REV. 0
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties that
may result from its use. No license is granted by implication or otherwise
under any patent or patent rights of Analog Devices.
a
AD7414/AD7415
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
www.analog.com
Fax: 781/326-8703
Analog Devices, Inc., 2001
SMBus/I
2
C
-Compatible, 10-Bit Digital
Temperature Sensors in SOT-23
FUNCTIONAL BLOCK DIAGRAM
SM BUS/I
2
C
INTERFACE
AS
GND
SDA
SCL
CONFIGURATION
REGISTER
T
HIGH
SETPOINT
REGISTER
T
LOW
SETPOINT
REGISTER
SETPOINT
COMPARATOR
ALERT
TEMPERATURE
VALUE
REGISTER
10-BIT
ANALOG-DIGITAL
CONVERTER
BANDGAP
TEMPERATURE
SENSOR
+V
DD
AD7414
SDA
SCL
+V
DD
SMBus/I
2
C
INTERFACE
10-BIT
ANALOG-DIGITAL
CONVERTER
BANDGAP
TEMPERATURE
SENSOR
CONFIGURATION
REGISTER
TEMPERATURE
VALUE
REGISTER
AD7415
AS
GND
FEATURES
10-Bit Temperature-to-Digital Converter
Temperature Range: 40 C to +85 C
Accuracy of 2 C
SMBus/I
2
C-Compatible Serial Interface
3 A Power-Down Current
Temperature Conversion Time: 29 s Typ
Space-Saving 6-Lead (AD7414) and 5-Lead (AD7415)
SOT-23 Packages
Pin-Selectable Addressing via AS
Overtemperature Indicator (AD7414 Only)
SMBus Alert Function (AD7414 Only)
Four Versions Allow Eight I
2
C Addresses (AD7414)
Two Versions Allow Six I
2
C Addresses (AD7415)
APPLICATIONS
Hard Disk Drives
Personal Computers
Electronic Test Equipment
Office Equipment
Domestic Appliances
Process Control
Cellular Phones
GENERAL DESCRIPTION
The AD7414/AD7415 is a complete temperature monitoring
system in 6-lead and 5-lead SOT-23 packages. It contains a
bandgap temperature sensor and 10-bit ADC to monitor and
digitize the temperature reading to a resolution of 0.25
C.
The AD7414/AD7415 provides a 2-wire serial interface that is
compatible with SMBus and I
2
C interfaces. The part comes in four
versions, AD7414/AD7415-0, AD7414/AD7415-1, AD7414-2
and the AD7414-3. The AD7414/AD7415-0 and AD7414/
AD7415-1 versions allow for a choice of three different SMBus
addresses for each version. All four AD7414 versions give the
possibility of eight different I
2
C addresses while the two AD7415
versions allow up to six I
2
C addresses to be used.
The AD7414/AD7415's 2.7 V supply voltage, low supply cur-
rent, serial interface, and small package size, make it ideal for a
variety of applications, including personal computers, office
equipment, cellular phones, and domestic appliances.
In the AD7414, on-chip registers can be programmed with high
and low temperature limits, and an open drain Over-Temperature
Indicator output (ALERT), which becomes active when a pro-
grammed limit is exceeded. A configuration register allows
programming of the sense of the ALERT output (active high
or active low). This output can be used as an interrupt or as an
SMBus alert.
PRODUCT HIGHLIGHTS
1. The AD7414/AD7415 has an on-chip temperature sensor
that allows an accurate measurement of the ambient tem-
perature to be made. It is capable of
2C temperature
accuracy.
2. SMBus/I
2
C-Compatible Serial Interface with pin-selectable
choice of three addresses per version of the AD7414/AD7415,
eight address options in total for the AD7414 and six in total
for the AD7415.
3. Supply voltage of 2.7 V to 5.5 V.
4. Space-saving 5-lead and 6-lead SOT-23 packages.
5. 10-bit temperature reading to 0.25
C resolution.
6. The AD7414 has an Over Temperature Indicator which can
be software disabled. Used as an interrupt of SMBus alert.
7. One-shot and automatic temperature conversion rates.
I
2
C is a registered trademark of Philips Corporation.
REV. 0
2
AD7414/AD7415SPECIFICATIONS
1
(T
A
= T
MIN
to T
MAX
, V
DD
= 2.7 V to 5.5 V, unless otherwise noted.)
Parameter
A Version
Unit
Test Conditions/Comments
TEMPERATURE SENSOR AND ADC
Accuracy
2
2.0
C max
V
DD
= 3 V
3.0
C max
V
DD
= 5.5 V
Resolution
10
Bits
Update Rate, t
R
800
ms typ
Temperature Conversion Time
25
s typ
POWER SUPPLIES
Supply Current
3
Peak Supply Current
4
1.2
mA typ
Peak current during conversion.
Inactive Serial Bus
5
Normal Mode @ 3 V
169
A typ
Supply current with serial bus inactive. Part not
Normal Mode @ 5 V
188
A typ
converting and D7 of Configuration Register = 0.
Active Serial Bus
6
Normal Mode @ 3 V
180
A typ
Supply current with serial bus active. Part not
Normal Mode @ 5 V
214
A typ
converting and D7 of Configuration Register = 0.
Shutdown Mode
3
A max
D7 of Configuration Register = 1. Typical values
are 0.04
A at 3 V and 0.5 A at 5 V.
DIGITAL INPUT
Input High Voltage, V
IH
2.4
V min
Input Low Voltage, V
IL
0.8
V max
Input Current, I
IN
1
A max
V
IN
= 0 V to V
DD
Input Capacitance, C
IN
10
pF max
All Digital Inputs
DIGITAL OUTPUT
Output High Voltage, V
OH
2.4
V min
Output Low Voltage, V
OL
0.4
V max
I
OL
= 1.6 mA
Output High Current, I
OH
1
mA max
V
OH
= 5 V
Output Capacitance, C
OUT
10
pF max
Typ = 3 pF
ALERT Output Saturation Voltage
0.8
V max
I
OUT
= 4 mA
AC ELECTRICAL CHARACTERISTICS
7, 8
Serial Clock Period, t
1
2.5
s min
See Figure 1
Data In Setup Time to SCL High, t
2
50
ns min
See Figure 1
Data Out Stable after SCL Low, t
3
0
ns min
See Figure 1
SDA Low Setup Time to SCL Low
(Start Condition), t
4
50
ns min
See Figure 1
SDA High Hold Time after SCL High
(Stop Condition), t
5
50
ns min
See Figure 1
SDA and SCL Fall Time, t
6
90
ns max
See Figure 1
Power-Up Time
4
s typ
NOTES
1
Temperature range as follows: A Version = 40
C to +85C.
2
Accuracy specifications apply only to voltages listed under Test Conditions. See Temperature Accuracy vs. Supply section for typical accuracy performance over the
full V
DD
supply range.
3
These current values can be used to determine average power consumption at different one-shot conversion rates. Average power consumption at the automatic
conversion rate of 1.25 kHz is 940
W.
4
This peak supply current is required for 29
s (the conversion time plus power-up time) out of every 800 s (the conversion rate).
5
These current values are derived by not issuing a stop condition at the end of a write or read, thus preventing the part from going into a conversion.
6
The current is derived assuming a 400 kHz serial clock being active continuously.
7
The SDA and SCL timing is measured with the input filters turned on so as to meet the Fast-Mode I
2
C specification. Switching off the input filters improves the
transfer rate but has a negative effect on the EMC behavior of the part.
8
Guaranteed by design. Not tested in production.
Specifications subject to change without notice.
REV. 0
3
AD7414/AD7415
PIN FUNCTION DESCRIPTIONS
Mnemonic Description
AS
Logic Input. Address Select Input which selects
one of three I
2
C addresses for the AD7414/
AD7415 (See Table I).
GND
Analog and Digital Ground.
V
DD
Positive Supply Voltage, 2.7 V to 5.5 V.
SDA
Digital I/O. Serial Bus Bidirectional Data. Open-
Drain Output.
ALERT
AD7414 Digital Output. Over Temperature Indica-
tor, becomes active when temperature exceeds
T
HIGH
. Open-Drain output.
SCL
Digital Input. Serial Bus Clock.
ABSOLUTE MAXIMUM RATINGS
*
V
DD
to GND . . . . . . . . . . . . . . . . . . . . . . . . . . 0.3 V to +7 V
SDA Input Voltage to GND . . . . . . . . . . . . . . 0.3 V to +7 V
SDA Output Voltage to GND . . . . . . . . . . . . . 0.3 V to +7 V
SCL Input Voltage to GND . . . . . . . . . . . . . . 0.3 V to +7 V
ALERT Output Voltage to GND . . . . . . . . . . 0.3 V to +7 V
Operating Temperature Range . . . . . . . . . . . 40
C to +85C
Storage Temperature Range . . . . . . . . . . . . 65
C to +150C
Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . 150
C
SOT-23, Power Dissipation . . . . . . . . . . . . . . . . . . . . 450 mW
JA
Thermal Impedance . . . . . . . . . . . . . . . . . . . . . . 240
C/W
Lead Temperature, Soldering
Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . . . 215
C
Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . . . 220
C
*Stresses above those listed under Absolute Maximum Ratings may cause perma-
nent 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.
PIN CONFIGURATIONS
SOT-23
AS
SDA
1
6
V
DD
SCL
3
4
GND 2
AD7414
TOP VIEW
(Not to Scale)
5
ALERT
SOIC
SCL
V
DD
4
5
NC
NC
1
8
ALERT
GND
3
6
SDA 2
7 AS
AD7414
TOP VIEW
(Not to Scale)
NC = NO CONNECT
SOT-23
AS
SDA
1
5
V
DD
SCL
3
4
GND
2
AD7415
TOP VIEW
(Not to Scale)
SC
t
1
SDA
DATA IN
SDA
DATA OUT
t
2
t
3
t
4
t
5
t
6
Figure 1. Diagram for Serial Bus Timing
CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily
accumulate on the human body and test equipment and can discharge without detection. Although
the AD7414/AD7415 features proprietary ESD protection circuitry, permanent damage may occur
on devices subjected to high-energy electrostatic discharges. Therefore, proper ESD precautions
are recommended to avoid performance degradation or loss of functionality.
WARNING!
ESD SENSITIVE DEVICE
REV. 0
AD7414/AD7415
4
ORDERING GUIDE
Temperature
Temperature
Package
Package
Branding
Min Qtys/
Model
Range
Error @ 3 V
Options
Description
Information
Reel
AD7414ART-0REEL7
40
C to +85C
2C
RT-6
6-Lead SOT-23
CHA
1
3000
AD7414ART-0REEL
40
C to +85C
2C
RT-6
6-Lead SOT-23
CHA
1
10000
AD7414ART-0500RL7
40
C to +85C
2C
RT-6
6-Lead SOT-23
CHA
1
500
AD7414ARM-0REEL7
40
C to +85C
2C
RM-8
8-Lead Mini_SO
CHA
1
3000
AD7414ARM-0REEL
40
C to +85C
2C
RM-8
8-Lead Mini_SO
CHA
1
10000
AD7414ARM-0
2
40
C to +85C
2C
RM-8
8-Lead Mini_SO
CHA
1
AD7414ART-1REEL7
40
C to +85C
2C
RT-6
6-Lead SOT-23
CHB
3
3000
AD7414ART-1REEL
40
C to +85C
2C
RT-6
6-Lead SOT-23
CHB
3
10000
AD7414ART-1500RL7
40
C to +85C
2C
RT-6
6-Lead SOT-23
CHB
3
500
AD7414ARM-1REEL7
40
C to +85C
2C
RM-8
8-Lead Mini_SO
CHB
3
3000
AD7414ARM-1REEL
40
C to +85C
2C
RM-8
8-Lead Mini_SO
CHB
3
10000
AD7414ARM-1
2
40
C to +85C
2C
RM-8
8-Lead Mini_SO
CHB
3
AD7414ART-2REEL7
40
C to +85C
2C
RT-6
6-Lead SOT-23
CHC
3
3000
AD7414ART-2REEL
40
C to +85C
2C
RT-6
6-Lead SOT-23
CHC
3
10000
AD7414ART-3REEL7
40
C to +85C
2C
RT-6
6-Lead SOT-23
CHD
3
3000
AD7414ART-3REEL
40
C to +85C
2C
RT-6
6-Lead SOT-23
CHD
3
10000
AD7415ART-0REEL7
40
C to +85C
2C
RT-5
5-Lead SOT-23
CGA
1
3000
AD7415ART-0REEL
40
C to +85C
2C
RT-5
5-Lead SOT-23
CGA
1
10000
AD7415ART-0500RL7
40
C to +85C
2C
RT-5
5-Lead SOT-23
CGA
1
500
AD7415ART-1REEL7
40
C to +85C
2C
RT-5
5-Lead SOT-23
CGB
3
3000
AD7415ART-1REEL
40
C to +85C
2C
RT-5
5-Lead SOT-23
CGB
3
10000
AD7415ART-1500RL7
40
C to +85C
2C
RT-5
5-Lead SOT-23
CGB
3
500
NOTES
1
Available to order.
2
This model shipped in tubes.
3
Contact factory for availability.
Table I. I
2
C Address Selection
Part Number
AS Pin
I
2
C Address
AD7414-0
Float
1001 000
AD7414-0
GND
1001 001
AD7414-0
V
DD
1001 010
AD7414-1
Float
1001 100
AD7414-1
GND
1001 101
AD7414-1
V
DD
1001 110
AD7414-2
N/A
1001 011
AD7414-3
N/A
1001 111
AD7415-0
Float
1001 000
AD7415-0
GND
1001 001
AD7415-0
V
DD
1001 010
AD7415-1
Float
1001 100
AD7415-1
GND
1001 101
AD7415-1
V
DD
1001 110
REV. 0
AD7414/AD7415
5
CIRCUIT INFORMATION
The AD7414/AD7415 is a stand-alone digital temperature sensor.
The on-chip temperature sensor allows an accurate measure-
ment of the ambient device temperature to be made. The 10-bit
A/D converter converts the temperature measured into a two's
complement format for storage in the Temperature Register.
The A/D converter is made up of a conventional successive-
approximation converter based around a capacitor DAC. The
serial interface is I
2
C and SMBus compatible. The AD7414
AD7415 requires a 2.7 V to 5.5 V power supply. The temperature
sensor has a working measurement range of 40
C to +85C.
FUNCTIONAL DESCRIPTION
Temperature measurement is initiated by a couple of methods.
The first uses an internal clock countdown of 800 ms, and a
conversion is performed. The internal oscillator is the only circuit
that is powered up between conversions and once it times out,
every 800 ms, a wake-up signal is sent to power up the rest of
the circuitry. A monostable is activated at the beginning of the
wake-up signal to ensure that sufficient time is given to the power-
up process. The monostable typically takes 4
s to time out. It
then takes typically 25
s for each conversion to be completed.
The new temperature value is loaded into the Temperature Value
Register and ready for reading by the I
2
C interface.
A temperature measurement is also initiated every time the one-
shot method is used. This method requires the user to write to
the One-Shot Bit in the Configuration Register when a tempera-
ture measurement is needed. Setting the One-Shot Bit to a 1 will
start a temperature conversion directly after the write operation.
The track/hold goes into hold approximately 4
s (monostable
timeout) after the STOP condition and a conversion is then
initiated. Typically 25
s later, the conversion is complete and
the Temperature Value Register is loaded with a new tempera-
ture value.
The measurement modes are compared with a high temperature
limit, stored in an 8-bit read/write register. This is applicable
only to the AD7414 as the AD7415 does not have an ALERT
pin and subsequently does not have an over-temperature moni-
toring function. If the measurement is greater than the high limit,
the ALERT pin is activated (if it has already been enabled in the
Configuration Register). There are two ways to deactivate the
ALERT pin again, firstly when the Alert Reset bit in the
Configuration register is set to a 1 by a write operation; and
secondly when the temperature measured is less than the value
in the T
LOW
Register. This ALERT pin is compatible with the
SMBus SMBALERT option.
Configuration functions consist of:
Switching between normal operation and full power-down.
Enabling or disabling the SCL and SDA filters.
Enabling or disabling the ALERT function.
Setting ALERT pin polarity.
C/ P
SDA
SCL
ALERT
AS
SUPPLY
2.7 V TO
5.5 V
GND
AD7414
V
DD
10 F
0.1 F
Figure 2. Typical Connection Diagram
MEASUREMENT TECHNIQUE
A common method of measuring temperature is to exploit the
negative temperature coefficient of a diode, or the base-emitter
voltage of a transistor, operated at constant current. Unfortu-
nately, this technique requires calibration to null out the effect
of the absolute value of V
BE
, which varies from device to device.
The technique used in the AD7414/AD7415 is to measure
the change in V
BE
when the device is operated at two differ-
ent currents.
This is given by:
V
BE
= KT/q
ln (N)
where:
K is Boltzmann's constant.
q is charge on the electron (1.6
10
19
Coulombs).
T is absolute temperature in Kelvins.
N is the ratio of the two currents.
TO ADC
V
OUT
+
V
OUT
SENSING
TRANSISTOR
V
DD
I
N I
SENSING
TRANSISTOR
Figure 3. Temperature Measurement Technique
Figure 3 shows the method the AD7414/AD7415 uses to measure
the ambient device temperature. To measure
V
BE
, the sensor
(substrate transistor) is switched between operating currents of
I and N
I. The resulting waveform is passed through a chopper-
stabilized amplifier that performs the functions of amplification
and rectification of the waveform to produce a dc voltage propor-
tional to DV
BE
. This voltage is measured by the ADC to give a
temperature output in 10-bit two's complement format.
REV. 0
AD7414/AD7415
6
TEMPERATURE DATA FORMAT
The temperature resolution of the ADC is 0.25
C which corre-
sponds to one LSB of the ADC. The ADC can theoretically
measure a temperature span of 255
C; the practical lowest value
is limited to 40
C due to device maximum ratings. The A grade
can measure a temperature range of 40
C to +85C. (Tem-
perature data format is shown in Table II.)
Table II. A-Grade Temperature Data Format
Digital Output
Temperature
DB9 . . . DB0
55
C
11 0010 0100
50
C
11 0011 1000
25
C
11 1001 1100
0.25
C
11 1111 1111
0
C
00 0000 0000
+0.25
C
00 0000 0001
+10
C
00 0010 1000
+25
C
00 0110 0100
+50
C
00 1100 1000
+75
C
01 0010 1100
+100
C
01 1001 0000
+125
C
01 1111 0100
A Grade Temperature Conversion Formula:
1. Positive Temperature = ADC Code/4
2. Negative Temperature = (ADC Code
* 512)/4
*DB9 is removed from the ADC Code.
INTERNAL REGISTER STRUCTURE
The AD7414 has five internal registers as shown in Figure 4.
Four are data registers and one is an Address Pointer Register.
ADDRESS
POINTER
REGISTER
TEMPERATURE
VALUE
REGISTER
CONFIGURATION
REGISTER
T
HIGH
REGISTER
T
LOW
REGISTER
SDA
SCL
D
A
T
A
SERIAL BUS INTERFACE
Figure 4. AD7414 Register Structure
The AD7415 has three internal registers as shown in Figure 5.
Two are data registers and one is an Address Pointer Register.
SERIAL BUS INTERFACE
ADDRESS
POINTER
REGISTER
TEMPERATURE
VALUE
REGISTER
SDA
SCL
D
A
T
A
CONFIGURATION
REGISTER
Figure 5. AD7415 Register Structure
Each data register has an address pointed to by the Address
Pointer Register when communicating with it. The Tempera-
ture Value Register is the only data register that is read only.
ADDRESS POINTER REGISTER
The Address Pointer Register is an 8-bit register that stores an
address that points to one of the four data registers of the
AD7414 and one of the two data registers of the AD7415. The
first byte of every serial write operation to the AD7414/AD7415
is the address of one of the data registers, which is stored in the
Address Pointer Register, and selects the data register to which
subsequent data bytes are written. Only the two LSBs of this
register are used to select a data register.
Table III. Address Pointer Register
P7
P6
P5
P4
P3
P2
P1
P0
0
0
0
0
0
0
Register Select
Table IV. AD7414 Register Address
P1
P0
Registers
0
0
Temperature Value Register (Read Only)
0
1
Configuration Register (Read/Write)
1
0
T
HIGH
Register (Read/Write)
1
1
T
LOW
Register (Read/Write)
Table V. AD7415 Register Address
P1
P0
Registers
0
0
Temperature Value Register (Read Only)
0
1
Configuration Register (Read/Write)
REV. 0
AD7414/AD7415
7
FRAME 1
SERIAL BUS ADDRESS BYTE
FRAME 2
ADDRESS POINTER REGISTER BYTE
R/
W
1
SCL
SDA
0
0
1
A2
A1
A0
P7
P6
P5
P4
P3
P2
P1
P0
ACK. BY
AD7414/AD7415
STOP BY
MASTER
START BY
MASTER
1
9
1
ACK. BY
AD7414/AD7415
9
Figure 6. Writing to the Address Pointer Register to Select a Register for a Subsequent Read Operation
FRAME 3
DATA BYTE
D7
D6
D5
D4
D3
D2
D1
D0
ACK. BY
AD7414/AD7415
STOP BY
MASTER
1
9
SCL (CONTINUED)
SDA (CONTINUED)
R/
W
1
SCL
SDA
0
0
1
A2
A1
A0
P7
P6
P5
P4
P3
P2
P1
P0
ACK. BY
AD7414/AD7415
START BY
MASTER
FRAME 1
SERIAL BUS ADDRESS BYTE
FRAME 2
ADDRESS POINTER REGISTER BYTE
1
9
1
ACK. BY
AD7414/AD7415
9
Figure 7. Writing to the Address Pointer Register followed by a Single Byte of Data to the Selected Register
Table VIII. AD7415 Configuration Register
D7
D6
D5
D4
D3
D2
D1
D0
PD
FLTR
TEST MODE
ONE
TEST
SHOT MODE
0
*
1
*
0s
*
0s
*
0s
*
*Default settings at Power-up.
In the AD7415, only three of the bits are used (D7, D6 and D2)
to set the operating modes, see Table IX. D0, D1 and D3 to D5
are used for factory settings and must have zeros written to them
during normal operation.
Table IX. AD7415 Configuration Register Settings
D7
Full Power-Down if = 1
D6
Bypass SDA and SCL Filtering if = 0
D2
Initiate a temperature conversion if set to a 1.
The bit status is not stored, thus this bit will be "0" if read.
If the AD7414/AD7415 is in power-down mode (D7 = 1), a tem-
perature conversion can still be initiated by the one-shot operation.
This involves a write operation to the Configuration Register
and setting the One-shot Bit to a 1 (D2 = 1) will cause the
AD7414/AD7415 to power-up, perform a single conversion
and power-down again. This is a very power-efficient mode.
Table VI. AD7414 Configuration Register
D7 D6
D5
D4
D3
D2
D1
D0
PD FLTR ALERT ALERT
ALERT ONE
TEST
EN
POLARITY RESET
SHOT
MODE
0
* 1*
0
*
0
*
0
*
0
*
0s
*
*Default settings at Power-up.
CONFIGURATION REGISTER (ADDRESS 01H)
The Configuration Register is an 8-bit read/write register that
is used to set the operating modes of the AD7414/AD7415. In the
AD7414, six of the MSBs are used (D7 to D2) to set the operating
modes, see Table VII. D0 and D1 are used for factory settings
and must have zeros written to them during normal operation.
Table VII. AD7414 Configuration Register Settings
D7
Full Power-Down if = 1
D6
Bypass SDA and SCL filtering if = 0
D5
Disable ALERT if = 1
D4
ALERT is active low if D4 = 0,
ALERT is active high if D4 = 1
D3
Reset the Alert pin if set to 1. The next temperature
conversion will have the ability to activate the Alert
function. The bit status is not stored, thus this bit will
be "0" if read.
D2
Initiate a temperature conversion if set to a 1. The bit
status is not stored, thus this bit will be "0" if read.
REV. 0
AD7414/AD7415
8
TEMPERATURE VALUE REGISTER (ADDRESS 00H)
The Temperature Value Register is a 10-bit read-only register
that stores the temperature reading from the ADC in two's
complement format. Two reads are necessary to read data from
this register. Table X shows the contents of the first byte to be
read while Table XI and Table XII show the contents of the
second byte to be read from AD7414 and AD7415 respectively.
In Table XI, D3 to D5 of the second byte are used as flag bits
and are obtained from other internal registers. They function
as follows:
ALERT _Flag:
The state of this bit is same as that of the
ALERT pin.
T
HIGH
_Flag:
This flag is set to a 1 when the temperature
measured goes above the T
HIGH
limit. It is
reset when the second temperature byte
(Table XI) is read. If the temperature is still
greater than the T
HIGH
limit after the read
operation, then the flag will be set again.
T
LOW
_Flag :
This flag is set to a 1 when the temperature
measured goes below the T
LOW
limit. It is
reset when the second temperature byte
(Table XI) is read. If the temperature is still
less than the T
LOW
limit after the read opera-
tion, then the flag will be set again.
The full theoretical span of the ADC is 255
C, but in practice
the temperature measurement range is limited to the operating
range of the device, 40
C to +85C for A grade.
Table X. Temperature Value Register (First Read)
D15
D14
D13
D12
D11
D10
D9
D8
MSB
B8
B7
B6
B5
B4
B3
B2
Table XI. AD7414 Temperature Value Register (Second Read)
D7
D6
D5
D4
D3
D2
D1
D0
B1
LSB
ALERT
T
HIGH
T
LOW
0
0
0
Flag
Flag
Flag
Table XII. AD7415 Temperature Value Register (Second Read)
D7
D6
D5
D4
D3
D2
D1
D0
B1
LSB
N/A
N/A
N/A
N/A
N/A
N/A
AD7414 T
HIGH
REGISTER (Address 02h)
The T
HIGH
Register is an 8-bit read/write register that stores the
upper limit that will activate the ALERT output. Therefore, if
the value in the Temperature Value Register is greater than the
value in the T
HIGH
Register, then the ALERT pin is activated (that
is, if ALERT is enabled in the Configuration Register). As it is
an 8-bit register the temperature resolution is 1
C.
Table XIII. T
HIGH
Register
D7
D6
D5
D4
D3
D2
D1
D0
MSB
B6
B5
B4
B3
B2
B1
B0
AD7414 T
LOW
REGISTER (Address 03h)
The T
LOW
Register is an 8-bit read/write register that stores the
lower limit that will deactivate the ALERT output. Therefore, if
the value in the Temperature Value Register is less than the
value in the T
LOW
Register, the ALERT pin is deactivated (that
is, if ALERT is enabled in the Configuration Register). As it is
an 8-bit register, the temperature resolution is 1
C.
SDA
NO ACK. BY
MASTER
START BY
MASTER
FRAME 1
SERIAL BUS ADDRESS BYTE
FRAME 2
SINGLE DATA BYTE FROM AD7414/AD7415
ACK. BY
AD7414/AD7415
1
9
1
9
D7
D6
D5
D4
D3
D2
D1
D0
R/
W
A0
A1
A2
1
0
1
SCL
STOP BY
MASTER
0
Figure 8. Reading a Single Byte of Data from a Selected Register
D7
D6
D5
D4
D3
D2
D1
D0
NO ACK. BY
MASTER
STOP BY
MASTER
FRAME 3
LEAST SIGNIFICANT DATA BYTE FROM AD7414/AD7415
1
9
SCL (CONTINUED)
SDA (CONTINUED)
R/
W
1
SCL
SDA
0
0
1
A2
A1
A0
D15
D14
D13
D12
D10
D11
D9
D8
ACK. BY
MASTER
START BY
MASTER
FRAME 1
SERIAL BUS ADDRESS BYTE
FRAME 2
MOST SIGNIFICANT DATA BYTE FROM AD7414/AD7415
1
9
1
ACK. BY
AD7414/AD7415
9
REV. 0
AD7414/AD7415
9
Table XIV. T
LOW
Register
D7
D6
D5
D4
D3
D2
D1
D0
MSB
B6
B5
B4
B3
B2
B1
B0
AD7414/AD7415 SERIAL INTERFACE
Control of the AD7414/AD7415 is carried out via the I
2
C-
compatible serial bus. The AD7414/AD7415 is connected to
this bus as a slave device, under the control of a master device,
e.g., the processor.
SERIAL BUS ADDRESS
Like all I
2
C-compatible devices, the AD7414/AD7415 has a
7-bit serial address. The four MSBs of this address for the
AD7414/AD7415 are set to 1001. The AD7414/AD7415 comes
in four versions, the AD7414/AD7415-0, AD7414/AD7415-1,
AD7414-2 and the AD7414-3. The first two versions have three
different I
2
C addresses available which are selected by either
tying the AS pin to GND, to VDD or letting the pin float (see
Table I). By giving different addresses for the four versions, up
to eight AD7414s or six AD7415s can be connected to a single,
serial bus, or the addresses can be set to avoid conflicts with
other devices on the bus.
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 will 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 R/
W bit, which deter-
mines the direction of the data transfer, i.e. whether data will
be written to or read from the slave device.
The peripheral whose address corresponds to the transmitted
address responds by pulling the data line low during the low
period before the ninth clock pulse, known as the Acknowl-
edge bit. All other devices on the bus now 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 then the master will write to the
slave device. If the R/
W bit is a 1 the master will read from
the slave device.
2. 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 may be interpreted as a STOP signal.
3. When all data bytes have been read or written, stop condi-
tions are established. In WRITE mode, the master will pull
the data line high during the 10th clock pulse to assert a
STOP condition. In READ mode, the master device will pull
the data line high during the low period before the 9th clock
pulse. This is known as No Acknowledge. The master will
then take the data line low during the low period before the
tenth clock pulse, then high during the tenth clock pulse to
assert a STOP condition.
Any number of bytes of data may be transferred over the serial
bus in one operation, but 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.
WRITING TO THE AD7414/AD7415
Depending on the register being written to, there are two differ-
ent writes for the AD7414/AD7415.
Writing to the Address Pointer Register for a Subsequent Read
In order to read data from a particular register, the Address
Pointer Register must contain the address of that register. If it
does not, the correct address must be written to the Address
Pointer Register by performing a single-byte write operation, as
shown in Figure 6. The write operation consists of the serial bus
address followed by the address pointer byte. No data is written
to any of the data registers. A read operation is then performed
to read the register.
Writing a Single Byte of Data to the Configuration Register,
T
HIGH
Register or T
LOW
Register
All three registers are 8-bit registers so only one byte of data can
be written to each register. Writing a single byte of data to one
of these registers consists of the serial bus address, the Data
Register address written to the Address Pointer Register, fol-
lowed by the data byte written to the selected data register. This
is illustrated in Figure 7.
READING DATA FROM THE AD7414/AD7415
Reading data from the AD7414/AD7415 is a one or two byte
operation. Reading back the contents of the Configuration Regis-
ter, T
HIGH
Register or T
LOW
Register is a single byte read operation
as shown in Figure 8. The register address previously having been
set up by a single byte write operation to the Address Pointer
Register. Once the register address has been set up, any number
of reads can be subsequently done from that register without
having to write to the Address Pointer Register again. If you
want to read from another register then you will have to write
to the Address Pointer Register again to set up the relevant
register address.
Reading data from the Temperature Value Register is a two byte
operation as shown in Figure 9. The same rules apply for a two
byte read as a single byte read.
SMBus ALERT
The AD7414 ALERT output is an SMBus interrupt line for
devices that want to trade their ability to master for an extra pin.
The AD7414 is a slave only device and uses the SMBus ALERT
to signal the host device that it wants to talk. The SMBus ALERT
on the AD7414 is used as an over temperature indicator.
The ALERT pin has an open-drain configuration which allows
the ALERT outputs of several AD7414s to be wired-AND
together when the ALERT pin is active low. Use D4 of the
Configuration Register to set the active polarity of the ALERT
output. The power-up default is active low. The ALERT function
can be disabled or enabled by setting D5 of the Configuration
Register to 1 or 0 respectively.
REV. 0
AD7414/AD7415
10
The host device can process the ALERT interrupt and simulta-
neously access all SMBus ALERT devices through the alert
response address. Only the device that pulled the ALERT low
will acknowledge the ARA (Alert Response Address). If more
than one device pulls the ALERT pin low, the highest priority
(lowest address) device will win communication rights via stan-
dard I
2
C arbitration during the slave address transfer.
The ALERT output becomes active when the value in the Tem-
perature Value Register exceeds the value in the T
HIGH
Register.
It is reset when a write operation to the Configuration register
sets D3 to a 1 or when the temperature falls below the value
stored in the T
LOW
Register.
The ALERT output requires an external pull-up resistor. This
can be connected to a voltage different from V
DD
provided the
maximum voltage rating of the ALERT output pin is not exceeded.
The value of the pull-up resistor depends on the application, but
should be as large as possible to avoid excessive sink currents
at the ALERT output, which can heat the chip and affect the
temperature reading.
POWER-ON DEFAULTS
The AD7414/AD7415 always powers up with the following
defaults:
Address Pointer Register pointing to the Temperature Value
Register.
T
HIGH
Register loaded with 7F Hex.
T
LOW
Register loaded with 80 Hex.
Configuration Register loaded with 40 Hex.
Note: The AD7415 does not have any T
HIGH
or T
LOW
registers.
OPERATING MODES
Mode 1
This is the power-on default mode of the AD7414/AD7415. In
this mode the AD7414/AD7415 does a temperature conversion
every 800 ms and then partially powers down until the next
conversion occurs.
If a one-shot operation (setting D2 of the Configuration register
to a 1) is performed between automatic conversions, a conversion
is initiated right after the write operation. After this conversion, the
part returns to performing a conversion every 800 ms
Depending on where a serial port access occurs during a conver-
sion, that conversion might or might not be aborted. If the
conversion is completed before the part recognizes a serial port
access then the Temperature Register will be updated with the
new conversion. If the conversion is completed after the part
recognizes a serial port access then the internal logic will prevent
the Temperature Register from being updated as corrupt data
could be read.
A temperature conversion can start anytime during a serial port
access (other than a one-shot operation), but the result of that
conversion will only be loaded into the Temperature Register if
serial port access is not active at the end of the conversion.
Mode 2
The only other mode in which the AD7414/AD7415 operates
is the full power-down mode. This mode is usually used when
temperature measurements are required at a very slow rate. The
power consumption of the part can be greatly reduced in this
mode by writing to the part to go to a full power-down. Full
power-down is initiated right after D7 of the Configuration
Register set to a 1.
When a temperature measurement is required, a write operation
can be performed to power-up the part and put it into one-shot
mode (setting D2 of the Configuration register to a 1). The
power-up takes approximately 4 ms. The part then performs a
conversion and is returned to full power-down. The temperature
value can be read in the full power-down mode as the serial
interface is still powered up.
POWER VS. THROUGHPUT
The two modes of operation for the AD7414/AD7415 will pro-
duce different power versus throughput performances. Mode 2
is the sleep mode of the part and it achieves the optimum power
performance.
Mode 1
In this mode continuous conversions are performed at a rate of
approximately one every 800 ms. Figure 10 shows the times and
the currents involved with this mode of operation for a 5 V supply.
At 5 V the current consumption for the part when converting is
1.1 mA typically and the quiescent current is 188
A typically.
The conversion time of 25
s plus power-up time of typically
4
s contributes 199.3 nW to the overall power dissipation in
the following way:
(29
s/800 ms) (5 1.1 mA) = 199.3 nW
The contribution to the total power dissipated by the remaining
time is 939.96
W.
(799.971 ms/800 ms)
(5 188 A) = 939.96 W
Thus the total power dissipated during each cycle is:
199.3 nW + 939.96
W = 940.16 W
I
DD
TIME
1.1mA
188 A
800ms
29 s
Figure 10. Mode 1 Power Dissipation
Mode 2
In this mode the part is totally powered down. All circuitry
except the serial interface is switched off. The most power effi-
cient way of operating in this mode is to use the one-shot
method. Write to the configuration register and set the one-shot
bit to a 1. The part will power-up in approximately 4 ms and
then perform a conversion. Once the conversion is finished the
device will power down again until the PD bit in the configura-
tion register is set to a 0 or the one-shot bit is set to a 1. Figure
11 shows the same timing as Figure 10 in mode 1, a one-shot is
initiated every 800 ms. If we take the voltage supply to be 5 V
we can work out the power dissipation in the following way. The
current consumption for the part when converting is 1.1 mA
typically and the quiescent current is 800 nA typically. The
conversion time of 25
s plus power-up time of typically 4 ms
contributes 199.3 nW to the overall power dissipation in the
following way:
(29
s/800 ms) (5 V 1.1 mA) = 199.3 nW
The contribution to the total power dissipated by the remaining
time is 3.9
W.
(799.971 ms/800 ms)
(5 V 800 nA) = 3.9 W
Thus the total power dissipated during each cycle is:
199.3 nW + 3.9
W = 4.1 W
REV. 0
AD7414/AD7415
11
I
DD
TIME
800ms
1.1mA
800nA
29 s
Figure 11. Mode 2 Power Dissipation
MOUNTING THE AD7414/AD7415
The AD7414/AD7415 can be used for surface or air-tempera-
ture sensing applications. If the device is cemented to a surface
with thermally conductive adhesive, the die temperature will be
within about 0.1
C of the surface temperature, thanks to the
device's low power consumption. Care should be taken to
insulate the back and leads of the device from the air, if the
ambient air temperature is different from the surface tempera-
ture being measured.
The ground pin provides the best thermal path to the die, so the
temperature of the die will be close to that of the printed circuit
ground track. Care should be taken to ensure that this is in good
thermal contact with the surface being measured.
As with any IC, the AD7414/AD7415 and its associated wiring
and circuits must be kept free from moisture to prevent leakage
and corrosion, particularly in cold conditions where condensation
is more likely to occur. Water-resistant varnishes and conformal
coatings can be used for protection. The small size of the AD7414/
AD7415 packages allows it to be mounted inside sealed metal
probes, which provide a safe environment for the device.
SUPPLY DECOUPLING
The AD7414/AD7415 should be at least decoupled with a
0.1
F ceramic capacitor between V
DD
and GND. This is par-
ticularly important if the AD7414/AD7415 is mounted remote
from the power supply.
TEMPERATURE ACCURACY VS. SUPPLY
The Temperature Accuracy specifications are guaranteed for
voltage supplies of 3 V and 5.5 V only. Figure 12 gives the typi-
cal performance characteristics of a large sample of parts over
the full voltage range of 2.7 V to 5.5 V. Figure 13 gives the
typical performance characteristics of one part over the full
voltage range of 2.7 V to 5.5 V.
SUPPLY VOLTAGE V
2.7
TEMPERA
T
URE ERR
OR
C
4
4
5.5
3
2
1
0
1
2
3
3.0
40 C
+40 C
+85 C
Figure 12. Typical Temperature Error vs. Supply for Large
Sample of Parts
SUPPLY VOLTAGE V
2.7
TEMPERA
T
URE ERR
OR
C
4
4
5.5
3
2
1
0
1
2
3
5.0
40 C
+40 C
+85 C
3.3
Figure 13. Typical Temperature Error vs. Supply for One
Part
TYPICAL TEMPERATURE ERROR GRAPH
Figure 14 shows typical temperature error plots for one device
with V
DD
at 3.3 V and at 5.5 V.
TEMPERATURE C
40
TEMPERA
T
URE ERR
OR
C
4
4
3
2
1
0
1
2
3
0
10
20
30
40
50
60
70
80
90
30 20 10
5.5V
3.3V
Figure 14. Typical Temperature Error @ 3.3 V and 5.5 V
REV. 0
12
C0246317/01(0)
PRINTED IN U.S.A.
AD7414/AD7415
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
6-Lead Plastic Surface-Mount SOT-23
(RT-6)
0.122 (3.10)
0.106 (2.70)
PIN 1
0.118 (3.00)
0.098 (2.50)
0.075 (1.90)
BSC
0.037 (0.95) BSC
1
3
4
5
6
2
0.071 (1.80)
0.059 (1.50)
0.009 (0.23)
0.003 (0.08)
0.022 (0.55)
0.014 (0.35)
10
0
0.020 (0.50)
0.010 (0.25)
0.006 (0.15)
0.000 (0.00)
0.051 (1.30)
0.035 (0.90)
SEATING
PLANE
0.057 (1.45)
0.035 (0.90)
8-Lead Mini_SO
(RM-8)
0.011 (0.28)
0.003 (0.08)
0.028 (0.71)
0.016 (0.41)
33
27
0.120 (3.05)
0.112 (2.84)
8
5
4
1
0.122 (3.10)
0.114 (2.90)
0.199 (5.05)
0.187 (4.75)
PIN 1
0.0256 (0.65) BSC
0.122 (3.10)
0.114 (2.90)
SEATING
PLANE
0.006 (0.15)
0.002 (0.05)
0.018 (0.46)
0.008 (0.20)
0.043 (1.09)
0.037 (0.94)
0.120 (3.05)
0.112 (2.84)
5-Lead Plastic Surface-Mount SOT-23
(RT-5)
0.1181 (3.00)
0.1102 (2.80)
PIN 1
0.0669 (1.70)
0.0590 (1.50)
0.1181 (3.00)
0.1024 (2.60)
1
3
4
5
0.0748 (1.90)
BSC
0.0374 (0.95) BSC
2
0.0079 (0.20)
0.0031 (0.08)
0.0217 (0.55)
0.0138 (0.35)
10
0
0.0197 (0.50)
0.0138 (0.35)
0.0059 (0.15)
0.0019 (0.05)
0.0512 (1.30)
0.0354 (0.90)
SEATING
PLANE
0.0571 (1.45)
0.0374 (0.95)
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