Document Outline
- Specifications
- Pinout
- Package drawings
- Ordering Guide
- Features
- Applications
- Product Description
- Timing characteristics
- Absolute Maximum Ratings
- Functional Block Diagram
- Pin Function Description
- Circuit Description
- PRODUCT HIGHLIGHTS
- CONVERTER DETAILS
- MICROCONTROLLER INTERFACING
- MOUNTING THE AD7314
- SUPPLY DECOUPLING
- TYPICAL TEMPERATURE ERROR GRAPHS
- DIAGRAMS
- Timing Diagram
- Load Circuit for Data Access Time and Bus Relinquish Time
- Serial Interface Diagram
- Typical Interface
- Typical ID Pin Interface
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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
AD7314
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
Low-Voltage, 10-Bit Digital Temperature
Sensor in 8-Lead SOIC
FUNCTIONAL BLOCK DIAGRAM
FEATURES
10-Bit Temperature-to-Digital Converter
35 C to +85 C Operating Temperature Range
2 C Accuracy
SPITM- 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
GENERAL DESCRIPTION
The AD7314 is a complete temperature monitoring system in
an 8-lead
SOIC 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 MICROWIRETM 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.
PRODUCT HIGHLIGHTS
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 +85C, with a
2C temperature accuracy.
2. Supply voltage of 2.65 V to 2.9 V.
3. Space-saving 8-lead
SOIC 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
A max.
SPI is a trademark of Motorola, Inc.
MICROWIRE is a trademark of National Semiconductor Corporation.
AD7314
BANDGAP
TEMPERATURE
SENSOR
SERIAL
BUS
INTERFACE
GND
ID
V
DD
CE
SCLK
SDI
SDO
10-BIT
ANALOG/DIGITAL
CONVERTER
TEMPERATURE
VALUE
REGISTER
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2
AD7314SPECIFICATIONS
1
(T
A
= T
MIN
to T
MAX
, V
DD
= 2.65 V to 2.9 V, unless otherwise noted.)
Parameter
Min
Typ
Max
Unit
Test Conditions/Comments
TEMPERATURE SENSOR AND ADC
Accuracy
2.0
C
T
A
= 35
C to +85C.
Resolution
10
Bits
Update Rate, t
R
400
s
Temperature Conversion Time
25
s
SUPPLIES
Supply Voltage
2.65
2.9
V
For Specified Performance
Supply Current
Normal Mode (Inactive)
250
300
A
Part not Converting
Normal Mode (Active)
1
mA
Part Converting
Shutdown Mode
1
A
Power Dissipation
860
W
V
DD
= 2.65 V. Using Normal Mode
(Auto Conversion)
Power Dissipation
V
DD
= 2.65 V. Using Shutdown Mode
1 sps
3
W
10 sps
3.3
W
100 sps
6
W
DIGITAL INPUT
Input High Voltage, V
IH
1.85
V
V
DD
= 2.65 V to 2.9 V
Input Low Voltage, V
IL
0.53
V
V
DD
= 2.65 V to 2.9 V
Input Current, I
IN
1
A
V
IN
= 0 V to V
DD
Input Capacitance, C
IN
10
pF
All Digital Inputs
DIGITAL OUTPUT
Output High Voltage, V
OH
2.4
V
I
SOURCE
= I
SINK
= 200
A
Output Low Voltage, V
OL
0.4
V
I
OL
= 200
A
Output Capacitance, C
OUT
50
pF
NOTES
1
All specifications apply for 35
C to +85C unless otherwise noted.
Specifications subject to change without notice.
TIMING CHARACTERISTICS
1, 2
Parameter
Limit
Unit
Comments
t
1
0
ns min
CE to SCLK Setup Time
t
2
50
ns min
SCLK High Pulsewidth
t
3
50
ns min
SCLK Low Pulsewidth
t
4
4
35
ns max
Data Access Time After SCLK Rising Edge
t
5
20
ns min
Data Setup Time Prior to SCLK Falling Edge
t
6
0
ns min
Data Hold Time After SCLK Falling Edge
t
7
0
ns min
CE to SCLK Hold Time
t
8
4
40
ns max
CE to SDO High Impedance
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 +85C unless otherwise noted.
4
Measured with the load circuit of Figure 2.
Specifications subject to change without notice.
(T
A
3
= T
MIN
to T
MAX
, V
DD
= 2.65 V to 2.9 V, unless otherwise noted. See Figure 1.)
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AD7314
3
ORDERING GUIDE
Temperature
Temperature
Package
Package
Branding
Model
Range
Error
Description
Option
Information
AD7314ARM
35
C to +85C
2C
8-Lead
SOIC
RM-8
CKA
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 +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
SOIC Package, Power Dissipation . . . . . . . . . . . . . . 450 mW
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 k
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
1.6V
200 A
I
OH
C
L
50pF
TO
OUTPUT
PIN
Figure 2. Load Circuit for Data Access Time and Bus
Relinquish Time
CE
SCLK
SDO
SDI
t
1
t
2
t
7
t
3
t
4
t
6
t
5
t
8
Figure 1. Timing Diagram
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
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AD7314
4
PIN FUNCTION DESCRIPTIONS
Pin No.
Mnemonic
Description
1
NC
No Connect.
2
CE
Chip Enable Input. The device is selected when this input is high. The SCLK input is disabled
when this pin is low.
3
SCLK
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.
4
GND
Analog and Digital Ground.
5
SDO
Serial Data Output. Logic output. Data is clocked out of the temperature value register at this pin.
6
SDI
Serial Data Input. Serial data to be loaded to the parts's control register is provided on this input.
7
ID
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 k
.
8
V
DD
Positive Supply Voltage, 2.65 V to 2.9 V.
PIN CONFIGURATION
SOIC
TOP VIEW
(Not to Scale)
8
7
6
5
1
2
3
4
NC = NO CONNECT
NC
SDO
CE
SCLK
GND
SDI
V
DD
AD7314
ID
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AD7314
5
CIRCUIT INFORMATION
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
SOIC 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 +85C.
CONVERTER DETAILS
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
s. At this time, the part wakes up and performs
a temperature conversion. This temperature conversion typically
takes 25
s, 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
s 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
s
later. Reading from the device again before conversion is com-
plete will again provide the same set of data.
Temperature Value Register
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).
Table I. Temperature Data Format
Digital Output
Temperature
DB9 . . . DB0
128
C
10 0000 0000
125
C
10 0000 1100
100
C
10 0111 0000
75
C
10 1101 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
+127
C
01 1111 1100
Serial Interface
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
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.
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