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ADT7312

Data Sheet

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APPLICATIONS INFORMATION

THERMAL RESPONSE TIME

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 tracking 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.

SUPPLY DECOUPLING

The ADT7312 must have a decoupling capacitor connected

between VDD and GND; otherwise, incorrect temperature read-

ings are obtained. A 0.1 µF decoupling capacitor, such as a high

frequency ceramic type, must be used and mounted as close as

possible to the VDD pads of the ADT7312.

If possible, the ADT7312 should be powered directly from the

system power supply (see Figure 21). This arrangement 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.

0.1µF

ADT7312

TTL/CMOS

LOGIC

CIRCUITS

POWER

SUPPLY

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

POWERING FROM A SWITCHING REGULATOR

Precision analog devices such as the ADT7312 require a well-

filtered power source. If the ADT7312 is powered from a

switching regulator, noise can 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

the ADT7312 VDD pins. The value of the components used should

be carefully 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 ADT7312 to ensure that the thermal

mass is kept as low as possible.

TEMPERATURE MONITORING

The ADT7312 is ideal for monitoring the thermal environment

of high temperature automotive applications. The ADT7312

measures and converts the temperature at the surface of its own

semiconductor chip.

When the ADT7312 is used to measure the temperature of a

nearby heat source, the thermal impedance between the heat

source and the ADT7312 must be considered. When the thermal

impedance is determined, the temperature of the heat source

can be inferred from the ADT7312 output. Most of the heat

transferred from the heat source to the thermal sensor on the

ADT7312 die is routed via the copper traces, the bond pads,

and GND.

Therefore, to measure the temperature of a heat source, it is

recommended that the thermal resistance between the GND

pads of the ADT7312 and the GND of the heat source be

reduced as much as possible.

QUICK GUIDE TO MEASURING TEMPERATURE

To measure temperature in continuous conversion mode

(default power-on mode), follow these steps.

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

consecutive 1s on DIN). This step ensures that all

internal circuitry is correctly 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

the device ID register, read the following registers:

•

Configuration register (Register Address 0x01)

•

TCRIT setpoint register (Register Address 0x04)

•

THIGH setpoint register (Register Address 0x06)

•

TLOW setpoint register (Register Address 0x07)

4. Compare the values in these registers to the default values

listed in Table 7. If all the readings match Table 7, the

interface is operational.

5. Write to the configuration register (Register Address 0x01)

to set the ADT7312 to the desired configuration. Read the

temperature value register (Register Address 0x02). It

should produce a valid temperature measurement.

Rev. A

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