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Preliminary Technical Data
FEATURES
Temperature accuracy: 0.25C from -20C to +105C 13- or 16-bit user selectable temperature-to-digital converter Low drift silicon temperature sensor No temperature calibration/correction required by user Power saving 1 sample per second (SPS) mode Fast first conversion on power-up of 6 ms I2C-compatible interface Operating temperature: -40C to +150C Operating voltage: 2.7 V to 5.5 V Critical overtemperature indicator Programmable overtemperature/undertemperature interrupt Low power consumption: 700 W typical at 3.3 V Shutdown mode for lower power: 7 W typical at 3.3 V 16-lead RoHS-compliant LFCSP package
0.25C Accurate, 16-Bit Digital I2C Temperature Sensor ADT7420
GENERAL DESCRIPTION
The ADT7420 is a high accuracy digital temperature sensor offering breakthrough performance over a wide industrial range, housed in an LFCSP package. It contains a band gap temperature reference and a 13-bit ADC to monitor and digitize the temperature to a 0.0625C resolution. The ADC resolution, by default, is set to 13 bits (0.0625C). This can be changed to 16 bits (0.0078C) by setting Bit 7 in the configuration register to 1 (Register Address 0x03). 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 A. The ADT7420 has a shutdown mode that powers down the device and offers a shutdown current of typically 2 A. The ADT7420 is rated for operation over the -40C to +150C temperature range. Pin A0 and Pin A1 are available for address selection, giving the ADT7420 four possible I2C addresses. The CT pin is an opendrain output that becomes active when the temperature exceeds a programmable critical temperature limit. The default critical temperature limit is 147C. The INT pin is also an open-drain output that becomes active when the temperature exceeds a programmable limit. The INT and CT pins can operate in either comparator or interrupt mode.
APPLICATIONS
RTD and thermistor replacement Medical equipment Cold junction compensation Industrial control and test Food transportation and storage Environmental monitoring and HVAC
FUNCTIONAL BLOCK DIAGRAM
VDD
12
TEMPERATURE VALUE REGISTER CONFIGURATION REGISTER
ADT7420
10
CT
TCRIT REGISTER THIGH REGISTER TLOW REGISTER THYST REGISTER STATUS REGISTER ID REGISTER SOFTWARE RESET REGISTER A0 A1
3 4
INTERNAL OSCILLATOR
TCRIT
INTERNAL REFERENCE
9
INT
THIGH
TEMPERATURE SENSOR
- MODULATOR
POINTER REGISTER
FILTER LOGIC
TLOW
I2C INTERFACE
11
1 2
SCL SDA
09013-001
GND
Figure 1.
Rev. PrA
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ADT7420 TABLE OF CONTENTS
Features .............................................................................................. 1 Applications ....................................................................................... 1 General Description ......................................................................... 1 Functional Block Diagram .............................................................. 1 Specifications..................................................................................... 3 I C Timing Specifications ............................................................ 4 Absolute Maximum Ratings ............................................................ 5 ESD Caution .................................................................................. 5 Pin Configuration and Function Descriptions ............................. 6 Typical Performance Characteristics ............................................. 7 Theory of Operation ........................................................................ 9 Circuit Information ...................................................................... 9 Converter Details.......................................................................... 9 Temperature Measurement ......................................................... 9 One-Shot Mode ............................................................................ 9 1 SPS Mode .................................................................................... 9 Shutdown ..................................................................................... 11 Fault Queue ................................................................................. 11 Temperature Data Format ......................................................... 12 Temperature Conversion Formulas ......................................... 12 Registers ........................................................................................... 13 Address Pointer Register ........................................................... 13
2
Preliminary Technical Data
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 ............................................................................................. 19 General Call ................................................................................ 19 INT and CT Outputs...................................................................... 21 Undertemperature and Overtemperature Detection ............ 21 Applications Information .............................................................. 23 Thermal Response Time ........................................................... 23 Supply Decoupling ..................................................................... 23 Temperature Monitoring ........................................................... 23 Outline Dimensions ....................................................................... 24 Ordering Guide .......................................................................... 24
Rev. PrA | Page 2 of 2
Preliminary Technical Data SPECIFICATIONS
TA = -40C to +125C, VDD = 2.7 V to 5.5 V, unless otherwise noted. Table 1.
Parameter TEMPERATURE SENSOR AND ADC Accuracy 1 Min Typ Max 0.20 2 0.25 0.50 0.50 3 0.75 -0.85 -1.0 13 16 Temperature Resolution 13-Bit 16-Bit Temperature Conversion Time Fast Temperature Conversion Time 1 SPS Conversion Time Temperature Hysteresis Repeatability 4 Drift 5 DC PSRR DIGITAL OUTPUTS (OPEN DRAIN) High Output Leakage Current, IOH Output High Current Output Low Voltage, VOL Output High Voltage, VOH Output Capacitance, COUT DIGITAL INPUTS Input Current Input Low Voltage, VIL Input High Voltage, VIH SCL, SDA Glitch Rejection Pin Capacitance POWER REQUIREMENTS Supply Voltage Supply Current At 3.3 V At 5.5 V 1 SPS Current At 3.3 V At 5.5 V Shutdown Current At 3.3 V At 5.5 V Power Dissipation Normal Mode Power Dissipation 1 SPS
1 2 3
ADT7420
Unit C C C C C C C Bits Bits
Test Conditions/Comments TA = -10C to +85C, VDD = 3.0 V TA = -20C to +105C, VDD = 2.7 V to 3.3 V TA = -40C to +125C, VDD = 2.7 V to 3.3 V TA = -10C to +105C, VDD = 4.5 V to 5.5 V TA = -40C to +125C, VDD = 4.5 V to 5.5 V TA = +125C to +150C, VDD = 4.5V to 5.5 V TA = +125C to +150C, VDD = 2.7 V to 3.3 V Twos complement temperature value of the sign bit plus 12 ADC bits (power-up default resolution) Twos complement temperature value of the sign bit plus 15 ADC bits (Bit 7 = 1 in the configuration register) 13-bit resolution (sign + 12-bit) 16-bit resolution (sign + 15-bit) Continuous conversion and one-shot conversion modes First conversion on power-up only Conversion time for 1 SPS mode Temperature cycle = 25C to 125C and back to 25C TA = 25C 500 hour stress test at +150C with VDD = 5.0V TA = 25C CT and INT pins pulled up to 5.5 V VOH = 5.5 V IOL = 2 mA @ 5.5 V, IOL = 1 mA @ 3.3 V
ADC Resolution
0.0625 0.0078 240 6 60 0.02 0.015 0.0073 0.1 0.1 5 1 0.4
C C ms ms ms C C C C/V A mA V V pF A V V ns pF V A A A A 15 25 A A W W
0.7 x VDD 3 1 0.4 0.7 x VDD 50 5 2.7 210 230 46 65 2.0 4.4 700 150 10 5.5 250 300
VIN = 0 V to VDD
Input filtering suppresses noise spikes of less than 50 ns
Peak current while converting, I2C interface inactive Peak current while converting, I2C interface inactive VDD = 3.3 V, 1 SPS mode, TA = 25C VDD = 5.5 V, 1 SPS mode, TA = 25C Supply current in shutdown mode Supply current in shutdown mode VDD = 3.3 V, normal mode at 25C Power dissipated for VDD = 3.3 V, TA = 25C
Accuracy specification includes repeatability. The equivalent 3- limits are 0.15C. This 3- specification is provided to enable comparison with other vendors who use these limits. For higher accuracy at 5 V operation, contact Analog Devices. 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. PrA | Page 3 of
ADT7420
I2C TIMING SPECIFICATIONS
Preliminary Technical Data
TA = -40C to +150C, 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 INTERFACE 1, 2 SCL Frequency SCL High Pulse Width, tHIGH SCL Low Pulse Width, tLOW SCL, SDA Rise Time, tR 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
1 2
Min 0 0.6 1.3
Typ
Max 400
Unit kHz s s s s s s s s s s s
Test Conditions/Comments See Figure 2
0.3 0.3 0.6 0.6 0.25 0.35 0.6 0 1.3
After this period, the first clock is generated Relevant for repeated start condition VDD 3.0 V VDD < 3.0 V
Sample tested during initial release to ensure compliance. All input signals are specified with input rise/fall times = 3 ns, measured between the 10% and 90% points. Timing reference points at 50% for inputs and outputs. Output load = 10 pF.
Timing Diagram
tLOW
SCL
tR
tF
tHD:STA
tHD:STA
SDA
tHD:DAT
tHIGH tSU:DAT
tSU:STA
tSU:STO
tBUF
P S S P
Figure 2. Serial Interface Timing Diagram
Rev. PrA | Page 4 of 4
09013-002
Preliminary Technical Data ABSOLUTE MAXIMUM RATINGS
Table 3.
Parameter VDD to GND SDA Voltage to GND 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 Range Storage Temperature Range Maximum Junction Temperature, TJMAX 16-Lead LFCSP (CP-16-17) Power Dissipation1 Thermal Impedance3 JA, Junction-to-Ambient (Still Air) JC, Junction-to-Case IR Reflow Soldering Peak Temperature (RoHS-Compliant Package) Time at Peak Temperature Ramp-Up Rate Ramp-Down Rate Time from 25C to Peak Temperature
1
ADT7420
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.
Rating -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 -40C to +150C -65C to +160C 150C WMAX = (TJMAX - TA2)/JA 121C/W 56C/W 220C 260C (0C) 20 sec to 40 sec 3C/sec maximum -6C/sec maximum 8 minutes maximum
ESD CAUTION
Values relate to package being used on a standard 2-layer PCB. This gives a worst-case JA and JC. 2 TA = ambient temperature. 3 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. PrA | Page 5 of
ADT7420 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
16 NC 15 NC 14 NC 13 NC
Preliminary Technical Data
SCL 1 SDA 2 A0 3 A1 4
12 VDD
ADT7420
TOP VIEW
(Not to Scale)
11 GND 10 CT 9 INT
NC 5
NOTES 1. NC = NO CONNECT. 2. THE EXPOSED PAD IS CONNECTED INTERNALLY. FOR INCREASED RELIABILITY OF THE SOLDER JOINTS AND MAXIMUM THERMAL CAPABILITY IT IS RECOMMENDED THAT THE PAD BE SOLDERED TO THE GROUND PLANE.
NC 7 NC 8
NC 6
Figure 3. Pin Configuration
Table 4. Pin Function Descriptions
Pin No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Mnemonic SCL SDA A0 A1 NC NC NC NC INT CT GND VDD NC NC NC NC Description 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 k. 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 k. 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. No Connect. No Connect. No Connect. 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 k. Critical Overtemperature Indicator. Logic output. Power-up default polarity is active low. Open-drain configuration. A pull-up resistor is required, typically 10 k. Analog and Digital Ground. Positive Supply Voltage (2.7 V to 5.5 V). The supply should be decoupled with a 0.1 F ceramic capacitor to ground. No Connect. No Connect. No Connect. No Connect.
Rev. PrA | Page 6 of
09013-004
Preliminary Technical Data TYPICAL PERFORMANCE CHARACTERISTICS
1.0
0.30
ADT7420
TEMPERATURE ERROR (C)
0.5
0.25
5.5V CONTINUOUS CONVERSION
0.20
3.0V CONTINUOUS CONVERSION
0
IDD (mA)
0.15
0.10
0.5
0.05
5.5V 1SPS
3.0V 1SPS
09013-027
09013-028
09013-032
1.0 -50
-30
-10
50 70 10 30 TEMPERATURE (C)
90
110
130
0 -100
-50
0
50
100
150
200
TEMPERATURE (C)
Figure 4. Temperature Accuracy at 3 V
Figure 6. Operating Supply Current vs. Temperature
1.0
30
25
TEMPERATURE ERROR (C)
SHUTDOWN IDD (A)
0.5
20
15
0
10
5.5V 5.0V
0.5
5
4.5V 3.6V
0 -100
3.3V 3.0V 2.7V
100 150 200
-50
0
50
-30
-10
50 70 10 30 TEMPERATURE (C)
90
110
130
09013-026
1.0 -50
TEMPERATURE (C)
Figure 7. Shutdown Current vs. Temperature
Figure 5. Temperature Accuracy at 5 V
Rev. PrA | Page 7 of
ADT7420
0.30 IDD CONTINUOUS CONVERSION
Preliminary Technical Data
160 140 120
0.25
0.20
TEMPERATURE (C)
IDD 1SPS
100 80 60 40
IDD (mA)
0.15
0.10
0.05
20 0
0 5 10 15 20 25 30 35 40
3.0
3.5
4.0
4.5
5.0
5.5
6.0
09013-029
SUPPLY VOLTAGE (V)
TIME (Seconds)
Figure 8. Average Operating Supply Current vs. Supply Voltage at 25C
Figure 10. Response to Thermal Shock
8 7 6
SHUTDOWN IDD (A)
5 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 at 25C
09013-030
Rev. PrA | Page 8 of
09013-031
0 2.5
Preliminary Technical Data THEORY OF OPERATION
CIRCUIT INFORMATION
The ADT7420 is a 13-bit digital temperature sensor that is extendable to 16 bits for greater resolution. An on-board temperature sensor generates a voltage proportional to absolute temperature, which is compared to an internal voltage reference and input to a precision digital modulator. The on-board 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 (-) 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. Configuration register functions consist of Switching between 13-bit and 16-bit resolution Switching between normal operation and full power-down Switching between comparator and interrupt event modes on the INT and CT pins Setting the active polarity of the CT and INT pins Setting the number of faults that activate CT and INT Enabling the standard one-shot mode and 1 SPS mode
ADT7420
TEMPERATURE MEASUREMENT
In normal mode, the ADT7420 runs an automatic conversion sequence. During this automatic conversion sequence, a conversion 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 147C, the CT pin asserts low. If the temperature exceeds 64C, the INT pin asserts low. Fast conversion temperature accuracy is typically within 5C. 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 TCRIT setpoint read/write register), a high temperature limit (stored in the 16-bit THIGH setpoint 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.
CONVERTER DETAILS
The - 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. The modulated output of the comparator is encoded using a circuit technique that results in I2C temperature data.
- MODULATOR INTEGRATOR COMPARATOR VOLTAGE REF AND VPTAT
ONE-SHOT MODE
Setting Bit 5 to 0 and Bit 6 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 to the one-shot 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. The one-shot mode is useful when one of the circuit design priorities is to reduce power consumption.
1 SPS MODE
1-BIT DAC
1-BIT
09013-012
In this mode, the part performs one measurement per second. A conversion takes only 60 ms, and it remains in the idle state for the remaining 940 ms period. This mode is enabled by writing 1 to Bit 5 and 0 to Bit 6 of the configuration register (Register Address 0x03).
TEMPERATURE VALUE REGISTER
CLOCK GENERATOR
LPF DIGITAL FILTER 13-BIT
Figure 11. - Modulator
Rev. PrA | Page 9 of 24
ADT7420
CT and INT Operation in One-Shot Mode
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 one-shot bits (Bit 5 and Bit 6 of the configuration register, Register Address 0x03) resets the INT pin.
TEMPERATURE 149C 148C 147C 146C 145C 144C 143C 142C 141C 140C
Preliminary Technical Data
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 5 = 0 and Bit 6 = 1of 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.
TCRIT
TCRIT - THYST
CT PIN POLARITY = ACTIVE LOW
CT PIN POLARITY = ACTIVE HIGH TIME
WRITE TO BIT 5 AND BIT 6 OF CONFIGURATION REGISTER.*
WRITE TO BIT 5 AND BIT 6 OF CONFIGURATION REGISTER.*
WRITE TO BIT 5 AND BIT 6 OF CONFIGURATION REGISTER.*
Figure 12. One-Shot CT Pin
Rev. PrA | Page 10 of
09013-013
*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.
Preliminary Technical Data
SHUTDOWN
The ADT7420 can be placed in shutdown mode by writing 1 to Bit 5 and 1 to Bit 6 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 5 and 0 to Bit 6 in the configuration register (Register Address 0x03). The ADT7420 typically takes 1 ms (with a 0.1 F 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.
ADT7420
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.
Rev. PrA | Page 11 of
ADT7420
TEMPERATURE DATA FORMAT
One LSB of the ADC corresponds to 0.0625C in 13-bit mode or 0.0078C in 16-bit mode. The ADC can theoretically measure a temperature range of 255C, but the ADT7420 is guaranteed to measure a low value temperature limit of -40C to a high value temperature limit of +150C. 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 compared with the low temperature limit stored in the TLOW setpoint register. 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. 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 power-on 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
Temperature -40C -25C -0.0625C 0C +0.0625C +25C +105C +125C +150C Digital Output (Binary) Bits[15:3] 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 Digital Output (Hex) 0x1D80 0x1E70 0x1FFF 0x000 0x001 0x190 0x690 0x7D0 0x960
Preliminary Technical Data
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. PrA | Page 12 of 2
Preliminary Technical Data 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
ADT7420
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 ADD7 P6 ADD6 P5 ADD5 P4 ADD4 P3 ADD3 P2 ADD2 P1 ADD1 P0 ADD0
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 register MSB. Table 6. ADT7420 Registers
Register Address 0x00 0x01 0x02 0x03 0x04 0x05 0x06 0x07 0x08 0x09 0x0A 0x0B 0x2F Description Temperature value most significant byte Temperature value least significant byte Status 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 Power-On Default 0x00 0x00 0x00 0x00 0x20 (64C) 0x00 (64C) 0x05 (10C) 0x00 (10C) 0x49 (147C) 0x80 (147C) 0x05 (5C) 0xCX 0xXX
TEMPERATURE VALUE REGISTERS
The temperature value most significant byte (MSB) and temperature value least significant byte (LSB) registers store the temperature measured by the internal temperature sensor. The temperature is stored in twos complement format with the MSB being the temperature sign bit. When reading from these registers, the eight MSBs (Bit 7 to Bit 15) are read first from Register Address 0x00 and then the eight LSBs (Bit 0 to Bit 7) are read from Register Address 0x01. Only the temperature value most significant byte (Register Address 0x00) needs to be loaded into the address pointer register because the address pointer autoincrements to the temperature value least significant byte address (Register Address 0x01). Bit 0 to Bit 2 are event alarm flags for TCRIT, THIGH, and TLOW. 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 LSB bits for the extended digital value.
Table 8. Temperature Value MSB Register (Register Address 0x00)
Bit [8:14] 15 Default Value 0000000 0 Type R R Name Temp Sign Description 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)
Bit 0 Default Value 0 Type R Name TLOW flag/LSB0 Description 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). 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). 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). Temperature value in twos complement format.
Rev. PrA | Page 13 of
1
0
R
THIGH flag/LSB1
2
0
R
TCRIT flag/LSB2
[3:7]
00000
R
Temp
ADT7420
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 hysterisis. The RDY bit is reset after a read from the Table 10. Status Register (Register Address 0x02)
Bit [0:3] 4 Default Value 0000 0 Type R R Name Unused TLOW THIGH TCRIT RDY
Preliminary Technical Data
temperature value register. In one-shot and 1 SPS modes, the RDY bit is reset after a write to the operation mode bits.
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.
5
0
R
6
0
R
7
1
R
Description Reads back 0. 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. 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 one-shot bits.
Table 11. Configuration Register (Register Address 0x03)
Bit [0:1] Default Value 00 Type R/W Name Fault queue Description 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. 00 = 1 fault (default). 01 = 2 faults. 10 = 3 faults. 11 = 4 faults. This bit selects the output polarity of the CT pin. 0 = active low. 1 = active high. This bit selects the output polarity of the INT pin. 0 = active low. 1 = active high. This bit selects between comparator mode and interrupt mode. 0 = interrupt mode 1 = comparator 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. 0 = 13-bit resolution. Sign bit + 12 bits gives a temperature resolution of 0.0625C. 1 = 16-bit resolution. Sign bit + 15 bits gives a temperature resolution of 0.0078C.
2
0
R/W
CT pin polarity
3
0
R/W
INT pin polarity
4
0
R/W
INT/CT mode
[5:6]
00
R/W
Operation mode
7
0
R/W
Resolution
Rev. PrA | Page 14 of 4
Preliminary Technical Data
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 temperature is stored in twos complement format with the MSB being the temperature sign bit. When reading from this register, the eight MSBs (Bit 15 to Bit 8) are read first from Register Address 0x04 and then the eight LSBs (Bit 7 to Bit 0) are read from Register Address 0x05. Only Register Address 0x04 (THIGH setpoint MSB) needs to be loaded into the address pointer register because the address pointer autoincrements to Register Address 0x05 (THIGH setpoint LSB). The default setting for the THIGH setpoint is 64C.
ADT7420
When reading from this register, the eight MSBs (Bit 15 to Bit 8) are read first from Register Address 0x06 and then the eight LSBs (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 as the address pointer autoincrements to Register Address 0x07 (TLOW setpoint LSB). The default setting for the TLOW setpoint is 10C.
TCRIT SETPOINT REGISTERS
The TCRIT setpoint MSB and TCRIT setpoint LSB registers store the critical overtemperature limit value. A critical overtemperature 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. When reading from this register, the eight MSBs (Bit 15 to Bit 8) are read first from Register Address 0x08 and then the eight LSBs (Bit 7 to Bit 0) are read from Register Address 0x09. Only Register Address 0x08 (TCRIT setpoint MSB) needs to be loaded into the address pointer register because the address pointer autoincrements to Register Address 0x09 (TCRIT setpoint LSB). The default setting for the TCRIT limit is 147C.
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.
Table 12. THIGH Setpoint MSB Register (Register Address 0x04)
Bit [15:8] Default Value 0x20 Type R/W Name THIGH MSB Description MSBs of the overtemperature limit, stored in twos complement format.
Table 13. THIGH Setpoint LSB Register (Register Address 0x05)
Bit [7:0] Default Value 0x00 Type R/W Name THIGH LSB Description LSBs of the overtemperature limit, stored in twos complement format.
Table 14. TLOW Setpoint MSB Register (Register Address 0x06)
Bit [15:8] Default Value 0x05 Type R/W Name TLOW MSB Description MSBs of the undertemperature limit, stored in twos complement format.
Table 15. TLOW Setpoint LSB Register (Register Address 0x07)
Bit [7:0] Default Value 0x00 Type R/W Name TLOW LSB Description LSBs of the undertemperature limit, stored in twos complement format.
Table 16. TCRIT Setpoint MSB Register (Register Address 0x08)
Bit [15:8] Default Value 0x49 Type R/W Name TCRIT MSB Description MSBs of the critical overtemperature limit, stored in twos complement format.
Table 17. TCRIT Setpoint LSB Register (Register Address 0x09)
Bit [7:0] Default Value 0x80 Type R/W Name TCRIT LSB Description LSBs of the critical overtemperature limit, stored in twos complement format.
Rev. PrA | Page 15 of
ADT7420
THYST SETPOINT 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 1C from 0C to 15C. The value in this register is subtracted from the THIGH and TCRIT values and added to the TLOW value to implement hysteresis.
Preliminary Technical Data
ID REGISTER
This 8-bit read-only register stores the manufacturer ID in Bit 3 to Bit 7 and the silicon revision in Bit 0 to Bit 2.
Table 18. THYST Setpoint Register (Register Address 0x0A)
Bit [3:0] [7:4] Default Value 0101 0000 Type R/W R/W Name THYST N/A Description Hysteresis value, from 0C to 15C. Stored in straight binary format. The default setting is 5C. Not used.
Table 19. ID Register (Register Address 0x0B)
Bit [2:0] [7:3] Default Value XXX 11001 Type R R Name Revision ID Manufacture ID Description Contains the silicon revision identification number Contains the manufacture identification number
Rev. PrA | Page 16 of
Preliminary Technical Data SERIAL INTERFACE
PULL-UP VDD
ADT7420
PULL-UP VDD
VDD
VDD
PULL-UP VDD 10k 10k
10k
10k
ADT7420
CT INT SCL SDA GND
0.1F
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.
2.
SERIAL BUS ADDRESS
Like all I2C-compatible devices, the ADT7420 has a 7-bit serial address. The five MSBs of this address for the ADT7420 are set 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 k. Table 20. I2C Bus Address Options
A6 1 1 1 1 A5 0 0 0 0 A4 0 0 0 0 Binary 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
3.
4.
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.
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. 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. 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. PrA | Page 17 of
09013-014
TO INTERRUPT PIN ON MICROCONTROLLER
A0 A1
ADT7420
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 THIGH setpoint, TLOW setpoint, and TCRIT setpoint registers, it is possible to write to both the MSB and the LSB registers in
1 SCL 9 1
Preliminary Technical Data
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
SDA START BY MASTER
1
0
0
1
0
A1
A0
R/W ACK. BY ADT7420
P7
P6
P5
P4
P3
P2
P1
P0 ACK. BY ADT7420
FRAME 1 SERIAL BUS ADDRESS BYTE 1 SCL (CONTINUED)
FRAME 2 ADDRESS POINTER REGISTER BYTE 9
SDA (CONTINUED)
D7
D6
D5
D4
D3
D2
D1
D0 ACK. BY ADT7420 STOP BY MASTER
FRAME 3 DATA BYTE
Figure 14. Writing to a Register Followed by a Single Byte of Data
1 SCL
9
1
9
SDA START BY MASTER
1
0
0
1
0
A1
A0
R/W ACK. BY ADT7420
P7
P6
P5
P4
P3
P2
P1
P0 ACK. BY ADT7420
FRAME 1 SERIAL BUS ADDRESS BYTE 1 SCL (CONTINUED) 9
FRAME 2 ADDRESS POINTER REGISTER BYTE 1 9
SDA (CONTINUED)
D15
D14
D13
D12
D11
D10
D9
D8 ACK. BY ADT7420
D7
D6
D5
D4
D3
D2
D1
D0 ACK. BY ADT7420 STOP BY MASTER
09013-016
FRAME 3 DATA BYTE
FRAME 4 DATA BYTE
Figure 15. Writing to a Register Followed by Two Bytes of Data
Rev. PrA | Page 18 of
09013-017
Preliminary Technical Data
READING DATA
Reading data from the ADT7420 is done in a single data byte operation for the configuration register, the status register, the THYST register, and the ID register. A two data byte read operation is needed for the temperature value register, 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 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 autoincrement 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.
1 SCL 9 1
ADT7420
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 the I2C bus commands (do not acknowledge) during the default values upload for approximately 200 s. The reset command address word is 0x2F.
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 s. The ADT7420 does not acknowledge any other general call commands.
9
SDA START BY MASTER
1
0
0
1
0
A1
A0
R/W ACK. BY ADT7420
P7
P6
P5
P4
P3
P2
P1
P0 ACK. BY ADT7420
FRAME 1 SERIAL BUS ADDRESS BYTE 1 SCL 9 1
FRAME 2 ADDRESS POINTER REGISTER BYTE
9
SDA REPEAT START BY MASTER
1
0
0
1
0
A1
A0
R/W ACK. BY ADT7420
D7
D6
D5
D4
D3
D2
D1
D0 NO ACK. BY STOP BY MASTER MASTER
09013-018
FRAME 3 SERIAL BUS ADDRESS BYTE
FRAME 4 DATA BYTE FROM CONFIGURATION REGISTER
Figure 16. Reading Back Data from the Configuration Register
Rev. PrA | Page 19 of
ADT7420
1 SCL 9 1
Preliminary Technical Data
9
SDA 1 START 0 0 1 0 A1 A0 R/W ACK. BY ADT7420 9 A7 A6 A1 A0 ACK. BY ADT7420 9
ADT7410 DEVICE ADDRESS
REGISTER ADDRESS[A7:A0]
SR SCL
1
1
SDA REPEAT START
1
0
A1
A0
R/W ACK. BY ADT7420
D7
D6
D1
D0 ACK. BY MASTER
D7
D6
D1
D0 NO ACK. BY MASTER
ADT7410 DEVICE ADDRESS
TEMPERATURE VALUE REGISTER MSB DATA
TEMPERATURE VALUE REGISTER LSB DATA
Figure 17. Reading Back Data from the Temperature Value Register
Rev. PrA | Page 20 of 2
09013-023
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.
Preliminary Technical Data INT AND CT OUTPUTS
The INT and CT pins are open-drain outputs, and both pins require a 10 k pull-up resistor to VDD.
ADT7420
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. Putting the ADT7420 into shutdown mode does not reset the INT state in comparator mode.
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 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. 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 82C 81C 80C 79C 78C 77C 76C 75C 74C 73C
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.
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. PrA | Page 21 of 2
09013-020
ADT7420
TEMPERATURE -13C -14C -15C -16C -17C -18C -19C -20C -21C -22C
Preliminary Technical Data
TLOW + 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. PrA | Page 22 of 2
09013-021
Preliminary Technical Data APPLICATIONS INFORMATION
THERMAL RESPONSE TIME
The time required for a temperature sensor to settle to a specified accuracy is a function of the thermal mass of the sensor and the thermal conductivity between the sensor and the object being sensed. Thermal mass is often considered equivalent to capacitance. Thermal conductivity is commonly specified using the symbol, Q, and can be thought of as thermal resistance. It is commonly specified in units of degrees per watt of power transferred across the thermal joint. The time required for the part to settle to the desired accuracy is dependent on the thermal contact established in a particular application and the equivalent power of the heat source. In most applications, it is best to determine the settling time empirically.
ADT7420
TEMPERATURE MONITORING
The ADT7420 is ideal for monitoring the thermal environment within electronic equipment. For example, the surface-mounted package accurately reflects the exact thermal conditions that affect nearby integrated circuits. The ADT7420 measures and converts the temperature at the surface of its own semiconductor chip. 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. When the thermal impedance is determined, the temperature of the heat source can be inferred from the ADT7420 output. As much as 60% of the heat transferred from the heat source to the thermal sensor on the ADT7420 die is discharged via the copper tracks, the package pins, and the bond pads. Of the pins on the ADT7420, the GND pin transfers most of the heat. Therefore, to measure the temperature of a heat source, it is recommended that the thermal resistance between the GND pin of the ADT7420 and the GND of the heat source be reduced as much as possible.
SUPPLY DECOUPLING
Decouple the ADT7420 with a 0.1 F ceramic capacitor between VDD and GND. This is particularly important when the ADT7420 is mounted remotely from the power supply. Precision analog products, such as the ADT7420, require a well-filtered power source. Because the ADT7420 operates from a single supply, it may seem convenient to tap into the digital logic power supply. Unfortunately, the logic supply is often a switch-mode design, which generates noise in the 20 kHz to 1 MHz range. In addition, fast logic gates can generate glitches hundreds of millivolts in amplitude due to wiring resistance and inductance. 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 F ceramic capacitor is critical for the temperature accuracy specifications to be achieved. This decoupling capacitor must be placed as close as possible to the VDD pin of the ADT7420.
TTL/CMOS LOGIC CIRCUITS
0.1F
ADT7420
POWER SUPPLY
Figure 20. Use of Separate Traces to Reduce Power Supply Noise
Rev. PrA | Page 23 of 2
09013-022
ADT7420 OUTLINE DIMENSIONS
PIN 1 INDICATOR 4.10 4.00 SQ 3.90 0.65 BSC 0.35 0.30 0.25
13 12 EXPOSED PAD 1 16
Preliminary Technical Data
PIN 1 INDICATOR
4 9 8 5
2.70 2.60 SQ 2.50
TOP VIEW 0.80 0.75 0.70 SEATING PLANE
0.45 0.40 0.35
0.25 MIN
BOTTOM VIEW
0.05 MAX 0.02 NOM COPLANARITY 0.08 0.20 REF
012909-B
COMPLIANT TO JEDEC STANDARDS MO-220-WGGC.
Figure 21. 16-Lead Lead Frame Chip Scale Package [LFCSP_WQ] 4 mm x 4 mm Body, Very Very Thin Quad (CP-16-17) Dimensions shown in millimeters and (inches)
ORDERING GUIDE
Model1 ADT7420UCPZ ADT7420UCPZ-R2 ADT7420UCPZ-RL7 EVAL-ADT7X20EBZ
1 2
Temperature Range -40C to +150C -40C to +150C -40C to +150C
Temperature Accuracy2 0.25C 0.25C 0.25C
Package Description 16-lead LFCSP_WQ 16-lead LFCSP_WQ 16-lead LFCSP_WQ Evaluation Board
Package Option CP-16-17 CP-16-17 CP-16-17
Z = RoHS Compliant Part. Maximum accuracy over the -20C to +105C temperature range.
I2C refers to a communications protocol originally developed by Philips Semiconductors (now NXP Semiconductors).
(c)2010 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. PR09013-0-6/10(PrA)
Rev. PrA | Page 24 of 24

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