Analog Devices ADT7461 a Datasheet

±1°C Temperature Monitor with

FEATURES

On-chip and remote temperature sensor

0.25°C resolution/1°C accuracy on remote channel
1°C resolution/3°C accuracy on local channel
Automatically cancels up to 3 kΩ (typ) of resistance in series

with remote diode to allow noise filtering

Extended, switchable temperature measurement range 0°C

to +127°C (default) or –55°C to +150°C
Pin- and register-compatible with ADM1032
2-wire SMBus serial interface with SMBus alert support
Programmable over/under temperature limits
Offset registers for system calibration

THERM

Up to two overtemperature fail-safe
Small 8-lead SOIC or MSOP package
170 µA operating current, 5.5 µA standby current

APPLICATIONS

Desktop and notebook computers
Industrial controllers
Smart batteries
Automotive
Enbedded systems
Burn-in applications
Instrumentation

outputs

Series Resistance Cancellation

ADT7461

GENERAL DESCRIPTION

The ADT74611 is a dual-channel digital thermometer and
under/over temperature alarm, intended for use in PCs and
thermal management systems. It is pin- and register-compatible
with the ADM1032. The ADT7461 has three additional features:
series resistance cancellation (where up to 3 kΩ (typical) of
resistance in series with the temperature monitoring diode may
be automatically cancelled from the temperature result, allowing

ALERT

noise filtering); configurable
switchable temperature measurement range.

The ADT7461 can accurately measure the temperature of a
remote thermal diode to ±1°C and the ambient temperature to
±3°C. The temperature measurement range defaults to 0°C to
+127°C, compatible with the ADM1032, but can be switched to
a wider measurement range of−55°C to +150°C. The ADT7461
communicates over a 2-wire serial interface compatible with
system management bus (SMBus) standards. An
signals when the on-chip or remote temperature is out of range.

THERM

The

output is a comparator output that allows on/off
control of a cooling fan. The
as a second

THERM

output, if required.

1

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.

output; and an extended,

ALERT

output can be reconfigured

ALERT

output

CONVERSION RATE

ON-CHIP

TEMPERATURE

SENSOR

ANALOG

MUX

D+

2

SRC

BLOCK

3

D–

EXTERNAL DIODE OPEN-CIRCUIT

ADT7461

DD

ADC

REGISTER

LOCAL TEMPERATURE

VALUE REGISTER

RUN/STANDBYBUSY

REMOTE TEMPERATURE

VALUE REGISTER

REMOTE OFFSET

REGISTER

SMBus INTERFACE

Figure 1. Functional Block Diagram

Rev. A

Information furnished by Analog Devices is believed to be accurate and reliable.
However, no responsibility is assumed by Analog Devices for its use, nor for any
infringements of patents or other rights of third parties that may result from its use.
Specifications subject to change without notice. No license is granted by implication
or otherwise under any patent or patent rights of Analog Devices. Trademarks and
registered trademarks are the property of their respective owners.

DIGITAL MUX

STATUS REGISTER

751 8

SCLKSDATAGNDV

ADDRESS POINTER

REGISTER

LOCAL TEMPERATURE

LOW LIMIT REGISTER

LOCAL TEMPERATURE

HIGH LIMIT REGISTER

LIMIT

COMPARATOR

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: [phone]
Fax: [phone] © 2004 Analog Devices, Inc. All rights reserved.

REMOTE TEMPERATURE

LOW LIMIT REGISTER

REMOTE TEMPERATURE

HIGH LIMIT REGISTER

DIGITAL MUX

LOCAL THERM LIMIT

REGISTER

EXTERNAL THERM LIMIT

REGISTER

CONFIGURATION

REGISTER

INTERRUPT

MASKING

4

THERM ALERT/

6

THERM2

04110-0-012

www.analog.com

ADT7461

TABLE OF CONTENTS

Specifications....................................................................................3

Serial Bus Interface....................................................................14

SMBus Timing Specifications ........................................................4

Absolute Maximum Ratings...........................................................5

ESD Caution.................................................................................5

Pin Configuration and Function Descriptions............................6

Typical Performance Characteristics............................................7

Functional Description ...................................................................9

Series Resistance Cancellation...................................................9

Temperature Measurement Method.........................................9

Temperature Measurement Results.........................................10

Temperature Measurement Range ..........................................10

Temperature Data Format........................................................10

ADT7461 Registers ...................................................................11

REVISION HISTORY

10/04—Changed from Rev. 0 to Rev. A

Addressing the Device..............................................................14

ALERT

Output...........................................................................16

Low Power Standby Mode........................................................16

Sensor Fault Detection ............................................................. 16

The ADT7461 Interrupt System.............................................. 16

Application Information ..........................................................18

Factors Affecting Diode Accuracy ..........................................18

Thermal Inertia and Self-Heating...........................................18

Layout Considerations..............................................................19

Application Circuit....................................................................20

Outline Dimensions......................................................................21

Ordering Guide .........................................................................21

Change to SMBus specifications................................................4

Changes to Figure 6 and Figure 10............................................7

Added Figure 9 and Figure 13....................................................7

Changes to Temperature Measurement section....................10

Changes to Figure 19 and Figure 25........................................16

Changes to Serial Bus Interface section..................................14

10/03—Revision 0: Initial Version

Rev. A | Page 2 of 24

ADT7461

SPECIFICATIONS

TA = −40°C to +120°C, VDD = 3 V to 5.5 V, unless otherwise noted.

Table 1.

Parameter Min Typ Max Unit Test Conditions

POWER SUPPLY

Supply Voltage, VDD 3.0 3.30 5.5 V
Average Operating Supply Current, IDD 170 215 µA 0.0625 conversions/sec rate1

5.5 10 µA Standby mode , –40°C ≤ TA ≤ +85°C

5.5 20 µA Standby mode, +85°C ≤ TA ≤ +120°C
Undervoltage Lockout Threshold 2.2 2.55 2.8 V VDD input, disables ADC, rising edge
Power-On-Reset Threshold 1 2.5 V

TEMPERATURE-TO-DIGITAL CONVERTER

Local Sensor Accuracy ±1 ±3 °C −40°C ≤ TA ≤ +100°C, 3 V ≤ VDD ≤ 3.6 V
Resolution 1 °C
Remote Diode Sensor Accuracy ±1 °C +60°C ≤ TA ≤ +100°C, −55°C ≤ T
±3 °C −40°C ≤ TA ≤ +120°C, −55°C ≤ T
Resolution 0.25 °C
Remote Sensor Source Current 96 µA High level

3

36 µA Middle level3
6 µA Low level3
Conversion Time 32.13 114.6 ms

From stop bit to conversion complete (both channels), one­shot mode with averaging switched on

3.2 12.56 ms

One-shot mode with averaging off (i.e., conversion rate = 16,
32, or 64 conversions per second)

Maximum Series Resistance Cancelled 3 kΩ Resistance split evenly on both the D+ and D– inputs

OPEN-DRAIN DIGITAL OUTPUTS

THERM, ALERT/THERM2

(

)
Output Low Voltage, VOL 0.4 V I
High Level Output Leakage Current, I
ALERT

Output Low Sink Current

SMBus INTERFACE

Logic Input High Voltage, V

3, 4

IH

OUT

0.1 1 µA V

OH

1 mA

OUT

ALERT

2.1 V 3 V ≤ VDD ≤ 3.6 V

= −6.0 mA3

= VDD 3

forced to 0.4 V

SCLK, SDATA

Logic Input Low Voltage, VIL 0.8 V 3 V ≤ VDD ≤ 3.6 V

SCLK, SDATA
Hysteresis 500 mV
SMBus Output Low Sink Current 6 mA SDATA forced to 0.6 V
Logic Input Current, IIH, IIL −1 +1 µA
SMBus Input Capacitance, SCLK, SDATA 5 pF
SMBus Clock Frequency 400 kHz
SMBus Timeout5 25 64 ms User programmable
SCLK Falling Edge to SDATA Valid Time 1 µs Master clocking in data

1

See for information on other conversion rates. Table 8

2

Guaranteed by characterization, but not production tested.

3

Guaranteed by design, but not production tested.

4

See section for more information. SMBUS Timing Specifications

5

Disabled by default. Details on how to enable it are in the SMBus section of this data sheet.

2

≤ +150°C, 3 V ≤ VDD ≤ 3.6 V

D

2

≤ +150°C, 3 V ≤ VDD ≤ 5.5 V

D

Rev. A | Page 3 of 24

ADT7461

SMBus TIMING SPECIFICATIONS

Table 2. SMBus Timing Specifications

Parameter Limit at T

f
t
t

SCLK

LOW

HIGH

400 kHz max

1.3 µs min Clock low period, between 10% points

0.6 µs min Clock high period, between 90% points

MIN

and T

tR 300 ns max Clock/data rise time
tF 300 ns max Clock/data fall time
t

600 ns min Start condition setup time

SU; STA

2

t

600 ns min Start condition hold time

HD; STA

3

t

100 ns min Data setup time

SU; DAT

t

HD; DAT

4

t

SU; STO

t

1.3 µs min Bus bree time between stop and start conditions

BUF

300 ns min Data hold time
600 ns min Stop condition setup time

1

Guaranteed by design, but 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.

MAX

1

Unit Description

SCLK

SDATA

t

t

HD;DAT

R

t

LOW

t

HD;STA

t

BUF

STOP START STOPSTART

t

F

t

HIGH

t

SU;DAT

Figure 2. Serial Bus Timing

t

SU;STA

t

HD;STA

t

SU;STO

04110-0-001

Rev. A | Page 4 of 24

ADT7461

ABSOLUTE MAXIMUM RATINGS

Table 3.

Parameter Rating

Positive Supply Voltage (VDD) to GND −0.3 V, +5.5 V
D+ −0.3 V to VDD + 0.3 V
D− to GND −0.3 V to +0.6 V

SCLK, SDATA,
THERM

Input Current, SDATA,
Input Current, D− ±1 mA
ESD Rating, All Pins (Human Body Model) 2000 V
Maximum Junction Temperature (TJ Max) 150°C
Storage Temperature Range −65°C to +150°C
IR Reflow Peak Temperature 220°C

Pb-Free Parts Only 260°C (±0.5°C)

Lead Temperature (Soldering 10 sec) 300°C

ALERT

THERM

−0.3 V to +5.5 V

−0.3 V to VDD + 0.3 V

−1 mA, +50 mA

Thermal Characteristics

8-Lead SOIC Package

= 121°C/W

θ

JA

8-Lead MSOP Package

= 142°C/W

θ

JA

Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.

ESD CAUTION

ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on
the human body and test equipment and can discharge without detection. Although this product features
proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy
electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance
degradation or loss of functionality.

Rev. A | Page 5 of 24

ADT7461

PIN CONFIGURATION AND FUNCTION DESCRIPTIONS

V

THERM

DD

D+
D–

1
2

ADT7461

TOP VIEW

3

(Not to Scale)

4

SCLK

8

SDATA

7

ALERT/THERM2

6

GND

5

04110-0-013

Figure 3. Pin Configuration

Table 4. Pin Function Descriptions

Pin No. Mnemonic Description

1 VDD Positive Supply, 3 V to 5.5 V.
2 D+ Positive Connection to Remote Temperature Sensor.
3 D− Negative Connection to Remote Temperature Sensor.

4

THERM

Open-drain output that can be used to turn a fan on/off or throttle a CPU clock in the event of an
overtemperature condition. Requires pull-up to V

.

DD

5 GND Supply Ground Connection.

6

ALERT/THERM2

Open-Drain Logic Output Used as Interrupt or SMBus Alert. This may also be configured as a second

output. Requires pull-up resistor.
7 SDATA Logic Input/Output, SMBus Serial Data. Open-Drain Output. Requires pull-up resistor.
8 SCLK Logic Input, SMBus Serial Clock. Requires pull-up resistor.

THERM

Rev. A | Page 6 of 24

ADT7461

TYPICAL PERFORMANCE CHARACTERISTICS

60

40

D+ TO GND

20

0

20

15

10

250mV EXTERNAL

100mV INTERNAL

5

–20

D+ TO V

–40

TEMPERATURE ERROR (°C)

–60

–80

0 20406080

CC

100

LEAKAGE RESISTANCE (MΩ)

Figure 4. Temperature Error vs. Leakage Resistance

0

–0.1

–0.2

–0.3

–0.4

–0.5

–0.6

TEMPERATURE ERROR (°C)

–0.7

–0.8

–3 –10 10 30 50 70 90 110 130 150

TEMPERATURE (°C)

Figure 5. Temperature Error vs. Actual Temperature Using 2N3906

04110-0-017

04110-0-022

0

–5

TEMPERATURE ERROR (°C)

–10

–15

020

250mV INTERNAL

FREQUENCY (MHz)

100mV EXTERNAL

40

Figure 7. Temperature Error vs. Power Supply Noise Frequency

0

–10

–20

–30

–40

–50

TEMPERATURE ERROR (°C)

–60

–70

0 5 10 15 20

CAPACITANCE (nF)

25

Figure 8. Temperature Error vs. Capacitance between D+ and D−

04110-0-015

04110-0-018

4

3

2

1

0

TEMPERATURE ERROR (°C)

–1

–2

0 100 200 300

40mV NO FILTER
60mV NO FILTER
40mV WITH FILTER
60mV WITH FILTER

FREQUENCY (MHz)

400 500 600

Figure 6. Temperature Error vs. Differential Mode Noise Frequency

(With and Without R-C-R Filter of 100 Ω–2.2 nF–100 Ω)

04110-0-027

Rev. A | Page 7 of 24

180

160

140

120

100

80

60

40

TEMPERATURE ERROR (°C)

20

0

–20

0 100 200 300

FREQUENCY (MHz)

100mV NO FILTER

100mV WITH FILTER

400 500 600

04110-0-024

Figure 9. Temperature Error vs. 100 mV Differential Mode Noise Frequency

(With and Without R-C-R Filter of 100 Ω–2.2 nF–100 Ω)

ADT7461

5

4

3

40mV NO FILTER
60mV NO FILTER
40mV WITH FILTER
60mV WITH FILTER

55

45

100mV NO FILTER

35

2

1

TEMPERATURE ERROR (°C)

0

–1

0 100 200 300

FREQUENCY (MHz)

400 500 600

Figure 10. Temperature Error vs. Common-Mode Noise Frequency

(With and Without R-C-R Filter of 100 Ω–2.2 nF–100 Ω)

40

35

30

25

(µA)

20

DD

I

15

10

5

0

0 100 200 300

SCL CLOCK FREQUENCY (kHz)

5.5V

3V

40050 150 250 350

Figure 11. Standby Supply Current vs. Clock Frequency

04110-0-025

04110-0-020

25

15

TEMPERATURE ERROR (°C)

5

–5

0 100 200 300

FREQUENCY (MHz)

100mV WITH FILTER

400 500 600

04110-0-026

Figure 13. Temperature Error vs. 100 mV Common-Mode Noise Frequency

(With and Without R-C-R Filter of 100 Ω–2.2 nF–100 Ω)

800

700

600

500

(µA)

400

DD

I

300

200

100

0

0.01 0.1 1 10
CONVERSION RATE (Hz)

5.5V

3V

04110-0-019

100

Figure 14. Operating Supply Current vs. Conversion Rate

7

6

5

4

(µA)

DD

I

3

2

1

0

3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 5.2 5.4
V

(V)

DD

Figure 12. Standby Current vs. Supply Voltage

04110-0-021

50
45
40
35
30
25
20
15
10

TEMPERATURE ERROR (°C)

5
0

–5

0 2 10 200 1k 2k 3k 4k

SERIES RESISTANCE (Ω)

3.3V T = –30

3.3V T = +25

3.3V T = +120

5.5V T = –30

5.5V T = +25

5.5V T = +120

Figure 15. Temperature Error vs. Series Resistance

04110-0-023

Rev. A | Page 8 of 24