AD7314ARM Analog Devices Inc, AD7314ARM Datasheet - Page 5

• Manufacturer Part Number: AD7314ARM
• Description: IC SENSOR TEMP 10BIT DGTL 8-MSOP
• Manufacturer: Analog Devices Inc

Specifications of AD7314ARM

• Rohs Status: RoHS non-compliant
• Function: Temp Monitoring System (Sensor)
• Topology: ADC, Register Bank
• Sensor Type: Internal
• Sensing Temperature: -35°C ~ 85°C
• Output Type: MICROWIRE™, QSPI™, SPI™
• Output Alarm: No
• Output Fan: No
• Voltage - Supply: 2.65 V ~ 5.5 V
• Operating Temperature: -35°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-MSOP, Micro8™, 8-uMAX, 8-uSOP,

REV. A
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,
and reference and serial interface logic functions in an MSOP
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 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 AD7314 is –35∞C to +85∞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 every 400 ms. At this time, the part wakes up and performs
a temperature conversion. This temperature conversion typically
takes 25 ms, 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 ms 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 ms
later. Reading from the device again 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 (–35∞C
to +85∞C).
–5–
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 being 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 15th SCLK cycle.
Data on the SDI line is latched in on the falling edge of the
serial clock while 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 10 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 10 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.
Temperature ( C)
–128
–125
–100
–75
–50
–25
–0.25
0
0.25
10
25
50
75
100
125
127
Table I. Temperature Data Format
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
AD7314