TC622/TC624
3.2
Hysteresis
3.0
3.1
DETAILED DESCRIPTION
Trip Point Programming
To prevent output “chattering” at the trip point tempera-
ture, the temperature detector in the TC622/TC624 has
2°C hysteresis (see Figure 3-2). The outputs are driven
active when the temperature crosses the set point
determined by the external resistor. As temperature
declines below the set point, the hysteresis action will
hold the outputs true until the temperature drops 2°C
below the threshold.
When the temperature of the device exceeds the pro-
grammed temperature trip point, T , the OUT and
OUT outputs are driven into their active states. The
desired trip point temperature is programmed with a
single external resistor connected between the T
SET
SET
input and V . The relationship between the resistor
CC
value and the trip point temperature is given by
Equation 3-1.
FIGURE 3-2:
TC622/TC624
HYSTERESIS
EQUATION 3-1:
Temperature
2.1312
R
= 0.5997 x T
TRIP
Set Point
(Set Point – 2 Degrees C)
Where:
R
= Programming resistor value in Ohms
TRIP
T = Desired trip temperature in degrees Kelvin.
OUT
For example, as shown in Figure 3-1, to program the
device to trip at 50°C, the programming resistor is:
OUT
2.1312
R
= 0.5997 x ((50 + 273.15)
) = 133.65kΩ
TRIP
FIGURE 3-1:
PROGRAMMING
RESISTOR VALUES VS.
TEMPERATURE
250
200
150
100
50
-55
-35
-15
5
25
45
65
85
105
125
TEMPERATURE (˚C)
2002 Microchip Technology Inc.
DS21440B-page 5
MICROCHIP [ MICROCHIP ]
