Datasheet ADT7420 Datasheet (ANALOG DEVICES)

±0.25°C Accurate, 16-Bit Digital

ADT7420

Rev. PrE

Preliminary Technical Data

FEATURES

High performance

Temperature accuracy

±0.20°C from −10°C to +85°C at 3.0 V to 3.3 V

±0.25°C from −20°C to +105°C from 3.0 V to 3.6 V
16-bit temperature resolution: 0.0078°C
Ultralow temperature drift: 0.0073°C
NIST traceable or equivalent
Fast first temperature conversion on power-up of 6 ms

Easy implementation

No temperature calibration/correction required by user
No linearity correction required

Low power

Power-saving 1 sample per second (SPS) mode
700 µW typical at 3.3 V in normal mode
7 µW typical at 3.3 V in shutdown mode

Wide operating ranges

Temperature range: −40°C to +150°C
Voltage range: 2.7 V to 5.5 V

Programmable interrupts

Critical overtemperature interrupt
Overtemperature/undertemperature interrupt

I2C-compatible interface
16-lead, 4 mm × 4 mm LFCSP RoHS-compliant package

APPLICATIONS

RTD and thermistor replacement
Thermocouple cold junction compensation
Medical equipment
Industrial control and test
Food transportation and storage
Environmental monitoring and HVAC
Laser diode temperature control

FUNCTIONAL BLOCK DIAGRAM

12

V

DD

A0

A1

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.

CONFIGURATION

RESET REGISTER

3

4

REGISTER

T

LOW

REGISTER

T

HYST

REGISTER

ID

REGISTER

SOFTWARE

TEMPERATURE

VALUE REGISTER

T

CRIT

REGISTER

T

HIGH

REGISTER

STATUS

REGISTER

POINTER

REGISTER

INTERNAL

REFERENCE

TEMPERATURE

SENSOR

ADT7420

I2C INTERFACE

11

GND

Figure 1.

I2C Temperature Sensor

GENERAL DESCRIPTION

The ADT7420 is a high accuracy digital temperature sensor
offering breakthrough performance over a wide industrial range,
housed in a 4 mm × 4 mm LFCSP package. It contains an internal
band gap reference, a temperature sensor, and a 16-bit ADC to
monitor and digitize the temperature to 0.0078°C resolution.
The ADC resolution, by default, is set to 13 bits (0.0625°C).
The ADC resolution is a user programmable mode that can be
changed through the serial interface.

The ADT7420 is guaranteed to operate over supply voltages from

2.7 V to 5.5 V. Operating at 3.3 V, the average supply current is typi­cally 210 μA. The ADT7420 has a shutdown mode that powers
down the device and offers a shutdown current of typically 2.0 μA
at 3.3 V. The ADT7420 is rated for operation over the −40°C to
+150°C temperature range.

Pin A0 and Pin A1 are available for address selection, giving the

ADT7420 four possible I2C addresses. The CT pin is an open-

drain output that becomes active when the temperature exceeds
a programmable critical temperature limit. The INT pin is also
an open-drain output that becomes active when the tempera­ture exceeds a programmable limit. The INT pin and CT pin
can operate in comparator and interrupt event modes.

PRODUCT HIGHLIGHTS

1. Ease of use, no calibration or correction required by the user.

2. Low power consumption.

3. Excellent long-term stability and reliability.

4. High accuracy for industrial, instrumentation, and medical
applications.

5. Packaged in a 16-lead, 4 mm × 4 mm LFCSP RoHS­compliant package.

10

INTERNAL

OSCILLATOR

Σ-∆

MODULATOR

FILTER

LOGIC

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: [phone] www.analog.com
Fax: [phone] ©2011 Analog Devices, Inc. All rights reserved.

T

T

T

CRIT

HIGH

LOW

CT

9

INT

1

SCL

2

SDA

09013-001

ADT7420 Preliminary Technical Data

TABLE OF CONTENTS

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

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

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

Product Highlights ........................................................................... 1

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

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

I2C Timing Specifications ............................................................ 5

Absolute Maximum Ratings ............................................................ 6

ESD Caution .................................................................................. 6

Pin Configuration and Function Descriptions ............................. 7

Typical Performance Characteristics ............................................. 8

Theory of Operation ...................................................................... 10

Circuit Information .................................................................... 10

Converter Details........................................................................ 10

Normal Mode .............................................................................. 10

One-Shot Mode .......................................................................... 10

1 SPS Mode .................................................................................. 11

Shutdown ..................................................................................... 11

Fault Queue ................................................................................. 11

Temperature Data Format ......................................................... 12

Temperature Conversion Formulas ......................................... 12

Registers ........................................................................................... 13

Address Pointer Register ........................................................... 13

Temperature Value Registers ..................................................... 13

Status Register ............................................................................. 14

Configuration Register .............................................................. 14

T

Setpoint Registers ............................................................. 15

HIGH

T

Setpoint Registers .............................................................. 15

LOW

T

Setpoint Registers .............................................................. 15

CRIT

T

Setpoint Register ............................................................... 16

HYST

ID Register................................................................................... 16

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

Serial Bus Address ...................................................................... 17

Writing Data ............................................................................... 18

Reading Data ............................................................................... 19

Reset ............................................................................................. 20

General Call ................................................................................ 20

INT and CT Outputs ...................................................................... 21

Undertemperature and Overtemperature Detection ............ 21

Applications Information .............................................................. 23

Thermal Response Time ........................................................... 23

Supply Decoupling ..................................................................... 23

Powering from a Switching Regulator ..................................... 23

Temperature Measurement ....................................................... 23

Quick Guide to Measuring Temperature ................................ 23

Outline Dimensions ....................................................................... 24

Ordering Guide .......................................................................... 24

Rev. PrE | Page 2 of 24

Preliminary Technical Data ADT7420

SPECIFICATIONS

TA = −40°C to +125°C, VDD = 2.7 V to 5.5 V, unless otherwise noted.

Table 1.

Parameter Min Typ Max Unit Test Conditions/Comments

TEMPERATURE SENSOR AND ADC

Accuracy
±0.25

±0.30 °C TA = −40°C to +105°C, VDD = 3.0 V
±0.35 °C TA = −40°C to +105°C, VDD = 2.7 V to 3.3 V
±0.50 °C TA = −40°C to +125°C, VDD = 3.0 V to 3.6 V
±0.503 °C TA = −10°C to +105°C, VDD = 4.5 V to 5.5 V
±0.65 °C TA = −40°C to +125°C, VDD = 4.5 V to 5.5 V

−0.85 °C TA = +150°C, VDD = 4.5 V to 5.5 V

−1.0 °C TA = +150°C, VDD = 2.7 V to 3.6 V
ADC Resolution 13 Bits Twos complement temperature value of the

16 Bits Twos complement temperature value of the

Temperature Resolution

Temperature Conversion Time 240 ms Continuous conversion and one-shot

Fast Temperature Conversion Time 6 ms First conversion on power-up only
1 SPS Conversion Time 60 ms Conversion time for 1 SPS mode
Temperature Hysteresis ±0.002 °C Temperature cycle = 25°C to 125°C and back

Repeatability

Drift5 0.0073 °C 500 hour stress test at +150°C with VDD = 5.0 V
DC PSRR 0.1 °C/V TA = 25°C
DIGITAL OUTPUTS (CT, INT, SDA—OPEN DRAIN)

High Output Leakage Current, IOH 0.1 5 µA CT and INT pins pulled up to 5.5 V

Output Low Voltage, V

Output High Voltage, VOH 0.7 × VDD V

Output Capacitance, C
DIGITAL INPUTS (SCL, SDA, A0, A1)

Input Current ±1 µA VIN = 0 V to VDD

Input Low Voltage, VIL 0.3 × VDD V SCL and SDA only

0.4 V A0 and A1 only

Input High Voltage, V

2 V A0 and A1 only

SCL, SDA Glitch Rejection 50 ns Input filtering suppresses noise spikes of less

Pin Capacitance 2 10 pF
POWER REQUIREMENTS

Supply Voltage 2.7 5.5 V

Supply Current

1

13-Bit 0.0625 °C 13-bit resolution (sign + 12-bit)
16-Bit 0.0078 °C 16-bit resolution (sign + 15-bit)

4

OL

OUT

IH

At 3.3 V 210 265 µA Peak current while converting, I2C interface

At 5.5 V 250 300 µA Peak current while converting, I2C interface

0.0017 ±0.20

±0.015 °C TA = 25°C

0.4 V IOL = 3 mA at 5.5 V, IOL = 1 mA at 3.3 V

2 pF

0.7 × VDD V SCL and SDA only

±0.25

2

°C TA = −10°C to +85°C, VDD = 3.0 V to 3.3 V
°C
°C

TA = −20°C to +105°C, VDD = 3.0 V to 3.6 V
TA = −20°C to +85°C, VDD = 2.7 V

sign bit plus 12 ADC bits (power-up default
resolution)

sign bit plus 15 ADC bits (Bit 7 = 1 in the
configuration register)

conversion modes

to 25°C

than 50 ns

inactive

inactive

Rev. PrE | Page 3 of 24

ADT7420 Preliminary Technical Data

Parameter Min Typ Max Unit Test Conditions/Comments

1 SPS Current

At 3.3 V 46 µA VDD = 3.3 V, 1 SPS mode, TA = 25°C
At 5.5 V 65 µA VDD = 5.5 V, 1 SPS mode, TA = 25°C

Shutdown Current

At 3.3 V 2.0 15 µA Supply current in shutdown mode
At 5.5 V 5.2 25 µA Supply current in shutdown mode

Power Dissipation Normal Mode 700 µW VDD = 3.3 V, normal mode at 25°C
Power Dissipation 1 SPS 150 µW Power dissipated for VDD = 3.3 V, TA = 25°C

1

Accuracy specification includes repeatability.

2

The equivalent 3 σ limits are ±0.15°C. This 3 σ specification is provided to enable comparison with other vendors who use these limits.

3

For higher accuracy at 5 V operation, contact Analog Devices, Inc.

4

Based on a floating average of 10 readings.

5

Drift includes solder heat resistance and life time test performed as per JEDEC Standard JESD22-A108.

Rev. PrE | Page 4 of 24

Preliminary Technical Data ADT7420

t

I2C TIMING SPECIFICATIONS

TA = −40°C to +150°C, VDD = 2.7 V to 5.5 V, unless otherwise noted. All input signals are specified with rise time (tR) = fall time (tF) = 5 ns
(10% to 90% of VDD) and timed from a voltage level of 1.6 V.

Table 2.

Parameter Min Typ Max Unit Test Conditions/Comments

SERIAL INTERFACE1 See Figure 2

SCL Frequency 0 400 kHz

SCL High Pulse Width, t

SCL Low Pulse Width, t

SCL, SDA Rise Time, tR 0.3 µs

SCL, SDA Fall Time, t

Hold Time (Start Condition), t

Setup Time (Start Condition), t

Data Setup Time, t

Setup Time (Stop Condition), t

Data Hold Time, t

HD:DAT

Bus-Free Time (Between Stop and Start Condition), t

Capacitive Load for Each Bus Line, CB

1

Sample tested during initial release to ensure compliance.

0.6 µs

HIGH

1.3 µs

LOW

F

0.6 µs After this period, the first clock is generated

HD:STA

0.6 µs Relevant for repeated start condition

SU:STA

0.02 µs

SU:DAT

0.6 µs

SU:STO

0.3 µs

(Master) 0.03 µs

1.3 µs

BUF

400 pF

Timing Diagram

SCL

SDA

t

BUF

P S

t

HD:STA

t

LOW

R

t

HD:DAT

t

F

t

HIGH

t

SU:DAT

t

SU:STA

S

Figure 2. Serial Interface Timing Diagram

t

HD:STA

t

SU:STO

P

09013-002

Rev. PrE | Page 5 of 24

ADT7420 Preliminary Technical Data

ABSOLUTE MAXIMUM RATINGS

Table 3.

Parameter Rating

VDD to GND −0.3 V to +7 V
SDA Voltage to GND −0.3 V to VDD + 0.3 V
SCL Output Voltage to GND −0.3 V to VDD + 0.3 V
A0 Input Voltage to GND −0.3 V to VDD + 0.3 V
A1 Input Voltage to GND −0.3 V to VDD + 0.3 V
CT and INT Output Voltage to GND −0.3 V to VDD + 0.3 V
ESD Rating (Human Body Model) 2.0 kV
Operating Temperature Range

1

−40°C to +150°C
Storage Temperature Range −65°C to +160°C
Maximum Junction Temperature, T

150°C

JMAX

16-Lead LFCSP (CP-16-17)

Power Dissipation2 W

MAX

= (T

JMAX

− T

3

A

Thermal Impedance4

θJA, Junction-to-Ambient (Still Air) 37°C/W
θJC, Junction-to-Case 33°C/W

IR Reflow Soldering 220°C

Peak Temperature (RoHS-Compliant

260°C (+0°C/−5°C)

Package)
Time at Peak Temperature 20 sec to 40 sec
Ramp-Up Rate 3°C/sec maximum
Ramp-Down Rate −6°C/sec maximum
Time from 25°C to Peak Temperature 8 minutes maximum

1

Sustained operation above 125°C results in a shorter product lifetime. For

more information, contact Analog Devices.

2

Values relate to package being used on a standard 2-layer PCB. This gives a

worst-case θJA and θJC.

3

TA = ambient temperature.

4

Junction-to-case resistance is applicable to components featuring a

preferential flow direction, for example, components mounted on a heat
sink. Junction-to-ambient is more useful for air-cooled, PCB-mounted
components.

)/θJA

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

Rev. PrE | Page 6 of 24

Preliminary Technical Data ADT7420

NOTES

1. NC = NO CONNEC

BONDED

2.

EXPOSED

FLO

PIN CONFIGURATION AND FUNCTION DESCRIPTIONS

C

C

C

C

N

N

N

N

5

4

6

3

1

1

1

1

17 EP

1

SCL

SDA

A0

A1

TO ENSURE CORRECT OPERATION, THE

ADT7420

2

TOP VIEW

3

(Not to Scale)

4

5

6

C

C

N

N

T. THE NC PIN IS NOT

TO THE DIE INTERNALLY.

PAD SHOULD EITHER BE LEFT

ATING OR CONNECTED TO GROUND.

Figure 3. Pin Configuration

Table 4. Pin Function Descriptions

Pin No. Mnemonic Description

1 SCL I2C Serial Clock Input. The serial clock is used to clock in and clock out data to and from any register of the ADT7420.

Open-drain configuration. A pull-up resistor is required, typically 10 kΩ.

2 SDA I2C Serial Data Input/Output. Serial data to and from the part is provided on this pin. Open-drain configuration. A

pull-up resistor is required, typically 10 kΩ.
3 A0 I2C Serial Bus Address Selection Pin. Logic input. Connect to GND or VDD to set an I2C address.
4 A1 I2C Serial Bus Address Selection Pin. Logic input. Connect to GND or VDD to set an I2C address.
5 NC No Connect. The NC pin is not bonded to the die internally.
6 NC No Connect. The NC pin is not bonded to the die internally.
7 NC No Connect. The NC pin is not bonded to the die internally.
8 NC No Connect. The NC pin is not bonded to the die internally.
9 INT Overtemperature and Undertemperature Indicator. Logic output. Power-up default setting is as an active low

comparator interrupt. Open-drain configuration. A pull-up resistor is required, typically 10 kΩ.
10 CT Critical Overtemperature Indicator. Logic output. Power-up default polarity is active low. Open-drain configuration.

A pull-up resistor is required, typically 10 kΩ.
11 GND Analog and Digital Ground.
12 VDD Positive Supply Voltage (2.7 V to 5.5 V). The supply should be decoupled with a 0.1 µF ceramic capacitor to ground.
13 NC No Connect. The NC pin is not bonded to the die internally.
14 NC No Connect. The NC pin is not bonded to the die internally.
15 NC No Connect. The NC pin is not bonded to the die internally.
16 NC No Connect. The NC pin is not bonded to the die internally.
17 EP Exposed Pad. To ensure correct operation, the exposed pad should either be left floating or connected to ground.

12

V

DD

11

GND

10

CT

9

INT

8

7

C

C

N

N

09013-004

Rev. PrE | Page 7 of 24

ADT7420 Preliminary Technical Data

TEMPER

A

TURE ERROR (°C)

1.00

TEMPER

A

TURE ERROR (°C)

1.00

I

(

µ

A)

300

SHUTDOWN I

(

µ

A)

30

300

I

(

µ

A)

8

S

HU

T

D

O

W

N

I

(

µ

A

)

TYPICAL PERFORMANCE CHARACTERISTICS

0.75

0.50

0.25

–0.25

–0.50

–0.75

–1.00

0.75

0.50

0.25

–0.25

–0.50

–0.75

–1.00

0

–40–60 –20 0 20 40

Figure 4. Temperature Accuracy at 3 V

0

–40–60 –20 0 20 40

Figure 5. Temperature Accuracy at 5 V

MAX ACCURACY LIMITS

MAX ACCURACY LIMITS

60 80 100 120 140

TEMPERATURE (°C)

MAX ACCURACY LIMITS

MAX ACCURACY LIMITS

60 80 100 120 140

TEMPERATURE (°C)

25

20

DD

15

10

5

0
–100 –50 0 50 100 150 200

09013-027

TEMPERATURE (°C)

5.5V

5.0V

4.5V

3.6V

3.3V

3.0V

2.7V

09013-032

Figure 7. Shutdown Current vs. Temperature

250

200

150

DD

100

50

0

2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0

09013-026

IDD CONTINUOUS CONVERSION

IDD 1SPS

SUPPLY VOLTAGE (V)

09013-029

Figure 8. Average Operating Supply Current vs. Supply Voltage

5.5V CONTINUOUS

250

200

150

DD

100

CONVERSION

3.0V CONTINUOUS
CONVERSION

5.5V 1SPS

50

0
–100 –50 0 50 100 150 200

3.0V 1SPS

TEMPERATURE (°C)

Figure 6. Operating Supply Current vs. Temperature

09013-028

7

6

5

DD

4

3

2

1

0

2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0

SUPPLY VOLTAGE (V)

Figure 9. Shutdown Current vs. Supply Voltage

09013-210

Rev. PrE | Page 8 of 24

Preliminary Technical Data ADT7420

140

DUT TEMPER

A

TURE

(

°C)

120

100

80

60

40

20

0

0 5 10 15 2520

IT TAKES LESS THAN
2 SECONDS TO REACH 63.2%
OF ITS TEMPERATURE SPAN

125°C

105°C

85°C

TIME (s)

09013-110

Figure 10. Thermal Response Time

Rev. PrE | Page 9 of 24

ADT7420 Preliminary Technical Data

THEORY OF OPERATION

CIRCUIT INFORMATION

The ADT7420 is a high accuracy digital temperature sensor that
uses a 16-bit ADC to monitor and digitize the temperature to

0.0078°C of resolution. The ADC resolution, by default, is set to
13 bits (0.0625°C). An internal temperature sensor generates a
voltage proportional to absolute temperature, which is com­pared to an internal voltage reference and input into a precision
digital modulator.

The internal temperature sensor has high accuracy and linearity
over the entire rated temperature range without needing correc­tion or calibration by the user.

The sensor output is digitized by a sigma-delta (Σ-∆) modulator,
also known as the charge balance type analog-to-digital conver­ter. This type of converter utilizes time-domain oversampling
and a high accuracy comparator to deliver 16 bits of resolution
in an extremely compact circuit.

CONVERTER DETAILS

The Σ-∆ modulator consists of an input sampler, a summing
network, an integrator, a comparator, and a 1-bit DAC. This
architecture creates a negative feedback loop and minimizes the
integrator output by changing the duty cycle of the comparator
output in response to input voltage changes. The comparator
samples the output of the integrator at a much higher rate than
the input sampling frequency. This oversampling spreads the
quantization noise over a much wider band than that of the
input signal, improving overall noise performance and
increasing accuracy.

Σ-∆ MODULATOR

INTEGRATOR

VOLTAGE REF

AND VPTAT

CLOCK

GENERATOR

Figure 11. Σ-Δ Modulator

The ADT7420 can be configured to operate in any one of the
following four operating modes: normal, one-shot, 1 SPS, and
shutdown.

COMPARATOR

1-BIT

DAC

LPF DIGITAL

FILTER

1-BIT

13-BIT/

16-BIT

TEMPERATURE

VALUE

REGISTER

09013-012

NORMAL MODE

In normal mode (default power-up mode) the ADT7420 runs
an automatic conversion sequence. During this automatic
conversion sequence, a conversion typically takes 240 ms to
complete and the ADT7420 is continuously converting. This
means that as soon as one temperature conversion is completed,
another temperature conversion begins. Each temperature
conversion result is stored in the temperature value registers
and is available through the I2C interface. In continuous conver­sion mode, the read operation provides the most recent
converted result.

On power-up, the first conversion is a fast conversion, taking
typically 6 ms. If the temperature exceeds 147°C, the CT pin
asserts low. If the temperature exceeds 64°C, the INT pin asserts
low. Fast conversion temperature accuracy is typically within ±5°C.

The conversion clock for the part is generated internally.
No external clock is required except when reading from
and writing to the serial port.

The measured temperature value is compared with a critical
temperature limit (stored in the 16-bit T
register), a high temperature limit (stored in the 16-bit T

setpoint read/write

CRIT

HIGH

set­point read/write register), and a low temperature limit (stored
in the 16-bit T

setpoint read/write register). If the measured

LOW

value exceeds these limits, the INT pin is activated; and if it exceeds
the T

limit, the CT pin is activated. The INT and CT pins are

CRIT

programmable for polarity via the configuration register, and the
INT and CT pins are also programmable for interrupt mode via
the configuration register.

ONE-SHOT MODE

Setting Bit 6 to 0 and Bit 5 to 1 of the configuration register
(Register Address 0x03) enables the one-shot mode. When this
mode is enabled, the ADT7420 immediately completes a
conversion and then goes into shutdown mode.

Wait for a minimum of 240 ms after writing to the operation
mode bits before reading back the temperature from the
temperature value register. This time ensures that the ADT7420
has time to power up and complete a conversion.

To obtain an updated temperature conversion, reset Bit 6 to 0
and Bit 5 to 1 in the configuration register (0x03).

The one-shot mode is useful when one of the circuit design
priorities is to reduce power consumption.

CT and INT Operation in One-Shot Mode

See Figure 12 for more information on one-shot CT pin
operation for T
limits is exceeded. Note that in interrupt mode, a read from
any register resets the INT and CT pins.

overtemperature events when one of the

CRIT

Rev. PrE | Page 10 of 24

Preliminary Technical Data ADT7420

TEMPER

A

TURE

POLARIT

For the INT pin in the comparator mode, if the temperature drops
below the T

HIGH

– T

value or goes above the T

HYST

LOW

+ T

HYST

value, a write to the operation mode bits (Bit 5 and Bit 6 of the
configuration register, Register Address 0x03) resets the INT pin.

For the CT pin in the comparator mode, if the temperature
drops below the T

CRIT

– T

value, a write to the operation

HYST

mode bits (Bit 6 = 0 and Bit 5 = 1 of the configuration register,
Register Address 0x03) resets the CT pin (see Figure 12).

Note that when using one-shot mode, ensure that the refresh
rate is appropriate to the application being used.

1 SPS MODE

In this mode, the part performs one measurement per second. A
conversion takes only 60 ms typically, and it remains in
the idle state for the remaining 940 ms period. This mode is
enabled by writing 1 to Bit 6 and 0 to Bit 5 of the configuration
register (Register Address 0x03).

SHUTDOWN

The ADT7420 can be placed in shutdown mode by writing 1
to Bit 6 and 1 to Bit 5 of the configuration register (Register
Address 0x03), in which case the entire IC is shut down and
no further conversions are initiated until the ADT7420 is
taken out of shutdown mode. The ADT7420 can be taken

out of shutdown mode by writing 0 to Bit 6 and 0 to Bit 5 in
the configuration register (Register Address 0x03). The

ADT7420 typically takes 1 ms (with a 0.1 µF decoupling

capacitor) to come out of shutdown mode. The conversion
result from the last conversion prior to shutdown can still be
read from the ADT7420 even when it is in shutdown mode.
When the part is taken out of shutdown mode, the internal
clock is started and a conversion is initiated.

FAULT QUEUE

Bit 0 and Bit 1 of the configuration register (Register Address
0x03) are used to set up a fault queue. The queue can facilitate up
to four fault events to prevent false tripping of the INT and CT pins
when the ADT7420 is used in a noisy temperature environment.
The number of faults set in the queue must occur consecutively
to set the INT and CT outputs. For example, if the number of
faults set in the queue is four, then four consecutive temperature
conversions must occur with each result exceeding a temperature
limit in any of the limit registers before the INT and CT pins are
activated. If two consecutive temperature conversions exceed a
temperature limit and the third conversion does not, the fault
count is reset back to zero.

149°C

148°C

WRITE TO

T

CRIT

T

CRIT

TIME

147°C

146°C

145°C

144°C

143°C

142°C

141°C

140°C

POLARITY = ACTIVE LOW

Y = ACTIVE HIGH

*THERE IS A 240ms DELAY BETWEEN WRITING TO THE CONFIGURATION REGISTER TO START

A STANDARD ONE-SHOT CONVERSION AND THE CT PIN GOING ACTIVE. THIS IS DUE TO THE
CONVERSION TIME. THE DELAY IS 60ms IN THE CASE OF A ONE-SHOT CONVERSION.

CT PIN

CT PIN

WRITE TO

BIT 5 AND BIT 6 OF

CONFIGURATION

REGISTER.*

WRITE TO

BIT 5 AND BIT 6 OF

CONFIGURATION

REGISTER.*

BIT 5 AND BIT 6 OF

CONFIGURATION

REGISTER.*

Figure 12. One-Shot CT Pin

– T

HYST

Rev. PrE | Page 11 of 24

ADT7420 Preliminary Technical Data

TEMPERATURE DATA FORMAT

One LSB of the ADC corresponds to 0.0625°C in 13-bit mode or

0.0078°C in 16-bit mode. The ADC can theoretically measure a
temperature range of 255°C, but the ADT7420 is guaranteed to
measure a low value temperature limit of −40°C to a high value
temperature limit of +150°C. The temperature measurement
result is stored in the 16-bit temperature value register and is
compared with the high temperature limits stored in the T
setpoint register and the T
pared with the low temperature limit stored in the T

setpoint register. It is also com-

HIGH

LOW

register.

Temperature data in the temperature value register, the T
setpoint register, the T

setpoint register, and the T

HIGH

setpoint

LOW

register are represented by a 13-bit twos complement word. The
MSB is the temperature sign bit. The three LSBs, Bit 0 to Bit 2, on
power-up, are not part of the temperature conversion result and
are flag bits for T

CRIT

, T

HIGH

, and T

. Table 5 shows the 13-bit

LOW

temperature data format without Bit 0 to Bit 2.

The number of bits in the temperature data-word can be extended
to 16 bits, twos complement, by setting Bit 7 to 1 in the confi­guration register (Register Address 0x03). When using a 16-bit
temperature data value, Bit 0 to Bit 2 are not used as flag bits
and are, instead, the LSB bits of the temperature value. The power­on default setting has a 13-bit temperature data value.

Reading back the temperature from the temperature value register
requires a 2-byte read. Designers that use a 9-bit temperature
data format can still use the ADT7420 by ignoring the last four
LSBs of the 13-bit temperature value. These four LSBs are Bit 6
to Bit 3 in Table 5.

Table 5. 13-Bit Temperature Data Format

Digital Output

Temperature

−40°C 1 1101 1000 0000 0x1D80

−25°C 1 1110 0111 0000 0x1E70

−0.0625°C 1 1111 1111 1111 0x1FFF
0°C 0 0000 0000 0000 0x000
+0.0625°C 0 0000 0000 0001 0x001
+25°C 0 0001 1001 0000 0x190
+105°C 0 0110 1001 0000 0x690
+125°C 0 0111 1101 0000 0x7D0
+150°C 0 1001 0110 0000 0x960

(Binary) Bits[15:3] Digital Output (Hex)

CRIT

setpoint

CRIT

TEMPERATURE CONVERSION FORMULAS

16-Bit Temperature Data Format

Positive Temperature = ADC Code (dec)/128

Negative Temperature = (ADC Code (dec) – 65,536)/128

where ADC Code uses all 16 bits of the data byte, including the
sign bit.

Negative Temperature = (ADC Code (dec) – 32,768)/128

where Bit 15 (sign bit) is removed from the ADC code.

13-Bit Temperature Data Format

Positive Temperature = ADC Code (dec)/16

Negative Temperature = (ADC Code (dec) − 8192)/16

where ADC Code uses the first 13 MSBs of the data byte,
including the sign bit.

Negative Temperature = (ADC Code (dec) – 4096)/16

where Bit 15 (sign bit) is removed from the ADC code.

10-Bit Temperature Data Format

Positive Temperature = ADC Code (dec)/2

Negative Temperature = (ADC Code (dec) − 1024)/2

where ADC Code uses all 10 bits of the data byte, including the
sign bit.

Negative Temperature = (ADC Code (dec) − 512)/2

where Bit 9 (sign bit) is removed from the ADC code.

9-Bit Temperature Data Format

Positive Temperature = ADC Code (dec)

Negative Temperature = ADC Code (dec) − 512

where ADC Code uses all nine bits of the data byte, including
the sign bit.

Negative Temperature = ADC Code (dec) − 256

where Bit 8 (sign bit) is removed from the ADC code.

Rev. PrE | Page 12 of 24

Preliminary Technical Data ADT7420

REGISTERS

The ADT7420 contains 14 registers:

• Nine temperature registers

• A status register

• An ID register

• A configuration register

• An address pointer register

• A software reset

All registers are eight bits wide. The temperature value registers,
the status register, and the ID register are read-only. The software
reset is a write-only register. On power-up, the address pointer
register is loaded with 0x00 and points to the temperature value
most significant byte register (Register Address 0x00).

Table 6. ADT7420 Registers

Register
Address

0x00 Temperature value most significant byte 0x00
0x01 Temperature value least significant byte 0x00
0x02 Status 0x00
0x03 Configuration 0x00
0x04 T
0x05 T
0x06 T
0x07 T
0x08 T
0x09 T
0x0A T
0x0B ID 0xCB
0x2F Software reset 0xXX

Description

setpoint most significant byte 0x20 (64°C)

HIGH

setpoint least significant byte 0x00 (64°C)

HIGH

setpoint most significant byte 0x05 (10°C)

LOW

setpoint least significant byte 0x00 (10°C)

LOW

setpoint most significant byte 0x49 (147°C)

CRIT

setpoint least significant byte 0x80 (147°C)

CRIT

setpoint 0x05 (5°C)

HYST

Power-On
Default

ADDRESS POINTER REGISTER

This register is always the first register written to during a write
to the ADT7420. It should be set to the address of the register
to which the write or read transaction is intended. Table 7
shows the register address of each register on the ADT7420. The
default value of the address pointer register is 0x00.

Table 7. Address Pointer Register

P7 P6 P5 P4 P3 P2 P1 P0

ADD7 ADD6 ADD5 ADD4 ADD3 ADD2 ADD1 ADD0

TEMPERATURE VALUE REGISTERS

The temperature value consists of two bytes, one most signifi­cant byte and one least significant byte. These values can be
read in two separate 1-byte reads or in a single 2-byte read. For a
2-byte read, only the address of the most significant byte must be
loaded into the address pointer register. After the most signifi­cant byte is read, the address pointer is auto-incremented so
that the least significant byte can read within the same transaction.

Bit 0 to Bit 2 are event alarm flags for T
the ADC is configured to convert the temperature to a 16-bit
digital value, then Bit 0 to Bit 2 are no longer used as flag bits
and are instead used as the LSBs for the extended digital value.

LOW

, T

HIGH

, and T

CRIT

. When

Table 8. Temperature Value MSB Register (Register Address 0x00)

Bit Default Value Type Name Description

[14:8] 0000000 R Temp Temperature value in twos complement format
15 0 R Sign Sign bit, indicates if the temperature value is negative or positive

Rev. PrE | Page 13 of 24

ADT7420 Preliminary Technical Data

Table 9. Temperature Value LSB Register (Register Address 0x01)

Default

Bit

0 0 R T

Contains the Least Significant Bit 0 of the 15-bit temperature value if the configuration

1 0 R T

Contains the Least Significant Bit 1 of the 15-bit temperature value if the configuration

2 0 R T

Contains the Least Significant Bit 2 of the 15-bit temperature value if the configuration

[7:3] 00000 R Temp Temperature value in twos complement format.

STATUS REGISTER

This 8-bit read-only register reflects the status of the overtempera­ture and undertemperature interrupts that can cause the CT and
INT pins to go active. It also reflects the status of a temperature
conversion operation. The interrupt flags in this register are
reset by a read operation to the status register and/or when the
temperature value returns within the temperature limits, including
hysteresis. The

value register. In one-shot and 1 SPS modes, the

after a write to the operation mode bits.

Value Type Name Description

flag/LSB0 Flags a T

LOW

LOW

resolution). When the temperature value is below T

register, Register Address 0x03[7] = 1 (16-bit resolution).

flag/LSB1 Flags a T

HIGH

HIGH

resolution). When the temperature value is above T

register, Register Address 0x03[7] = 1 (16-bit resolution).

flag/LSB2 Flags a T

CRIT

event if the configuration register, Register Address 0x03[7] = 0 (13-bit

CRIT

resolution). When the temperature value exceeds T

register, Register Address 0x03[7] = 1 (16-bit resolution).

RDY

bit is reset after a read from the temperature

RDY

bit is reset

event if the configuration register, Register Address 0x03[7] = 0 (13-bit

, this bit it set to 1.

LOW

event if the configuration register, Register Address 0x03[7] = 0 (13-bit

, this bit it set to 1.

HIGH

, this bit it set to 1.

CRIT

CONFIGURATION REGISTER

This 8-bit read/write register stores various configuration modes
for the ADT7420, including shutdown, overtemperature and
undertemperature interrupts, one-shot, continuous conversion,
interrupt pins polarity, and overtemperature fault queues.

Table 10. Status Register (Register Address 0x02)

Default

Bit

Value Type Name Description

[3:0] 0000 R Unused Reads back 0.
4 0 R T

This bit is set to 1 when the temperature goes below the T

LOW

when the status register is read and/or when the temperature measured goes back above the limit
set in the setpoint T

5 0 R T

This bit is set to 1 when the temperature goes above the T

HIGH

when the status register is read and/or when the temperature measured goes back below the limit
set in the setpoint T

6 0 R T

This bit is set to 1 when the temperature goes above the T

CRIT

when the status register is read and/or when the temperature measured goes back below the limit
set in the setpoint T

7 1 R

This bit goes low when the temperature conversion result is written into the temperature value

RDY

register. It is reset to 1 when the temperature value register is read. In one-shot and 1 SPS modes,
this bit is reset after a write to the operation mode bits.

LOW

HIGH

CRIT

+ T

− T

− T

registers.

HYST

registers.

HYST

registers.

HYST

temperature limit. The bit clears to 0

LOW

temperature limit. The bit clears to 0

HIGH

temperature limit. This bit clears to 0

CRIT

Rev. PrE | Page 14 of 24

Preliminary Technical Data ADT7420

Table 11. Configuration Register (Register Address 0x03)

Default

Bit

Value Type Name Description

[1:0] 00

00 = 1 fault (default).
01 = 2 faults.
10 = 3 faults.
11 = 4 faults.

2 0

0 = active low.
1 = active high.

3 0

0 = active low.
1 = active high.

4 0

0 = interrupt mode
1 = comparator mode

[6:5] 00

00 = continuous conversion (default). When one conversion is finished, the ADT7420 starts another.
01 = one shot. Conversion time is typically 240 ms.
10 = 1 SPS mode. Conversion time is typically 60 ms. This operational mode reduces the average current

11 = shutdown. All circuitry except interface circuitry is powered down.

7 0

0 = 13-bit resolution. Sign bit + 12 bits gives a temperature resolution of 0.0625°C.
1 = 16-bit resolution. Sign bit + 15 bits gives a temperature resolution of 0.0078°C.

R/W

R/W

R/W

R/W

R/W

R/W

T

SETPOINT REGISTERS

HIGH

The T
the overtemperature limit value. An overtemperature event
occurs when the temperature value stored in the temperature
value register exceeds the value stored in this register. The INT
pin is activated if an overtemperature event occurs. The temper­ature is stored in twos complement format with the MSB being
the temperature sign bit.

When reading from this register, the eight most significant bits
(Bit 15 to Bit 8) are read first from Register Address 0x04 and
then the eight least significant bits (Bit 7 to Bit 0) are read from
Register Address 0x05 (T
Address 0x04 (T
the address pointer register because the address pointer auto­increments to Register Address 0x05 (T

The default setting for the T

T

LOW

The T
the undertemperature limit value. An undertemperature event
occurs when the temperature value stored in the temperature
value register is less than the value stored in this register. The
INT pin is activated if an undertemperature event occurs. The
temperature is stored in twos complement format with the MSB
being the temperature sign bit.

setpoint MSB and T

HIGH

HIGH

SETPOINT REGISTERS

setpoint MSB and T

LOW

Fault queue These two bits set the number of undertemperature/overtemperature faults that can occur before setting the

CT pin polarity This bit selects the output polarity of the CT pin.

INT pin polarity This bit selects the output polarity of the INT pin.

INT/CT mode This bit selects between comparator mode and interrupt mode.

Operation mode These two bits set the operational mode for the ADT7420.

Resolution This bit sets up the resolution of the ADC when converting.

INT and CT pins. This helps to avoid false triggering due to temperature noise.

consumption.

When reading from this register, the eight most significant bits

setpoint LSB registers store

HIGH

(Bit 15 to Bit 8) are read first from Register Address 0x06 and
then the eight least significant bits (Bit 7 to Bit 0) are read from
Register Address 0x07. Only Register Address 0x06 (T
MSB) needs to be loaded into the address pointer register because
the address pointer auto-increments to Register Address 0x07
(T

setpoint LSB).

LOW

The default setting for the T

T

SETPOINT REGISTERS

CRIT

The T

setpoint MSB and T

CRIT

setpoint is 10°C.

LOW

setpoint LSB registers store

CRIT

the critical overtemperature limit value. A critical overtempe-

setpoint LSB). Only Register

HIGH

setpoint MSB) needs to be loaded into

rature event occurs when the temperature value stored in the
temperature value register exceeds the value stored in this
register. The CT pin is activated if a critical overtemperature

setpoint LSB).

HIGH

setpoint is 64°C.

HIGH

event occurs. The temperature is stored in twos complement
format with the MSB being the temperature sign bit.

When reading from this register, the eight most significant bits

setpoint LSB registers store

LOW

(Bit 15 to Bit 8) are read first from Register Address 0x08 (T
setpoint MSB) and then the eight least significant bits (Bit 7 to
Bit 0) are read from Register Address 0x09 (T
Only Register Address 0x08 (T

setpoint MSB) needs to be

CRIT

CRIT

loaded into the address pointer register because the address
pointer auto-increments to Register Address 0x09 (T
LSB). The default setting for the T

Rev. PrE | Page 15 of 24

limit is 147°C.

CRIT

setpoint

LOW

CRIT

setpoint LSB).

setpoint

CRIT

ADT7420 Preliminary Technical Data

Table 12. T

Setpoint MSB Register (Register Address 0x04)

HIGH

Bit Default Value Type Name Description

[15:8] 0x20

Table 13. T

Setpoint LSB Register (Register Address 0x05)

HIGH

R/W

T

MSB MSBs of the overtemperature limit, stored in twos complement format.

HIGH

Bit Default Value Type Name Description

[7:0] 0x00

Table 14. T

Setpoint MSB Register (Register Address 0x06)

LOW

R/W

T

LSB LSBs of the overtemperature limit, stored in twos complement format.

HIGH

Bit Default Value Type Name Description

[15:8] 0x05

Table 15. T

Setpoint LSB Register (Register Address 0x07)

LOW

R/W

T

MSB MSBs of the undertemperature limit, stored in twos complement format.

LOW

Bit Default Value Type Name Description

[7:0] 0x00

Table 16. T

Setpoint MSB Register (Register Address 0x08)

CRIT

R/W

T

LSB LSBs of the undertemperature limit, stored in twos complement format.

LOW

Bit Default Value Type Name Description

[15:8] 0x49

Table 17. T

Setpoint LSB Register (Register Address 0x09)

CRIT

R/W

T

MSB MSBs of the critical overtemperature limit, stored in twos complement format.

CRIT

Bit Default Value Type Name Description

[7:0] 0x80

R/W

T

LSB LSBs of the critical overtemperature limit, stored in twos complement format.

CRIT

T

SETPOINT REGISTER

HYST

This 8-bit read/write register stores the temperature hysteresis
value for the T

HIGH

, T

LOW

, and T

temperature limits. The

CRIT

temperature hysteresis value is stored in straight binary format
using four LSBs. Increments are possible in steps of 1°C from
0°C to 15°C. The value in this register is subtracted from the
T

HIGH

and T

values and added to the T

CRIT

value to imple-

LOW

ment hysteresis.

ID REGISTER

This 8-bit read-only register stores the manufacture ID in Bit 3
to Bit 7 and the silicon revision in Bit 0 to Bit 2. The default
setting for the ID register is 0xCB.

Table 18. T

Setpoint Register (Register Address 0x0A)

HYST

Bit Default Value Type Name Description

[3:0] 0101

[7:4] 0000

R/W

R/W

T

Hysteresis value, from 0°C to 15°C. Stored in straight binary format. The default setting is 5°C.

HYST

N/A Not used.

Table 19. ID Register (Register Address 0x0B)

Bit Default Value Type Name Description

[2:0] 011 R Revision ID Contains the silicon revision identification number
[7:3] 11001 R Manufacture ID Contains the manufacture identification number

Rev. PrE | Page 16 of 24

Preliminary Technical Data ADT7420

PULL-U

P

PULL-U

P

PULL-U

P

ON

SERIAL INTERFACE

V

DD

10kΩ

TO INTERRUPT PIN

MICROCONTROLLER

V

DD

10kΩ

Figure 13. Typical I2C Interface Connection

Control of the ADT7420 is carried out via the I2C-compatible
serial interface. The ADT7420 is connected to this bus as a slave
and is under the control of a master device.

Figure 13 shows a typical I2C interface connection.

SERIAL BUS ADDRESS

Like most I2C-compatible devices, the ADT7420 has a 7-bit
serial address. The five MSBs of this address for the ADT7420
are hardwired internally to 10010. Pin A1 and Pin A0 set the
two LSBs. These pins can be configured two ways, low and
high, to give four different address options. Table 20 shows
the different bus address options available. The recommended
pull-up resistor value on the SDA and SCL lines is 10 kΩ.

Table 20. I2C Bus Address Options

Binary

Hex A6 A5 A4 A3 A2 A1 A0

1 0 0 1 0 0 0 0x48
1 0 0 1 0 0 1 0x49
1 0 0 1 0 1 0 0x4A
1 0 0 1 0 1 1 0x4B

The serial bus protocol operates as follows:

1. The master initiates data transfer by establishing a start
condition, defined as a high-to-low transition on the serial
data line, SDA, while the serial clock line, SCL, remains
high. This indicates that an address/data stream is going
to follow. 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 read/
write (R/W) bit. The R/W bit determines whether data is

written to, or read from, the slave device.

ADT7420

CT

INT

A0
A1

V

SCL

SDA

GND

V

DD

DD

10kΩ

0.1µF

V

DD

10kΩ

09013-014

2. 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 then
remain idle while the selected device waits for data to be
read from or written to it. If the R/W bit is a 0, the master

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

3. Data is sent over the serial bus in sequences of nine clock
pulses, eight bits of data followed by an acknowledge bit
from the receiver of data. Transitions on the data line must
occur during the low period of the clock signal and remain
stable during the high period as a low-to-high transition when
the clock is high, which can be interpreted as a stop signal.

4. When all data bytes have been read or written, stop condi­tions are established. In write mode, the master pulls the
data line high during the 10th clock pulse to assert a stop
condition. In read mode, the master device pulls the data
line high during the low period before the ninth clock
pulse. This is known as a no acknowledge. The master
takes the data line low during the low period before the
10th clock pulse, then high during the 10th clock pulse to
assert a stop condition.

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.

Rev. PrE | Page 17 of 24

ADT7420 Preliminary Technical Data

191

191

WRITING DATA

It is possible to write either a single byte of data or two bytes to
the ADT7420, depending on which registers are to be written.

Writing a single byte of data requires the serial bus address, the
data register address written to the address pointer register,
followed by the data byte written to the selected data register.
This is shown in Figure 14.

For the T
registers, it is possible to write to both the MSB and the LSB

setpoint, T

HIGH

SCL

setpoint, and T

LOW

setpoint

CRIT

registers in the same write transaction. Writing two bytes of
data to these registers requires the serial bus address, the data
register address of the MSB register written to the address
pointer register, followed by the two data bytes written to the
selected data register. This is shown in Figure 15.

If more than the required number of data bytes is written to a
register, the register ignores these extra data bytes. To write to
a different register, a start or repeated start is required.

9

SCL

SDA

START BY

MASTER

SCL (CONTINUED)

SDA

START BY

MASTER

1 0 0 1 0 A1 A0 P7 P6 P5 P4 P3 P2 P1 P0

FRAME 1

SERIAL BUS ADDRESS BYTE

SCL (CONTINUED)

SDA (CONTINUED)

R/W

ACK. BY
ADT7420

ADDRESS POINTER REGISTER BYTE

D7 D6 D5 D4 D3 D2 D1 D0

FRAME 3

DATA BYTE

Figure 14. Writing to a Register Followed by a Single Byte of Data

1 0 0 1 0 A1 A0 P7 P6 P5 P4 P3 P2 P1 P0

FRAME 1

SERIAL BUS ADDRESS BYTE

R/W

ACK. BY

ADT7420

ADDRESS POINTER REGISTER BYTE

91

FRAME 2

FRAME 2

91

ACK. BY
ADT7420

9

ACK. BY
ADT7420

ACK. BY
ADT7420

STOP BY
MASTER

91

SDA (CONTINUED)

D15 D14 D13 D12 D11 D10 D9 D8

FRAME 3

DATA BYTE

ACK. BY
ADT7420

D7 D6 D5 D4 D3 D2 D1 D0

FRAME 4

DATA BYTE

ACK. BY
ADT7420

STOP BY
MASTER

09013-017

Figure 15. Writing to a Register Followed by Two Bytes of Data

Rev. PrE | Page 18 of 24

Preliminary Technical Data ADT7420

REPE

1

991

SD

SD

READING DATA

Reading data from the ADT7420 is done in a single data byte
operation for the configuration register, the status register,
the T
read operation is needed for the temperature value register,
T
setpoint register. Reading back the contents of an 8-bit register
similar to the configuration register is shown in Figure 16.
Reading back the contents of the temperature value register is
shown in Figure 17.

Reading back from any register first requires a single-byte write
operation to the address pointer register to set up the address of

setpoint register, and the ID register. A two data byte

HYST

setpoint register, T

HIGH

SCL

setpoint register, and the T

LOW

CRIT

the register that is going to be read from. In the case of reading
back from the 2-byte registers, the address pointer automatically
increments from the MSB register address to the LSB register
address.

To read from another register, execute another write to the
address pointer register to set up the relevant register address.
Thus, block reads are not possible, that is, there is no I2C address
pointer auto-increment except when reading back from a 16-bit
register. If the address pointer register has previously been set
up with the address of the register that is going to receive a read
command, there is no need to repeat a write operation to set up
the register address again.

FRAME 1

BYTE

FRAME 3

BYTE

0

R/W P7 P6 P5 P4 P3 P2 P1 P0

ACK. BY
ADT7420

ADDRESS POINTER REGISTER BYTE

9 91

R/W D7 D6 D5 D4 D3 D2 D1 D0

ACK. BY
ADT7420

DATA BYTE FROM CONFIGURATION

FRAME 2

NO ACK. BY

FRAME 4

REGISTER

ACK. BY

ADT7420

MASTER

STOP BY
MASTER

SDA

START BY

MASTER

SCL

SDA

AT START

BY MASTER

1 0 0 1 A1 A0

SERIAL BUS ADDRESS

1

1 0 0 1 A10 A0

SERIAL BUS ADDRESS

Figure 16. Reading Back Data from the Configuration Register

SCL

SCL

A

START

1 1

1 0 0

ADT7410 DEVICE ADDRESS REGISTER ADDRESS[A7:A0]

1 19 9

SR

1

0 A1 A0

R/W

ACK. BY

ADT7420

9

A7 A6

A1 A0

ACK. BY
ADT7420

9

A

REPEAT

START

NOTES

1. A START CONDITION AT THE BEGINNING IS DEFINED AS A HIGH-TO-LOW TRANSITION ON SDA WHILE SCL REMAINS HIGH.

2. A STOP CONDITION AT THE END IS DEFINED AS A LOW-TO-HIGH TRANSITION ON SDA WHILE SCL REMAINS HIGH.

3. THE MASTER GENERATES THE NO ACKNOWLEDGE AT THE END OF THE READBACK TO SIGNAL THAT IT DOES NOT WANT ADDITIONAL DATA.

4. TEMPERATURE VALUE REGISTER MSB DATA AND TEMPERATURE VALIUE REGISTER LSB DATA ARE ALWAYS SEPARATED BY A LOW ACK BIT.

5. THE R/W BIT IS SET TO A1 TO INDICATE A READBACK OPERATION.

01 A1 A0

ADT7410 DEVICE ADDRESS

R/W

ACK. BY
ADT7420

D6

TEMPERATURE

VALUE REGISTER

MSB DATA

D1 D0D7

ACK. BY
MASTER

D6

TEMPERATURE

VALUE REGISTER

LSB DATA

D1 D0D7

NO
ACK. BY
MASTER

09013-023

Figure 17. Reading Back Data from the Temperature Value Register

Rev. PrE | Page 19 of 24

ADT7420 Preliminary Technical Data

RESET

To reset the ADT7420 without having to reset the entire I2C bus,
an explicit reset command is provided. This uses a particular
address pointer word as a command word to reset the part and
upload all default settings. The ADT7420 does not respond to
(does not acknowledge) I2C bus commands while the default
values upload for approximately 200 µs. Use the following
sequence to perform a reset:

1. Write to the ADT7420 using the appropriate address.

2. Get acknowledge.

3. Set the register address to 0x2F.

4. Get acknowledge.

5. Apply stop condition.

6. Wait 200 µs for the part to reset its registers to the default
power-up settings.

GENERAL CALL

When a master issues a slave address consisting of seven 0s with
the eighth bit (R/W bit) set to 0, this is known as the general call
address. The general call address is for addressing every device
connected to the I2C bus. The ADT7420 acknowledges this
address and reads in the following data byte.

If the second byte is 0x06, the ADT7420 is reset, completely
uploading all default values. The ADT7420 does not respond
to the I2C bus commands (do not acknowledge) while the
default values upload for approximately 200 µs.

The ADT7420 does not acknowledge any other general call
commands.

Rev. PrE | Page 20 of 24

Preliminary Technical Data ADT7420

TEMPER

A

TURE

INT AND CT OUTPUTS

The INT and CT pins are open-drain outputs, and both pins
require a 10 kΩ pull-up resistor to VDD. The ADT7420 must be
fully powered up to VDD before reading INT and CT data.

UNDERTEMPERATURE AND OVERTEMPERATURE
DETECTION

The INT and CT pins have two undertemperature/overtempera­ture modes: comparator mode and interrupt mode. The interrupt
mode is the default power-up overtemperature mode. The INT
output pin becomes active when the temperature is greater than
the temperature stored in the T
the temperature stored in the T
pin reacts after this event depends on the overtemperature mode
selected.

Figure 18 illustrates the comparator and interrupt modes for
events exceeding the T

limit with both pin polarity settings.

HIGH

Figure 19 illustrates the comparator and interrupt modes for
events exceeding the T

limit with both pin polarity settings.

LOW

setpoint register or less than

HIGH

setpoint register. How this

LOW

Comparator Mode

In comparator mode, the INT pin returns to its inactive status
when the temperature drops below the T
rises above the T

LOW

+ T

HYST

limit.

HIGH

− T

HYST

limit or

Putting the ADT7420 into shutdown mode does not reset the
INT state in comparator mode.

Interrupt Mode

In interrupt mode, the INT pin goes inactive when any ADT7420
register is read. Once the INT pin is reset, it goes active again
only when the temperature is greater than the temperature stored
in the T
in the T

setpoint register or less than the temperature stored

HIGH

setpoint register.

LOW

Placing the ADT7420 into shutdown mode resets the INT pin
in the interrupt mode.

82°C

81°C

80°C

79°C

78°C

77°C

76°C

75°C

74°C

73°C

(COMPARATOR MO DE)

POLARITY = ACTIVE LOW

(INTERRUPT MODE)

POLARITY = ACTIVE LOW

(COMPARATOR MO DE)

POLARITY = ACTIVE HIGH

(INTERRUPT MODE)

POLARITY = ACTIVE HIGH

INT PIN

INT PIN

INT PIN

INT PIN

READ

Figure 18. INT Output Temperature Response Diagram for T

READ READ

Overtemperature Events

HIGH

T

HIGH

T

– T

HIGH

HYST

TIME

09013-020

Rev. PrE | Page 21 of 24

ADT7420 Preliminary Technical Data

TEMPER

A

TURE

POLARIT

POLARIT

–13°C

–14°C

T

–15°C

–16°C

–17°C

–18°C

–19°C

–20°C

–21°C

–22°C

+ T

LOW

HYST

T

LOW

(COMPARATOR MO DE)

POLARITY = ACTIVE LOW

(INTERRUPT MODE)

POLARITY = ACTIVE LOW

(COMPARATOR MO DE)

(INTERRUPT MODE)

Figure 19. INT Output Temperature Response Diagram for T

INT PIN

INT PIN

INT PIN

Y = ACTIVE HIGH

INT PIN

Y = ACTIVE HIGH

READ

READ READ

Undertemperature Events

LOW

TIME

09013-021

Rev. PrE | Page 22 of 24

Preliminary Technical Data ADT7420

APPLICATIONS INFORMATION

THERMAL RESPONSE TIME

Thermal response is a function of the thermal mass of the
temperature sensor, but it is also heavily influenced by the mass
of the object the IC is mounted to. For example, a large PCB
containing large amounts of copper tracking can act as a large
heat sink and slow the thermal response. For a faster thermal
response, it is recommended to mount the sensor on as small a
PCB as possible.

Figure 10 shows the typical response time of less than two
seconds to reach 63.2% of its temperature span. The tempera­ture value is read back as a 16-bit value through the digital
interface. The response time includes all delays incurred on
chip during signal processing.

SUPPLY DECOUPLING

The ADT7420 must have a decoupling capacitor connected
between VDD and GND; otherwise, incorrect temperature
readings will be obtained. A 0.1 µF decoupling capacitor such as
a high frequency ceramic type must be used and mounted as
close as possible to the VDD pin of the ADT7420.

If possible, the ADT7420 should be powered directly from the
system power supply. This arrangement, shown in Figure 20,
isolates the analog section from the logic-switching transients.
Even if a separate power supply trace is not available, generous
supply bypassing reduces supply-line induced errors. Local
supply bypassing consisting of a 0.1 µF ceramic capacitor is
critical for the temperature accuracy specifications to be
achieved.

TTL/CMOS

LOGIC

CIRCUITS

POWER

SUPPLY

Figure 20. Use of Separate Traces to Reduce Power Supply Noise

0.1µF

ADT7420

09013-022

POWERING FROM A SWITCHING REGULATOR

Precision analog devices such as the ADT7420 require a well­filtered power source. If the ADT7420 is powered from a
switching regulator, noise may be generated above 50 kHz that
may affect the temperature accuracy specifications. To prevent
this, an RC filter should be used between the power supply and

ADT7420 VDD. The value of components used should be carefully

considered to ensure that the peak value of the supply noise is
less than 1 mV. The RC filter should be mounted as far away as
possible from the ADT7420 to ensure that the thermal mass is
kept as low as possible.

TEMPERATURE MEASUREMENT

The ADT7420 accurately measures and converts the tempera­ture at the surface of its own semiconductor chip. Thermal
paths run through the leads, the exposed pad, as well as the
plastic package. When the ADT7420 is used to measure the
temperature of a nearby heat source, the thermal impedance
between the heat source and the ADT7420 must be considered
because this impacts the accuracy and thermal response of the
measurement.

For air or surface temperature measurements, take care to
isolate the package, leads, and exposed pad from ambient air
temperature. Use of a thermally conductive adhesive can help to
achieve a more accurate surface temperature measurement.

QUICK GUIDE TO MEASURING TEMPERATURE

The following is a quick guide for measuring temperature in
continuous conversion mode (default power-up mode). Execute
each step sequentially.

1. After powering up the ADT7420, verify the setup by
reading the device ID (Register Address 0x0B). It should
read 0xCB.

2. After consistent consecutive readings are obtained from
Step 1, proceed to read the configuration register (0x03),
T

(0x08, 0x09), T

CRIT

0x07) registers. Compare to the specified defaults in Table 6.
If all the readings match, the interface is operational.

3. Write to the configuration register to set the ADT7420 to
the desired configuration.

4. Read the temperature value MSB register, followed by the
temperature value LSB register. Both registers should
produce a valid temperature measurement.

(0x04, 0x05), and T

HIGH

LOW

(0x06,

Rev. PrE | Page 23 of 24

ADT7420 Preliminary Technical Data

4.10

SE

INDIC

OUTLINE DIMENSIONS

0.35

0.30

0.25

13

12

9

8

BOTTOM VIEWTOP VIEW

COPLANARITY

0.08

PIN 1
INDICAT

16

EXPOSED

1

PAD

4

5

FOR PROPER CONNECTION OF
THE EXPOSED PAD, REFER TO
THE PIN CONFIGURATION AND
FUNCTION DESCRIPTIONS
SECTION OF THIS DATA SHEET.

2.70

2.60 SQ

2.50

0.25 MIN

R

O

PIN 1

ATOR

0.80

0.75

0.70

ATING

PLANE

4.00 SQ

3.90

0.65
BSC

0.45

0.40

0.35

0.05 MAX

0.02 NOM

0.20 REF

COMPLIANTTOJEDEC STANDARDS MO-220-WGGC.

012909-B

Figure 21. 16-Lead Lead Frame Chip Scale Package [LFCSP_WQ]

4 mm × 4 mm Body, Very Thin Quad

(CP-16-17)

Dimensions shown in millimeters

ORDERING GUIDE

Model1 Operating Temperature Range Package Description Package Option

ADT7420UCPZ-R2 −40°C to +150°C 16-lead LFCSP_WQ CP-16-17
ADT7420UCPZ-RL7 −40°C to +150°C 16-lead LFCSP_WQ CP-16-17
EVAL-ADT7X20EBZ Evaluation Board

1

Z = RoHS Compliant Part.

©2011 Analog Devices, Inc. All rights reserved. Trademarks and

registered trademarks are the property of their respective owners.

PR09013-0-11/11(PrE)

Rev. PrE | Page 24 of 24