AN773

M
AN773
Application Circuits of the TC620/TC621Solid-State
Temperature Sensors
Author:
thermistor to sense a remote temperature. Internal
heating will not affect the temperature sensing
accuracy.
Microchip Technology Inc.
INTRODUCTION
Figure 2 is a schematic of a heating and cooling controller using a single TC620 and a TC4469 Quad
CMOS driver. In this example, the TC620 is programmed for maximum and minimum temperature set
points with a hysteresis of 5°.
The TC620/TC621are solid-state temperature sensors
that are easy to program and interface with control
equipment. The TC620 senses the temperature internally, while the TC621 uses an external thermistor.
Figure 1 shows how the devices are connected.
INPUT SECTION
The TC620/TC621 data sheet (DS21439) describes
how to calculate the correct resistance value for any
desired temperature. It also gives a graphical depiction
of the outputs for varying temperatures.
Typically, a heating/cooling thermostat has a wide
enough temperature range to allow heating and cooling
from 45°F to 85°F (7°C to 29°C). The calculations that
follow show how this range was incorporated into the
design. The TC620 programming inputs have a resistance-to-temperature ratio of approximately 782Ω / °C.
Since the TC620 senses temperatures internally, its
outputs must be limited to 1 mA. The device can source
or sink higher currents, but internal self-heating may
cause errors in the temperature sensing. The TC621
can source or sink 10 mA, since it uses an external
8
1.2V
REF
High Set
TC620/TC621
t°
+
Thermistor 1
(TC621 Only)
Low Set
AMP
+
2
+
AMP
-
3
+
AMP
-
+
COMP
-
7
+
COMP
-
6
S R
Q
FIGURE 1:
Q
Latch
Gnd
Low Limit
High Limit
“C” (Standard) Denotes Cooling Option
(True High Control Output)
5 Regulate
…
4
VCC
“H” (Option) Denotes Heating Option
(True Low Control Output)
TC620/TC621 Block Diagram.
 2003 Microchip Technology Inc.
DS00773B-page 1
AN773
12 VDC
+
10 µF
+
0.1 µF
Cool
14
2.2 kΩ
20 kΩ
TC4469
8
7
6
93.1 kΩ, 1% 2
1
2
13
3
4
12
2.2 kΩ
2.2 kΩ
Comfort
Zone
TC620-C
95.3 kΩ, 1% 3
Heat
5
4
5
6
11
8
9
10
7
Cooling Contactor
12 VDC Coil
Heat/Cool
FIGURE 2:
Heating Contactor
12 VDC Coil
Heating/Cooling Thermostat Controller.
To get the desired range, we need a potentiometer that
will provide a 22°C variation (29°C - 7°C = 22°C). Multiply this temperature range by the resistance versus
temperature ratio to get the needed resistance for the
potentiometer:
EQUATION
Plugging this value back into the resistance calculation
formula, we will verify that the maximum trip temperature is greater than the desired high end of the window:
EQUATION
T=
782 x 22 = 17.2 kΩ
A 20 kΩ potentiometer will meet this requirement. Now
each programming resistor can be calculated. For the
low end of the window, the minimum programming
resistor value should be:
EQUATION
RTRIP = 0.783 x T + 91...RTRIP = 96.5 kΩ
T = 7°C (45°C)
By adding the 20 kΩ potentiometer value to this, we
get:
EQUATION
96.5 kΩ + 20 kΩ = 116.5 kΩ total resistance
(RTRIP - 91)
0.783
T = 32°C (89.6°C)
The previously calculated resistance values will span
both ends of the desired heating and cooling window
(45°F to 85°F).
To program an acceptable hysteresis for the thermostat, the Low Set resistor must be lower in value than
the High Set resistor. A resistance versus temperature
ratio of 782Ω / °C for temperatures below 70°C will give
a good guideline for calculating the hysteresis. For a
hysteresis of 5°, the difference in resistance is:
EQUATION
RDIFF = 782 x 5...RDIFF = 391 kΩ
Subtracting the 3.91 kΩ from the 96.5 kΩ will give the
Low Set resistor value:
EQUATION
96.5 kΩ - 3.91 kΩ = 92.6 kΩ
DS00773B-page 2
 2003 Microchip Technology Inc.
AN773
two set points (our previously calculated 5° hysteresis),
this indicator will be lit. The third driver controls the
heating contactor. It is enabled when the Heat/Cool
selector switch is open and the Regulate output is low.
When the Heat/Cool selector switch is closed, the third
driver is disabled and the fourth driver will be enabled
to control the cooling contactor. This driver will turn on
the cooling contactor when the Regulate output is high.
The logic features of the TC4469 CMOS Driver are
used to prevent the heating and cooling contactors
from operating simultaneously.
Choosing standard 1% resistance values closest to the
calculated values gives:
EQUATION
RHIGH Set = 95.3 kΩ
RLOW Set = 93.1 kΩ
With the 20 kΩ potentiometer connected to both programming resistors, the Low Set resistor's 5° hysteresis will track the High Set resistor, as the potentiometer
is manually adjusted by the user for different
temperatures.
The TC620/TC621 will operate with any supply
between 4.5 VDC and 18 VDC. The TC4469 Quad
CMOS Driver can source 300 mA continuously. The
coils on the Heating and Cooling contactors must be of
the appropriate type and voltage rating for the circuit.
OUTPUT SECTION
The Low Limit and High Limit outputs will go high when
the device (or thermistor, TC621) reaches the programmed temperature for each corresponding input.
The Regulate output is a latch that goes high when
both programmed temperatures have been reached,
and goes low when the device temperature decreases
to below both set points. Figure 3 shows the outputs
with respect to input set points and temperature
changes.
24 VAC EQUIPMENT
Most heating and cooling equipment is designed to
operate with a 24 VAC secondary voltage. The schematic in Figure 4 is an example of a 24 VAC system
that drives 24 VAC relays and operates on an internally
self-generated 15 VDC. Because the TC620 and the
TC4469 are CMOS devices, their current requirements
are extremely low. Using triac switches to energize the
relays keeps the component costs to a minimum, while
reliability stays high.
The application in Figure 2 uses a TC4469 Quad
CMOS Driver. This device has four independent drivers, each with a logic AND gate as an input. The AND
gate has one non-inverting input and one inverting
input. The first driver is used to drive an LED indicator.
Depending on the position of the Heat/Cool selector
switch, either the Heat or Cool LED indicator will be lit.
The second driver is used to drive the “Comfort Zone”
LED indicator. When the temperature is between the
Regulate ON
“H” Option
This design requires only four wires from the thermostat to the main control for a heating/cooling system. An
additional fifth wire for a manual fan switch would make
it compatible with standard 5-wire residential and
commercial heating/cooling systems.
Regulate ON
“C” Option
Regulate ON
“H” Option
High Limit ON
High
Set Point
Low Limit ON
Low
Set Point
Temperature
FIGURE 3:
TC620/TC621 Input and Output Logic.
 2003 Microchip Technology Inc.
DS00773B-page 3
AN773
1N4001
750, 1/2W
+
0.1 µF
Cool
15V
14
20 kΩ
Heating
Contactor
Cooling
Contactor
120 VAC
+
220 µF
24 VAC
93.1 kΩ,
1%
2
95.3 kΩ,
1%
3
2.2 kΩ
13
7
6
3
4
12
5
5
6
11
8
9
10
8
TC620-C
TC4469
1
2
4
2.2 kΩ
Heat
2.2 kΩ
Comfort
Zone
2N6071B
7
2N6071B
3 kΩ
3 kΩ
FIGURE 4:
Heat/Cool
24 VAC Heating/Cooling Thermostat Controller.
SOLAR HEAT CONTROLLER
Figure 5 shows an external temperature sensor for a
pool solar heating panel pump control. The TC620
should be a part with the “H” option bonding. This
inverts the Regulate output logic. This is necessary
when using “NTC”-type thermistors because the internal logic is designed to function with a “PTC”-type thermistor. The external thermistor used in this design is an
NTC (negative temperature coefficient) thermistor. One
manufacturer is Keystone™ Carbon. Their part is
RL1006-53.4K-140-D1, which has a resistance of
100 kΩ at 25°C. Another vendor is Thermometrics®.
Their part is D200B104L. This thermistor assembly is
attached to the solar panel in a manner that will allow it
to sense heat generated by direct exposure to the sun.
EQUATION
RTRIP = 0.783 x T + 91
RTRIP Low = 111.9 kΩ ≈ 113 kΩ 1%
RTRIP High = 120.6 kΩ ≈ 121 kΩ 1%
As the sun heats the thermistor assembly, the pump will
turn on at 100°F and stay on until the thermistor assembly temperature decreases to 80°F. This ensures that
the solar panel has time to heat up before the pump is
energized, and that the pump will turn off before the
solar panel has cooled below the pool temperature.
The complete controller consists of nine low-cost
components.
This, then, energizes the pump when the sun is heating
the panels, and turns off the pump when the sky
becomes cloudy or the sun goes down. To prevent
rapid cycling of the controller during partly-cloudy
skies, the hysteresis is set for a wide (20°F) span.
The thermal time constant of the solar panel will also
aid in the prevention of rapid pump cycling, if the thermal resistance between the thermistor assembly and
the solar panel itself is low. The Low Set temperature is
set for 26.7°C (80°F) and the High Set temperature is
set for 37.8°C (100°F). The resistor values are
calculated:
DS00773B-page 4
 2003 Microchip Technology Inc.
AN773
Pump Relay
240 VAC
100k
@ 25°C
+
T
+
220 µF
Time
Clock
NTC
Pump
Motor
8
1
120 VAC
9 VAC
-
113 kΩ, 1%
121 kΩ, 1%
2
7
TC621-H
3
6
5
MTP3055E
240 VAC
4
FIGURE 5:
Pool Solar Heat Control.
SUMMARY
The TC620 and TC621 are programmable logic output
temperature sensors. These sensors feature dual thermal interrupt outputs (high limit and low limit) which can
be programmed with a single external resistor. The
TC620 and TC621 can be used to provide simple on/off
control for a wide range of applications, such as a
cooling fan or heater.
 2003 Microchip Technology Inc.
DS00773B-page 5
AN773
NOTES:
DS00773B-page 6
 2003 Microchip Technology Inc.
Note the following details of the code protection feature on Microchip devices:
•
Microchip products meet the specification contained in their particular Microchip Data Sheet.
•
Microchip believes that its family of products is one of the most secure families of its kind on the market today, when used in the
intended manner and under normal conditions.
•
There are dishonest and possibly illegal methods used to breach the code protection feature. All of these methods, to our
knowledge, require using the Microchip products in a manner outside the operating specifications contained in Microchip's Data
Sheets. Most likely, the person doing so is engaged in theft of intellectual property.
•
Microchip is willing to work with the customer who is concerned about the integrity of their code.
•
Neither Microchip nor any other semiconductor manufacturer can guarantee the security of their code. Code protection does not
mean that we are guaranteeing the product as “unbreakable.”
Code protection is constantly evolving. We at Microchip are committed to continuously improving the code protection features of our
products. Attempts to break microchip’s code protection feature may be a violation of the Digital Millennium Copyright Act. If such
acts allow unauthorized access to your software or other copyrighted work, you may have a right to sue for relief under that Act.
Information contained in this publication regarding device
applications and the like is intended through suggestion only
and may be superseded by updates. It is your responsibility to
ensure that your application meets with your specifications. No
representation or warranty is given and no liability is assumed
by Microchip Technology Incorporated with respect to the
accuracy or use of such information, or infringement of patents
or other intellectual property rights arising from such use or
otherwise. Use of Microchip’s products as critical components in
life support systems is not authorized except with express
written approval by Microchip. No licenses are conveyed,
implicitly or otherwise, under any intellectual property rights.
Trademarks
The Microchip name and logo, the Microchip logo, KEELOQ,
MPLAB, PIC, PICmicro, PICSTART, PRO MATE and
PowerSmart are registered trademarks of Microchip Technology
Incorporated in the U.S.A. and other countries.
FilterLab, microID, MXDEV, MXLAB, PICMASTER, SEEVAL
and The Embedded Control Solutions Company are registered
trademarks of Microchip Technology Incorporated in the U.S.A.
Accuron, dsPIC, dsPICDEM.net, ECONOMONITOR,
FanSense, FlexROM, fuzzyLAB, In-Circuit Serial Programming,
ICSP, ICEPIC, microPort, Migratable Memory, MPASM, MPLIB,
MPLINK, MPSIM, PICC, PICkit, PICDEM, PICDEM.net,
PowerCal, PowerInfo, PowerTool, rfPIC, Select Mode,
SmartSensor, SmartShunt, SmartTel and Total Endurance are
trademarks of Microchip Technology Incorporated in the U.S.A.
and other countries.
Serialized Quick Turn Programming (SQTP) is a service mark of
Microchip Technology Incorporated in the U.S.A.
All other trademarks mentioned herein are property of their
respective companies.
© 2003, Microchip Technology Incorporated, Printed in the
U.S.A., All Rights Reserved.
Printed on recycled paper.
Microchip received QS-9000 quality system
certification for its worldwide headquarters,
design and wafer fabrication facilities in
Chandler and Tempe, Arizona in July 1999
and Mountain View, California in March 2002.
The Company’s quality system processes and
procedures are QS-9000 compliant for its
PICmicro ® 8-bit MCUs, KEELOQ® code hopping
devices, Serial EEPROMs, microperipherals,
non-volatile memory and analog products. In
addition, Microchip’s quality system for the
design and manufacture of development
systems is ISO 9001 certified.
 2003 Microchip Technology Inc.
DS00773B - page 7
M
WORLDWIDE SALES AND SERVICE
AMERICAS
ASIA/PACIFIC
Corporate Office
Australia
2355 West Chandler Blvd.
Chandler, AZ 85224-6199
Tel: 480-792-7200 Fax: 480-792-7277
Technical Support: 480-792-7627
Web Address: http://www.microchip.com
Microchip Technology Australia Pty Ltd
Suite 22, 41 Rawson Street
Epping 2121, NSW
Australia
Tel: 61-2-9868-6733 Fax: 61-2-9868-6755
Rocky Mountain
China - Beijing
2355 West Chandler Blvd.
Chandler, AZ 85224-6199
Tel: 480-792-7966 Fax: 480-792-4338
Atlanta
3780 Mansell Road, Suite 130
Alpharetta, GA 30022
Tel: 770-640-0034 Fax: 770-640-0307
Boston
2 Lan Drive, Suite 120
Westford, MA 01886
Tel: 978-692-3848 Fax: 978-692-3821
Chicago
333 Pierce Road, Suite 180
Itasca, IL 60143
Tel: 630-285-0071 Fax: 630-285-0075
Dallas
4570 Westgrove Drive, Suite 160
Addison, TX 75001
Tel: 972-818-7423 Fax: 972-818-2924
Detroit
Tri-Atria Office Building
32255 Northwestern Highway, Suite 190
Farmington Hills, MI 48334
Tel: 248-538-2250 Fax: 248-538-2260
Kokomo
2767 S. Albright Road
Kokomo, Indiana 46902
Tel: 765-864-8360 Fax: 765-864-8387
Los Angeles
18201 Von Karman, Suite 1090
Irvine, CA 92612
Tel: 949-263-1888 Fax: 949-263-1338
San Jose
Microchip Technology Inc.
2107 North First Street, Suite 590
San Jose, CA 95131
Tel: 408-436-7950 Fax: 408-436-7955
Toronto
6285 Northam Drive, Suite 108
Mississauga, Ontario L4V 1X5, Canada
Tel: 905-673-0699 Fax: 905-673-6509
Microchip Technology Consulting (Shanghai)
Co., Ltd., Beijing Liaison Office
Unit 915
Bei Hai Wan Tai Bldg.
No. 6 Chaoyangmen Beidajie
Beijing, 100027, No. China
Tel: 86-10-85282100 Fax: 86-10-85282104
China - Chengdu
Microchip Technology Consulting (Shanghai)
Co., Ltd., Chengdu Liaison Office
Rm. 2401-2402, 24th Floor,
Ming Xing Financial Tower
No. 88 TIDU Street
Chengdu 610016, China
Tel: 86-28-86766200 Fax: 86-28-86766599
China - Fuzhou
Microchip Technology Consulting (Shanghai)
Co., Ltd., Fuzhou Liaison Office
Unit 28F, World Trade Plaza
No. 71 Wusi Road
Fuzhou 350001, China
Tel: 86-591-7503506 Fax: 86-591-7503521
China - Hong Kong SAR
Microchip Technology Hongkong Ltd.
Unit 901-6, Tower 2, Metroplaza
223 Hing Fong Road
Kwai Fong, N.T., Hong Kong
Tel: 852-2401-1200 Fax: 852-2401-3431
China - Shanghai
Microchip Technology Consulting (Shanghai)
Co., Ltd.
Room 701, Bldg. B
Far East International Plaza
No. 317 Xian Xia Road
Shanghai, 200051
Tel: 86-21-6275-5700 Fax: 86-21-6275-5060
China - Shenzhen
Microchip Technology Consulting (Shanghai)
Co., Ltd., Shenzhen Liaison Office
Rm. 1812, 18/F, Building A, United Plaza
No. 5022 Binhe Road, Futian District
Shenzhen 518033, China
Tel: 86-755-82901380 Fax: 86-755-82966626
China - Qingdao
Rm. B503, Fullhope Plaza,
No. 12 Hong Kong Central Rd.
Qingdao 266071, China
Tel: 86-532-5027355 Fax: 86-532-5027205
India
Microchip Technology Inc.
India Liaison Office
Divyasree Chambers
1 Floor, Wing A (A3/A4)
No. 11, O’Shaugnessey Road
Bangalore, 560 025, India
Tel: 91-80-2290061 Fax: 91-80-2290062
Japan
Microchip Technology Japan K.K.
Benex S-1 6F
3-18-20, Shinyokohama
Kohoku-Ku, Yokohama-shi
Kanagawa, 222-0033, Japan
Tel: 81-45-471- 6166 Fax: 81-45-471-6122
Korea
Microchip Technology Korea
168-1, Youngbo Bldg. 3 Floor
Samsung-Dong, Kangnam-Ku
Seoul, Korea 135-882
Tel: 82-2-554-7200 Fax: 82-2-558-5934
Singapore
Microchip Technology Singapore Pte Ltd.
200 Middle Road
#07-02 Prime Centre
Singapore, 188980
Tel: 65-6334-8870 Fax: 65-6334-8850
Taiwan
Microchip Technology (Barbados) Inc.,
Taiwan Branch
11F-3, No. 207
Tung Hua North Road
Taipei, 105, Taiwan
Tel: 886-2-2717-7175 Fax: 886-2-2545-0139
EUROPE
Austria
Microchip Technology Austria GmbH
Durisolstrasse 2
A-4600 Wels
Austria
Tel: 43-7242-2244-399
Fax: 43-7242-2244-393
Denmark
Microchip Technology Nordic ApS
Regus Business Centre
Lautrup hoj 1-3
Ballerup DK-2750 Denmark
Tel: 45 4420 9895 Fax: 45 4420 9910
France
Microchip Technology SARL
Parc d’Activite du Moulin de Massy
43 Rue du Saule Trapu
Batiment A - ler Etage
91300 Massy, France
Tel: 33-1-69-53-63-20 Fax: 33-1-69-30-90-79
Germany
Microchip Technology GmbH
Steinheilstrasse 10
D-85737 Ismaning, Germany
Tel: 49-89-627-144 0 Fax: 49-89-627-144-44
Italy
Microchip Technology SRL
Centro Direzionale Colleoni
Palazzo Taurus 1 V. Le Colleoni 1
20041 Agrate Brianza
Milan, Italy
Tel: 39-039-65791-1 Fax: 39-039-6899883
United Kingdom
Microchip Ltd.
505 Eskdale Road
Winnersh Triangle
Wokingham
Berkshire, England RG41 5TU
Tel: 44 118 921 5869 Fax: 44-118 921-5820
12/05/02
DS00773B-page 8
 2003 Microchip Technology Inc.
Similar pages