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AD7814ART
10-Bit Digital Temperature Sensor in 6-Lead SOT-23
REV. B
10-Bit Digital Temperature Sensor
in 6-Lead SOT-23
FUNCTIONAL BLOCK DIAGRAM
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
GENERAL DESCRIPTIONThe AD7814 is a complete temperature monitoring system in
an SOT-23 package or 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 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 ap-
plications, including personal computers, office equipment, and
domestic appliances.
SPI is a trademark of Motorola, Inc.
MICROWIRE is a trademark of National Semiconductor, Inc.
PRODUCT HIGHLIGHTSThe 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.Supply voltage of +2.7 V to +5.5 V.Space-saving 6-lead SOT-23 package and 8-lead µSOIC
package.10-bit temperature reading to +0.25°C resolution.The AD7814 features a standby mode that reduces the
current consumption to 1µA.
AD7814–SPECIFICATIONS1, 2NOTES
1All specifications apply for –55°C to +125°C unless otherwise stated.
2Guaranteed by design and characterization, not production tested.
3For VDD = +2.7 V to +3 V and TA = –40°C to +85°C, the typical temperature error is ±2°C.
Specifications subject to change without notice.
TIMING CHARACTERISTICS1, 2, 3NOTESGuaranteed by design and characterization, not production tested.All input signals are specified with tr = tf = 5 ns (10% to 90% of VDD) and timed from a voltage level of 1.6 V.See Figure 2.Measured with the load circuit of Figure 1.
(TA = TMIN to TMAX, VDD = +2.7 V to +5.5 V, unless otherwise noted)
(TA = TMIN to TMAX, VDD = +2.7 V to +5.5 V, unless otherwise noted)
ORDERING GUIDE*Temperature error is over 0°C to +85°C temperature range.
ABSOLUTE MAXIMUM RATINGS*VDD to GND . . . . . . . . . . . . . . . . . . . . . . . . . . –0.3V to +7V
Digital Input Voltage to GND . . . . . . . –0.3 V to VDD + 0.3 V
Digital Output Voltage to GND . . . . . –0.3 V to VDD + 0.3 V
Operating Temperature Range . . . . . . . . . . –55°C to +125°C
Storage Temperature Range . . . . . . . . . . . . –65°C to +150°C
Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . . +150°C
SOT-23, Power Dissipation . . . . . . . . . . . . . . . . . . . . 450 mW
θJA 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
θJA Thermal Impedance . . . . . . . . . . . . . . . . . . . . 206°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.
CAUTIONESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000V readily
accumulate on the human body and test equipment and can discharge without detection.
Although the AD7814 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.
Figure 1.Load Circuit for Data Access Time and Bus
Relinquish Time
AD7814
PIN FUNCTION DESCRIPTIONSCLK
DOUT
PIN CONFIGURATIONS
SOT-23�SOIC
CIRCUIT INFORMATIONThe 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 an 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 +2.7V 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 DETAILSThe 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 25µs, 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 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 shut-
down 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 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 available, typically 25µs later. Similarly, when the
part is taken out of shutdown mode, the internal clock oscil-
lator is restarted and the conversion result is available, typicallyµs later. Reading from the device again before conversion is
complete will again provide the same set of data.
TEMPERATURE VALUE REGISTERThe 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
SERIAL INTERFACEThe 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 interface 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.
AD7814
Read OperationFigure 2 shows the timing diagram for a serial read from the
AD7814. The CS line enables the SCLK input. Ten bits of data
are transferred during a read operation. Read operations occur
during streams of 16 clock pulses. 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 DOUT line remains in the state of the
last bit of data clocked out of the AD7814 until CS returns
high, at which time the DOUT line goes into three-state.
Write OperationFigure 2 also shows the timing diagram for a serial write to the
AD7814. The write operation takes place at the same time as
the read operation. Data is clocked into the Control Register on
the part on the rising edge of SCLK. Only the third bit in the
data stream provides a user-controlled function. This third bit is
the power-down bit which, when set to a 1, puts the AD7814
into shutdown mode. The first two bits of the data stream are
don’t cares while all other bits in the data stream other, than the
power-down bit, should be 0 to ensure correct operation of the
AD7814. Data is loaded to the Control Register on the fifteenth
falling SCLK edge and the data takes effect at this time i.e., if
the part is programmed to go into shutdown, it does so at this
point. If the CS is brought high before this fifteenth SCLK edge,
the Control Register will not be loaded and the power-down
status of the part will not change.
MICROPROCESSOR INTERFACINGThe AD7814’s serial interface allows for easy interface to most
microcomputers and microprocessors. Figures 3 through 6 show
some typical interface circuits.
The serial interface on the AD7814 consists of four wires: CS,
DIN, DOUT and SCLK. All interface circuits shown utilize all
four interface lines. However, it is possible to operate the inter-
face with three wires. If the application does not require the
power-down facility offered by the AD7814, the DIN line can
be tied permanently low. Thus, the interface can be operated
from just three wires, SCLK, CS, and DOUT.
Figure 2.Serial Interface Timing Diagram
The serial data transfer to and from the AD7814 requires a
16-bit read operation. Many 8-bit microcontrollers have 8-bit
serial ports and this 16-bit data transfer is handled as two 8-bit
transfers. Other microcontrollers and DSP processors transfer
16 bits of data in a serial data operation.
AD7814 to MC68HC11 InterfaceFigure 3 shows an interface between the AD7814 and the
MC68HC11 microcontroller. The MC68HC11 is configured in
the master mode with its CPOL bit set to a logic one and its
CPHA bit set to a logic one. When the MC68HC11 is config-
ured like this, its SCLK line idles high between data transfers.
Data is transferred to and from the AD7814 in two 8-bit serial
data operations. The diagram shows the full (four-wire) inter-
face. PC1 of the MC68HC11 is configured as an output and
used to drive the CS input.
Figure 3.AD7814 to MC68HC11 Interface
AD7814 to 8051 InterfaceAn interface circuit between the AD7814 and the micro-
controller is shown in Figure 3. The 8xC51 is configured in its
Mode 0 serial interface mode. The serial clock line of the 8xC51
(on P3.1) idles high between data transfers. Data is transferred
to and from the AD7814 in two 8-bit serial data operations. The
AD7814 outputs the MSB of its data stream as the first valid
bit while the 8xC51 expects the LSB first. Thus, the data read
into the serial buffer needs to be rearranged before the correct
data word from the AD7814 is available in the accumulator.
