ADT7320UCPZ AD [Analog Devices], ADT7320UCPZ Datasheet - Page 23

• Manufacturer Part Number: ADT7320UCPZ
• Manufacturer: AD [Analog Devices]

Preliminary Technical Data
APPLICATIONS INFORMATION
THERMAL RESPONSE TIME
The time required for a temperature sensor to settle to a specified
accuracy is a function of the thermal mass of the sensor and the
thermal conductivity between the sensor and the object being sensed.
Thermal mass is often considered equivalent to capacitance.
Thermal conductivity is commonly specified using the symbol,
Q, and can be thought of as thermal resistance. It is commonly
specified in units of degrees per watt of power transferred across
the thermal joint. The time required for the part to settle to the
desired accuracy is dependent on the thermal contact established
in that particular application and the equivalent power of the
heat source. In most applications, the settling time is best
determined empirically.
SUPPLY DECOUPLING
The ADT7320 should be decoupled with a 0.1 μF ceramic capacitor
between V
ADT7320 is mounted remotely from the power supply. Precision
analog products, such as the ADT7320, require a well-filtered
power source.
Because the ADT7320 operates from a single supply, it may
seem convenient to tap into the digital logic power supply.
Unfortunately, the logic supply is often a switch-mode design,
which generates noise in the 20 kHz to 1 MHz range. In addition,
fast logic gates can generate glitches hundreds of millivolts in
amplitude due to wiring resistance and inductance.
If possible, the ADT7320 should be powered directly from the
system power supply. This arrangement, shown in Figure 22,
isolates the analog section from the logic-switching transients.
Even if a separate power supply trace is not available, generous
supply bypassing reduces supply-line induced errors. Local supply
bypassing consisting of a 0.1 μF ceramic capacitor is critical for
the temperature accuracy specifications to be achieved. This
decoupling capacitor must be placed as close as possible to the
V
DD
TTL/CMOS
CIRCUITS
pin of the ADT7320.
LOGIC
Figure 22. Use of Separate Traces to Reduce Power Supply Noise
DD
and GND. This is particularly important when the
SUPPLY
POWER
0.1µF
ADT7320
Rev. PrA | Page 23 of 24
TEMPERATURE MONITORING
The ADT7320 is ideal for monitoring the thermal environment
within hazardous automotive applications. The die accurately reflects
the exact thermal conditions that affect nearby integrated circuits.
The ADT7320 measures and converts the temperature at the
surface of its own semiconductor chip. When the ADT7320 is
used to measure the temperature of a nearby heat source, the
thermal impedance between the heat source and the ADT7320
must be considered.
When the thermal impedance is determined, the temperature of
the heat source can be inferred from the ADT7320 output. As
much as 60% of the heat transferred from the heat source to the
thermal sensor on the ADT7320 die is discharged via the copper
tracks and the bond pads. Of the pads on the ADT7320, the
GND pad transfers most of the heat. Therefore, to measure the
temperature of a heat source, it is recommended that the thermal
resistance between the ADT7320 GND pad and the GND of the
heat source be reduced as much as possible.
ADT7320