ADT7320

Data Sheet

Rev. 0 | Page 22 of 24

APPLICATIONS INFORMATION

THERMAL RESPONSE TIME

POWERING FROM A SWITCHING REGULATOR

Thermal response is a function of the thermal mass of the

temperature sensor, but it is also heavily influenced by the

mass of the object that the IC is mounted to. For example, a large

PCB containing large amounts of copper tracing can act as a

large heat sink and slow the thermal response. For a faster thermal

response, it is recommended that the sensor be mounted on a

PCB that is as small as possible.

Precision analog devices such as the ADT7320 require a well-

filtered power source. If the ADT7320 is powered from a switching

regulator, noise may be generated above 50 kHz that may affect

the temperature accuracy specifications. To prevent this, an RC

filter should be used between the power supply and ADT7320

considered to ensure that the peak value of the supply noise is

less than 1 mV. The RC filter should be mounted as far away as

possible from the ADT7320 to ensure that the thermal mass is

kept as low as possible.

Figure 10 shows the typical response time of less than 2 seconds to

reach 63.2% of the temperature span of the DUT. The temperature

values are the digital bytes read back through the digital interface.

The response time includes all delays incurred on chip during

signal processing.

TEMPERATURE MEASUREMENT

The ADT7320 accurately measures and converts the temperature

at the surface of its own semiconductor chip. Thermal paths run

through the leads, the exposed pad, as well as the plastic package.

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 because this

impedance affects the accuracy and thermal response of the

measurement.

SUPPLY DECOUPLING

The ADT7320 must have a decoupling capacitor connected

readings will be obtained. A 0.1 μF decoupling capacitor, such

as a high frequency ceramic type, must be used and mounted as

If possible, the ADT7320 should be powered directly from the

system power supply. This arrangement, shown in Figure 21,

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.

For air or surface temperature measurements, take care to isolate

the package, leads, and exposed pad from ambient air temperature.

Use of a thermally conductive adhesive can help to achieve a

more accurate surface temperature measurement.

QUICK GUIDE TO MEASURING TEMPERATURE

The following is a quick guide for measuring temperature in

continuous conversion mode (default power-up mode). Execute

each step sequentially.

0.1µF

ADT7320

TTL/CMOS

LOGIC

CIRCUITS

POWER

SUPPLY

1.

After power-up, reset the serial interface (load 32

consecutive 1s on DIN). This ensures all internal circuitry

is properly initialized.

2.

Verify the setup by reading the device ID

(Register Address 0x03). It should read 0xC3.

3.

After consistent consecutive readings are obtained from

Step 2, read the configuration register (Register Address 0x01),

with the specified defaults in Table 6. If all the readings

match, the interface is operational.

Figure 21. Use of Separate Traces to Reduce Power Supply Noise

4.

Write to the configuration register to set the ADT7320 to

the desired configuration. Read the temperature value register.

It should produce a valid temperature measurement.