LM56 Dual Output Low Power Thermostat

April 2000

LM56
Dual Output Low Power Thermostat
General Description Features
The LM56 is a precision low power thermostat. Two stable n Digital outputs support TTL logic levels
temperature trip points (VT1 and VT2) are generated by divid- n Internal temperature sensor
ing down the LM56 1.250V bandgap voltage reference using n 2 internal comparators with hysteresis
3 external resistors. The LM56 has two digital outputs. OUT1 n Internal voltage reference
goes LOW when the temperature exceeds T1 and goes n Currently available in 8-pin SO plastic package
HIGH when the the temperature goes below (T1–THYST).
n Future availability in the 8-pin Mini-SO8 package
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. Key Specifications
The LM56 is available in an 8-lead Mini-SO8 surface mount n Power Supply Voltage 2.7V–10V
package and an 8-lead small outline package.
n Power Supply Current 230 µA (max)
n VREF 1.250V ± 1% (max)
Applications
n Microprocessor Thermal Management n Hysteresis Temperature 5˚C
n Appliances n Internal Temperature Sensor
n Portable Battery Powered 3.0V or 5V Systems Output Voltage (+6.20 mV/˚C x T) +395 mV
n Fan Control n Temperature Trip Point Accuracy:
n Industrial Process Control
LM56BIM LM56CIM
n HVAC Systems
+25˚C ± 2˚C (max) ± 3˚C (max)
n Remote Temperature Sensing
n Electronic System Protection +25˚C to +85˚C ± 2˚C (max) ± 3˚C (max)
−40˚C to +125˚C ± 3˚C (max) ± 4˚C (max)

Simplified Block Diagram and Connection Diagram

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Order LM56BIM LM56BIMX LM56CIM LM56CIMX LM56BIMM LM56BIMMX LM56CIMM LM56CIMMX

Number
NS M08A M08A M08A M08A MUA08A MUA08A MUA08A MUA08A
Package
SOP-8 SOP-8 SOP-8 SOP-8 MSOP-8 MSOP-8 MSOP-8 MSOP-8
Number
2500 Units 2500 Units 3500 Units 3500 Units
Transport
Rail Tape & Rail Tape & Rail Tape & Reel Rail Tape & Reel
Media
Reel Reel
Package LM56BIM LM56BIM LM56CIM LM56CIM T02B T02B T02C T02C
Marking

© 2000 National Semiconductor Corporation DS012893 www.national.com

LM56
Typical Application

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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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 LM56
Absolute Maximum Ratings (Note 1) Vapor Phase (60 seconds) 215˚C
Infrared (15 seconds) 220˚C
Input Voltage 12V
Storage Temperature −65˚C to + 150˚C
Input Current at any pin (Note 2) 5 mA
Package Input Current(Note 2) 20 mA
Operating Ratings(Note 1)
Package Dissipation at TA = 25˚C
(Note 3) 900 mW Operating Temperature Range TMIN ≤ TA ≤ TMAX
ESD Susceptibility (Note 4) LM56BIM, LM56CIM −40˚C ≤ TA ≤ +125˚C
Human Body Model 1000V Positive Supply Voltage (V+) +2.7V to +10V
Machine Model 200V Maximum VOUT1 and VOUT2 +10V
Soldering Information
SO Package (Note 5) :

LM56 Electrical Characteristics

The following specifications apply for V+ = 2.7 VDC, and VREF load current = 50 µA unless otherwise specified. Boldface lim-
its apply for TA = TJ = TMIN to TMAX; all other limits TA = TJ = 25˚C unless otherwise specified.
Typical LM56BIM LM56CIM Units
Symbol Parameter Conditions (Note 6) Limits Limits (Limits)
(Note 7) (Note 7)
Temperature Sensor
Trip Point Accuracy (Includes ±2 ±3 ˚C (max)
VREF, Comparator Offset, and +25˚C ≤ TA ≤ +85˚C ±2 ±3 ˚C (max)
Temperature Sensitivity errors) −40˚C ≤ TA ≤ +125˚C ±3 ±4 ˚C (max)
Trip Point Hysteresis TA = −40˚C 4 3 3 ˚C (min)
6 6 ˚C (max)
TA = +25˚C 5 3.5 3.5 ˚C (min)
6.5 6.5 ˚C (max)
TA = +85˚C 6 4.5 4.5 ˚C (min)
7.5 7.5 ˚C (max)
TA = +125˚C 6 4 4 ˚C (min)
8 8 ˚C (max)
Internal Temperature +6.20 mV/˚C
Sensitivity
Temperature Sensitivity Error ±2 ±3 ˚C (max)
±3 ±4 ˚C (max)
Output Impedance −1 µA ≤ IL ≤ +40 µA 1500 1500 Ω (max)
Line Regulation +3.0V ≤ V ≤ +10V,
+
± 0.36 ± 0.36 mV/V (max)
+25 ˚ C ≤ TA ≤ +85 ˚ C
+3.0V ≤ V+ ≤ +10V, ± 0.61 ± 0.61 mV/V (max)
−40 ˚ C ≤ TA < 25 ˚ C
+2.7V ≤ V+ ≤ +3.3V ± 2.3 ± 2.3 mV (max)
VT1 and VT2 Analog Inputs
IBIAS Analog Input Bias Current 150 300 300 nA (max)
+
VIN Analog Input Voltage Range V −1 V
GND V
VOS Comparator Offset 2 8 8 mV (max)
VREF Output
VREF VREF Nominal 1.250V V
VREF Error ±1 ±1 % (max)
± 12.5 ± 12.5 mV (max)
∆VREF/∆V +
Line Regulation +3.0V ≤ V ≤ +10V
+
0.13 0.25 0.25 mV/V (max)
+2.7V ≤ V+ ≤ +3.3V 0.15 1.1 1.1 mV (max)
∆VREF/∆IL Load Regulation Sourcing +30 µA ≤ IL ≤ +50 µA 0.15 0.15 mV/µA
(max)

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LM56
LM56 Electrical Characteristics
The following specifications apply for V+ = 2.7 VDC, and VREF load current = 50 µA unless otherwise specified. Boldface lim-
its apply for TA = TJ = TMIN to TMAX; all other limits TA = TJ = 25˚C unless otherwise specified.
Symbol Parameter Conditions Typical Limits Units
(Note 6) (Note 7) (Limits)
V+ Power Supply
IS Supply Current V+ = +10V 230 µA (max)
V+ = +2.7V 230 µA (max)
Digital Outputs
IOUT(“1”) Logical “1” Output Leakage V+ = +5.0V 1 µA (max)
Current
VOUT(“0”) Logical “0” Output Voltage IOUT = +50 µA 0.4 V (max)
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is func-
tional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. The guaranteed speci-
fications 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 maxi-
mum 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: The maximum power dissipation must be derated at elevated temperatures and is dictated by TJmax (maximum junction temperature), θJA (junction to am-
bient 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 4: 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 5: See AN450 “Surface Mounting Methods and Their Effects on Product Reliability” or the section titled “Surface Mount” found in any post 1986 National Semi-
conductor Linear Data Book for other methods of soldering surface mount devices.
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 VREF Output Voltage vs OUT1 and OUT2 Voltage
Temperature Load Current Levels vs Load Current

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Trip Point Hysteresis vs Temperature Sensor Temperature Sensor

Temperature Output Voltage vs Output Accuracy vs
Temperature Temperature

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Trip Point Comparator Bias Current OUT1 and OUT2 Leakage

Accuracy vs Temperature vs Temperature Current vs Temperature

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LM56
Typical Performance Characteristics (Continued)

VTEMP Output
Line Regulation vs Temperature

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VREF Start-Up Response VTEMP Start-Up Response

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 LM56
Functional Description

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1.0 PIN DESCRIPTION

V+ This is the positive supply voltage pin. This pin
should be bypassed with 0.1 µF capacitor to
ground.
GND This is the ground pin.
VREF This is the 1.250V bandgap voltage reference out-
put 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 ac-
tive LOW. It goes LOW when the temperature is
greater than T1 and goes HIGH when the tempera-
ture drops below T1–5˚C. This output is not in-
tended to directly drive a fan motor.
OUT2 This is an open collector digital output. OUT2 is ac-
tive LOW. It goes LOW when the temperature is DS012893-16
greater than the T2 set point and goes HIGH when VT1 = 1.250V x (R1)/(R1 + R2 + R3)
the temperature is less than T2–5˚C. This output is VT2 = 1.250V x (R1 + R2)/(R1 + R2 + R3)
not intended to directly drive a fan motor. where:
VT1 This is the input pin for the temperature trip point (R1 + R2 + R3) = 27 kΩ and
VT1 or T2 = [6.20 mV/˚C x T] + 395 mV therefore:
voltage for OUT1.
R1 = VT1/(1.25V) x 27 kΩ
VT2 This is the input pin for the low temperature trip R2 = (VT2/(1.25V) x 27 k)Ω–R1
point voltage for OUT2. R3 = 27 kΩ − R1 − R2

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LM56
Application Hints range of −40˚C to +125˚C, for example, is specified at ± 3˚C
for the LM56BIM. Note this trip point error specification does
not include any error introduced by the tolerance of the ac-
2.0 LM56 TRIP POINT ACCURACY SPECIFICATION
tual resistors used, nor any error introduced by power supply
For simplicity the following is an analysis of the trip point ac- variation.
curacy using the single output configuration show in Figure 2
If the resistors have a ± 0.5% tolerance, an additional error of
with a set point of 82˚C.
± 0.4˚C will be introduced. This error will increase to ± 0.8˚C
Trip Point Error Voltage = VTPE, when both external resistors have a ± 1% tolerance.
Comparator Offset Error for VT1E
Temperature Sensor Error = VTSE 3.0 BIAS CURRENT EFFECT ON
TRIP POINT ACCURACY
Reference Output Error = VRE
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 tem-
perature approaches trip point level the bias current will start
to flow into the resistor network. When the temperature sen-
sor 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 de-
fined by the following equations:
DS012893-17

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
where IB = 300 nA (the maximum specified error).
4. VRE = 1.250V x ( ± 0.01) R2/(R1 + R2)
The effect of the bias current on the second trip point can be
Using Equations from page 1 of the datasheet. defined by the following equations:
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 where IB = 300 nA (the maximum specified error).
proven by the fact the specification for the trip point accuracy
The closer the two trip points are to each other the more sig-
stated in the Electrical Characteristic for the temperature
nificant the error is. Worst case would be when VT1 = VT2 =
VREF/2.

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 LM56
Application Hints (Continued)

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FIGURE 3. Simplified Schematic

4.0 MOUNTING CONSIDERATIONS As with any IC, the LM56 and accompanying wiring and cir-
The majority of the temperature that the LM56 is measuring cuits must be kept insulated and dry, to avoid leakage and
is the temperature of its leads. Therefore, when the LM56 is corrosion. This is especially true if the cirucit may operate at
placed on a printed circuit board, it is not sensing the tem- cold temperatures where condensation can occur.
perature of the ambient air. It is actually sensing the tem- Printed-circuit coatings and varnishes such as Humiseal and
perature difference of the air and the lands and printed circuit epoxy paints or dips are often used to ensure that moisture
board that the leads are attached to. The most accurate tem- cannot corrode the LM56 or its connections.
perature sensing is obtained when the ambient temperature
is equivalent to the LM56’s lead temperature.

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LM56
Application Hints (Continued)

5.0 VREF AND VTEMP CAPACTIVE LOADING

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FIGURE 4. Loading of VREF and VTEMP

The LM56 VREF and VTEMP outputs handle capacitive load- The circuit shown inFigure 5 will reduce the effective bias
ing well. Without any special precautions, these outputs can current error for VT2 as discussed in Section 3.0 to be
drive any capacitive load as shown in Figure 4 . 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
6.0 NOISY ENVIRONMENTS following equations:
Over the specified temperature range the LM56 VTEMPout-
put has a maximum output impedance of 1500Ω. In an ex-
tremely 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 im- where IB = 300 nA (the maximum specified error).
pedance will form a 106 Hz lowpass filter. Since the thermal Similarly, bias current affect on VT2 can be defined by:
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.

7.0 APPLICATIONS CIRCUITS

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
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
DS012893-20 set by R1, R2, and the voltage reference. This fault detection
output from the comparator now can be used to turn on a
FIGURE 5. Reducing Errors Caused by Bias Current
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 ap-
proximately 75˚C.

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 LM56
Application Hints (Continued)

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FIGURE 6. Audio Power Amplifier Overtemperature Detector

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FIGURE 7. Simple Thermostat

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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

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 LM56 Dual Output Low Power Thermostat
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)

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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accordance with instructions for use provided in the safety or effectiveness.
labeling, can be reasonably expected to result in a
significant injury to the user.
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