NSC LM56 Dual output low power thermostat Datasheet

LM56
Dual Output Low Power Thermostat
General Description
Features
The LM56 is a precision low power thermostat. Two stable
temperature trip points (VT1 and VT2) are generated by
dividing down the LM56 1.250V bandgap voltage reference
using 3 external resistors. The LM56 has two digital outputs.
OUT1 goes LOW when the temperature exceeds T1 and
goes HIGH when the the temperature goes below
(T1–THYST). Similarly, OUT2 goes LOW when the temperature exceeds T2 and goes HIGH when the temperature goes
below (T2–THYST). THYST is an internally set 5˚C typical
hysteresis.
n
n
n
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Digital outputs support TTL logic levels
Internal temperature sensor
2 internal comparators with hysteresis
Internal voltage reference
Available in 8-pin SO and Mini-SO8 plastic packages
Key Specifications
The LM56 is available in an 8-lead Mini-SO8 surface mount
package and an 8-lead small outline package.
j Power Supply Voltage
2.7V–10V
j Power Supply Current
230 µA (max)
1.250V ± 1% (max)
j VREF
j Hysteresis Temperature
Applications
n
n
n
n
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n
n
n
5˚C
j Internal Temperature Sensor Output Voltage:
Microprocessor Thermal Management
Appliances
Portable Battery Powered 3.0V or 5V Systems
Fan Control
Industrial Process Control
HVAC Systems
Remote Temperature Sensing
Electronic System Protection
(+6.20 mV/˚C x T) + 395 mV
n Temperature Trip Point Accuracy:
+25˚C
+25˚C to +85˚C
−40˚C to +125˚C
LM56BIM
LM56CIM
± 2˚C (max)
± 2˚C (max)
± 3˚C (max)
± 3˚C (max)
± 3˚C (max)
± 4˚C (max)
Simplified Block Diagram and Connection Diagram
01289302
01289301
Order
Number
NS Package
Number
Transport
Media
Package
Marking
LM56BIM LM56BIMX LM56CIM LM56CIMX LM56BIMM LM56BIMMX LM56CIMM LM56CIMMX
M08A
M08A
M08A
M08A
MUA08A
MUA08A
MUA08A
MUA08A
SOP-8
SOP-8
SOP-8
SOP-8
MSOP-8
MSOP-8
MSOP-8
MSOP-8
1000 Units
3500 Units
1000 Units
3500 Units
2500 Units
2500 Units
Rail
Tape &
Reel
Rail
Tape &
Reel
LM56BIM
LM56BIM
LM56CIM
LM56CIM
© 2006 National Semiconductor Corporation
DS012893
Tape & Reel Tape & Reel Tape & Reel Tape & Reel
T02B
T02B
T02C
T02C
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LM56 Dual Output Low Power Thermostat
January 2006
LM56
Typical Application
01289303
VT1 = 1.250V x (R1)/(R1 + R2 + R3)
VT2 = 1.250V x (R1 + R2)/(R1 + R2 + R3)
where:
(R1 + R2 + R3) = 27 kΩ and
VT1 or T2 = [6.20 mV/˚C x T] + 395 mV therefore:
R1 = VT1/(1.25V) x 27 kΩ
R2 = (VT2/(1.25V) x 27 kΩ) − R1
R3 = 27 kΩ − R1 − R2
FIGURE 1. Microprocessor Thermal Management
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Input Voltage
Operating Ratings(Note 1)
12V
Input Current at any pin (Note 2)
Operating Temperature
Range
5 mA
Package Input Current(Note 2)
900 mW
ESD Susceptibility (Note 5)
Human Body Model - Pin 3 Only:
1000V
Machine Model
Positive Supply Voltage (V+)
+2.7V to +10V
Maximum VOUT1 and VOUT2
+10V
Soldering process must comply with National Semiconductor’s Reflow Temperature Profile specifications. Refer to
www.national.com/packaging.(Note 3)
800V
All other pins
TMIN ≤ TA ≤ TMAX
−40˚C ≤ TA ≤ +125˚C
LM56BIM, LM56CIM
20 mA
Package Dissipation at TA = 25˚C
(Note 4)
LM56
Absolute Maximum Ratings (Note 1)
125V
Storage Temperature
−65˚C to + 150˚C
LM56 Electrical Characteristics
The following specifications apply for V+ = 2.7 VDC, and VREF load current = 50 µA unless otherwise specified. Boldface limits
apply for TA = TJ = TMIN to TMAX; all other limits TA = TJ = 25˚C unless otherwise specified.
Symbol
Parameter
Conditions
Typical
LM56BIM
LM56CIM
Units
(Note 6)
Limits
Limits
(Limits)
(Note 7)
(Note 7)
±2
±2
±3
±3
±3
±4
3
3
˚C (min)
6
6
˚C (max)
Temperature Sensor
Trip Point Accuracy (Includes
VREF, Comparator Offset, and
+25˚C ≤ TA ≤ +85˚C
Temperature Sensitivity errors)
−40˚C ≤ TA ≤ +125˚C
Trip Point Hysteresis
TA = −40˚C
4
TA = +25˚C
5
TA = +85˚C
6
TA = +125˚C
6
Internal Temperature
˚C (max)
˚C (max)
˚C (max)
3.5
3.5
˚C (min)
6.5
6.5
˚C (max)
4.5
4.5
˚C (min)
7.5
7.5
˚C (max)
4
4
˚C (min)
8
8
˚C (max)
+6.20
mV/˚C
Sensitivity
Temperature Sensitivity Error
±2
±3
±3
±4
˚C (max)
˚C (max)
Output Impedance
−1 µA ≤ IL ≤ +40 µA
1500
1500
Ω (max)
Line Regulation
+3.0V ≤ V ≤ +10V,
+25 ˚C ≤ TA ≤ +85 ˚C
± 0.36
± 0.36
mV/V (max)
+3.0V ≤ V+ ≤ +10V,
−40 ˚C ≤ TA < 25 ˚C
± 0.61
± 0.61
mV/V (max)
+2.7V ≤ V+ ≤ +3.3V
± 2.3
± 2.3
mV (max)
300
300
nA (max)
+
VT1 and VT2 Analog Inputs
IBIAS
Analog Input Bias Current
VIN
Analog Input Voltage Range
VOS
150
Comparator Offset
V+ − 1
V
GND
V
2
8
8
mV (max)
VREF Output
VREF
VREF Nominal
1.250V
VREF Error
∆VREF/∆V+
Line Regulation
+3.0V ≤ V+ ≤ +10V
0.13
+2.7V ≤ V ≤ +3.3V
0.15
+
∆VREF/∆IL
Load Regulation Sourcing
+30 µA ≤ IL ≤ +50 µA
3
V
±1
± 12.5
±1
± 12.5
mV (max)
0.25
0.25
mV/V (max)
% (max)
1.1
1.1
mV (max)
0.15
0.15
mV/µA (max)
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LM56
Symbol
Parameter
Conditions
Typical
Limits
Units
(Note 6)
(Note 7)
(Limits)
230
µA (max)
V = +2.7V
230
µA (max)
V+ = +5.0V
1
µA (max)
0.4
V (max)
V+ Power Supply
IS
Supply Current
V+ = +10V
+
Digital Outputs
IOUT(“1”)
Logical “1” Output Leakage
Current
VOUT(“0”)
Logical “0” Output Voltage
IOUT = +50 µA
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is
functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. The guaranteed
specifications apply only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed test
conditions.
Note 2: When the input voltage (VI) at any pin exceeds the power supply (VI < GND or VI > V+), the current at that pin should be limited to 5 mA. The 20 mA
maximum package input current rating limits the number of pins that can safely exceed the power supplies with an input current of 5 mA to four.
Note 3: Reflow temperature profiles are different for lead-free and non-lead-free packages.
Note 4: The maximum power dissipation must be derated at elevated temperatures and is dictated by TJmax (maximum junction temperature), θJA (junction to
ambient thermal resistance) and TA (ambient temperature). The maximum allowable power dissipation at any temperature is PD = (TJmax–TA)/θJA or the number
given in the Absolute Maximum Ratings, whichever is lower. For this device, TJmax = 125˚C. For this device the typical thermal resistance (θJA) of the different
package types when board mounted follow:
Package Type
θJA
M08A
110˚C/W
MUA08A
250˚C/W
Note 5: The human body model is a 100 pF capacitor discharge through a 1.5 kΩ resistor into each pin. The machine model is a 200 pF capacitor discharged
directly into each pin.
Note 6: Typicals are at TJ = TA = 25˚C and represent most likely parametric norm.
Note 7: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level).
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LM56
Typical Performance Characteristics
Quiescent Current vs Temperature
VREF Output Voltage vs Load Current
01289304
01289305
OUT1 and OUT2 Voltage Levels vs Load Current
Trip Point Hysteresis vs Temperature
01289307
01289332
Temperature Sensor Output Voltage vs Temperature
Temperature Sensor Output Accuracy vs Temperature
01289308
01289309
5
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LM56
Typical Performance Characteristics
(Continued)
Trip Point Accuracy vs Temperature
Comparator Bias Current vs Temperature
01289310
01289311
OUT1 and OUT2 Leakage Current vs Temperature
VTEMP Output Line Regulation vs Temperature
01289331
01289312
VREF Start-Up Response
VTEMP Start-Up Response
01289313
01289314
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LM56
Functional Description
01289315
Pin Descriptions
V+
This is the positive supply voltage pin. This pin
should be bypassed with a 0.1 µF capacitor to
ground.
GND This is the ground pin.
VREF This is the 1.250V bandgap voltage reference output
pin. In order to maintain trip point accuracy this pin
should source a 50 µA load.
VTEMP This is the temperature sensor output pin.
OUT1 This is an open collector digital output. OUT1 is
active LOW. It goes LOW when the temperature is
greater than T1 and goes HIGH when the temperature drops below T1– 5˚C. This output is not intended
to directly drive a fan motor.
OUT2 This is an open collector digital output. OUT2 is
active LOW. It goes LOW when the temperature is
greater than the T2 set point and goes HIGH when
the temperature is less than T2– 5˚C. This output is
not intended to directly drive a fan motor.
This is the input pin for the temperature trip point
VT1
voltage for OUT1.
This is the input pin for the low temperature trip point
VT2
voltage for OUT2.
01289316
VT1 = 1.250V x (R1)/(R1 + R2 + R3)
VT2 = 1.250V x (R1 + R2)/(R1 + R2 + R3)
where:
(R1 + R2 + R3) = 27 kΩ and
VT1 or T2 = [6.20 mV/˚C x T] + 395 mV therefore:
R1 = VT1/(1.25V) x 27 kΩ
R2 = (VT2/(1.25V) x 27 k)Ω–R1
R3 = 27 kΩ − R1 − R2
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LM56
not include any error introduced by the tolerance of the
actual resistors used, nor any error introduced by power
supply variation.
Application Hints
1.0 LM56 TRIP POINT ACCURACY SPECIFICATION
If the resistors have a ± 0.5% tolerance, an additional error of
± 0.4˚C will be introduced. This error will increase to ± 0.8˚C
when both external resistors have a ± 1% tolerance.
For simplicity the following is an analysis of the trip point
accuracy using the single output configuration show in Figure 2 with a set point of 82˚C.
Trip Point Error Voltage = VTPE,
2.0 BIAS CURRENT EFFECT ON TRIP POINT
ACCURACY
Bias current for the comparator inputs is 300 nA (max) each,
over the specified temperature range and will not introduce
considerable error if the sum of the resistor values are kept
to about 27 kΩ as shown in the typical application of Figure
1 . This bias current of one comparator input will not flow if
the temperature is well below the trip point level. As the
temperature approaches trip point level the bias current will
start to flow into the resistor network. When the temperature
sensor output is equal to the trip point level the bias current
will be 150 nA (max). Once the temperature is well above the
trip point level the bias current will be 300 nA (max). Therefore, the first trip point will be affected by 150 nA of bias
current. The leakage current is very small when the comparator input transistor of the different pair is off (see Figure
3) .
The effect of the bias current on the first trip point can be
defined by the following equations:
Comparator Offset Error for VT1E
Temperature Sensor Error = VTSE
Reference Output Error = VRE
01289317
FIGURE 2. Single Output Configuration
1. VTPE = ± VT1E − VTSE + VRE
Where:
2. VT1E = ± 8 mV (max)
3. VTSE = (6.20 mV/˚C) x ( ± 3˚C) = ± 18.6 mV
4. VRE = 1.250V x ( ± 0.01) R2/(R1 + R2)
Using Equations from page 1 of the datasheet.
VT1=1.25VxR2/(R1+R2)=(6.20 mV/˚C)(82˚C) +395 mV
Solving for R2/(R1 + R2) = 0.7227
then,
5. VRE = 1.250V x ( ± 0.01) R2/(R1 + R2) = (0.0125) x
(0.7227) = ± 9.03 mV
The individual errors do not add algebraically because, the
odds of all the errors being at their extremes are rare. This is
proven by the fact the specification for the trip point accuracy
stated in the Electrical Characteristic for the temperature
range of −40˚C to +125˚C, for example, is specified at ± 3˚C
for the LM56BIM. Note this trip point error specification does
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where IB = 300 nA (the maximum specified error).
The effect of the bias current on the second trip point can be
defined by the following equations:
where IB = 300 nA (the maximum specified error).
The closer the two trip points are to each other the more
significant the error is. Worst case would be when VT1 = VT2
= VREF/2.
8
LM56
Application Hints
(Continued)
01289318
FIGURE 3. Simplified Schematic
3.0 MOUNTING CONSIDERATIONS
The majority of the temperature that the LM56 is measuring
is the temperature of its leads. Therefore, when the LM56 is
placed on a printed circuit board, it is not sensing the temperature of the ambient air. It is actually sensing the temperature difference of the air and the lands and printed circuit
board that the leads are attached to. The most accurate
temperature sensing is obtained when the ambient temperature is equivalent to the LM56’s lead temperature.
As with any IC, the LM56 and accompanying wiring and
circuits must be kept insulated and dry, to avoid leakage and
corrosion. This is especially true if the circuit operates at cold
temperatures where condensation can occur. Printed-circuit
coatings are often used to ensure that moisture cannot
corrode the LM56 or its connections.
9
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LM56
Application Hints
(Continued)
4.0 VREF AND VTEMP CAPACITIVE LOADING
01289319
FIGURE 4. Loading of VREF and VTEMP
The LM56 VREF and VTEMP outputs handle capacitive loading well. Without any special precautions, these outputs can
drive any capacitive load as shown in Figure 4 .
6.0 APPLICATIONS CIRCUITS
5.0 NOISY ENVIRONMENTS
Over the specified temperature range the LM56 VTEMPoutput has a maximum output impedance of 1500Ω. In an
extremely noisy environment it may be necessary to add
some filtering to minimize noise pickup. It is recommended
that 0.1 µF be added from V+ to GND to bypass the power
supply voltage, as shown in Figure 4 . In a noisy environment
it may be necessary to add a capacitor from the VTEMP
output to ground. A 1 µF output capacitor with the 1500Ω
output impedance will form a 106 Hz lowpass filter. Since the
thermal time constant of the VTEMP output is much slower
than the 9.4 ms time constant formed by the RC, the overall
response time of the VTEMP output will not be significantly
affected. For much larger capacitors this additional time lag
will increase the overall response time of the LM56.
01289320
FIGURE 5. Reducing Errors Caused by Bias Current
The circuit shown in Figure 5 will reduce the effective bias
current error for VT2 as discussed in Section 3.0 to be
equivalent to the error term of VT1. For this circuit the effect
of the bias current on the first trip point can be defined by the
following equations:
where IB = 300 nA (the maximum specified error).
Similarly, bias current affect on VT2 can be defined by:
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sensing element is at the same temperature as the heat sink,
the sensor’s leads are mounted to pads that have feed
throughs to the back side of the PC board. Since the LM56 is
sensing the temperature of the actual PC board the back
side of the PC board also has large ground plane to help
conduct the heat to the device. The comparator’s output
goes low if the heat sink temperature rises above a threshold
set by R1, R2, and the voltage reference. This fault detection
output from the comparator now can be used to turn on a
cooling fan. The circuit as shown in design to turn the fan on
when heat sink temperature exceeds about 80˚C, and to turn
the fan off when the heat sink temperature falls below approximately 75˚C.
(Continued)
where IB = 300 nA (the maximum specified error).
The current shown in Figure 6 is a simple overtemperature
detector for power devices. In this example, an audio power
amplifier IC is bolted to a heat sink and an LM56 Celsius
temperature sensor is mounted on a PC board that is bolted
to the heat sink near the power amplifier. To ensure that the
01289321
FIGURE 6. Audio Power Amplifier Overtemperature Detector
01289322
FIGURE 7. Simple Thermostat
11
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LM56
Application Hints
LM56
Physical Dimensions
inches (millimeters) unless otherwise noted
8-Lead (0.150" Wide) Molded Small Outline Package, JEDEC
Order Number LM56BIM, LM56BIMX, LM56CIM or LM56CIMX
NS Package Number M08A
8-Lead Molded Mini Small Outline Package (MSOP)
(JEDEC REGISTRATION NUMBER M0-187)
Order Number LM56BIMM, LM56BIMMX, LM56CIMM, or LM56CIMMX
NS Package Number MUA08A
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LM56 Dual Output Low Power Thermostat
Notes
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves
the right at any time without notice to change said circuitry and specifications.
For the most current product information visit us at www.national.com.
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