NCT22, NCT24
Low Cost Single Trip Point
Temperature Sensor
The NCT22 and NCT24 are programmable solid state temperature
sensors designed to replace mechanical switches in sensing and
control applications. Both devices integrate the temperature sensor
with a voltage reference and all required detector circuitry. The desired
temperature set point is set by the user with a single external resistor.
Ambient temperature is sensed and compared to the programmed
setpoint. The OUT and OUT outputs are driven to their active state
when the measured temperature exceeds the programmed setpoint.
The NCT22 has a power supply voltage range of 4.5 V to 18 V
while the NCT24 operates over a power supply range of 2.7 V to 4.5 V.
Both devices are useable over a temperature range of –40°C to
+125°C. Both devices feature low supply current making them
suitable for many portable applications.
The devices are offered in surface mount packages.
Features
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MARKING
DIAGRAM
8
8
1
xx
A
L
Y
W
SOIC–8
D SUFFIX
CASE 751
1
= 22 or 24
= Assembly Location
= Wafer Lot
= Year
= Work Week
NCTxx
ALYW
•
Temperature Set Point Easily Programs with a Single External
Resistor
•
Operates with 2.7 V Power Supply (NCT24)
•
Small SOIC Package
•
Cost Effective
Applications
PIN CONNECTIONS
N/C 1
OUT 2
OUT 3
GND
4
(Top View)
NCT22
NCT24
8 N/C
7 V
DD
6
N/C
5 T
SET
•
•
•
•
•
Power Supply Over–Temperature Detection
Consumer Electronics
Fire/Heat Detection
UPSs, Amplifiers, Motors
CPU Thermal Management in PCs
ORDERING INFORMATION
See detailed ordering and shipping information in the package
dimensions section on page 5 of this data sheet.
+9 V
+
9V
Battery
–
R
SET
1
Sensor
Sounder
NCT22
7
NC
V
DD
8
5
T
SET
NC
6
4
NC
OUT 3
2
CONTROL
ASIC
GND OUT
ALARM
Figure 1. Heat Monitor for Smoke Detector
©
Semiconductor Components Industries, LLC, 2002
1
June, 2002 – Rev. 1
Publication Order Number:
NCT22/D
NCT22, NCT24
MAXIMUM RATINGS*
Rating
Supply Voltage
NCT22
NCT24
Input Voltage (Any Input)
Operating Temperature Range
Maximum Junction Temperature
Storage Temperature Range
Lead Temperature (Soldering, 10 seconds)
Symbol
V
CC
20
5.5
–
–
–
Value
Unit
V
GND –0.3 to V
DD
+0.3
–40 to +125
+150
–65 to +150
+300
V
°C
°C
°C
°C
T
stg
–
*Stresses above those listed under “Absolute Maximum Ratings’’ may cause permanent damage to the device. These are stress ratings only
and functional operation of the device at these or any other conditions above those indicated in the operational sections of the specifications
is not implied. Exposure to Absolute Maximum Rating Conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(Over Operating Temperature Range, unless otherwise specified)
Characteristics
Supply Voltage
Range
Supply Current
V
OH
Device
NCT22
NCT24
NCT22
NCT24
NCT22
Test Conditions
–
5.0 V
v
V
DD
v
18 V
2.7 V
v
V
DD
v
4.5 V
5.0 V
v
V
DD
v
18 V
–40°C
v
T
A
v
+125°C
I
OH
= 250
µA
I
OH
= 500
µA
–40°C
v
T
A
v
+85°C
I
OL
= 500
µA
I
OL
= 1.0 mA
–40°C
v
T
A
v
+125°C
I
OL
= 1.0 mA
2.7 V
v
V
DD
v
4.5 V
–40°C
v
T
A
v
+125°C
I
OH
= 250
µA
I
OH
= 500
µA
–40°C
v
T
A
v
+85°C
I
OL
= 500
µA
I
OL
= 1.0 mA
–40°C
v
T
A
v
+125°C
I
OL
= 1.0 mA
T
SET
= Programmed Temperature
T
SET
= Programmed Temperature
–
Min
4.5
2.7
–
–
Typ
–
–
200
170
Max
18
4.5
600
300
Unit
V
µA
V
0.9 x V
DD
0.8 x V
DD
–
–
–
–
–
–
–
–
–
–
V
0.15 x V
DD
0.30 x V
DD
0.35 x V
DD
V
0.9 x V
DD
0.8 x V
DD
–
–
–
T–5
T–5
–
–
–
–
–
–
–
T"1
T"1
2.0
2.0
–
–
V
0.1 x V
DD
0.2 x V
DD
0.25 x V
DD
T+5
T+5
–
–
°C
°C
V
OL
NCT22
V
OH
NCT24
V
OL
NCT24
Absolute Accuracy
Trip Point Hysteresis
NCT22
NCT24
NCT22
NCT24
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NCT22, NCT24
DETAILED DESCRIPTION
Trip Point Programming
Hysteresis
The NCT22 and NCT24 are single point temperature
detectors ideal for use in a wide variety of applications.
When the temperature of the device exceeds the
programmed temperature trip point, T
SET
, 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
input and V
CC
. The
relationship between the resistor value and the trip point
temperature is given by the equation below.
RTRIP
+
0.5997
T2.1312
Where Rtrip
+
Programming resistor value in Ohms
T = Desired trip temperature in degrees Kelvin.
To prevent output “chattering’’ at the trip point
temperature, the temperature detector in the NCT22/24 has
2°C of hysteresis (see Figure 3).
The outputs are driven active when the temperature
crosses the setpoint determined by the external resistor. As
temperature declines below the setpoint, the hysteresis
action will hold the outputs true until the temperature drops
2°C below the threshold.
TEMPERATURE
SET POINT
(SET POINT–2°C)
OUT
For example, to program the device to trip at 50°C, the
programming resistor is:
RTRIP
+
0.5997
250
((50
)
273.15)2.1312)
+
133, 652
W
OUT
Figure 3. NCT22/24 Hysteresis
RESISTANCE (kΩ)
200
APPLICATIONS
Over–Temperature Shutdown
150
100
50
–55
–35
–15
5
25
45
65
85
105 125
TEMPERATURE (°C)
Figure 2. Programming Resistor Values
vs. Temperature
The NCT22 can be used to create a simple
over–temperature shutdown circuit. In this circuit,
temperature is sensed within the system enclosure (internal
system ambient), or at the heatsink itself. When measured
temperature exceeds a preset limit, a fault is indicated and
the system shuts down.
Figure 4 illustrates a simple over–temperature shutdown
circuit using the NCT22 sensor. As shown, the NCT22
outputs are driven active when the heatsink temperature
equals the trip point temperature set by R
SET
. When this
happens, the crowbar circuit is activated, causing the supply
output to fold back to zero. The NCT22 outputs remain
active until the heatsink temperature falls a minimum of 2°C
(built–in hysteresis) below the trip point temperature, at
which time the device again allows normal supply operation.
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NCT22, NCT24
V
CC
OUTPUT DEVICE
V
OUT
R
SET
NCT22
T
SET
V
DD
OVERTEMP
OUT
GND OUT
POWER
GOOD
SIGNAL
CROWBAR
CIRCUIT
HEATSINK SURFACE
Figure 4. NCT22 Power Supply Over–Temperature Shutdown
Cooling and Heating Applications
The NCT22/24 can be used to control a DC fan as shown
in Figure 5. The fan turns on when the sensed temperature
rises above T
SET
and remains on until the temperature falls
below T
SET
–2°C.
+2.7 to 4.5 V
+12 V
Figure 6 shows the NCT22 acting as a heater thermostat.
Circuit operation is identical to that of the cooling fan
application.
+4.5 to 18.0 V
+12 V
R
SET
1
5
6
4
NC
V
DD
7
8
3
N–CHANNEL
LOGIC
LEVEL
MOSFET
+
–
DC FAN
R
SET
1
5
6
4
NC
V
DD
7
8
HEATER
T
SET
NC
NCT24
NC
OUT
GND
OUT
NC
T
SET
NCT22
OUT
NC
GND
OUT
2
N–CHANNEL
LOGIC
LEVEL
MOSFET
TEMPERATURE
T
SET
TEMPERATURE
OUT
FAN “ON”
T
SET
T
SET
–2°C
T
SET
–2°C
OUT
HEATER “ON”
Figure 5. NCT24 As a Fan Controller for Notebook PCs
Figure 6. NCT22 As a Heater Thermostat
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4
NCT22, NCT24
ORDERING INFORMATION
Device
NCT22DR2
NCT24DR2
Voltage
Operation
4.5 V to 18 V
2.7 V to 4.5 V
Package
SOIC–8
SOIC–8
Ambient
Temperature
–40°C to +125°C
–40°C to +125°C
Shipping
2500 Units Tape and Reel
2500 Units Tape and Reel
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