ADT7420_12 [ADI]
±0.25°C Accurate, 16-Bit Digital I2C Temperature Sensor; 为± 0.25A ° C精度， 16位数字I2C温度传感器
| 型号： | ADT7420_12 |
| 厂家： | 
ADI |
| 描述： | ±0.25°C Accurate, 16-Bit Digital I2C Temperature Sensor |
| 文件： | 总24页 (文件大小：419K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
0.25°C Accurate, 16-Bit Digital
I2C Temperature Sensor
Data Sheet
ADT7420
FEATURES
GENERAL DESCRIPTION
High performance
Temperature accuracy
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.
0.20°C from −10°C to +85°C at 3.0 V
0.25°C from −20°C to +105°C from 2.7 V to 3.3 V
16-bit 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
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 typi-
cally 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.
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
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 tempera-
ture exceeds a programmable limit. The INT pin and CT pin
can operate in comparator and interrupt event modes.
Critical overtemperature interrupt
Overtemperature/undertemperature interrupt
I2C-compatible interface
16-lead, 4 mm × 4 mm LFCSP RoHS-compliant package
PRODUCT HIGHLIGHTS
APPLICATIONS
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.
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
5. Packaged in a 16-lead, 4 mm × 4 mm LFCSP RoHS-
compliant package.
FUNCTIONAL BLOCK DIAGRAM
12
V
DD
10 CT
CONFIGURATION
REGISTER
TEMPERATURE
INTERNAL
VALUE REGISTER
OSCILLATOR
T
T
T
CRIT
INTERNAL
T
T
CRIT
REGISTER
LOW
REFERENCE
REGISTER
9
INT
Σ-Δ
MODULATOR
T
T
TEMPERATURE
SENSOR
HYST
HIGH
HIGH
LOW
REGISTER
REGISTER
ID
STATUS
REGISTER
REGISTER
ADT7420
FILTER
LOGIC
SOFTWARE
RESET REGISTER
POINTER
REGISTER
3
4
1
2
SCL
SDA
A0
A1
2
I C INTERFACE
11
GND
Figure 1.
Rev. 0
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Technical Support
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ADT7420
Data Sheet
TABLE OF CONTENTS
Features .............................................................................................. 1
Temperature Value Registers .................................................... 13
Status Register............................................................................. 14
Configuration Register .............................................................. 14
THIGH Setpoint Registers............................................................. 15
TLOW Setpoint Registers.............................................................. 15
TCRIT Setpoint Registers.............................................................. 15
THYST Setpoint Register............................................................... 16
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
Applications....................................................................................... 1
General Description ......................................................................... 1
Product Highlights ........................................................................... 1
Functional Block Diagram .............................................................. 1
Revision History ............................................................................... 2
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
REVISION HISTORY
12/12—Revision 0: Initial Version
Rev. 0 | Page 2 of 24
Data Sheet
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
0.202
0.25
0.31
0.35
0.50
0.503
0.66
Unit
Test Conditions/Comments
TEMPERATURE SENSOR AND ADC
Accuracy1
0.0017
°C
°C
°C
°C
°C
°C
°C
°C
°C
Bits
TA = −10°C to +85°C, VDD = 3.0 V
TA = −20°C to +105°C, VDD = 2.7 V to 3.3 V
TA = −40°C to +105°C, VDD = 3.0 V
TA = −40°C to +105°C, VDD = 2.7 V to 3.3 V
TA = −40°C to +125°C, VDD = 2.7 V to 3.3 V
TA = −10°C to +105°C, VDD = 4.5 V to 5.5 V
TA = −40°C to +125°C, VDD = 4.5 V to 5.5 V
TA = +150°C, VDD = 4.5 V to 5.5 V
−0.85
−1.0
13
TA = +150°C, VDD = 2.7 V to 3.3 V
ADC Resolution
Twos complement temperature value of the
sign bit plus 12 ADC bits (power-up default
resolution)
16
Bits
Twos complement temperature value of the
sign bit plus 15 ADC bits (Bit 7 = 1 in the
configuration register)
Temperature Resolution
13-Bit
16-Bit
0.0625
0.0078
240
°C
°C
ms
13-bit resolution (sign + 12-bit)
16-bit resolution (sign + 15-bit)
Continuous conversion and one-shot
conversion modes
Temperature Conversion Time
Fast Temperature Conversion Time
1 SPS Conversion Time
6
60
ms
ms
°C
First conversion on power-up only
Conversion time for 1 SPS mode
Temperature cycle = 25°C to 125°C and back
to 25°C
Temperature Hysteresis4
0.002
Repeatability5
Drift6
0.015
0.0073
0.1
°C
°C
TA = 25°C
500 hour stress test at +150°C with VDD = 5.0 V
TA = 25°C
DC PSRR
°C/V
DIGITAL OUTPUTS (CT, INT, SDA—OPEN DRAIN)
High Output Leakage Current, IOH
Output Low Voltage, VOL
Output High Voltage, VOH
Output Capacitance, COUT
DIGITAL INPUTS (SCL, SDA, A0, A1)
Input Current
0.1
2
5
0.4
µA
V
V
CT and INT pins pulled up to 5.5 V
IOL = 3 mA at 5.5 V, IOL = 1 mA at 3.3 V
0.7 × VDD
pF
1
µA
V
V
V
V
VIN = 0 V to VDD
Input Low Voltage, VIL
0.3 × VDD
0.4
SCL and SDA only
A0 and A1 only
SCL and SDA only
A0 and A1 only
Input High Voltage, VIH
0.7 × VDD
2
SCL, SDA Glitch Rejection
50
2
ns
Input filtering suppresses noise spikes of less
than 50 ns
Pin Capacitance
POWER REQUIREMENTS
Supply Voltage
Supply Current
At 3.3 V
10
pF
V
2.7
5.5
210
250
265
300
µA
µA
Peak current while converting, I2C interface
inactive
Peak current while converting, I2C interface
inactive
At 5.5 V
1 SPS Current
At 3.3 V
At 5.5 V
46
65
µA
µA
VDD = 3.3 V, 1 SPS mode, TA = 25°C
VDD = 5.5 V, 1 SPS mode, TA = 25°C
Rev. 0 | Page 3 of 24
ADT7420
Data Sheet
Parameter
Min
Typ
Max
Unit
Test Conditions/Comments
Shutdown Current
At 3.3 V
At 5.5 V
Power Dissipation Normal Mode
Power Dissipation 1 SPS
2.0
5.2
700
150
15
25
µA
µA
µW
µW
Supply current in shutdown mode
Supply current in shutdown mode
VDD = 3.3 V, normal mode at 25°C
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 Temperature Hysteresis does not include repeatability.
5 Based on a floating average of 10 readings.
6 Drift includes solder heat resistance and life time test performed as per JEDEC Standard JESD22-A108.
Rev. 0 | Page 4 of 24
Data Sheet
ADT7420
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
SERIAL INTERFACE1
Min Typ Max
Unit
Test Conditions/Comments
See Figure 2
SCL Frequency
0
0.6
1.3
400
kHz
μs
μs
μs
μs
μs
μs
μs
μs
μs
μs
pF
SCL High Pulse Width, tHIGH
SCL Low Pulse Width, tLOW
SCL, SDA Rise Time, tR
0.3
0.3
SCL, SDA Fall Time, tF
Hold Time (Start Condition), tHD:STA
Setup Time (Start Condition), tSU:STA
Data Setup Time, tSU:DAT
Setup Time (Stop Condition), tSU:STO
Data Hold Time, tHD:DAT (Master)
Bus-Free Time (Between Stop and Start Condition), tBUF
Capacitive Load for Each Bus Line, CB
0.6
0.6
0.02
0.6
0.03
1.3
After this period, the first clock is generated
Relevant for repeated start condition
400
1 Sample tested during initial release to ensure compliance.
Timing Diagram
tR
tF
tLOW
tHD:STA
SCL
tHIGH
tSU:STA
tSU:STO
tHD:STA
tHD:DAT
tSU:DAT
SDA
tBUF
S
P
S
P
Figure 2. Serial Interface Timing Diagram
Rev. 0 | Page 5 of 24
ADT7420
Data Sheet
ABSOLUTE MAXIMUM RATINGS
Table 3.
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.
Parameter
Rating
VDD to GND
SDA Voltage to GND
−0.3 V to +7 V
−0.3 V to VDD + 0.3 V
−0.3 V to VDD + 0.3 V
−0.3 V to VDD + 0.3 V
−0.3 V to VDD + 0.3 V
−0.3 V to VDD + 0.3 V
2.0 kV
−40°C to +150°C
−65°C to +160°C
150°C
SCL Output Voltage to GND
A0 Input Voltage to GND
A1 Input Voltage to GND
CT and INT Output Voltage to GND
ESD Rating (Human Body Model)
Operating Temperature Range1
Storage Temperature Range
Maximum Junction Temperature, TJMAX
16-Lead LFCSP (CP-16-17)
Power Dissipation2
ESD CAUTION
3
WMAX = (TJMAX − TA )/θJA
Thermal Impedance4
θJA, Junction-to-Ambient (Still Air)
θJC, Junction-to-Case
37°C/W
33°C/W
IR Reflow Soldering
220°C
Peak Temperature (RoHS-Compliant
Package)
260°C (+0°C/−5°C)
Time at Peak Temperature
Ramp-Up Rate
Ramp-Down Rate
20 sec to 40 sec
3°C/sec maximum
−6°C/sec maximum
8 minutes maximum
Time from 25°C to Peak Temperature
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.
Rev. 0 | Page 6 of 24
Data Sheet
ADT7420
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
17 EP
SCL
SDA
A0
1
2
3
4
12
V
DD
ADT7420
TOP VIEW
(Not to Scale)
11 GND
10 CT
9
INT
A1
NOTES
1. NC = NO CONNECT. THE NC PIN IS NOT
BONDED TO THE DIE INTERNALLY.
2. TO ENSURE CORRECT OPERATION, THE
EXPOSED PAD SHOULD EITHER BE LEFT
FLOATING 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
4
5
6
7
8
9
A0
A1
NC
NC
NC
NC
INT
I2C Serial Bus Address Selection Pin. Logic input. Connect to GND or VDD to set an I2C address.
I2C Serial Bus Address Selection Pin. Logic input. Connect to GND or VDD to set an I2C address.
No Connect. The NC pin is not bonded to the die internally.
No Connect. The NC pin is not bonded to the die internally.
No Connect. The NC pin is not bonded to the die internally.
No Connect. The NC pin is not bonded to the die internally.
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
12
13
14
15
16
17
GND
VDD
NC
NC
NC
NC
EP
Analog and Digital Ground.
Positive Supply Voltage (2.7 V to 5.5 V). The supply should be decoupled with a 0.1 μF ceramic capacitor to ground.
No Connect. The NC pin is not bonded to the die internally.
No Connect. The NC pin is not bonded to the die internally.
No Connect. The NC pin is not bonded to the die internally.
No Connect. The NC pin is not bonded to the die internally.
Exposed Pad. To ensure correct operation, the exposed pad should either be left floating or connected to ground.
Rev. 0 | Page 7 of 24
ADT7420
Data Sheet
TYPICAL PERFORMANCE CHARACTERISTICS
30
25
20
15
10
5
1.00
0.75
0.50
MAX ACCURACY LIMITS
0.25
0
–0.25
5.5V
5.0V
MAX ACCURACY LIMITS
–0.50
–0.75
4.5V
3.6V
3.3V
3.0V
2.7V
0
–100
–1.00
–50
0
50
100
150
200
–60 –40 –20
0
20
40
60
80
100 120 140
TEMPERATURE (°C)
TEMPERATURE (°C)
Figure 7. Shutdown Current vs. Temperature
Figure 4. Temperature Accuracy at 3 V
300
250
200
150
100
50
1.00
0.75
0.50
I
CONTINUOUS CONVERSION
DD
MAX ACCURACY LIMITS
0.25
0
–0.25
–0.50
–0.75
I
1SPS
DD
MAX ACCURACY LIMITS
0
2.5
–1.00
3.0
3.5
4.0
4.5
5.0
5.5
6.0
–60 –40 –20
0
20
40
60
80
100 120 140
TEMPERATURE (°C)
SUPPLY VOLTAGE (V)
Figure 5. Temperature Accuracy at 5 V
Figure 8. Average Operating Supply Current vs. Supply Voltage
8
7
6
5
4
3
2
1
0
300
250
200
150
100
50
5.5V CONTINUOUS
CONVERSION
3.0V CONTINUOUS
CONVERSION
5.5V 1SPS
3.0V 1SPS
0
–100
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
–50
0
50
100
150
200
SUPPLY VOLTAGE (V)
TEMPERATURE (°C)
Figure 9. Shutdown Current vs. Supply Voltage
Figure 6. Operating Supply Current vs. Temperature
Rev. 0 | Page 8 of 24
Data Sheet
ADT7420
140
120
100
80
125°C
105°C
85°C
IT TAKES LESS THAN
2 SECONDS TO REACH 63.2%
OF ITS TEMPERATURE SPAN
60
40
20
0
0
5
10
15
20
25
TIME (s)
Figure 10. Thermal Response Time
Rev. 0 | Page 9 of 24
ADT7420
Data Sheet
THEORY OF OPERATION
CIRCUIT INFORMATION
NORMAL MODE
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 com-
pared to an internal voltage reference and input into a precision
digital modulator.
In normal mode (default power-up mode) the ADT7420 runs
an automatic conversion sequence. During this automatic con-
version 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.
The internal temperature sensor has high accuracy and linearity
over the entire rated temperature range without needing correc-
tion or calibration by the user.
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 sensor output is digitized by a sigma-delta (Σ-Δ) modulator,
also known as the charge balance type analog-to-digital conver-
ter. This type of converter utilizes time-domain oversampling
and a high accuracy comparator to deliver 16 bits of resolution
in an extremely compact circuit.
The conversion clock for the part is generated internally.
No external clock is required except when reading from
and writing to the serial port.
CONVERTER DETAILS
The measured temperature value is compared with a critical
temperature limit (stored in the 16-bit TCRIT setpoint read/write
register), a high temperature limit (stored in the 16-bit THIGH set-
point read/write register), and a low temperature limit (stored
in the 16-bit TLOW setpoint read/write register). If the measured
value exceeds these limits, the INT pin is activated; and if it exceeds
the TCRIT limit, the CT pin is activated. The INT and CT pins are
programmable for polarity via the configuration register, and the
INT and CT pins are also programmable for interrupt mode via
the configuration register.
The Σ-Δ 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.
ONE-SHOT MODE
Σ-∆ MODULATOR
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.
INTEGRATOR
COMPARATOR
VOLTAGE REF
AND VPTAT
Wait for a minimum of 240 ms after writing to the operation
mode bits before reading back the temperature from the tem-
perature value register. This time ensures that the ADT7420
has time to power up and complete a conversion.
1-BIT
DAC
1-BIT
TEMPERATURE
VALUE
REGISTER
CLOCK
GENERATOR
LPF DIGITAL
FILTER
To obtain an updated temperature conversion, reset Bit 6 to 0
and Bit 5 to 1 in the configuration register (0x03).
13-BIT/
16-BIT
Figure 11. Σ-Δ Modulator
The one-shot mode is useful when one of the circuit design
priorities is to reduce power consumption.
The ADT7420 can be configured to operate in any one of the
following four operating modes: normal, one-shot, 1 SPS, and
shutdown.
Rev. 0 | Page 10 of 24
Data Sheet
ADT7420
CT and INT Operation in One-Shot Mode
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.
See Figure 12 for more information on one-shot CT pin
operation for TCRIT overtemperature events when one of the
limits is exceeded. Note that in interrupt mode, a read from
any register resets the INT and CT pins.
For the INT pin in the comparator mode, if the temperature drops
below the THIGH – THYST value or goes above the TLOW + THYST
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 TCRIT – THYST value, a write to the operation
mode bits (Bit 6 = 0 and Bit 5 = 1 of the configuration register,
Register Address 0x03) resets the CT pin (see Figure 12).
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.
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
TEMPERATURE
149°C
148°C
147°C
146°C
145°C
144°C
143°C
142°C
141°C
140°C
T
CRIT
T
– T
HYST
CRIT
CT PIN
POLARITY = ACTIVE LOW
CT PIN
POLARITY = ACTIVE HIGH
TIME
WRITE TO
WRITE TO
WRITE TO
BIT 5 AND BIT 6 OF BIT 5 AND BIT 6 OF BIT 5 AND BIT 6 OF
CONFIGURATION
REGISTER.*
CONFIGURATION
REGISTER.*
CONFIGURATION
REGISTER.*
*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.
Figure 12. One-Shot CT Pin
Rev. 0 | Page 11 of 24
ADT7420
Data Sheet
TEMPERATURE DATA FORMAT
TEMPERATURE CONVERSION FORMULAS
16-Bit 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 TCRIT
setpoint register and the THIGH setpoint register. It is also com-
pared with the low temperature limit stored in the TLOW setpoint
register.
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
Temperature data in the temperature value register, the TCRIT
setpoint register, the THIGH setpoint register, and the TLOW setpoint
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 TCRIT, THIGH, and TLOW. Table 5 shows the 13-bit
temperature data format without Bit 0 to Bit 2.
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
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 confi-
guration 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 power-
on default setting has a 13-bit temperature data value.
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
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.
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
Table 5. 13-Bit Temperature Data Format
the sign bit.
Digital Output
Temperature (Binary) Bits[15:3]
Digital Output (Hex)
0x1D80
0x1E70
0x1FFF
0x000
0x001
0x190
0x690
0x7D0
0x960
Negative Temperature = ADC Code (dec) − 256
−40°C
−25°C
−0.0625°C
0°C
+0.0625°C
+25°C
+105°C
+125°C
+150°C
1 1101 1000 0000
1 1110 0111 0000
1 1111 1111 1111
0 0000 0000 0000
0 0000 0000 0001
0 0001 1001 0000
0 0110 1001 0000
0 0111 1101 0000
0 1001 0110 0000
where Bit 8 (sign bit) is removed from the ADC code.
Rev. 0 | Page 12 of 24
Data Sheet
ADT7420
REGISTERS
The ADT7420 contains 14 registers:
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.
•
•
•
•
•
•
Nine temperature registers
A status register
An ID register
A configuration register
An address pointer register
A software reset
Table 7. Address Pointer Register
P7
P6
P5
P4
P3
P2
P1
P0
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).
ADD7 ADD6 ADD5 ADD4 ADD3 ADD2 ADD1 ADD0
TEMPERATURE VALUE REGISTERS
The temperature value consists of two bytes, one most signifi-
cant 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 signifi-
cant byte is read, the address pointer is auto-incremented so that
the least significant byte can read within the same transaction.
Table 6. ADT7420 Registers
Register
Address
Power-On
Default
Description
0x00
0x01
0x02
0x03
0x04
0x05
0x06
0x07
0x08
0x09
0x0A
0x0B
0x2F
Temperature value most significant byte
Temperature value least significant byte
Status
0x00
0x00
0x00
0x00
0x20 (64°C)
0x00 (64°C)
0x05 (10°C)
0x00 (10°C)
0x49 (147°C)
0x80 (147°C)
0x05 (5°C)
0xCB
Bit 0 to Bit 2 are event alarm flags for TLOW, THIGH, and TCRIT. When
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.
Configuration
THIGH setpoint most significant byte
THIGH setpoint least significant byte
TLOW setpoint most significant byte
TLOW setpoint least significant byte
TCRIT setpoint most significant byte
TCRIT setpoint least significant byte
THYST setpoint
ID
Software reset
0xXX
Table 8. Temperature Value MSB Register (Register Address 0x00)
Bit
Default Value
Type
Name
Temp
Sign
Description
[14:8]
15
0000000
0
R
R
Temperature value in twos complement format
Sign bit, indicates if the temperature value is negative or positive
Table 9. Temperature Value LSB Register (Register Address 0x01)
Default
Value
Bit
Type Name
Description
0
0
R
R
R
R
TLOW flag/LSB0
Flags a TLOW event if the configuration register, Register Address 0x03[7] = 0 (13-bit
resolution). When the temperature value is below TLOW, this bit it set to 1.
Contains the Least Significant Bit 0 of the 15-bit temperature value if the configuration
register, Register Address 0x03[7] = 1 (16-bit resolution).
1
0
THIGH flag/LSB1 Flags a THIGH event if the configuration register, Register Address 0x03[7] = 0 (13-bit
resolution). When the temperature value is above THIGH, this bit it set to 1.
Contains the Least Significant Bit 1 of the 15-bit temperature value if the configuration
register, Register Address 0x03[7] = 1 (16-bit resolution).
2
0
TCRIT flag/LSB2
Temp
Flags a TCRIT event if the configuration register, Register Address 0x03[7] = 0 (13-bit
resolution). When the temperature value exceeds TCRIT, this bit it set to 1.
Contains the Least Significant Bit 2 of the 15-bit temperature value if the configuration
register, Register Address 0x03[7] = 1 (16-bit resolution).
[7:3]
00000
Temperature value in twos complement format.
Rev. 0 | Page 13 of 24
ADT7420
Data Sheet
STATUS REGISTER
CONFIGURATION REGISTER
This 8-bit read-only register reflects the status of the overtempera-
ture 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
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.
RDY
hysteresis. The
bit is reset after a read from the temperature
RDY
value register. In one-shot and 1 SPS modes, the
after a write to the operation mode bits.
bit is reset
Table 10. Status Register (Register Address 0x02)
Default
Bit
Value
Type
Name
Unused
TLOW
Description
Reads back 0.
[3:0] 0000
R
R
4
5
6
7
0
0
0
1
This bit is set to 1 when the temperature goes below the TLOW temperature limit. The bit clears to 0
when the status register is read and/or when the temperature measured goes back above the limit
set in the setpoint TLOW + THYST registers.
R
R
R
THIGH
TCRIT
RDY
This bit is set to 1 when the temperature goes above the THIGH temperature limit. The bit clears to 0
when the status register is read and/or when the temperature measured goes back below the limit
set in the setpoint THIGH − THYST registers.
This bit is set to 1 when the temperature goes above the TCRIT temperature limit. This bit clears to 0
when the status register is read and/or when the temperature measured goes back below the limit
set in the setpoint TCRIT − THYST registers.
This bit goes low when the temperature conversion result is written into the temperature value
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.
Table 11. Configuration Register (Register Address 0x03)
Default
Bit
Value
Type
Name
Description
[1:0]
00
W
Fault queue
These two bits set the number of undertemperature/overtemperature faults that can occur before setting the
INT and CT pins. This helps to avoid false triggering due to temperature noise.
R/
00 = 1 fault (default).
01 = 2 faults.
10 = 3 faults.
11 = 4 faults.
2
0
W
W
W
W
CT pin polarity
INT pin polarity
INT/CT mode
This bit selects the output polarity of the CT pin.
R/
R/
R/
R/
0 = active low.
1 = active high.
3
0
This bit selects the output polarity of the INT pin.
0 = active low.
1 = active high.
4
0
This bit selects between comparator mode and interrupt mode.
0 = interrupt mode
1 = comparator mode
[6:5]
00
Operation mode
These two bits set the operational mode for the ADT7420.
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
consumption.
11 = shutdown. All circuitry except interface circuitry is powered down.
This bit sets up the resolution of the ADC when converting.
7
0
W
Resolution
R/
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.
Rev. 0 | Page 14 of 24
Data Sheet
ADT7420
When reading from this register, the eight most significant bits
(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 (TLOW setpoint
MSB) needs to be loaded into the address pointer register because
the address pointer auto-increments to Register Address 0x07
(TLOW setpoint LSB).
THIGH SETPOINT REGISTERS
The THIGH setpoint MSB and THIGH setpoint LSB registers store
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 temper-
ature is stored in twos complement format with the MSB being
the temperature sign bit.
The default setting for the TLOW setpoint is 10°C.
TCRIT SETPOINT REGISTERS
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 (THIGH setpoint LSB). Only Register
Address 0x04 (THIGH setpoint MSB) needs to be loaded into
the address pointer register because the address pointer auto-
increments to Register Address 0x05 (THIGH setpoint LSB).
The TCRIT setpoint MSB and TCRIT setpoint LSB registers store
the critical overtemperature limit value. A critical overtempe-
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
event occurs. The temperature is stored in twos complement
format with the MSB being the temperature sign bit.
The default setting for the THIGH setpoint is 64°C.
When reading from this register, the eight most significant bits
(Bit 15 to Bit 8) are read first from Register Address 0x08 (TCRIT
setpoint MSB) and then the eight least significant bits (Bit 7 to
Bit 0) are read from Register Address 0x09 (TCRIT setpoint LSB).
Only Register Address 0x08 (TCRIT setpoint MSB) needs to be
loaded into the address pointer register because the address pointer
auto-increments to Register Address 0x09 (TCRIT setpoint LSB).
TLOW SETPOINT REGISTERS
The TLOW setpoint MSB and TLOW setpoint LSB registers store
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.
The default setting for the TCRIT limit is 147°C.
Table 12. THIGH Setpoint MSB Register (Register Address 0x04)
Bit
Default Value
Type
Name
Description
[15:8]
0x20
R/
THIGH MSB MSBs of the overtemperature limit, stored in twos complement format.
W
Table 13. THIGH Setpoint LSB Register (Register Address 0x05)
Bit
Default Value
Type
Name
Description
[7:0]
0x00
R/
THIGH LSB
LSBs of the overtemperature limit, stored in twos complement format.
W
Table 14. TLOW Setpoint MSB Register (Register Address 0x06)
Bit
Default Value
Type
Name
Description
[15:8]
0x05
R/
TLOW MSB
MSBs of the undertemperature limit, stored in twos complement format.
W
Table 15. TLOW Setpoint LSB Register (Register Address 0x07)
Bit
Default Value
Type
Name
Description
[7:0]
0x00
R/
TLOW LSB
LSBs of the undertemperature limit, stored in twos complement format.
W
Table 16. TCRIT Setpoint MSB Register (Register Address 0x08)
Bit
Default Value
Type
Name
Description
[15:8]
0x49
R/
TCRIT MSB
MSBs of the critical overtemperature limit, stored in twos complement format.
W
Table 17. TCRIT Setpoint LSB Register (Register Address 0x09)
Bit
Default Value
Type
Name
Description
[7:0]
0x80
R/
TCRIT LSB
LSBs of the critical overtemperature limit, stored in twos complement format.
W
Rev. 0 | Page 15 of 24
ADT7420
Data Sheet
THYST SETPOINT REGISTER
ID REGISTER
This 8-bit read/write register stores the temperature hysteresis
value for the THIGH, TLOW, and TCRIT temperature limits. The
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
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.
T
HIGH and TCRIT values and added to the TLOW value to imple-
ment hysteresis.
Table 18. THYST Setpoint Register (Register Address 0x0A)
Bit
Default Value Type Name Description
[3:0]
[7:4]
0101
0000
R/
R/
THYST
N/A
Hysteresis value, from 0°C to 15°C. Stored in straight binary format. The default setting is 5°C.
Not used.
W
W
Table 19. ID Register (Register Address 0x0B)
Bit
Default Value
Type Name
Description
[2:0]
[7:3]
011
R
Revision ID
Manufacture ID
Contains the silicon revision identification number
Contains the manufacture identification number
11001
R
Rev. 0 | Page 16 of 24
Data Sheet
ADT7420
SERIAL INTERFACE
PULL-UP
PULL-UP
PULL-UP
V
V
V
V
DD
DD
DD
DD
V
10kΩ
0.1µF
10kΩ
DD
10kΩ
10kΩ
ADT7420
CT
SCL
SDA
INT
TO INTERRUPT PIN
ON MICROCONTROLLER
A0
A1
GND
Figure 13. Typical I2C Interface Connection
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
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.
W
read from or written to it. If the R/ bit is a 0, the master
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.
W
writes to the slave device. If the R/ 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 condi-
tions 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.
Table 20. I2C Bus Address Options
Binary
A6
1
1
1
1
A5
0
0
0
0
A4
0
0
0
0
A3
1
1
1
1
A2
0
0
0
0
A1
0
0
1
1
A0
0
1
0
1
Hex
0x48
0x49
0x4A
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/
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.
W
W
write (R/ ) bit. The R/ bit determines whether data is
written to, or read from, the slave device.
Rev. 0 | Page 17 of 24
ADT7420
Data Sheet
For the THIGH setpoint, TLOW setpoint, and TCRIT setpoint
WRITING DATA
registers, it is possible to write to both the MSB and the LSB
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.
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.
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.
1
9
1
9
SCL
1
0
0
1
0
A1
A0
P7
P6
P5
P4
P3
P2
P1
P0
R/W
SDA
START BY
ACK. BY
ADT7420
ACK. BY
ADT7420
MASTER
FRAME 1
SERIAL BUS ADDRESS BYTE
FRAME 2
ADDRESS POINTER REGISTER BYTE
1
9
SCL (CONTINUED)
SDA (CONTINUED)
D7
D6
D5
D4
D3
D2
D1
D0
ACK. BY STOP BY
ADT7420 MASTER
FRAME 3
DATA BYTE
Figure 14. Writing to a Register Followed by a Single Byte of Data
1
1
9
1
9
SCL
SDA
0
0
1
0
A1
A0
P7
P6
P5
P4
P3
P2
P1
P0
R/W
START BY
MASTER
ACK. BY
ADT7420
ACK. BY
ADT7420
FRAME 1
FRAME 2
SERIAL BUS ADDRESS BYTE
ADDRESS POINTER REGISTER BYTE
1
9
1
9
SCL (CONTINUED)
SDA (CONTINUED)
D15
D14
D13
D12
D11 D10
D9
D8
D7
D6
D5
D4
D3
D2
D1
D0
ACK. BY STOP BY
ACK. BY
ADT7420
ADT7420 MASTER
FRAME 3
DATA BYTE
FRAME 4
DATA BYTE
Figure 15. Writing to a Register Followed by Two Bytes of Data
Rev. 0 | Page 18 of 24
Data Sheet
ADT7420
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.
READING DATA
Reading data from the ADT7420 is done in a single data byte
operation for the configuration register, the status register,
the THYST setpoint register, and the ID register. A two data byte
read operation is needed for the temperature value register,
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.
THIGH setpoint register, TLOW setpoint register, and the TCRIT
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
1
9
1
9
SCL
0
1
0
0
1
A1
A0
R/W
P7
P6
P5
P4
P3
P2
P1
P0
SDA
START BY
MASTER
ACK. BY
ADT7420
ACK. BY
ADT7420
FRAME 1
FRAME 2
SERIAL BUS ADDRESS
BYTE
ADDRESS POINTER REGISTER BYTE
1
1
9
1
9
SCL
0
0
1
0
A1
A0
R/W
D7
D6
D5
D4
D3
D2
D1
D0
SDA
REPEAT START
BY MASTER
ACK. BY
ADT7420
NO ACK. BY STOP BY
MASTER MASTER
FRAME 3
FRAME 4
SERIAL BUS ADDRESS
BYTE
DATA BYTE FROM CONFIGURATION
REGISTER
Figure 16. Reading Back Data from the Configuration Register
1
9
1
9
SCL
SDA
R/W
A7
A6
A1
A0
1
0
0
1
0
A1
A0
START
ADT7410 DEVICE ADDRESS
ACK. BY
ADT7420
REGISTER ADDRESS[A7:A0]
1
ACK. BY
ADT7420
1
9
9
SR
SCL
D7
D6
TEMPERATURE
D1
D0
D7
D6
D1
D0
SDA
R/W
1
0
A1
A0
REPEAT
START
ACK. BY
ADT7420
ACK. BY
MASTER
NO
ACK. BY
MASTER
ADT7410 DEVICE ADDRESS
TEMPERATURE
VALUE REGISTER
MSB DATA
VALUE REGISTER
LSB DATA
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.
Figure 17. Reading Back Data from the Temperature Value Register
Rev. 0 | Page 19 of 24
ADT7420
Data Sheet
RESET
GENERAL CALL
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:
When a master issues a slave address consisting of seven 0s with
W
the eighth bit (R/ 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.
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.
The ADT7420 does not acknowledge any other general call
commands.
6. Wait 200 µs for the part to reset its registers to the default
power-up settings.
Rev. 0 | Page 20 of 24
Data Sheet
ADT7420
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.
Comparator Mode
In comparator mode, the INT pin returns to its inactive status
when the temperature drops below the THIGH − THYST limit or
rises above the TLOW + THYST limit.
UNDERTEMPERATURE AND OVERTEMPERATURE
DETECTION
Putting the ADT7420 into shutdown mode does not reset the
INT state in comparator mode.
The INT and CT pins have two undertemperature/overtempera-
ture 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 THIGH setpoint register or less than
the temperature stored in the TLOW setpoint register. How this
pin reacts after this event depends on the overtemperature mode
selected.
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 THIGH setpoint register or less than the temperature stored
in the TLOW setpoint register.
Placing the ADT7420 into shutdown mode resets the INT pin
in the interrupt mode.
Figure 18 illustrates the comparator and interrupt modes for
events exceeding the THIGH limit with both pin polarity settings.
Figure 19 illustrates the comparator and interrupt modes for
events exceeding the TLOW limit with both pin polarity settings.
TEMPERATURE
82°C
81°C
80°C
79°C
78°C
77°C
76°C
75°C
74°C
73°C
THIGH
THIGH – THYST
INT PIN
(COMPARATOR MODE)
POLARITY = ACTIVE LOW
INT PIN
(INTERRUPT MODE)
POLARITY = ACTIVE LOW
INT PIN
(COMPARATOR MODE)
POLARITY = ACTIVE HIGH
INT PIN
(INTERRUPT MODE)
POLARITY = ACTIVE HIGH
TIME
READ
READ
READ
Figure 18. INT Output Temperature Response Diagram for THIGH Overtemperature Events
Rev. 0 | Page 21 of 24
ADT7420
Data Sheet
TEMPERATURE
–13°C
–14°C
–15°C
–16°C
–17°C
–18°C
–19°C
–20°C
–21°C
–22°C
T
LOW + THYST
TLOW
INT PIN
(COMPARATOR MODE)
POLARITY = ACTIVE LOW
INT PIN
(INTERRUPT MODE)
POLARITY = ACTIVE LOW
INT PIN
(COMPARATOR MODE)
POLARITY = ACTIVE HIGH
INT PIN
(INTERRUPT MODE)
POLARITY = ACTIVE HIGH
TIME
READ
READ
READ
Figure 19. INT Output Temperature Response Diagram for TLOW Undertemperature Events
Rev. 0 | Page 22 of 24
Data Sheet
ADT7420
APPLICATIONS INFORMATION
THERMAL RESPONSE TIME
POWERING FROM A SWITCHING REGULATOR
Precision analog devices, such as the ADT7420 require a well-
filtered 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 the 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.
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 tempera-
ture 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.
TEMPERATURE MEASUREMENT
The ADT7420 accurately measures and converts the tempera-
ture 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.
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.
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.
TTL/CMOS
LOGIC
1. After powering up the ADT7420, verify the setup by
reading the device ID (Register Address 0x0B). It should
read 0xCB.
CIRCUITS
0.1µF
ADT7420
2. After consistent consecutive readings are obtained from
Step 1, proceed to read the configuration register (0x03),
POWER
SUPPLY
T
CRIT (0x08, 0x09), THIGH (0x04, 0x05), and TLOW (0x06,
0x07) registers. Compare to the specified defaults in Table 6.
If all the readings match, the interface is operational.
Figure 20. Use of Separate Traces to Reduce Power Supply Noise
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.
Rev. 0 | Page 23 of 24
ADT7420
Data Sheet
OUTLINE DIMENSIONS
4.10
4.00 SQ
3.90
0.35
0.30
0.25
PIN 1
INDICATOR
PIN 1
INDICATOR
13
16
1
0.65
BSC
12
EXPOSED
PAD
2.70
2.60 SQ
2.50
4
5
9
8
0.45
0.40
0.35
0.25 MIN
TOP VIEW
BOTTOM VIEW
0.80
0.75
0.70
FOR PROPER CONNECTION OF
THE EXPOSED PAD, REFER TO
THE PIN CONFIGURATION AND
FUNCTION DESCRIPTIONS
0.05 MAX
0.02 NOM
COPLANARITY
0.08
SECTION OF THIS DATA SHEET.
SEATING
PLANE
0.20 REF
COMPLIANT TO JEDEC STANDARDS MO-220-WGGC.
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
ADT7420UCPZ-R2
ADT7420UCPZ-RL7
EVAL-ADT7X20EBZ
Operating Temperature Range
−40°C to +150°C
−40°C to +150°C
Package Description
16-lead LFCSP_WQ
16-lead LFCSP_WQ
Evaluation Board
Package Option
CP-16-17
CP-16-17
1 Z = RoHS Compliant Part.
I2C refers to a communications protocol originally developed by Philips Semiconductors (now NXP Semiconductors).
©2012 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D09013-0-12/12(0)
Rev. 0 | Page 24 of 24
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