a
Low-Voltage, 10-Bit Digital Temperature
Sensor in 8-Lead SOIC
AD7314
FUNCTIONAL BLOCK DIAGRAM
BANDGAP
TEMPERATURE
SENSOR
10-BIT
ANALOG/DIGITAL
CONVERTER
ID
GND
TEMPERATURE
VALUE
REGISTER
V
DD
FEATURES
10-Bit Temperature-to-Digital Converter
–35 C to +85 C Operating Temperature Range
2 C Accuracy
SPI™- and DSP-Compatible Serial Interface
Shutdown Mode
Space-Saving SOIC Package
APPLICATIONS
Hard Disk Drives
Personal Computers
Electronic Test Equipment
Office Equipment
Domestic Appliances
Process Control
Mobile Phones
AD7314
SERIAL
BUS
INTERFACE
CE
SCLK
SDI
SDO
GENERAL DESCRIPTION
PRODUCT HIGHLIGHTS
The AD7314 is a complete temperature monitoring system in
an 8-lead
µSOIC
package. 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 AD7314 has a flexible serial interface that allows easy
interfacing to most microcontrollers. The interface is compat-
ible with SPI, QSPI and MICROWIRE™ protocol and is also
compatible with DSPs. The part features a standby mode that
is controlled via the serial interface.
The AD7314’s low supply current and SPI-compatible interface,
make it ideal for a variety of applications, including personal
computers, office equipment, and domestic appliances.
1. The AD7314 has an on-chip temperature sensor that allows
an accurate measurement of the ambient temperature. The
measurable temperature range is –35°C to +85°C, with a
±
2°C temperature accuracy.
2. Supply voltage of 2.65 V to 2.9 V.
3. Space-saving 8-lead
µSOIC
package.
4. 10-bit temperature reading to 0.25°C resolution.
5. The AD7314 features a standby mode that reduces the
current consumption to 1
µA
max.
SPI is a trademark of Motorola, Inc.
MICROWIRE is a trademark of National Semiconductor Corporation.
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.
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
AD7314–SPECIFICATIONS
Parameter
TEMPERATURE SENSOR AND ADC
Accuracy
Resolution
Update Rate, t
R
Temperature Conversion Time
SUPPLIES
Supply Voltage
Supply Current
Normal Mode (Inactive)
Normal Mode (Active)
Shutdown Mode
Power Dissipation
Power Dissipation
1 sps
10 sps
100 sps
DIGITAL INPUT
Input High Voltage, V
IH
Input Low Voltage, V
IL
Input Current, I
IN
Input Capacitance, C
IN
DIGITAL OUTPUT
Output High Voltage, V
OH
Output Low Voltage, V
OL
Output Capacitance, C
OUT
1
(T
A
= T
MIN
to T
MAX
, V
DD
= 2.65 V to 2.9 V, unless otherwise noted.)
Typ
Max
±
2.0
10
400
25
Unit
°C
Bits
µs
µs
V
µA
mA
µA
µW
µW
µW
µW
V
V
µA
pF
V
V
pF
Test Conditions/Comments
T
A
= –35°C to +85°C.
Min
2.65
250
1
860
2.9
300
1
For Specified Performance
Part not Converting
Part Converting
V
DD
= 2.65 V. Using Normal Mode
(Auto Conversion)
V
DD
= 2.65 V. Using Shutdown Mode
3
3.3
6
1.85
0.53
±
1
10
2.4
0.4
50
V
DD
= 2.65 V to 2.9 V
V
DD
= 2.65 V to 2.9 V
V
IN
= 0 V to V
DD
All Digital Inputs
I
SOURCE
= I
SINK
= 200
µA
I
OL
= 200
µA
NOTES
1
All specifications apply for –35°C to +85°C unless otherwise noted.
Specifications subject to change without notice.
TIMING CHARACTERISTICS
Parameter
t
1
t
2
t
3
t
4 4
t
5
t
6
t
7
t
8 4
Limit
0
50
50
35
20
0
0
40
1, 2
(T
A3
= T
MIN
to T
MAX
, V
DD
= 2.65 V to 2.9 V, unless otherwise noted. See Figure 1.)
Comments
CE to SCLK Setup Time
SCLK High Pulsewidth
SCLK Low Pulsewidth
Data Access Time After SCLK Rising Edge
Data Setup Time Prior to SCLK Falling Edge
Data Hold Time After SCLK Falling Edge
CE to SCLK Hold Time
CE to SDO High Impedance
Unit
ns min
ns min
ns min
ns max
ns min
ns min
ns min
ns max
NOTES
1
Guaranteed by design and characterization, not production tested.
2
All input signals are specified with tr = tf = 5 ns (10% to 90% of V
DD
) and timed from a voltage level of 1.6 V.
3
All specifications apply for –35°C to +85°C unless otherwise noted.
4
Measured with the load circuit of Figure 2.
Specifications subject to change without notice.
–2–
REV. 0
AD7314
CE
t
1
SCLK
t
2
t
3
t
7
t
4
SDO
t
8
t
5
SDI
t
6
Figure 1. Timing Diagram
ABSOLUTE MAXIMUM RATINGS
1
V
DD
to GND . . . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V to +7 V
Digital Input Voltage to GND . . . . . . . –0.3 V to V
DD
+ 0.3 V
Digital Output Voltage to GND . . . . . –0.3 V to V
DD
+ 0.3 V
Operating Temperature Range . . . . . . . . . . . –35°C to +85°C
Storage Temperature Range . . . . . . . . . . . . –65°C to +150°C
Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . . . 150°C
SOT-23, Power Dissipation . . . . . . . . . . . . . . . . . . . . 450 mW
θ
JA
Thermal Impedance . . . . . . . . . . . . . . . . . . . . 240°C/W
Lead Temperature, Soldering
Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . 215°C
Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . . 220°C
µSOIC
Package, Power Dissipation . . . . . . . . . . . . . . 450 mW
θ
JA
Thermal Impedance . . . . . . . . . . . . . . . . . . . . 206°C/W
Lead Temperature, Soldering
Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . 215°C
Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . . 220°C
Latch-Up for ID Pin
2
. . . . . . . . . . . . . . . . . . . . . . . .
≤
–70 mA
Latch-Up for All Other Pins . . . . . . . . . . . . . . . . .
≥
–110 mA
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
Correct usage of the ID pin will prevent any latch-up occurring. We recommend
that in an application the ID pin should be either tied via a 100 kΩ resistor to V
DD
or left open circuit. If the application complies with our recommendation, the ID
pin will never see –70 mA.
200 A
I
OL
TO
OUTPUT
PIN
1.6V
C
L
50pF
200 A
I
OH
Figure 2. Load Circuit for Data Access Time and Bus
Relinquish Time
ORDERING GUIDE
Model
AD7314ARM
Temperature
Range
–35°C to +85°C
Temperature
Error
±
2°C
Package
Description
8-Lead
µSOIC
Package
Option
RM-8
Branding
Information
CKA
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 AD7314 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
–3–
AD7314
PIN FUNCTION DESCRIPTIONS
Pin No.
1
2
3
Mnemonic
NC
CE
SCLK
Description
No Connect.
Chip Enable Input. The device is selected when this input is high. The SCLK input is disabled
when this pin is low.
Serial Clock Input. This is the clock input for the serial port. The serial clock is used to clock
data out of the temperature value register of the AD7314 and also to clock data into the control
register on the part.
Analog and Digital Ground.
Serial Data Output. Logic output. Data is clocked out of the temperature value register at this pin.
Serial Data Input. Serial data to be loaded to the parts’s control register is provided on this input.
Identification. This pin can be used by a master device to identify the AD7314 in an SPI Bus
system. This pin has an internal pull-down resistor of 1 kΩ.
Positive Supply Voltage, 2.65 V to 2.9 V.
4
5
6
7
8
GND
SDO
SDI
ID
V
DD
PIN CONFIGURATION
SOIC
NC 1
CE 2
8 V
DD
AD7314
7 ID
TOP VIEW
SCLK 3
6 SDI
(Not to Scale)
GND 4
5 SDO
NC = NO CONNECT
–4–
REV. 0
AD7314
CIRCUIT INFORMATION
Table I. Temperature Data Format
The AD7314 is a 10-bit digital temperature sensor. The part
houses an on-chip temperature sensor, a 10-bit A/D converter, a
reference and serial interface logic functions in an
µSOIC
package.
The A/D converter section consists of a conventional successive-
approximation converter based around a capacitor DAC. The
parts are capable of running on a 2.65 V to 2.9 V power supply.
The on-chip temperature sensor allows an accurate measurement
of the ambient device temperature to be made. The working
measurement range of the AD7314 is –35°C to +85°C.
CONVERTER DETAILS
Temperature
–128°C
–125°C
–100°C
–75°C
–50°C
–25°C
–0.25°C
0°C
+0.25°C
+10°C
+25°C
+50°C
+75°C
+100°C
+125°C
+127°C
Serial Interface
Digital Output
DB9 . . . DB0
10 0000 0000
10 0000 1100
10 0111 0000
10 1101 0100
11 0011 1000
11 1001 1100
11 1111 1111
00 0000 0000
00 0000 0001
00 0010 1000
00 0110 0100
00 1100 1000
01 0010 1100
01 1001 0000
01 1111 0100
01 1111 1100
The conversion clock for the part is internally generated so no
external clock is required except when reading from and writing
to the serial port. In normal mode, an internal clock oscillator
runs the automatic conversion sequence. A conversion is initi-
ated every 400
µs.
At this time, the part wakes up and performs
a temperature conversion. This temperature conversion typically
takes 25
µs,
at which time the part automatically shuts down.
The result of the most recent temperature conversion is avail-
able in the serial output register at any time. The AD7314 can
be placed in a shutdown mode, via the Control Register, in
which case, the on-chip oscillator is shut down and no further
conversions are initiated until the AD7314 is taken out of shut-
down mode. The conversion result from the last conversion prior
to shutdown can still be read from the AD7314 even when it is
in shutdown mode.
In the automatic conversion mode, every time a read or write
operation takes place, the internal clock oscillator is restarted at
the end of the read or write operation. The result of the conver-
sion is available, typically 25
µs
later. Similarly, when the part is
taken out of shutdown mode, the internal clock oscillator is
restarted and the conversion result is available, typically 25
µs
later. Reading from the device again before conversion is com-
plete will again provide the same set of data.
Temperature Value Register
The serial interface on the AD7314 consists of four wires, CE,
SCLK, SDI and SDO. The interface can be operated in 3-wire
mode with SDI tied to Ground, in which case the interface has
read-only capability, with data being read from the data register
via the SDO line. The SDI line is used to write the part into
standby mode, if required. The CE line is used to select the
device when more than one device is connected to the serial
clock and data lines. To ensure that the serial port is reset prop-
erly after power-up, the CE must be at a logic low before the
first serial port access. The serial clock is active only when CE is
high. For correct data synchronization it is important that the
CE be low when the serial port is not been accessed.
The part operates in a slave mode and requires an externally
applied serial clock to the SCLK input to access data from the
data register. The serial interface on the AD7314 is designed to
allow the part to be interfaced to systems that provide a serial
clock that is synchronized to the serial data, such as the 80C51,
87C51, 68HC11, 68HC05, and PIC16Cxx microcontrollers as
well as DSP processors.
A read operation from the AD7314 accesses data from the
Temperature Value Register while a write operation to the part
writes data to the Control Register. Input data is not loaded into
the Control Register until the rising edge of the fifteenth SCLK
cycle. Data on the SDI line is latched in on the falling edge of
the serial clock whilst data is updated on the SDO line on the
rising edge of the serial clock.
Read Operation
The temperature value register is a read-only register that stores
the temperature reading from the ADC in 10-bit twos comple-
ment format. The temperature data format is shown in Table I.
This shows the full theoretical range of the ADC from –128°C
to +127°C, but in practice the temperature measurement range
is limited to the operating temperature range of the device (–35°C
to +85°C).
Figure 3 shows the interface diagram for a serial read from the
AD7314. The CE line enables the SCLK input. A leading zero
and ten bits of data are transferred during a read operation. Read
operations occur during streams of 16 clock pulses. Output data
is updated on the rising edge of SCLK. The serial data is accessed
in a number of bytes if ten bits of data are being read. At the
end of the read operation, the SDO line remains in the state of
the last bit of data clocked out of the AD7314 until CE returns
low, at which time the SDO line goes into three-state.
REV. 0
–5–
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