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PDF AD7814 Data sheet ( Hoja de datos )
| Número de pieza | AD7814 | |
| Descripción | 10-Bit Digital Temperature Sensor | |
| Fabricantes | Analog Devices | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de AD7814 (archivo pdf) en la parte inferior de esta página. Total 8 Páginas | ||
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FEATURES
10-Bit Temperature-to-Digital Converter
–55؇C to +125؇C Operating Temperature Range
؎2؇C Accuracy
SPI- and DSP-Compatible Serial Interface
Shutdown Mode
Space-Saving SOT-23 Package
APPLICATIONS
Hard Disk Drives
Personal Computers
Electronic Test Equipment
Office Equipment
Domestic Appliances
Process Control
10-Bit Digital Temperature Sensor
in 6-Lead SOT-23
AD7814
FUNCTIONAL BLOCK DIAGRAM
GND
BAND GAP
TEMPERATURE
SENSOR
AD7814
10-BIT
ANALOG/DIGITAL
CONVERTER
TEMPERATURE
VALUE
REGISTER
SERIAL
BUS
INTERFACE
VDD
CS
SCLK
DIN
DOUT
GENERAL DESCRIPTION
The AD7814 is a complete temperature monitoring system in a
SOT-23 package or 8-lead MSOP package. 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 AD7814 has a flexible serial interface that allows easy inter-
facing to most microcontrollers. The interface is compatible
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 AD7814’s wide supply voltage range, 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 AD7814 has an on-chip temperature sensor that allows
an accurate measurement of the ambient temperature. The
measurable temperature range is –55°C to +125°C, with a
± 2°C temperature accuracy.
2. Supply voltage of 2.7 V to 5.5 V
3. Space-saving 6-lead SOT-23 package and 8-lead MSOP
package
4. 10-bit temperature reading to 0.25°C resolution
5. Standby mode that reduces the current consumption to 1 µA
Purchase of licensed I2C components of Analog Devices or one of its sublicensed
Associated Companies conveys a license for the purchaser under the Philips I 2C
Patent Rights to use these components in an I2C system, provided that the system
conforms to the I2C Standard Specification as defined by Philips.
REV. E
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. Trademarks and
registered trademarks are the property of their respective owners.
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 © 2004 Analog Devices, Inc. All rights reserved.
1 page  
AD7814
CIRCUIT INFORMATION
The AD7814 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 a SOT-23
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 2.7 V to 5.5 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 AD7814 is –55°C to +125°C.
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 approximately every 350 µs. At this time, the part wakes up
and performs a temperature conversion. This temperature con-
version typically takes 25 µs, at which time the part automati-
cally shuts down. The result of the most recent temperature
conversion is available in the serial output register at any time.
Once the conversion is finished, an internal oscillator starts
counting and is designed to time out every 350 µs. The AD7814
then powers up and does a conversion. Please note that if the
CS is brought low every 350 µs (± 30%), then the same tempera-
ture value will be output onto the DOUT line every time with-
out changing. It is recommended that the CS line is not brought
low every 350 µs (± 30%). The ± 30% covers process variation.
The CS should become active (high to low) outside this range.
The device is designed to autoconvert every 350 µs. If the
AD7814 is accessed during the conversion process, an internal
signal is generated to prevent any update of the temperature
value register during the conversion. Otherwise the user could
read back spurious data. The design of this feature results in this
internal lockout signal being reset only at the start of the next
autoconversion. Therefore, if the CS line goes active before the
internal lockout signal has been reset to its inactive mode, the
internal lockout signal will not be reset. To ensure that no lock-
out signal is set, bring the CS low at a greater or less time than
350 µs (± 30%). This will mean that the AD7814 is not inter-
rupted during a conversion process. The AD7814 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 AD7814 is taken out of shutdown mode. The
conversion result from the last conversion prior to shutdown can
still be read from the AD7814 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 con-
version is typically available 25 µs later. Similarly, when the
part is taken out of shutdown mode, the internal clock oscil-
lator is restarted and the conversion result is typically available
25 µs later. Reading from the device before conversion is com-
plete will 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 (–55°C
to +125°C). A typical performance curve is shown in Figure 7.
Table I. Temperature Data Format
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
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
SERIAL INTERFACE
The serial interface on the AD7814 consists of four wires CS,
SCLK, DIN, and DOUT. The interface can be operated in
3-wire mode with DIN tied to Ground, in which case the inter-
face has read-only capability, with data being read from the data
register via the DOUT line. The DIN line is used to write the part
into standby mode, if required. The CS line is used to select the
device when more than one device is connected to the serial
clock and data lines.
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 AD7814 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 AD7814 accesses data from the
temperature value register, while a write operation to the part
writes data to the control register.
REV. E
–5–
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| PDF Descargar | [ Datasheet AD7814.PDF ] | |
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