ADT7301

Rev. B | Page 9 of 16

THEORY OF OPERATION

bit that acts as a sign bit. The part houses an on-chip temperature

sensor, a 13-bit A/D converter, a reference circuit, and serial

interface logic functions in SOT-23 and MSOP packages. The

ADC section consists of a conventional successive approximation

converter based around a capacitor DAC. The parts run on a

2.7 V to 5.25 V power supply.

The on-chip temperature sensor allows an accurate measure-

ment of the ambient device temperature to be made. The

specified measurement range of the ADT7301 is −40°C to

+150°C. Greater than 125°C, the ADT7301 is limited to 5%

of its 55°C operational lifetime. The structural integrity of the

device may start to deteriorate when continuously operated at

absolute maximum voltage and temperature specifications.

CONVERTER DETAILS

The conversion clock for the part is internally generated. No

external clock is required except when reading from and writing

to the serial port. In normal mode, an internal clock oscillator

runs an automatic conversion sequence. During this automatic

conversion sequence, a conversion is initiated every 1.5 second.

At this time, the part powers up its analog circuitry and performs

a temperature conversion. This temperature conversion typically

takes 1.2 ms, after which the analog circuitry of the part auto-

matically shuts down. The analog circuitry powers up again when

the 1.5 second timer times out and the next conversion begins.

Since the serial interface circuitry never shuts down, the result

of the most recent temperature conversion is always available in

the serial output register.

The ADT7301 can be placed into shutdown mode via the control

register. This means that the on-chip oscillator is shut down and

no further conversions are initiated until the ADT7301 is taken

out of shutdown mode. The ADT7301 can be taken out of

shutdown mode by writing all 0s into the control register. The

conversion result from the last conversion prior to shutdown

can still be read from the ADT7301 even when it is in shutdown

mode.

In normal conversion mode, the internal clock oscillator is reset

after every read or write operation. This causes the device to start

a temperature conversion, the result of which is typically available

1.2 ms later. Similarly, when the part is taken out of shutdown

mode, the internal clock oscillator is started and a conversion is

initiated. The conversion result is available 1.2 ms later. Every

result is stored in a buffer register and is loaded into the

temperature value register only at the first falling SCLK edge of

every serial port activity. Serial port activity does not interfere

with conversion processes, and every conversion is completed,

even during a read operation. A conversion has to be completed

before a read occurs, otherwise its result is not loaded into the

temperature value register and instead is loaded into the buffer

register. A new conversion is triggered at the end of each serial

port activity, except when a conversion is already in progress.