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ASTEC Semiconductor
AS273
Over-Temperature Detector
Features
¥
Programmable to three different
over-temperature thresholds
¥
2.5 V temperature compensated
bandgap reference trimmed to 1%
¥
Open collector output goes low
on over-temp condition
¥
±3¡C temperature accuracy
¥
Reference shunt current serves to
program over-temp threshold
¥
Available with 5¡C or 10¡C of
temperature hysteresis
¥
Available in a wide range of over-
temp thresholds to fit most
temperature monitoring
applications
¥
Now available in the SOT-223 for
improved substrate temperature
sensing
Description
The AS273 is a series of programmable over-temperature
detectors. Each is internally composed of a precision 2.5 V
shunt reference, a proportional-to-absolute temperature
thermal sensor, a comparator with controlled hysteresis, and
an open collector output that indicates an over-temp condi-
tion. The threshold for the over-temp signal can be set to any
of three values on a given part by controlling the magnitude
of the reference shunt current.
The AS273 has an excellent absolute temperature accuracy
of ±3¡C for each of the three over-temp thresholds. The low
power dissipation minimizes any temperature sensing errors
due to self-heating. There is either 5¡C or 10¡C of tempera-
ture hysteresis to prevent bouncing when an over-temp con-
dition is removed.
The packaging options available with the AS273 make it
appealing to a wide variety of temperature-sensing applica-
tions. The TO-92 package can be mechanically clamped to a
heat sink to monitor the temperature of power devices. The
8L-SOIC and SOT-223 surface mount packages allow for
temperature sensing in high component density applications.
SEMICONDUCTOR
Pin Configuration Ñ Top view
OUT
TO-92 (LP) SOT-223 (G)
GROUND
VREF
OUT
GROUND
VREF
SOIC (D)
VREF
DO NOT USE
DO NOT USE
GROUND
OUT
N/C
N/C
N/C
1
2
3
4
8
7
6
5
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ASTEC Semiconductor
AS273 Over-Temperature Detector
Ordering Information
Functional Block Diagram
Pin Function Description
Pin Number Function Description
1 VREF 2.5 V shunt reference; current into VREF pin also programs
over-temperature trip point to one of three TOT values
2 GND Circuit ground and silicon substrate
3 OUT Open collector output. Output low when die temperature exceeds
programmed trip point
Circuit Type:
Over-Temperature Detector
Temperature Option:
(Refer to Table A)
Packaging Option:
A
B
T
13
Package Style:
D
G
LP
Hysteresis Option:
1
5
= Ammo Pack
= Bulk
= Tube
= Tape and Reel (13" Reel Dia)
= SOIC
= SOT-223
= TO-92
= 10°C
= 5°C
AS273 D 1 D A
Ð
+
CURRENT
PROGRAMMING
1
3
2
VREF
2.5 V
+
Ð
GND
OUT
4 mV/K
Table A – Temperature Options
Code TOT1 TOT2 TOT3
D 40 45 50
F 75 80 85
G 90 95 100
H 105 110 115
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ASTEC Semiconductor
AS273Over-Temperature Detector
Absolute Maximum Ratings
Parameter Symbol Rating Unit
Reference Current VREF ±10 mA
Output Current IOUT ±10 mA
Output Voltage VOUT 18 V
Continuous Power Dissipation at 25¡C
TO-92 PD775 mW
8-SOIC PD750 mW
SOT-223 PD1000 mW
Junction Temperature TJ150 ¡C
Storage Temperature TSTG Ð65 to 150 ¡C
Lead Temp, Soldering 10 Seconds TL300 ¡C
Stresses greater than those listed under ABSOLUTE MAXIMUM RATINGS may cause permanent damage to the device. This is a
stress rating only and functional operation of the device at these or any other conditions above those indicated in the operational sec-
tions of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect reliability.
Typical Thermal Resistances
Package θJA θJC Typical Derating
SOT-223 115¡C/W 8¡C/W 8.7 mW/¡C
TO-92 160¡C/W 80¡C/W 6.3 mW/¡C
8L SOIC 175¡C/W 45¡C/W 5.7 mW/¡C
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ASTEC Semiconductor
AS273 Over-Temperature Detector
Electrical Characteristics
Electrical Characteristics are guaranteed over the full junction temperature range (0 to 125¡C). Ambient temperature must be derated
based upon power dissipation and package thermal characteristics.
Parameter Symbol Test Condition Min. Typ. Max. Unit
Reference
Reference Voltage VREF IREF = 2 mA, TJ= 25¡C 2.500 2.525 2.550 V
Load Regulation VId 0.65 mA ≤IREF ≤5.5 mA 5 10 mV
Average Temperature Coefficient ∆VREG/∆T 0.65 mA ≤IREF ≤5.5 mA 75 ppm/¡C
Output
Saturation Voltage VOL IOUT = 4 mA; TJ> TOT 200 400 mV
Breakdown Voltage BV IOUT = 100 µA; TJ< TOT 18 30 V
Leakage Current IOH VOUT = 18 V; TJ< TOT 1 1000 nA
Over-Temp Sensing
Temperature Accuracy TOT(1) 0.7 mA ≤IREF ≤1.3 mA Ð3 +3 ¡C
TOT(2) 1.55 mA ≤IREF ≤2.6 mA Ð3 +3 ¡C
TOT(3) 3.0 mA ≤IREF ≤5.0 mA Ð3 +3 ¡C
Hysteresis HOT
Percentage Error in Nominal Hysteresis
Ð30 +30 %
+5V
IREF
OUTVREF
GND
AS273
RLOAD
2 kΩ
Test Circuit
Figure 1. Test Circuit for Output Hysteresis Curve
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ASTEC Semiconductor
AS273Over-Temperature Detector
Typical Performance Curves
Figure 2
Figure 4
Figure 3
Figure 5
0 25 50 75 100 125 150
300
275
250
225
200
175
150
125
100
Minimum Reference Current for Regulation
Junction Temperature, TJ (°C)
Turn-on Current, IREF (µA)
0 200 400 600 800 1000
3
2
1
0
Turn-on Characteristic of Reference
Reference Current, IREF (µA)
Reference Voltage, VREF (V)
0 25 50 75
Junction Temperature, TJ (°C)
100 125 150
2.55
2.54
2.53
2.52
2.51
2.50
Temperature Regulation of Reference
Reference Voltage, VREF (V)
0 25 50 75
Junction Temperature, TJ (°C)
100 125 150
10
9
8
7
6
5
4
3
2
1
0
Load Regulation of Reference Over-temperature
Load Regulation (mV)
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ASTEC Semiconductor
AS273 Over-Temperature Detector
Typical Performance Curves
Figure 6
Figure 8
Figure 7
0.001 0.01 0.1 1 10
900
800
700
600
500
400
300
200
100
Output Saturation Characteristic
Output Voltage, VOUT (mV)
125°C
100°C
75°C
50°C
25°C
0°C
Saturation Current, IOUT (mA)
88 90 92 94
Over-temperature Threshold (°C)
96 98 100 102
0
10
20
30
40
50
IREF = 1 mA IREF = 2 mA IREF = 4 mA
Typical Over-temperature Threshold Distribution – Option G
Distribution of Population (%)
0 2 4 6 8 10 12
120
100
80
60
40
20
0
8L SOIC
TO-92
SOT-223
Time (s)
Percent of Thermal Equilibrium (%)
Thermal Response by Package in a Stirred Oil Bath
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ASTEC Semiconductor
Theory of Operation
The AS273 is an over-temperature detector that
gives an over-temp signal when the device
junction temperature exceeds a programmed
over-temp threshold. Over-temp threshold pro-
gramming is accomplished by controlling the
magnitude of the reference shunt current.
Over-temperature Condition
Internal to the AS273 is a temperature sensor
which creates a voltage proportional to the
absolute temperature (PTAT) of the die. This
PTAT voltage is compared with a fraction of the
reference voltage corresponding to the over-
temperature threshold. When the PTAT voltage
exceeds the reference voltage, the comparator is
tripped and an over-temp signal is given to the
output. The output consists of an open collector
transistor that pulls low on an over-temp condi-
tion. Built into the comparator is temperature hys-
teresis, which keeps the over-temp signal until
the junction temperature has fallen 5¡C (or 10¡C)
below the over-temp threshold. Figure 9 shows
the output of the AS273 (with 10¡C of hysteresis)
over a range of junction temperature.
AS273Over-Temperature Detector
Figure 9. Temperature Characteristic of Output with 10¡C of Hysteresis
5
0
IREF = 4 mA
5
0
IREF = 2 mA
5
0
IREF = 1 mA
OT1 OT2 OT3OT1-5OT1-10
Output Voltage, V
Junction Temperature, TJ (°C)
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ASTEC Semiconductor
Current Programming
There are three different over-temp thresholds
for each AS273. The detector senses the amount
of current being shunted through the 2.5 V refer-
ence of pin 1 and programs an over-temp thresh-
old based on the magnitude of that current. Fig-
ure 10 illustrates the ranges of reference shunt
current, I
REF
, associated with each of the three
over-temp thresholds, OT1, OT2 and OT3.
AS273 Over-Temperature Detector
Figure 10. Reference Shunt Current Programming Ranges of Over-temperature Thresholds
OT3
OT2
OT1
0 1 2 3 4 5
Over-temperature Thresholds (°C)
Reference Shunt Current, IREF (mA)
Output Disabled
Transition Regions
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ASTEC Semiconductor
Typical Detector Applications
Over-Temperature Detector
The AS273 senses the ambient temperature and
turns on its open collector output to indicate an
over-temp condition. Each AS273 can be pro-
grammed to any one of its three over-temp
thresholds by forcing a different range of current
into the reference pin.
Dual Speed Fan Control
The diagram of Figure 12 shows an easy way to
implement smart fan control. When the tempera-
ture is below the over-temp trip point set by R1,
the detectorÕs open collector output is off. There-
fore, the fan speed is controlled by the ratio
between R2 and R3. When the temperature
exceeds the over-temp set point, the open col-
lector is turned on, and fan motor runs at its full
speed.
AS273Over-Temperature Detector
Figure 11.
Figure 12.
VCC
R2R1
VOUT
REF OUT
GND
AS273
+12 V
R1
9.1 kΩ
REF OUT
GND
AS273
R2
10 kΩ
R3
10 kΩ
Q1
M
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ASTEC Semiconductor
AS273 Over-Temperature Detector
Over-Temperature Protection with
Latch (Low Current)
The diagram of Figure 13 illustrates how a power
supply can be shut down with a simple two-
transistor latch. When the programmed over-
temp is reached, the open collector output of the
AS273 enables the latch and pulls V
CC
below the
under-voltage threshold of the AS3842, shutting
off the AS3842. The latch can be disabled only
with a power reset.
Over-Temperature Protection with
Hysteresis
In this over-temperature circuit, the hysteresis of
the AS273 is used to automatically restart the
power supply after the temperature drops below
the hysteresis temperature window. R1 supplies
the current to power the AS273 after the AS3842
and the power supply are shut down. R2 and
the external zener set the over-temperature trip
point.
Figure 13.
Figure 14.
VCC
ICC = 400 mA
MAX.
REF OUT
GND
AS273
COMP VREG
VFB VCC
SENSE OUT
RT/CT GND
AS3842
R1
1 k
R3
350 Ω
+
R2
350 Ω
V BULK
R1
REF OUT
GND
AS273
R2 COMP VREG
VFB VCC
SENSE OUT
RT/CT GND
AS3842
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ASTEC Semiconductor
AS273Over-Temperature Detector
Adjustable Hysteresis Temperature
Detector
The hysteresis of the AS273 can be increased by
reprogramming the device to a lower tempera-
ture set point upon over-temp. A higher tempera-
ture is set by R1. When the temperature exceeds
the high-temp set point, the open collector output
is turned on and allows R2 to rob current from the
reference pin and resets the AS273 to the low-
temp set point. As a result, the hysteresis esca-
lates by the difference between the high-temp
and the low-temp set points.
Three-State Temperature Sensor
In the Three-State Temperature Sensor shown in
Figure 16, a low-temp trip point is selected by R1
and a high-temp trip point is selected by the two-
transistor latch. When the temperature is below
the low-temp set point, V
OUT
is in the high state
(V
OUT
= 5.0 V). When the temperature exceeds
the low-temp set point, the two-transistor latch is
set and V
OUT
is pulled low (V
OUT
= 2.5 V). The
latch also supplies extra current to the reference
pin to reset the IC to sense a higher temperature.
Once the high-temp is reached, the output will
turn ÒonÓ (V
OUT
= 0.2 V). This circuit is highly use-
ful in applications where a stand-by, a warning
and a shut-down state are required.
Figure 15.
Figure 16.
VCC
R2
R1
VOUT
REF OUT
GND
AS273
VCC
+5 V
R1
2.4 kΩ
REF OUT
GND
AS273
R2
1 kΩR3
1.5 kΩ
R5
2 kΩ
R4
470 ΩR6
500 Ω
+
VO
C1
1 µF
Stand-by State:
Warning State:
Shut-down State:
T < T1, T2
T1 < T < T2
T1, T2 < T
VO = 5.0 V
VO = 2.5 V
VO = 0.2 V
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ASTEC Semiconductor
AS273 Over-Temperature Detector
Notes
