

during the low period before the ninth clock pulse. This is

known as no acknowledge. The master will then take the

data line low during the low period before the tenth clock

pulse, then high during the tenth clock pulse to assert a stop

condition.

Any number of bytes of data may be transferred over the

serial bus in one operation, but it is not possible to mix read

and write in one operation because the type of operation is

determined at the beginning and cannot subsequently be

changed without starting a new operation. In the case of the

ADT7481, write operations contain either one or two bytes,

while read operations contain one byte.

1

9

1

9

SCL

D7

D6

D5

D4

D3

D2

D1

D0

0

1

R/W

0

1

SDA

ACK. BY

ADT7481

ACK. BY

ADT7481

START BY

MASTER

FRAME 1 DATA

SERIAL BUS ADDRESS BYTE

FRAME 2

ADDRESS POINTER REGISTER BYTE

1

9

SCL (CONTINUED)

SDA (CONTINUED)

D7

D6

D5

D4

D3

D2

D1

D0

ACK. BY

ADT7481

STOP BY

MASTER

FRAME 3

DATA

BYTE

Figure 15. Writing a Register Address to the Address Pointer Register, then Writing Data to the Selected Register

1

9

1

9

SCL

SDA

1

0

1

0

1

R/W

D7

D6

D5

D4

D3

D2

D1

D0

ACK. BY

ADT7481

ACK. BY STOP BY

ADT7481 MASTER

START BY

MASTER

FRAME 2

FRAME 1 DATA

SERIAL BUS ADDRESS BYTE

ADDRESS POINTER REGISTER BYTE

Figure 16. Writing to the Address Pointer Register Only

1

9

1

9

SCL

0

1

0

1

R/W

D7

D6

D5

D4

D3

D2

D1

D0

SDA

ACK. BY

ADT7481

ACK. BY STOP BY

ADT7481 MASTER

START BY

MASTER

FRAME 2

FRAME 1 DATA

SERIAL BUS ADDRESS BYTE

ADDRESS POINTER REGISTER BYTE

Figure 17. Reading from a Previously Selected Register

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ADT7481

When reading data from a register there are two possible

scenarios:

the SMBALERT line is pulled low by one of the devices, the

following procedure occurs as illustrated in Figure 18.

• If the address pointer register value of the ADT7481 is

unknown or not the desired value, it is necessary to set it

to the correct value before data can be read from the

desired data register. This is done by performing a write

to the ADT7481 as before, but only the data byte

containing the register read address is sent, as data is not

to be written to the register. This is shown in Figure 16.

MASTER

RECEIVES

SMBALERT

ALERT RESPONSE

ADDRESS

DEVICE

NO

ACK

START

RD ACK

STOP

ADDRESS

MASTER SENDS

ARA AND READ

COMMAND

DEVICE SENDS

ITS ADDRESS

Figure 18. Use of SMBALERT

A read operation is then performed consisting of the

serial bus address, R/W bit set to 1, followed by the data

byte read from the data register (shown in Figure 17).

• If the address pointer register is already at the desired

address, data can be read from the corresponding data

register without first writing to the address pointer

register, and the bus transaction shown in Figure 16 can

be omitted.

1. SMBALERT is pulled low.

2. Master initiates a read operation and sends the

alert response address (ARA = 0001 100). This is

a general call address that must not be used as a

specific device address.

3. The device with a low ALERT output responds to

the alert response address, and the master reads the

address from the responding device. An LSB of 1

is added because the device address is comprised

of seven bits. The address of the device is now

known and it can be interrogated in the usual way.

4. If more than one device has a low ALERT output,

the one with the lowest device address will have

priority, in accordance with normal SMBus

arbitration.

5. Once the ADT7481 has responded to the alert

response address, it will reset its ALERT output,

provided that the error condition that caused the

ALERT no longer exists. If the SMBALERT line

remains low, the master sends the ARA again, and

so on until all devices with low ALERT outputs

respond.

NOTES:It is possible to read a data byte from a data register

without first writing to the address pointer register.

However, if the address pointer register is already at the

correct value, it is not possible to write data to a register

without writing to the address pointer register. This is

because the first data byte of a write is always written to the

address pointer register.

Remember that some of the ADT7481 registers have

different addresses for read and write operations. The write

address of a register must be written to the address pointer

if data is to be written to that register, but it may not be

possible to read data from that address. The read address of

a register must be written to the address pointer before data

can be read from that register.

ALERT Output

Pin 8 can be configured as an ALERT output. The ALERT

output goes low whenever an out−of−limit measurement is

detected, or if the remote temperature sensor is open circuit.

It is an open−drain output and requires a pullup. Several

ALERT outputs can be wire−OR’ed together, so that the

common line will go low if one or more of the ALERT

outputs goes low.

The ALERT output can be used as an interrupt signal to a

processor, or it may be used as an SMBALERT. Slave

devices on the SMBus cannot normally signal to the bus

master that they want to talk, but the SMBALERT function

allows them to do so.

Masking the ALERT Output

The ALERT output can be masked for local, Remote 1,

Remote 2 or all three channels. This is done by setting the

appropriate mask bits in either the Configuration 1 register

(read address = 0x03, write address = 0x09) or in the

consecutive ALERT register (address = 0x22)

To mask ALERTs due to local temperature, set Bit 5 of the

consecutive ALERT register to 1. Default = 0.

To mask ALERTs due to Remote 1 temperature, set Bit 1 of

the Configuration 1 register to 1. Default = 0.

To mask ALERTs due to Remote 2 temperature, set Bit 0 of

the Configuration 1 register to 1. Default = 0.

One or more ALERT outputs can be connected to a

common SMBALERT line connected to the master. When

To mask ALERTs due to any channel, set Bit 7 of the

Configuration 1 register to 1. Default = 0.

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ADT7481

Low Power Standby Mode

Interrupt System

The ADT7481 can be put into low power standby mode

by setting Bit 6 (Mon/STBY bit) of the Configuration 1

register (Read Address 0x03, Write Address 0x09) to 1. The

ADT7481 operates normally when Bit 6 is 0. When Bit 6 is

1, the ADC is inhibited, and any conversion in progress is

terminated without writing the result to the corresponding

value register.

The SMBus is still enabled in low power standby mode.

Power consumption in this standby mode is reduced to a

typical of 5 mA if there is no SMBus activity, or up to 30 mA

if there are clock and data signals on the bus.

When the device is in standby mode, it is still possible to

initiate a one−shot conversion of both channels by writing to

the one−shot register (Address 0x0F), after which the device

will return to standby. It does not matter what is written to

the one−shot register, all data written to it is ignored. It is also

possible to write new values to the limit register while in

standby mode. ALERT and THERM are not available in

standby mode and, therefore, should not be used because the

state of these pins is unreliable.

The ADT7481 has two interrupt outputs, ALERT and

THERM. Both outputs have different functions and

behavior. ALERT is maskable and responds to violations of

software−programmed temperature limits or an

open−circuit fault on the remote diode. THERM is intended

as a fail−safe interrupt output that cannot be masked.

If the Remote 1, Remote 2, or local temperature exceeds

the programmed high temperature limits, or equals or

exceeds the low temperature limits, the ALERT output is

asserted low. An open−circuit fault on the remote diode also

causes ALERT to assert. ALERT is reset when serviced by

a master reading its device address, provided the error

condition has gone away, and the status register has been

reset.

The THERM output asserts low if the Remote 1,

Remote 2, or local temperature exceeds the programmed

THERM limits. The THERM temperature limits should

normally be equal to or greater than the high temperature

limits. THERM is automatically reset when the temperature

falls back within the (THERM − hysteresis) limit. The local

and remote THERM limits are set by default to 85°C. A

hysteresis value can be programmed, in which case THERM

will reset when the temperature falls to the limit value minus

the hysteresis value. This applies to both local and remote

measurement channels. The power−on hysteresis default

value is 10°C, but this may be reprogrammed to any value

after powerup.

Sensor Fault Detection

The ADT7481 has internal sensor fault detection circuitry

at its D+ input. This circuit can detect situations where a

remote diode is not connected, or is incorrectly connected,

to the ADT7481. If the voltage at D+ exceeds V − 1.0 V

DD

(typical), it signifies an open circuit between D+ and D−, and

consequently, trips the simple voltage comparator. The

output of this comparator is checked when a conversion is

initiated. Bit 2 (D1 open flag) of the Status Register 1

(Address 0x02) is set if a fault is detected on the Remote 1

channel. Bit 2 (D2 open flag) of the Status Register 2

(Address 0x23) is set if a fault is detected on the Remote 2

channel. If the ALERT pin is enabled, setting this flag will

cause ALERT to assert low.

The hysteresis loop on the THERM outputs is useful when

THERM is used for on/off control of a fan. The user’s

system can be set up so that when THERM asserts, a fan can

be switched on to cool the system. When THERM goes high

again, the fan can be switched off. Programming a hysteresis

value protects from fan jitter, a condition wherein the

temperature hovers around the THERM limit, and the fan is

constantly being switched on and off.

If a remote sensor is not used with the ADT7481, then the

D+ and D− inputs of the ADT7481 need to be tied together

to prevent the open flag from being continuously set.

Most temperature sensing diodes have an operating

temperature range of −55°C to +150°C. Above 150°C, they

lose their semiconductor characteristics and approximate

conductors instead. This results in a diode short, setting the

open flag. The remote diode in this case no longer gives an

Table 12. THERM Hysteresis

THERM Hysteresis

Binary Representation

0°C

1°C

0 000 0000

0 000 0001

0 000 1010

10°C

Figure 19 shows how the THERM and ALERT outputs

operate. A user may wish to use the ALERT output as a

SMBALERT to signal to the host via the SMBus that the

temperature has risen. The user could use the THERM

output to turn on a fan to cool the system, if the temperature

continues to increase. This method would ensure that there

is a fail−safe mechanism to cool the system, without the need

for host intervention.

accurate temperature measurement.

A read of the

temperature result register will give the last good

temperature measurement. The user should be aware that

while the diode fault is triggered, the temperature

measurement on the remote channels is likely to be

inaccurate.

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16

ADT7481

TEMPERATURE

100°C

90°C

80°C

70°C

60°C

50°C

40°C

When the THERM2 limit is exceeded, the THERM2

signal asserts low.

THERM LIMIT

• If the temperature continues to increase and exceeds the

THERM limit, the THERM output asserts low.

• , there is no hysteresis value shown.

• As the system cools further, and the temperature falls

below the THERM2 limit, the THERM2 signal resets.

Again, no hysteresis value is shown for THERM2.

THERM LIMIT−HYSTERESIS

HIGH TEMP LIMIT

RESET BY MASTER

4

ALERT

The temperature measurement could be either the local or

the remote temperature measurement.

1

THERM

2

3

Applications Information

Figure 19. Operation of the ALERT and THERM

Interrupts

Noise Filtering

For temperature sensors operating in noisy environments,

previous practice was to place a capacitor across the D+ and

D− pins to help combat the effects of noise. However, large

capacitances affect the accuracy of the temperature

measurement, leading to a recommended maximum

capacitor value of 1,000 pF.

• If the measured temperature exceeds the high

temperature limit, the ALERT output will assert low.

• If the temperature continues to increase and exceeds the

THERM limit, the THERM output asserts low. This can

be used to throttle the CPU clock or switch on a fan.

• The THERM output de−asserts (goes high) when the

temperature falls to THERM limit minus hysteresis. In

Figure 19, the default hysteresis value of 10°C is

shown.

• The ALERT output de−asserts only when the

temperature has fallen below the high temperature

limit, and the master has read the device address and

cleared the status register.

Pin 8 on the ADT7481 can be configured as either an

ALERT output or as an additional THERM output.

THERM2 will assert low when the temperature exceeds the

programmed local and/or remote high temperature limits. It

is reset in the same manner as THERM, and it is not

maskable. The programmed hysteresis value also applies to

THERM2.

Factors Affecting Diode Accuracy

Remote Sensing Diode

The ADT7481 is designed to work with substrate

transistors built into processors or with discrete transistors.

Substrate transistors will generally be PNP types with the

collector connected to the substrate. Discrete types can be

either a PNP or an NPN transistor connected as a diode (base

shorted to collector). If an NPN transistor is used, the

collector and base are connected to D+ and the emitter to D−.

If a PNP transistor is used, the collector and base are

connected to D− and the emitter to D+.

To reduce the error due to variations in both substrate and

discrete transistors, a number of factors should be taken into

consideration:

• The ideality factor, n , of the transistor is a measure of

f

Figure 20 shows how THERM and THERM2 might

operate together to implement two methods of cooling the

system. In this example, the THERM2 limits are set lower

than the THERM limits. The THERM2 output could be used

to turn on a fan. If the temperature continues to rise and

exceeds the THERM limits, the THERM output could

provide additional cooling by throttling the CPU.

the deviation of the thermal diode from ideal behavior.

The ADT7481 is trimmed for an n value of 1.008. Use

f

the following equation to calculate the error introduced

at a temperature, T (°C), when using a transistor where

n does not equal 1.008. Consult the processor data

f

sheet for the n values.

f

TEMPERATURE

ǒ

Ǔ

ǒ

Ǔ

DT + n_f* 1.008 ń1.008 273.15 Kelvin ) T

(eq. 2)

90°C

THERM LIMIT

80°C

70°C

60°C

To factor this in, the user can write the DT value to the

offset register. It will then automatically be added to, or

subtracted from, the temperature measurement by the

ADT7481.

THERM2 LIMIT

50°C

• Some CPU manufacturers specify the high and low

40°C

30°C

current levels of the substrate transistors. The high

current level of the ADT7481, I

, is 233 mA. The

HIGH

THERM2

low level current, I , is 14 mA. If the ADT7481

LOW

1

4

current levels do not match the current levels specified

by the CPU manufacturer, it may become necessary to

remove an offset. The CPU data sheet will advise

whether this offset needs to be removed and how to

THERM

3

2

Figure 20. Operation of the THERM and THERM2

Interrupts

http://onsemi.com

17

ADT7481

calculate it. This offset may be programmed to the

offset register. It is important to note that if more than

one offset must be considered, the algebraic sum of

these offsets must be programmed to the offset register.

• Place the ADT7481 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 range from 4 to 8 inches.

If a discrete transistor is being used with the ADT7481, the

best accuracy is obtained by choosing devices according to

the following criteria:

• Base−emitter voltage greater than 0.25 V at 6 mA, at the

highest operating temperature.

• Route the D+ and D− tracks close together, in parallel,

with grounded guard tracks on each side. To minimize

inductance and reduce noise pick up, a 5 mil track

width and spacing is recommended. Provide a ground

plane under the tracks if possible.

• Base−emitter voltage less than 0.95 V at 100 mA, at the

lowest operating temperature.

5MIL

GND

• Base resistance less than 100 W.

• Small variation in h (say 50 to 150) that indicates

D+

FE

tight control of V characteristics.

BE

Transistors, such as 2N3904, 2N3906, or equivalents in

SOT−23 packages, are suitable devices to use.

D–

Thermal Inertia and Self−Heating

GND

Accuracy depends on the temperature of the remote

sensing diode and/or the local temperature sensor being at

the same temperature as that being measured. A number of

factors can affect this. Ideally, the sensor should be in good

thermal contact with the part of the system being measured;

otherwise, the thermal inertia caused by the sensor’s mass

causes a lag in the response of the sensor to a temperature

change.

Figure 21. Typical Arrangement of Signal Tracks

• Try to minimize the number of copper/solder joints that

can cause thermocouple effects. Where copper/solder

joints are used, make sure that they are in both the D+

and D− path and at the same temperature.

In the case of the remote sensor, this should not be a

problem, since it will either be a substrate transistor in the

processor or a small package device, such as an SOT−23,

placed in close proximity to it.

• Thermocouple effects should not be a major problem as

1°C corresponds to about 200 mV, and thermocouple

voltages are about 3 mV/°C of temperature difference.

• Unless there are two thermocouples with a large

temperature differential between them, thermocouple

voltages should be much less than 200 mV.

The on−chip sensor, however, will often be remote from

the processor and only monitors the general ambient

temperature around the package. In practice, the ADT7481

package will be in electrical, and hence, thermal contact with

a PCB and may also be in a forced airflow. How accurately

the temperature of the board and/or the forced airflow

reflects the temperature to be measured will also affect the

accuracy of the measurement. Self−heating, due to the

power dissipated in the ADT7481 or the remote sensor,

causes the chip temperature of the device (or remote sensor)

to rise above ambient. However, the current forced through

the remote sensor is so small that self−heating is negligible.

The worst−case condition occurs when the ADT7481 is

converting at 64 conversions per second while sinking the

maximum current of 1 mA at the ALERT and THERM

output. In this case, the total power dissipation in the device

• Place a 0.1 mF bypass capacitor close to the V pin. In

DD

extremely noisy environments, an input filter capacitor

may be placed across D+ and D− close to the

ADT7481. This capacitance can affect the temperature

measurement, so care must be taken to ensure that any

capacitance seen at D+ and D− is a maximum of 1,000

pF. This maximum value includes the filter capacitance,

plus any cable or stray capacitance between the pins

and the sensor diode.

• If the distance to the remote sensor is more than 8

inches, the use of twisted pair cable is recommended. A

total of 6 feet to 12 feet of cable is needed.

• For really long distances (up to 100 feet), use shielded

twisted pair, such as Belden No. 8451 microphone

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

shield to GND close to the ADT7481. Leave the remote

end of the shield unconnected to avoid ground loops.

Because the measurement technique uses switched

current sources, excessive cable or filter capacitance can

affect the measurement. When using long cables, the filter

capacitance can be reduced or removed.

is about 4.5 mW. The thermal resistance, q , of the

JA

MSOP−10 package is about 142°C/W.

Layout Considerations

Digital boards can be electrically noisy environments, and

the ADT7481 measures very small voltages from the remote

sensor, so care must be taken to minimize noise induced at

the sensor inputs. Take the following precautions:

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18

ADT7481

Application Circuit

The SCLK and SDATA pins of the ADT7481 can be

interfaced directly to the SMBus of an I/O controller, such

as the Intel® 820 chipset.

Figure 22 shows a typical application circuit for the

ADT7481, using discrete sensor transistors. The pullups on

SCLK, SDATA, and ALERT are required only if they are not

already provided elsewhere in the system.

V

3.0 to 3.6 V

DD

ADT7481

0.1mF

TYP 10kW

D1+

SCLK

SDATA

ALERT

THERM

2N3904/06

OR

CPU THERMAL

DIODE

5.0 V or 12 V

SMBUS

CONTROLLER

D1–

D2+

D2–

V

DD

TYP 10kW

GND

FAN CONTROL

CIRCUIT

FAN ENABLE

Figure 22. Typical Application Circuit

ORDERING INFORMATION

†

Device Order Number*

ADT7481ARMZ

Package Type

Shipping

50 Tube

Branding

T08

SMBus Address

10-Lead MSOP

4C

4B

ADT7481ARMZ-REEL

ADT7481ARMZ-R7

ADT7481ARMZ-001

ADT7481ARMZ-1RL

ADT7481ARMZ-1R7

3000 Tape & Reel

1000 Tape & Reel

50 Tube

T08

T0M

3000 Tape & Reel

1000 Tape & Reel

T0M

†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.

*The “Z’’ suffix indicates Pb−Free package available.

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19

ADT7481

PACKAGE DIMENSIONS

MSOP10

CASE 846AC−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.

Protected by U.S. Patents 5,195,827; 5,867,012, 5,982,221; 6,097,239; 6,133,753; 6,169,442, other patents pending.

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

ADT7481/D

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20

是否无铅：	不含铅	生命周期：	Obsolete
包装说明：	LEAD FREE, MSOP-10	针数：	10
Reach Compliance Code：	unknown	风险等级：	5.17
最大精度（摄氏度）：	2.5 Cel	其他特性：	HYSTERESIS IS 0.5V
主体宽度：	3 mm	主体高度：	1.025 mm
主体长度或直径：	3 mm	外壳：	PLASTIC
JESD-609代码：	e3	安装特点：	SURFACE MOUNT
位数：	8	端子数量：	10
最大工作电流：	4 mA	最高工作温度：	120 °C
最低工作温度：		输出接口类型：	2-WIRE INTERFACE
封装主体材料：	PLASTIC/EPOXY	封装等效代码：	TSSOP10,.19,20
封装形状/形式：	SQUARE	电源：	3.3 V
传感器/换能器类型：	TEMPERATURE SENSOR,SWITCH/DIGITAL OUTPUT,SERIAL	子类别：	Other Sensors
最大供电电压：	3.6 V	最小供电电压：	3 V
表面贴装：	YES	端子面层：	Tin (Sn)
端接类型：	SOLDER	Base Number Matches：	1

型号	制造商	描述	替代类型	文档
ADT7481ARMZ-REEL	ONSEMI	Dual Channel Temperature Sensor and Overtemperature Alarm	类似代替
ADT7481ARMZ	ONSEMI	Dual Channel Temperature Sensor and Overtemperature Alarm	类似代替
ADT7481ARMZ-1RL	ONSEMI	Dual Channel Temperature Sensor and Overtemperature Alarm	类似代替

型号	制造商	描述	价格	文档
ADT7481ARMZ-1REEL	ADI	Dual Channel Temperature Sensor and Over Temperature Alarm	获取价格
ADT7481ARMZ-1REEL7	ADI	Dual Channel Temperature Sensor and Over Temperature Alarm	获取价格
ADT7481ARMZ-1RL	ONSEMI	Dual Channel Temperature Sensor and Overtemperature Alarm	获取价格
ADT7481ARMZ-R7	ONSEMI	Dual Channel Temperature Sensor and Overtemperature Alarm	获取价格
ADT7481ARMZ-REEL	ADI	Dual Channel Temperature Sensor and Over Temperature Alarm	获取价格
ADT7481ARMZ-REEL	ONSEMI	Dual Channel Temperature Sensor and Overtemperature Alarm	获取价格
ADT7481ARMZ-REEL7	ADI	Dual Channel Temperature Sensor and Over Temperature Alarm	获取价格
ADT7482	ADI	Dual Channel Temperature Sensor and Overtemperature Alarm	获取价格
ADT7482	ONSEMI	Dual Channel Temperature Sensor and Overtemperature Alarm	获取价格
ADT7482ARMZ	ADI	Dual Channel Temperature Sensor and Overtemperature Alarm	获取价格

ADT7481ARMZ-1R7

ADT7481ARMZ-1R7 概述

ADT7481ARMZ-1R7 规格参数

ADT7481ARMZ-1R7 数据手册

ADT7481ARMZ-1R7 替代型号

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