a
AD7414/AD7415
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REV. B
ⴞ0.5ⴗC Accurate, 10-Bit Digital
Temperature Sensors in SOT-23
FUNCTIONAL BLOCK DIAGRAM
SDA
SCL
V
DD
SMBus/I
2
C
INTERFACE
10-BIT
ANALOG-DIGITAL
CONVERTER
BAND GAP
TEMPERATURE
SENSOR
CONFIGURATION
REGISTER
TEMPERATURE
VALUE
REGISTER
AD7415
AS
GND
SMBus/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
BAND GAP
TEMPERATURE
SENSOR
V
DD
AD7414
FEATURES
10-Bit Temperature-to-Digital Converter
Temperature Range: –40ⴗC to +85ⴗC
Typical Accuracy of ⴞ0.5ⴗC at 40ⴗC
SMBus/I2C® 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)
4 Versions Allow 8 I2C Addresses (AD7414)
2 Versions Allow 6 I2C 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 sys-
tem in 6-lead and 5-lead SOT-23 packages. It contains a band
gap 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 com-
patible with SMBus and I
2
C interfaces. The part comes in four
versions, the AD7414/AD7415-0, AD7414/AD7415-1, AD7414-2,
and AD7414-3. The AD7414/AD7415-0 and AD7414/AD7415-1
versions provide 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 current,
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 overtemperature indi-
cator output (ALERT) that becomes active when a programmed
limit is exceeded. A Configuration register allows programming
of the state 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 temperature
to be made. It is capable of ±0.5∞C temperature accuracy.
2. SMBus/I
2
C compatible serial interface with pin selectable
choice of three addresses per version of the AD7414/AD7415,
and 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 overtemperature indicator that can be
software disabled. Used as an interrupt of SMBus alert.
7. One-shot and automatic temperature conversion rates.
REV. B
–2–
AD7414/AD7415–SPECIFICATIONS
1
(TA = TMIN to TMAX, VDD = 2.7 V to 5.5 V, unless otherwise noted.)
Parameter A Version Unit Test Conditions/Comments
TEMPERATURE SENSOR AND ADC
Accuracy
2
±0.5 ∞C typ V
DD
= 3 V @ +40∞C
–0.87 to +0.82
3
∞C max V
DD
= 3 V @ +40∞C
±1.5 ∞C max V
DD
= 3 V @ –40∞C to +70∞C
±2.0 ∞C max V
DD
= 3 V @ –40∞C to +85∞C
±1.87
3
∞C max V
DD
= 5.5 V @ +40∞C
±2.0 ∞C typ V
DD
= 5.5 V @ –40∞C to +85∞C
±3.0 ∞C max V
DD
= 5.5 V @ –40∞C to +85∞C
Resolution 10 Bits
Update Rate, t
R
800 ms typ
Temperature Conversion Time 25 ms typ
POWER SUPPLIES
Supply Current
4
Peak Supply Current
5
1.2 mA typ Current during Conversion
Supply Current – Nonconverting 900 mA max Peak Current between Conversions
Inactive Serial Bus
6
Normal Mode @ 3 V 169 mA typ Supply Current with Serial Bus Inactive. Part not
Normal Mode @ 5 V 188 mA typ converting and D7 of Configuration Register = 0.
Active Serial Bus
7
Normal Mode @ 3 V 180 mA typ Supply Current with Serial Bus Active. Part not
Normal Mode @ 5 V 214 mA typ converting and D7 of Configuration Register = 0.
Shutdown Mode 3 mA max D7 of Configuration Register = 1. Typical values
are 0.04 mA at 3 V and 0.5 mA 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
IN8
±1mA max V
IN
= 0 V to V
DD
Input Capacitance, C
IN
10 pF max All Digital Inputs
DIGITAL OUTPUT (OPEN-DRAIN)
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
1mA 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
9, 10
Serial Clock Period, t
1
2.5 ms 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
0ns 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 ms typ
NOTES
1
Temperature range as follows: A Version = –40∞C to +85∞C.
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
100% production tested at 40∞C to these limits.
4
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 mW.
5
This peak supply current is required for 29 ms (the conversion time plus power-up time) out of every 800 ms (the conversion rate).
6
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.
7
The current is derived assuming a 400 kHz serial clock being active continuously.
8
On power-up, the initial input current, I
IN
, on the AS pin is typically 50 mA.
9
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.
10
Guaranteed by design. Not tested in production.
Specifications subject to change without notice.
REV. B –3–
AD7414/AD7415
PIN FUNCTION DESCRIPTIONS
Mnemonic Description
AS Logic Input. Address select input that selects one
of three I
2
C addresses for the AD7414/AD7415
(see Table I). Recommend a pull-up or pull-down
resistor of 1 kW.
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. Overtemperature indicator
becomes active when temperature exceeds T
HIGH
.
Open-drain output.
SCL Digital Input. Serial bus clock.
ABSOLUTE MAXIMUM RATINGS
1
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 +85∞C
Storage Temperature Range . . . . . . . . . . . . –65∞C to +150∞C
Junction Temperature
2
. . . . . . . . . . . . . . . . . . . . . . . . . 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
MSOP, Power Dissipation . . . . . . . . . . . . . . . . . . . . . 450 mW
␪
JA
Thermal Impedance . . . . . . . . . . . . . . . . . . . . 206∞C/W
Lead Temperature Soldering
Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . . . . 215∞C
Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . . . 220∞C
NOTES
1
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.
2
Maximum junction temperature is calculated using: T
J
= T
AMBMAX
⫹ ( ␪
JA
⫻ W
MAX
).
␪
JA
=
Junction-to-Ambient Thermal Resistance, W
MAX
= Maximum Power Dissi-
pated in the device, and T
AMBMAX
= Maximum Ambient Temperature.
SCL
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
PIN CONFIGURATIONS
SOT-23
AS SDA
16
V
DD
SCL34
GND 2
AD7414
TOP VIEW
(Not to Scale) 5ALERT
MSOP
SCL V
DD
45
NC NC
18
ALERT GND36
SDA 2 7 AS
AD7414
TOP VIEW
(Not to Scale)
NC = NO CONNECT
SOT-23
AS SDA
15
VDD SCL
34
GND 2
AD7415
TOP VIEW
(Not to Scale)
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. B
AD7414/AD7415
–4–
ORDERING GUIDE
Temperature Temperature Package Package Branding Minimum
Model Range Error @ 3 V Options Description Information Quantities/Reel
AD7414ART-0REEL7 –40∞C to +85∞C±2∞CRT-6 6-Lead SOT-23 CHA
1
3,000
AD7414ART-0REEL –40∞C to +85∞C±2∞CRT-6 6-Lead SOT-23 CHA
1
10,000
AD7414ART-0500RL7 –40∞C to +85∞C±2∞CRT-6 6-Lead SOT-23 CHA
1
500
AD7414ARM-0REEL7 –40∞C to +85∞C±2∞CRM-8 8-Lead MSOP CHA
1
3,000
AD7414ARM-0REEL –40∞C to +85∞C±2∞CRM-8 8-Lead MSOP CHA
1
10,000
AD7414ARM-0
2
–40∞C to +85∞C±2∞CRM-8 8-Lead MSOP CHA
1
AD7414ART-1REEL7 –40∞C to +85∞C±2∞CRT-6 6-Lead SOT-23 CHB
3
3,000
AD7414ART-1REEL –40∞C to +85∞C±2∞CRT-6 6-Lead SOT-23 CHB
3
10,000
AD7414ART-1500RL7 –40∞C to +85∞C±2∞CRT-6 6-Lead SOT-23 CHB
3
500
AD7414ARM-1REEL7 –40∞C to +85∞C±2∞CRM-8 8-Lead MSOP CHB
3
3,000
AD7414ARM-1REEL –40∞C to +85∞C±2∞CRM-8 8-Lead MSOP CHB
3
10,000
AD7414ARM-1
2
–40∞C to +85∞C±2∞CRM-8 8-Lead MSOP CHB
3
AD7414ART-2REEL7 –40∞C to +85∞C±2∞CRT-6 6-Lead SOT-23 CHC
3
3,000
AD7414ART-2REEL –40∞C to +85∞C±2∞CRT-6 6-Lead SOT-23 CHC
3
10,000
AD7414ART-3REEL7 –40∞C to +85∞C±2∞CRT-6 6-Lead SOT-23 CHD
3
3,000
AD7414ART-3REEL –40∞C to +85∞C±2∞CRT-6 6-Lead SOT-23 CHD
3
10,000
AD7415ART-0REEL7 –40∞C to +85∞C±2∞CRT-5 5-Lead SOT-23 CGA
1
3,000
AD7415ART-0REEL –40∞C to +85∞C±2∞CRT-5 5-Lead SOT-23 CGA
1
10,000
AD7415ART-0500RL7 –40∞C to +85∞C±2∞CRT-5 5-Lead SOT-23 CGA
1
500
AD7415ART-1REEL7 –40∞C to +85∞C±2∞CRT-5 5-Lead SOT-23 CGB
3
3,000
AD7415ART-1REEL –40∞C to +85∞C±2∞CRT-5 5-Lead SOT-23 CGB
3
10,000
AD7415ART-1500RL7 –40∞C to +85∞C±2∞CRT-5 5-Lead SOT-23 CGB
3
500
NOTES
1
Available to order.
2
This model shipped in tubes.
3
Contact factory for availability.
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. B
AD7414/AD7415
–5–
CIRCUIT INFORMATION
The AD7414/AD7415 is a standalone digital temperature sensor.
The on-chip temperature sensor allows an accurate measurement
of the ambient device temperature to be made. The 10-bit A/D
converter converts the temperature measured into a twos comple-
ment 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 +85∞C.
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 ms to time out. It then
takes typically 25 ms 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 temperature
measurement is needed. Setting the One-Shot bit to a 1 will start
a temperature conversion directly after the write operation. The
track-and-hold goes into hold approximately 4 ms (monostable
timeout) after the STOP condition and a conversion is then initiated.
Typically 25 ms later, the conversion is complete and the Tem-
perature Value register is loaded with a new temperature 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 since the AD7415 does not have an ALERT pin
and subsequently does not have an overtemperature monitoring
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: first when the Alert Reset bit in the Configura-
tion register is set to a 1 by a write operation, and second 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
VDD
10␮F0.1␮F1k⍀
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 different currents.
This is given by:
DVKTqnN
BE =¥
()
1
where:
K is Boltzmann’s constant.
q is the charge on the electron (1.6 ¥ 10
–19
Coulombs).
T is the absolute temperature in Kelvins.
N is the ratio of the two currents.
TO ADC
VOUT +
VOUT –
SENSING
TRANSISTOR
VDD
INⴛI
SENSING
TRANSISTOR
Figure 3. Temperature Measurement Technique
Figure 3 shows the method the AD7414/AD7415 uses to measure
the ambient device temperature. To measure DV
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 twos complement format.
REV. B
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 the device maximum ratings. The A grade
can measure a temperature range of –40∞C to +85∞C. (Tempera-
ture data format is shown in Table II.)
Table II. A Grade Temperature Data Format
Digital Output
Temperature DB9 . . . DB0
–55∞C11 0010 0100
–50∞C11 0011 1000
–25∞C11 1001 1100
–0.25∞C11 1111 1111
0∞C00 0000 0000
+0.25∞C00 0000 0001
+10∞C00 0010 1000
+25∞C00 0110 0100
+50∞C00 1100 1000
+75∞C01 0010 1100
+100∞C01 1001 0000
+125∞C01 1111 0100
A Grade Temperature Conversion Formula:
Positive Temperature ADC Code
=4
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
THIGH
REGISTER
TLOW
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 Temperature
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
00000 0Register Select
Table IV. AD7414 Register Address
P1 P0 Registers
00Temperature Value Register (Read-Only)
01Configuration Register (Read/Write)
10T
HIGH
Register (Read/Write)
11T
LOW
Register (Read/Write)
Table V. AD7415 Register Address
P1 P0 Registers
00Temperature Value Register (Read-Only)
01Configuration Register (Read/Write)
REV. B
AD7414/AD7415
–7–
FRAME 1
SERIAL BUS ADDRESS BYTE
FRAME 2
ADDRESS POINTER REGISTER BYTE
R/W
1
SCL
SDA 001A2 A1 A0 P7 P6 P5 P4 P3 P2 P1 P0
ACK. BY
AD7414/AD7415
STOP BY
MASTER
START BY
MASTER
19
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
19
SCL (CONTINUED)
SDA (CONTINUED)
R/W
1
SCL
SDA 001A2 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
191
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), which 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.
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.
Table VII. AD7414 Configuration Register Setting
REV. B
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 twos comple-
ment 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 the 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, 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 operation, 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 +85∞C for A grade.
Table X. Temperature Value Register (First Read)
D15 D14 D13 D12 D11 D10 D9 D8
MSB B8 B7B6B5B4B3B2
Table XI. AD7414 Temperature Value Register (Second Read)
D7 D6 D5 D4 D3 D2 D1 D0
B1 LSB ALERT_ T
HIGH_
T
LOW_
00 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, the ALERT pin is activated (that is, if
ALERT is enabled in the Configuration register). Since 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). Since 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
191 9
D7 D6 D5 D4 D3 D2 D1 D0
R/W
A0A1A2101
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
19
SCL (CONTINUED)
SDA (CONTINUED)
R/W
1
SCL
SDA 001A2 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
19
1
ACK. BY
AD7414/AD7415
9
Figure 9. Reading Two Bytes of Data from the Temperature Value Register
REV. B
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 com-
patible 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 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 determines
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, 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, since 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 conditions
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 ninth clock
pulse. This is known as No Acknowledge. The master will
then take 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.
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 different
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, followed 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 1- or 2-byte opera-
tion. Reading back the contents of the Configuration register,
T
HIGH
register, or T
LOW
register is a single-byte read operation, as
shown in Figure 8. The register address was previously 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
subsequently be done from that register without having to write
to the Address Pointer register again. To read from another
register, the Address Pointer register will have to be written to
again to set up the relevant register address.
Reading data from the Temperature Value register is a 2-byte
operation, as shown in Figure 9. The same rules apply for a
2-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 to the host device that it wants to talk. The SMBus
ALERT on the AD7414 is used as an overtemperature indicator.
The ALERT pin has an open-drain configuration that 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. B
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 that 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 conversion,
that conversion might or might not be aborted. If the conversion
is completed before the part recognizes a serial port access, the
Temperature register will be updated with the new conversion. If
the conversion is completed after the part recognizes a serial
port access, the internal logic will prevent the Temperature
register from being updated since 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
the 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 is set to 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 since 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
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 mA typically.
The conversion time of 25 ms plus power-up time of typically
4ms contributes 199.3 nW to the overall power dissipation in the
following way:
29 800 5 1 1 199 3msms mA nW/..
()
¥¥
()
=
The contribution to the total power dissipated by the remaining
time is 939.96 mW.
799 971 800 5 1 1 199 3./ . .ms ms A W
()
¥¥
()
=mm
Thus the total power dissipated during each cycle is:
199 3 939 96 940 16.. .nW W W+=mm
IDD
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 efficient
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 Configuration register is
set to a 0 or the one-shot bit is set to 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 ms plus the
power-up time of typically 4 ms contributes 199.3 nW to the overall
power dissipation in the following way:
29 800 5 1 1 199 3msmsVmA nW/..
()
¥¥
()
=
The contribution to the total power dissipated by the remaining
time is 3.9 mW.
799 971 800 5 800 3 9./ .ms ms V nA W
()
¥¥
()
=m
Thus the total power dissipated during each cycle is:
199 3 3 9 4 1...nW W W+=mm
REV. B
AD7414/AD7415
–11–
IDD
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 temperature
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 tem-
perature is different from the surface temperature 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 them to be mounted inside sealed
metal probes, which provide a safe environment for the device.
SUPPLY DECOUPLING
The AD7414/AD7415 should at least be decoupled with a 0.1 mF
ceramic capacitor between V
DD
and GND. This is particularly
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
TEMPERATURE ERROR – ⴗC
–4
4
5.5
–3
–2
–1
0
1
2
3
3.0
–40ⴗC
+40ⴗC
+85ⴗC
Figure 12. Typical Temperature Error vs. Supply for Large
Sample of Parts
SUPPLY VOLTAGE – V
2.7
TEMPERATURE ERROR – ⴗC
–4
4
5.5
–3
–2
–1
0
1
2
3
5.0
–40ⴗC
+40ⴗC
+85ⴗC
3.3
Figure 13. Typical Temperature Error vs. Supply for One Part
TYPICAL TEMPERATURE ERROR GRAPH
Figure 14 shows the typical temperature error plots for one device
with V
DD
at 3.3 V and at 5.5 V.
TEMPERATURE – ⴗC
–40
TEMPERATURE ERROR – ⴗC
–4
4
–3
–2
–1
0
1
2
3
0102030405060708090–30 –20 –10
5.5V
3.3V
Figure 14. Typical Temperature Error @ 3.3 V and 5.5 V
Figure 15 shows a histogram of the temperature error at ambient
temperature (40∞C) over approximately 6,000 units. Figure 15
shows that over 70% of the AD7414/AD7415 devices tested
have a temperature error within ±0.3∞C.
0
100
200
300
400
500
600
700
800
900
0.810 0.27 0.54 1.08
NUMBER OF UNITS
AMBIENT TEMPERATURE = 40ⴗC
ⴚ1.08 ⴚ0.54ⴚ0.81 ⴚ0.27
TEMPERATURE ERROR – ⴗC
Figure 15. Ambient Temperature Error @ 3 V
REV. B
–12–
C02463–0–11/02(B)
PRINTED IN U.S.A.
AD7414/AD7415
OUTLINE DIMENSIONS
5-Lead Plastic Surface-Mount Package [SOT-23]
(RT-5)
Dimensions shown in millimeters
PIN 1
1.60 BSC 2.80 BSC
1.90
BSC
0.95 BSC
1 3
4 5
2
0.22
0.08
0.60
0.45
0.30
10ⴗ
0ⴗ
0.50
0.30
0.15 MAX SEATING
PLANE
1.45 MAX
1.30
1.15
0.90
COMPLIANT TO JEDEC STANDARDS MO-178AA
2.90 BSC
8-Lead MSOP Package [MSOP]
(RM-8)
Dimensions shown in millimeters
0.23
0.08
0.80
0.40
8ⴗ
0ⴗ
85
4
1
4.90
BSC
PIN 1
0.65 BSC
3.00
BSC
SEATING
PLANE
0.15
0.00
0.38
0.22
1.10 MAX
3.00
BSC
COMPLIANT TO JEDEC STANDARDS MO-187AA
COPLANARITY
0.10
6-Lead Plastic Surface-Mount Package [SOT-23]
(RT-6)
Dimensions shown in millimeters
1 3
4 5
2
6
2.90 BSC
PIN 1
1.60 BSC 2.80 BSC
1.90
BSC
0.95 BSC
0.22
0.08
0.60
0.45
0.30
10ⴗ
0ⴗ
0.50
0.30
0.10 MAX
1.30
1.15
0.90
SEATING
PLANE
1.45 MAX
COMPLIANT TO JEDEC STANDARDS MO-178AB
Revision History
Location Page
11/02—Data Sheet changed from REV. A to REV. B.
Changes to ABSOLUTE MAXIMUM RATINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
10/02—Data Sheet changed from REV. 0 to REV. A.
Changes to SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Changes to PIN FUNCTION DESCRIPTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Changes to ABSOLUTE MAXIMUM RATINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
ORDERING GUIDE updated . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Change to Figure 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Added to TYPICAL TEMPERATURE ERROR GRAPH section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Added Figure 15 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
OUTLINE DIMENSIONS updated . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12