TC620CEPA datasheet(5/20 Pages) MICROCHIP

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DS20001439E-page 5

TC620/TC621

3.0

DETAILED DESCRIPTION

The TC620 has a positive temperature coefficient tem-

perature sensor and a dual threshold detector. Tem-

perature set point programming is accomplished with

external resistors from the HIGH SET and LOW SET

inputs to VDD. The HIGH LIMIT and LOW LIMIT outputs

remain low as long as measured temperature is below

set point values. As measured temperature increases,

the LOW LIMIT output is driven high when temperature

equals the LOW SET set point (±3°C max). If tempera-

ture continues to climb, the HIGH LIMIT output is driven

high when temperature equals the HIGH SET set point

(Figure 3-1). The CONTROL (hysteresis) output is

latched in its active state at the temperature specified

by the HIGH SET resistor. CONTROL is maintained

active until temperature falls to the value specified by

the LOW SET resistor.

FIGURE 3-1:

TC620/TC621 Input vs.

Output Logic.

3.1

Programming the TC620

The resistor values to achieve the desired trip point

temperatures on HIGH SET and LOW SET are

calculated using Equation 3-1:

EQUATION 3-1:

For example, a 50°C setting on either the HIGH SET

or LOW SET input is calculated using Equation 3-2 as

follows:

EQUATION 3-2:

Care must be taken to ensure the LOW SET program-

ming resistor is a smaller value than the HIGH SET

programming resistor. Failure to do this will result in

erroneous operation of the CONTROL output.

Care must also be taken to ensure the LOW SET

temperature setting is at least 5°C lower than the HIGH

SET temperature setting.

Figure 3-2 can help the user obtain an estimate of the

external resistor values required for the desired LOW

SET and HIGH SET trip points.

FIGURE 3-2:

TC620 Sense Resistors vs.

Trip Temperature.

3.2

Built-in Hysteresis

prevent

output

“chattering”

when

measured

temperature is at (or near) the programmed trip point

values, the LOW SET and HIGH SET inputs each have

built-in hysteresis of -2°C below the programmed

settings (Figure 3-3).

FIGURE 3-3:

Built-In Hysteresis on Low

Limit and High Limit Outputs.

As shown, the outputs remain in their active state

(hysteresis) until temperature falls an additional 2°C

below the user’s setting.

Low Set Point

High Set Point

Low Limit Output

High Limit Output

Control Output (Cool Option

Control Output (Heat Option)

Temperature

RTRIP = 0.5997 x T

2.1312

Where:

RTRIP = Programming resistor in Ohms

T = The desired trip point temperature in degrees

Kelvin.

RSET = 0.5997 x ((50 + 273.15)

2.1312) = 133.6 k



TEMPERATURE (°C)

-55

-35

-15

105

125

100

150

200

250

Set Point

(Set Point 2°C)

High Limit

or Low Limit

Output

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