ANALOG DEVICES ADT7408 Service Manual

±2°C Accurate, 12-Bit Digital

A1A0A

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FEATURES

12-bit temperature-to-digital converter
±2°C accuracy
Operation from −20°C to +125°C
Operation from 3 V to 3.6 V

240 μA typical average supply current
Selectable 1.5°C, 3°C, 6°C hysteresis
SMBus-/I2C®-compatible interface
Dual-purpose event pin: comparator or interrupt
8-lead LFCSP_VD, 3 mm × 3 mm (JEDEC MO-229 VEED-4)

package
Complies with JEDEC standard JC-42.4 memory module
Thermal sensor component specification

APPLICATIONS

Memory module temperature monitoring
Isolated sensors
Environmental control systems
Computer thermal monitoring
Thermal protection
Industrial process control
Power system monitors

1

2

2

3

Temperature Sensor

FUNCTIONAL BLOCK DIAGRAM

DD

8

12- / 10-Bit

LPF

B

I

T

-

1

1-BIT

DAC

MANUFACTURER’S

ID REGISTER

FACTORY

RESERVED

REGISTER

4

V

ss

Figure 1.

TEMPERATURE

SENSOR

REFERENCE

CLK

AND TIMING

GENERATION

ADT7408

DECIMATOR

+

–

∑-∆

ADDRESS

POINTER

REGISTER

SMBus/I²C I NTERFACE

ADT7408

DIGITAL CO MPARATOR

–

+

CAPABILITY

REGISTER

CONFIGURATIO N

REGISTER

ALARM TEMP

UPPER

BOUNDARY TRIP

REGISTER

ALARM TEMP

LOWER

BOUNDARY TRIP

REGISTER

CRITICAL TEMP

REGISTER

TEMPER ATURE

REGISTER

7

5

6

EVENT#

SDA

SCL

05716-001

GENERAL DESCRIPTION

The ADT7408 is the first digital temperature sensor that complies
with JEDEC standard JC-42.4 for the mobile platform memory
module. The ADT7408 contains a band gap temperature sensor
and a 12-bit ADC to monitor and digitize the temperature to a
resolution of 0.0625°C.

There is an open-drain EVENT# output that is active when the

onitoring temperature exceeds a critical programmable limit or

m
when the temperature falls above or below an alarm window.
This pin can operate in either comparator or interrupt mode.
There are three slave device address pins that allow up to eight
ADT7408s to be used in a system that monitors temperature of
various components and subsystems.

Rev. 0

Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Anal og Devices for its use, nor for any infringements of patents or ot her
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.

The ADT7408 is specified for operation at supply voltages from

3.0 V t

o 3.6 V. Operating at 3.3 V, the average supply current is
less than 240 µA typical. The ADT7408 offers a shutdown mode
that powers down the device and gives a shutdown current of 3 μA
typical. The ADT7408 is rated for operation over the −20°C to
+125°C temperature range. The ADT7408 is available in a lead­free, 8-lead LFCSP_VD, 3 mm × 3 mm (JEDEC MO-229 VEED-4)
package.

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: [phone] www.analog.com
Fax: [phone] ©2006 Analog Devices, Inc. All rights reserved.

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TABLE OF CONTENTS

Features.............................................................................................. 1

Applications....................................................................................... 1

Functional Block Diagram .............................................................. 1

General Description ......................................................................... 1

Revision History ............................................................................... 2

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

Timing Characteristics ................................................................ 4

Timing Diagram........................................................................... 4

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

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

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

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

Theory of Operation ........................................................................ 8

Circuit Information...................................................................... 8

Converter Details.......................................................................... 8

Address Pointer Register (Write Only).................................... 10

Capability Register (Read Only) .............................................. 10

Configuration Register (Read/Write)...................................... 11

Temperature Trip Point Registers ............................................ 13

ID Registers................................................................................. 14

Temperature Data Format......................................................... 15

Event Pin Functionality............................................................. 16

Serial Interface............................................................................ 17

SMBus/I

Application Information................................................................ 21

Thermal Response Time ........................................................... 21

Self-Heating Effects.................................................................... 21

Supply Decoupling..................................................................... 21

Temperature Monitoring........................................................... 21

Outline Dimensions....................................................................... 22

2

C Communications ................................................... 18

Modes of Operation ..................................................................... 8

Registers........................................................................................... 10

REVISION HISTORY

3/06—Revision 0: Initial Version

Ordering Guide .......................................................................... 22

Rev. 0 | Page 2 of 24

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SPECIFICATIONS

All specifications TA = −20°C to +125°C, VDD = 3.0 V to 3.6 V, unless otherwise noted.

Table 1.

Parameter Symbol Min Typ Max Unit Test Conditions/Comments

TEMPERATURE SENSOR AND ADC

Local Sensor Accuracy (C Grade) ±0.5 ±2.0 °C
±1 ±3.0 °C
±1 ±4.0 °C

75°C ≤ T
40°C ≤ T

−20°C ≤ T
ADC Resolution 12 Bits
Temperature Resolution 0.0625 °C
Temperature Conversion Time 60 125 ms
Long Term Drift 0.081 °C Drift over 10 years, if part is operated at 55°C

EVENT# OUTPUT (OPEN DRAIN)

Output Low Voltage, VOL 0.4 V IOL = 3 mA
Pin Capacitance 10 pF
High Output Leakage Current IOH 0.1 1 µA EVENT# = 3.6 V
Rise Time
Fall Time1 t

1

tLH 30 ns

30 ns

HL

RON Resistance (Low Output)1 15 Ω Supply and temperature dependent

DIGITAL INPUTS

Input Current IIH, IIL −1 +1 µA VIN = 0 V to VDD
Input Low Voltage VIL 0.8 V

Input High Voltage VIH 2.1 V

3.0 V ≤

3.0 V ≤ V
SCL, SDA Glitch Rejection1 50 ns Input filtering suppresses noise spikes of less than 50 ns
Pin Capacitance1 10 pF

DIGITAL OUTPUT (OPEN DRAIN)

Output Low Current
Output Low Voltage VOL 0.4 V

IOL 6 mA SDA forced to 0.6 V

3.0 V ≤
Output High Voltage VOH 2.1 V
Output Capacitance

1

C

10 pF

OUT

POWER REQUIREMENTS

Supply Voltage VDD 3.0 3.3 3.6 V
Average Supply Current IDD 240 500 µA
Supply Current I

360 550 µA Device current while converting

DD_CONV

Shutdown Mode at 3.3 V 3 20 µA
Average Power Dissipation PD 790 µW VDD = 3.3 V, normal mode at 25°C

1

Guaranteed by design and characterization, not production tested.

≤ 95°C, 3.0 V ≤ VDD ≤ 3.6 V active range

A

≤ 125°C, 3.0 V ≤ VDD ≤ 3.6 V monitor range

A

≤ 125°C, 3.0 V ≤ VDD ≤ 3.6 V

A

≤ 3.6 V

V

DD

≤ 3.6 V

DD

V

DD

≤ 3.6 V at I

OPULL_UP

= 350 μA

Rev. 0 | Page 3 of 24

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TIMING CHARACTERISTICS

TA = −20°C to +125°C, VDD = 3.0 V to 3.6 V, unless otherwise noted.

Table 2.

Parameter

SCL Clock Frequency f
Bus Free Time Between a Stop (P) and Start (S) Condition t
Hold Time After (Repeated) Start Condition t

Repeated Start Condition Setup Time t
High Period of the SCL Clock t
Low Period of the SCL Clock t
Fall Time of Both SDA and SCL Signals tF 300 ns
Rise Time of Both SDA and SCL Signals tR 1000 ns
Data Setup Time t
Data Hold Time t
Setup Time for Stop Condition t
Capacitive Load for Each Bus Line, C

1

Guaranteed by design and characterization, not production tested.

1

B

Symbol Min Typ Max Unit Comments

10 100 kHz

SCL

4.7 s

BUF

4.0 s

HD:STA

4.7 s

SU:STA

4.0 50 s

HIGH

4.7 s

LOW

250 ns

SU:DAT

300 ns

HD:DAT

4.0 s

SU:STO

After this period, the first clock
is genera

ted.

400 pF

TIMING DIAGRAM

V

IH

SCL

SDA

t

V

V

V

HD:STA

IL

IH

IL

t

BUF

PS P

t

LOW

t

R

t

HD:DAT

t

R

t

F

Figure 2. SMBus/I

t

F

t

HIGH

2

C Timing Diagram

t

SU:DAT

t

t

SU:STA

S

SU:STO

05716-002

Rev. 0 | Page 4 of 24

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ABSOLUTE MAXIMUM RATINGS

Table 3.

Parameter Rating

VDD to VSS –0.3 V to +7 V
SDA Input Voltage to VSS –0.3 V to VDD + 0.3 V
SDA Output Voltage to VSS –0.3 V to VDD + 0.3 V
SCL Input Voltage to VSS –0.3 V to VDD + 0.3 V
EVENT# Output Voltage to VSS –0.3 V to VDD + 0.3 V
Operating Temperature Range –55°C to +150°C
Storage Temperature Range –65°C to +160°C
Maximum Junction Temperature, T

150°C

JMAX

Thermal Resistance1

θJA, Junction-to-Ambient (Still Air)

85oC/W

IR Reflow Soldering Profile Refer to Figure 3

1

Power Dissipation P

temperature. Thermal resistance value relates to the package being used on
a standard 2-layer PCB, which gives a worst-case θJA. Some documents may
publish junction-to-case thermal resistance θJC, but it refers to a component
that is mounted on an ideal heat sink. As a result, junction-to-ambient
thermal resistance is more practical for air-cooled, PCB-mounted
components.

MAX

= (T

− TA)/θJA, where TA is the ambient

JMAX

Stresses above those listed under Absolute Maximum Ratings
ma

y 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.

RAMP UP

3°C/SE COND MAX

217°C

TEMPERATURE (° C)

60 – 150 SECONDS

260 – 5/+0°C

150°C – 200°C

RAMP DOW N

6°C/SECOND

MAX.

TIME (S econds

Figure 3.

60 – 180 SECONDS 20 – 40 SECONDS

480 SECONDS MAX.

LFCSP Pb-Free Reflow Profile Based on JEDEC J-STD-20C

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.

05716-003

Rev. 0 | Page 5 of 24

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PIN CONFIGURATION AND FUNCTION DESCRIPTIONS

A0 1

ADT7408

A1 2

TOP VIEW

A2 3

(Not to scal e)

4

SS

Figure 4. Pin Configuration

8 V

DD

7 EVENT#

6 SCL

5 SDA

05716-004

Table 4. Pin Function Descriptions

Pin No. Mnemonic Description

1 A0 SMBus/I2C Serial Bus Address Selection Pin. Logic input. Can be set to VSS or VDD.
2 A1 SMBus/I2C Serial Bus Address Selection Pin. Logic input. Can be set to VSS or VDD.
3 A2 SMBus/I2C Serial Bus Address Selection Pin. Logic input. Can be set to VSS or VDD.
4 V
5 SDA

Negative Supply or Ground.

SS

SMBus/I

2

C Serial Data Input/Output. Serial data to be loaded into the part’s registers and read from these registers

is provided on this pin. Open-drain configuration; it needs a pull-up resistor.

6 SCL

Serial Clock Input. This is the clock input f

or the serial port. The serial clock is used to clock data into and clock data

out from any register of the ADT7408. Open-drain configuration needs a pull-up resistor.
7 EVENT# Active Low. Open-drain event output pin. Driven low on comparator level or alert interrupt.
8 VDD Positive Supply Power. The supply should be decoupled to ground.

Rev. 0 | Page 6 of 24

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TYPICAL PERFORMANCE CHARACTERISTICS

0.4

VDD = 3.3V

0.3

0.2

0.1

0

–0.1

–0.2

TEMPERATURE E RROR (° C)

–0.3

–0.4

–40 20 400–20 60 80 100 120 140

TEMPERATURE (° C)

Figure 5. Temperature Accuracy

05716-015

5.0
TA = 85°C

4.5

4.0

3.5

3.0

2.5

2.0

1.5

SHUTDOWN CURRENT (µA)

1.0

0.5

0

3.0 3. 1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4.0

SUPPLY VOLTAGE (V)

Figure 8. Shutdown Current vs. Supply Voltage

05716-016

450

400

350

300

250

200

150

100

AVERAGE SUPPLY CURRENT (µA)

50

0

–40 –20 0 20 40 60 80 100 120 140

CONVERTING 3.3V

AVERAGE 3.3V

TEMPERATURE ( °C)

Figure 6. Supply Current vs. Temperature

300

TA = 85°C

275

250

225

200

0.25

TA = 85°C
V

= 3.3V ± 10%

DD

A 0.1µF CAPACIT OR IS CO NNECTED AT THE V

0.20

0.15

0.10

TEMPERATURE E RROR (° C)

0.05

05716-017

0

0123 54

SUPPLY RIPPLE FREQUENCY (MHz)

PIN.

DD

05716-018

6

Figure 9. Temperature Accuracy vs. Supply Ripple Frequency

175

AVERAGE SUPPLY CURRENT (µA)

150

3.0 3. 1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4.0

SUPPLY VOLTAGE (V)

05716-019

Figure 7. Supply Current vs. Supply Voltage

Rev. 0 | Page 7 of 24

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THEORY OF OPERATION

CIRCUIT INFORMATION

The ADT7408 is a 12-bit digital temperature sensor presented
in 13 bits, including the sign bit format (see the bit map in the
Temperature Value Register (Read Only) section). Its output is

os complement in that Bit D12 is the sign bit and Bit D0 to

tw
Bit D11 are data bits. An on-board sensor generates a voltage
precisely proportional to absolute temperature, which is
compared to an internal voltage reference and input to a
precision digital modulator. Overall accuracy for the ADT7408
is ±2°C from 75°C to 95°C, ±3°C from 40°C to +125°C, and
±4°C from −20°C to +125°C, with excellent transducer linearity.
The serial interface is SMBus-/I

2

C-compatible, and the open-

drain output of the ADT7408 is capable of sinking 6 mA.

The on-board temperature sensor has excellent accuracy and

arity over the entire rated temperature range without

line
needing correction or calibration by the user.

A first-order ∑-∆ modulator, also known as the charge balance
t

ype analog-to-digital converter (ADC), digitizes the sensor
output. This type of converter utilizes time domain oversampling
and a high accuracy comparator to deliver 12 bits of effective
accuracy in an extremely compact circuit.

CONVERTER DETAILS

The ∑-∆ modulator consists of an input sampler, a summing
network, an integrator, a comparator, and a 1-bit DAC, as
shown in Figure 10. This architecture creates a negative
feedback loop that minimizes the integrator output by changing
the duty cycle of the comparator output in response to input
voltage changes. There are two simultaneous but different
sampling operations in the device. The comparator samples the
output of the integrator at a much higher rate than the input
sampling frequency, that is, oversampling. Oversampling
spreads the quantization noise over a much wider band than
that of the input signal, improving overall noise performance
and increasing accuracy.

The modulated output of the comparator is encoded using a
cir

cuit technique that results in SMBus/I

Σ-∆ MODULATOR

VOLTAGE REF

AND VPTAT

CLOCK

GENERATOR

INTEGRATOR

+

–

Figure 10. First-Order Σ-Δ Modulator

1-BIT

DAC

LPF DIGITAL

COMPARATOR

2

C temperature data.

+

–

1-BIT

FILTER

12-BIT

TEMPERATURE
VALUE REGISTER

5716-005

MODES OF OPERATION

The conversion clock for the part is internally generated. No
external clock is required except when reading from and writing
to the serial port. In normal mode, the internal clock oscillator
runs an automatic conversion sequence that initiates a
conversion every 100 ms. At this time, the part powers up its
analog circuitry and performs a temperature conversion. This
temperature conversion typically takes 60 ms, after which time
the analog circuitry of the part automatically shuts down. The
analog circuitry powers up again 40 ms later, when the 100 ms
timer times out and the next conversion begins. Because the
SMBus/I
recent temperature conversion is always available in the
temperature value register.

The ADT7408 can be placed in shutdown mode via the
co
shut down, and no further conversions are initiated until the
ADT7408 is taken out of shutdown mode by writing 0 to Bit D8
in the configuration register. The conversion result from the last
conversion prior to shutdown can still be read from the ADT7408,
even when it is in shutdown mode.

In normal conversion mode, the internal clock oscillator is reset
a
start a temperature conversion, the result of which is typically
available 60 ms later. Similarly, when the part is taken out of
shutdown mode, the internal clock oscillator starts, and a
conversion is initiated. The conversion result is typically available
60 ms later. Reading from the device before a conversion is com­plete does not stop the ADT7408 from converting; the part does
not update the temperature value register immediately after the
conversion but waits until communication to the part is finished.
This read operation provides the previous result. It is possible to
miss a conversion result if the SCL frequency is very slow
(communication is greater than 40 ms), because the next
conversion will have started. There is a 40 ms window between
the end of one conversion and the start of the next conversion
for the temperature value register to be updated with a new
temperature value.

The measured temperature value is compared with the
t

emperature set at the alarm temperature upper boundary trip
register, the alarm temperature lower boundary trip register,
and the critical temperature trip register. If the measured value
exceeds these limits, then the EVENT# pin is activated. This
EVENT# output is programmable for interrupt mode, comparator
mode, and the output polarity via the configuration register.

The thermal sensor continuously monitors the temperature and
u
data is latched internally by the device and can be read by
software from the bus host at any time.

2

C circuitry never shuts down, the result of the most

nfiguration register, in which case the on-chip oscillator is

fter every read or write operation. This causes the device to

pdates the temperature data 10 times per second. Temperature

Rev. 0 | Page 8 of 24