ADT7302ARM AD [Analog Devices], ADT7302ARM Datasheet - Page 8

• Manufacturer Part Number: ADT7302ARM
• Manufacturer: AD [Analog Devices]

ADT7302
CIRCUIT INFORMATION
The ADT7302 is a 13-bit digital temperature sensor with a 14
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 ADT7302 is −40°C to
+125°C. 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 ADT7302 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 ADT7302 is
taken out of shutdown mode. The ADT7302 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 ADT7302 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 ADT7302 to stop converting; the part starts
again when serial communication is finished. This read
operation provides the previous result.
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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 +125°C. The
temperature data format is shown in Table 5, which shows the
temperature measurement range of the device (–40°C to
+125°C). A typical performance curve is shown in Figure 6.
Table 5. Temperature Data Format
Temperature
−40°C
−30°C
−25°C
−10°C
−0.03125°C
0°C
+0.03125°C
+10°C
+25°C
+50°C
+75°C
+100°C
+125°C
Temperature Conversion Formula
1.
2.
01, 0010, 1100, 0000
–40°C
00, 1001, 0110, 0000
00, 0000, 0000, 0001
Positive Temperature = ADC Code(d)/32
Negative Temperature = (ADC Code*(d)
Negative Temperature = (ADC Code(d)*
–30°C
–0.03125 °C
*Using all 14 bits of the data byte, includes the sign bit.
*DB13 (sign bit) is removed from the ADC code
Figure 12. Temperature to Digital Transfer Function
11, 1111, 1111, 1111
11, 1100, 0100, 0000
11, 1011, 0000, 0000
Preliminary Technical Data
Digital Output DB13…DB0
11, 1011 0000 0000
11, 1100 0100 0000
11, 1100 1110 0000
11, 1110 1100 0000
11, 1111 1111 1111
00, 0000 0000 0000
00, 0000 0000 0001
00, 0001 0100 0000
00, 0011 0010 0000
00, 0110 0100 0000
00, 1001 0110 0000
00, 1100 1000 0000
00, 1111 1010 0000
TEMPERATURE (°C)
75°C
–
–
16384)/32
8192)/32
125°C