ADT75BRMZ-REEL7(RevB) 데이터 시트보기 (PDF) - Analog Devices

부품명

상세내역

제조사

ADT75BRMZ-REEL7
(Rev.:RevB)

±1°C Accurate, 12-Bit Digital Temperature Sensor

Analog Devices 

Data Sheet

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. Thus, the time required for the ADT75 to

settle to the desired accuracy is dependent on the package

selected, the thermal contact established in that particular

application, and the equivalent power of the heat source. In most

applications, it is best to determine empirically the settling time.

SELF-HEATING EFFECTS

The temperature measurement accuracy of the ADT75 may be

degraded in some applications due to self-heating. Errors can be

introduced from the quiescent dissipation and power dissipated

when converting. The magnitude of these temperature errors is

dependent on the thermal conductivity of the ADT75 package,

the mounting technique, and the effects of airflow. At 25°C, static

dissipation in the ADT75 is typically 798.6 µW operating at 3.3 V.

In the 8-lead MSOP package mounted in free air, this accounts

for a temperature increase due to self-heating of

ΔT = PDISS × θJA = 798.6 µW × 205.9°C/W = 0.16°C

It is recommended that current dissipated through the device be

kept to a minimum, because it has a proportional effect on the

temperature error.

Using the power-down mode can reduce the current dissipated

through the ADT75 subsequently reducing the self-heating effect.

When the ADT75 is in power-down mode and operating at 25°C,

static dissipation in the ADT75 is typically 78.6 µW with VDD =

3.3 V and the power-up/conversion rate is 1 SPS (sample per

second). In the 8-lead MSOP package mounted in free air, this

accounts for a temperature increase due to self-heating of

ΔT = PDISS × θJA = 78.6 µW × 205.9°C/W = 0.016°C

ADT75

SUPPLY DECOUPLING

Decouple the ADT75 with a 0.1 µF ceramic capacitor between

VDD and GND. This is particularly important when the ADT75

is mounted remotely from the power supply. Precision analog

products, such as the ADT75, require a well-filtered power

source. Because the ADT75 operates from a single supply, it

may seem convenient to tap into the digital logic power supply.

However, 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 mV in amplitude

due to wiring resistance and inductance.

If possible, power the ADT75 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. Place this

decoupling capacitor as close as possible to the ADT75 VDD pin.

TTL/CMOS

LOGIC

CIRCUITS

0.1µF ADT75

POWER

SUPPLY

Figure 22. Use Separate Traces to Reduce Power Supply Noise

Rev. B | Page 21 of 24

Share Link: