TC621XCPA データシートの表示（PDF） - TelCom Semiconductor, Inc
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TC621XCPA Datasheet PDF : 6 Pages
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5V, DUAL TRIP POINT
TEMPERATURE SENSORS
TC620
TC621
Using The TC621
The TC621 operation is identical to that of the TC620,
but requires an external NTC thermistor. Use the resistance
versus temperature curve of the thermistor to determine the
values of the programming resistors. Note that the pin
numbers for the HIGH SET and LOW SET programming
resistors for the TC621 are reversed versus that of the
TC620 (i.e. the resistor value on HIGH SET [pin 2] should
always be lower than the one connected to LOW SET [pin
3]). Also note that the outputs of the TC621 are LOW TRUE
when used with an NTC thermistor.
TC621 Thermistor Selection
The TC621 uses an external thermistor to monitor the
controlling temperature. A thermistor with a resistance value
of approximately 100kΩ at 25°C is recommended.
A temperature setpoint is selected by picking a resistor
whose value is equal to the resistance of the thermistor at the
desired temperature. For example, a 30kΩ resistor between
HIGH TEMP (pin 2) and VDD (pin 8) sets the high tempera-
ture trip point at +51°C and a 49kΩ resistor on LOW TEMP
(pin 3) sets the low temperature trip point to +41°C.
TC620/621 Outputs
Both devices have complimentary output stages. They
are rated at a source or sink current of 1mA maximum.
TYPICAL NTC THERMISTOR
350
APPLICATIONS
Dual Speed Temperature Control
The Dual Speed Temperature Control uses a TC620
and a TC4469 quad driver. Two of the drivers are configured
in a simple oscillator. When the temperature is below the
LOW TEMP set point, the output of the driver is OFF. When
the temperature exceeds the LOW TEMP set point, the
TC4469 gates the oscillator signal to the outputs of the
driver. This square wave signal modulates the remaining
outputs and drives the motor at a low speed. If this speed
cannot keep the temperature below the HIGH TEMP set
point, then the driver turns on continuously which increases
the fan speed to high. The TC620 will monitor the tempera-
ture and only allow the fan to operate when needed, and at
the required speed to maintain the desired temperature. A
higher power option can be designed by adding a resistor
and a power MOSFET.
Temperature Controlled Fan
In this application, a high and a low temperature is
selected by two ‘set’ resistors. The TC620 monitors the
ambient temperature and turns the FET switch on when the
temperature exceeds the HIGH TEMP set point. The fan
remains on until the temperature decreases to the LOW
TEMP set point. This provides the hysteresis. In this appli-
cation, the fan turns on only when required.
The TC621 uses an external thermistor to monitor the
ambient temperature. This adds one part, but allows more
flexibility in location of the sensor.
300
250
200
150
100
50
0
0
10
20
30
40
50
60
70
TEMPERATURE (°C)
Figure 4. Typical Thermistor Resistance vs. Temperature
2-18
TELCOM SEMICONDUCTOR, INC.
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