ADT7301

Preliminary Technical Data

Rev. PrJ | Page 8 of 14

CIRCUIT INFORMATION

The ADT7301 is a 13-bit digital temperature sensor with a 14

th

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

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

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

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 measure-

ment of the ambient device temperature to be made. The

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

+150°C. At +150°C, the ADT7301 is limited to 5% of its +55°C

operational lifetime. The structural integrity of the device starts

to deteriorate when operated at voltage and temperature

maximum 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

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

performs a temperature conversion. This temperature

conversion typically takes 800 µs, after which time the analog

circuitry of the part automatically shuts down. The analog

circuitry powers up again when the 1 second timer times out

and the next conversion begins. The result of the most recent

temperature conversion is always available in the serial output

register because the serial interface circuitry never shuts down.

The ADT7301 can be placed in a shutdown mode via the con-

trol register, in which case 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 zeros into the control register.

The conversion result from the last conversion prior to shut-

down 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 800 µs 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 800 µs

later, typically. Reading from the device before a conversion is

complete causes the ADT7301 to stop converting; the part starts

again when serial communication is finished. This read

operation provides the previous result.

TEMPERATURE VALUE REGISTER

The temperature value register is a 14-bit read-only register that

stores the temperature reading from the ADC in 13-bit twos

complement format plus a sign bit. The MSB (DB13) is the sign

bit. The ADC can theoretically measure a 255°C temperature

span. The internal temperature sensor is guaranteed to a low

value limit of –40°C and a high limit of +150°C. The

temperature data format is shown in Table 5, which shows the

temperature measurement range of the device (–40°C to

+150°C). A typical performance curve is shown in Figure 6.

Table 5. Temperature Data Format

Temperature

Digital Output DB13…DB0

−40°C

11, 1011 0000 0000

−30°C

11, 1100 0100 0000

−25°C

11, 1100 1110 0000

−10°C

11, 1110 1100 0000

−0.03125°C

11, 1111 1111 1111

0°C

00, 0000 0000 0000

+0.03125°C

00, 0000 0000 0001

+10°C

00, 0001 0100 0000

+25°C

00, 0011 0010 0000

+50°C

00, 0110 0100 0000

+75°C

00, 1001 0110 0000

+100°C

00, 1100 1000 0000

+125°C

00, 1111 1010 0000

+150°C

01, 0010 1100 0000

Temperature Conversion Formula

1.

Positive Temperature = ADC Code(d)/32

2.

*Using all 14 bits of the data byte, includes the sign bit.

*DB13 (sign bit) is removed from the ADC code

–40°C

–0.03125 °C

–30°C

11, 1111, 1111, 1111

11, 1100, 0100, 0000

11, 1011, 0000, 0000

TEMPERATURE (°C)

75°C

150°C

01, 0010, 1100, 0000

00, 1001, 0110, 0000

00, 0000, 0000, 0001

Figure 12. Temperature to Digital Transfer Function