ADT6501ARJP045 AD [Analog Devices], ADT6501ARJP045 Datasheet - Page 10

• Manufacturer Part Number: ADT6501ARJP045
• Description: Low Cost, 2.7 V to 5.5 V, Micropower Temperature Switches in SOT-23
• Manufacturer: AD [Analog Devices]

ADT6501/ADT6502/ADT6503/ADT6504
APPLICATION 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 ADT6501/ADT6502/ADT6503/ADT6504 to
settle to the desired accuracy is dependent on the characteristics
of the SOT-23 package, the thermal contact established in that
particular application, and the equivalent power of the heat
source. In most applications, the settling time is probably best
determined empirically.
SELF-HEATING EFFECTS
The temperature measurement accuracy of the
ADT6501/ADT6502/ADT6503/ADT6504 can 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 ADT650x
package, the mounting technique, and the effects of airflow. At
25°C, static dissipation in the ADT650x is typically TBD μW
operating at 3.3 V. In the 5-lead SOT-23 package mounted in
free air, this accounts for a temperature increase due to self-
heating of
It is recommended that current dissipated through the device be
kept to a minimum, because it has a proportional effect on the
temperature error.
ΔT = P
DISS
× θ
JA
= TBD μW × 240°C/W = TBD°C
Rev. PrA | Page 10 of 16
SUPPLY DECOUPLING
The ADT6501/ADT6502/ADT6503/ADT6504 should be
decoupled with a 0.1 μF ceramic capacitor between V
GND. This is particularly important when the ADT650x are
mounted remotely from the power supply. Precision analog
products, such as the ADT650x, require a well-filtered power
source. Because the ADT650x operate from a single supply, it
might 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 mV
in amplitude due to wiring resistance and inductance.
If possible, the ADT650x should be powered directly from the
system power supply. This arrangement, shown in Figure 19,
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
advisable for the temperature accuracy specifications to be
achieved. This decoupling capacitor must be placed as close as
possible to the ADT650x V
TTL/CMOS
CIRCUITS
LOGIC
Figure 19. Use Separate Traces to Reduce Power Supply Noise
POWER
SUPPLY
Preliminary Technical Data
CC
pin.
0.1 µ F
ADT650x
DD
and