Programming the Hysteresis Voltage of Universal Voltage Monitors MC34161, MC33161 and NCV33161

AND8426/D
Programming the
Hysteresis Voltage Of
Universal Voltage Monitors
MC34161, MC33161 and
NCV33161
http://onsemi.com
APPLICATION NOTE
Prepared by: Cimiy Chan
ON Semiconductor
Device
MC34161
MC33161
NCV33161
Application
Input Voltage
Output Power
Topology
I/O Isolation
Universal Voltage Monitor
N/A
N/A
N/A
N/A
Circuit Description
Figure 1. General Block Diagram of MC34161/MC33161
The Figure 1 shows the basic block diagram of MC34161/MC33161. It can be used for wide variety of voltage sensing
application. They offer the circuit designer an economical solution for positive and negative voltage detection. The circuit
consists of two comparators with hysteresis, a unique mode select input for channel programming, a output of 2.54 V reference,
and two open collector outputs capable of sinking in excess of 10 mA.
Most of the comparators for the voltage monitoring provide hysteresis which is used for reducing the sensitivity to noise or
a slowly moving input (low slew rate) signal. From the information of MC34161/MC33161 datasheet, the hysteresis is fixed
to around 25 mV typically. However, this hysteresis value may not be enough for some applications for reducing the sensitivity
© Semiconductor Components Industries, LLC, 2011
August, 2011 − Rev. 1
1
Publication Order Number:
AND8426/D
AND8426/D
to noise or comparator input voltage fluctuation. For example, at the automotive application, the noise level or voltage
fluctuation (divided down to comparator input) may be as high as 300 mV − 400 mV during system operating. Therefore, a
comprehensive and easy way to increase the hysteresis is definitely a need for the MC34161/MC33161 application under high
noise level.
This document demonstrates the steps to show how to program the hysteresis voltage. And also, simulation results together
with laboratory bench test verification will be shown.
Vin
+5V
MC33161
R1
R3
R2
Vref
VCC
IN1
Mode Sel
IN2
OUT1
GND
OUT2
R6
R5
Out
R4
Figure 2. Schematic for Programming the Hysteresis Voltage
The configuration in the Figure 2 shows the circuit schematic for programming the hysteresis voltage. Basically, the
hysteresis can be adjusted by varying R2, R3 and R4. Moreover, R1 and R2 are also used for the purpose of dividing down
the external VIN voltage. As mentioned before, R2, R3 and R4 can affect the amount of hysteresis voltage, it is necessary to
find the easy way for the user to set the hysteresis voltage to fit for his own application. For R5 and R6, for typical application
it sets as R5 = 200k and R6 = 10k.
From the circuit simulation result, it is found that R3 variation (fix R1, R2 and R4) can provide very good linear relationship
with hysteresis voltage and Figure 3 depicts it:
Hysteresis Voltage versus R3 (R1=10K, R2=3K)
R4=100K
R4=300K
R4=500K
1.6
1.4
Hysteresis (V)
1.2
1
0.8
0.6
0.4
0.2
0
0
2
4
6
8
10
12
14
R3 (Kohms)
Figure 3. Chart to Show the Linear Relationship Between R3 and Hysteresis Voltage
http://onsemi.com
2
16
AND8426/D
For given VIN+ and DVIN (i,e. Hysteresis Voltage) with fixed R2 and R4, we are required to evaluate R1 and R3 to complete
the system configuration. The charts shown at next page will help us how to evaluate R1 and R3. All the equations attached
at charts are formed by the method of linear regression using known values which are acquired from simulation results.
DVIN/VIN+ Ratio versus R3 (R1=10K, R2=3K, R4=100K)
0.25
(DVIN/VIN+) = 0.0125* R3 + 0.0483
DVIN/VIN+ Ratio
0.2
0.15
0.1
0.05
0
0
2
4
6
8
10
12
14
16
4
16
R3 (Kohms)
Figure 4. Chart for DVIN/VIN+ Ratio versus R3
VIN+ versus R3 (R1=10K, R2=3K, R4=100K)
6.6
6.5
VIN+ = 0.0578* R3 + 5.6569
6.4
6.3
VIN+ (V)
6.2
6.1
6
5.9
5.8
5.7
5.6
0 24 681
01
R3 ( Kohms)
Figure 5. Chart for VIN+ versus R3
http://onsemi.com
3
21
AND8426/D
Steps to Evaluate R1 and R3 for Given VIN+ and DVIN
Vin
R1
R2
3K
+5V
MC33161
R3
Vref
VCC
IN1
Mode Sel
IN2
OUT1
GND
OUT2
R5
200K
R6
10K
Out
R4
100K/300K/500K
Figure 6. Circuit for Evaluation of R1 and R3
1. Fix R2 = 3k, R4 = 100k/300k/500k (see step 3 for detail)
2. For given VIN+ and DVIN, calculate the ratio of DVIN/VIN+.
3. From Figure 4 chart with make use of the equation provided, evaluate R3 based on the calculated DVIN/VIN+. If R3 is
found to be negative, try to use R4 = 300k (use Figure 10) or R4 = 500k (use Figure 12) and repeat R3 evaluation.
4. From Figure 5 (if R4 = 300k, use Figure 11. If R4 = 500k use Figure 13) chart with make use of the equation
provided, evaluate VIN+ based on the R3 which is defined at step 3, say VIN+’ It should be noted that the VIN+’ value
here is NOT the one that will be used, it is just for intermediate value to proceed the calculation.
5. Evaluate R1’ based on the formula: (VIN+’)*(R1’ + R2) = (VIN+)*(R1 + R2) where R1 = 10k, R3 = 3k.
6. So, R1 (notate as R1’ at step 5), R2, R3 and R4 are evaluated.
Example
The customer wants to have the application of which Output is low when VIN = 3 V and output is high when VIN = 2.75 V.
Step 1:
Fix R2 = 3K, R4 = 100k
Step 2:
VIN+ = 3 V and required hysteresis DVIN
= 3 – 2.75
= 0.25 V
= 0.25 / 3
So the (DVIN/VIN+) ratio
= 0.0833
Step 3:
From the Figure 4 chart with make use of equation,
we have
0.08333 = 0.0125 * R3 + 0.0483
Therefore, R3 = (0.08333 – 0.0483)/0.0125
R3 = 2.803k
Step 4:
From the Figure 5 chart with make use of equation,
we have
VIN+’ = 0.0578 * 2.803 + 5.6569
VIN+’ = 5.819 V
Step 5:
Evaluate R1 by the formula mentioned at step 5,
5.819 * (R1 + 3) = 3 * (10 + 3)
R1 = 3.702k
So, the system will give VIN+ = 3 V with DVIN = 0.25 V for R1 = 3.702k, R2 = 3k, R3 = 2.803k, R4 = 100k.
http://onsemi.com
4
AND8426/D
Validation by PSPICE Simulation
Now, we put those resistor values into PSPICE for functional validation.
Figure 7. MC33161 PSPICE Schematic Model
Note: For the comparators portion, LM324 (U1A/U1B), R18(R19) and R53(R54) are used to provide 25 mV hysteresis
which is the “intrinsic” amount per datasheet quoted. And input characteristics of LM324 is quite similar to those of real
MC33161.
8.0V
6.0V
4.0V
2.0V
0V
0s
10ms
V(OUT) V(VIN)
20ms
30ms
40ms
50ms
Time
60ms
70ms
80ms
90ms
Figure 8. Simulation Result (VIN+ = 2.9907 V, VIN− = 2.7450 V, DVIN = 2.9907 − 2.7450 = 0.2457 V)
So, the simulation result is consistent with theoretical calculation.
http://onsemi.com
5
100ms
AND8426/D
Validation by Laboratory Evaluation
Recall the resistor sets R1 to R4
R1 = 3.702k
R2 = 3k
R3 = 2.803k
R4 = 100k
At laboratory, the following resistor values are used:
R1 = 3.6k + 100 W = 3.70k
R2 = 3k
R3 = 2.7k + 100 W = 2.80k
R4 = 100k
All resistors are tolerance 1%
Figure 9. Scope Capture (VIN+ = 2.989 V, VIN− = 2.722 V, DVIN = 2.989 − 2.722 = 0.267 V)
So the evaluation result in laboratory bench is also consistent with theoretical calculation.
Cautions For Selection of Resistor R3 to R4
1. R3 should be used lower than 15k, otherwise there will have some non linear behavior with either VIN+ or
DVIN/VIN+
2. R4 should be used higher than 100k.
The following charts provide VIN+ and DVIN/VIN+ versus R3 for R4 = 300k and R4 = 500k. Those may be used if DVIN/VIN+
are too small for R4 = 100k configuration.
http://onsemi.com
6
AND8426/D
DVIN/VIN+ Ratio versus R3 (R1=10K, R2=3K, R4=300K)
0.14
(DVIN/VIN+) = 0.006815* R3 + 0.02785
0.12
DVIN/VIN+ Ratio
0.1
0.08
0.06
0.04
0.02
0
0
2
4
6
8
10
12
14
16
14
16
R3 (Kohms)
Figure 10. Chart for DVIN/VIN+ Ratio versus R3 (R4 = 300k)
VIN+ versus R3 (R1=10K, R2=3K, R4=300K)
5.95
VIN+ = 0.02125* R3 + 5.5724
5.9
5.85
VIN+ (V)
5.8
5.75
5.7
5.65
5.6
5.55
0
2
4
6
8
10
R3 (Kohms)
Figure 11. Chart for VIN+ versus R3 (R4 = 300k)
http://onsemi.com
7
12
AND8426/D
DVIN/VIN+ Ratio versus R3 (R1=10K, R2=3K, R4=500K)
0.12
(DVIN/VIN+) = 0.005183* R3 + 0.02332
DVIN/VIN+ Ratio
0.1
0.08
0.06
0.04
0.02
0
0
2
4
6
8
10
12
14
16
R3 (Kohms)
Figure 12. Chart for DVIN/VIN+ Ratio versus R3 (R4 = 500k)
VIN+ versus R3 (R1=10K, R2=3K, R4=500K)
5.8
VIN+ = 0.0139* R3 + 5.555
5.75
VIN+ (V)
5.7
5.65
5.6
5.55
0
2
4
6
8
10
R3 (Kohms)
Figure 13. Chart for VIN+ versus R3 (R4 = 500k)
http://onsemi.com
8
12
14
16
AND8426/D
ON Semiconductor and
are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC reserves the right to make changes without further notice
to any products herein. SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does SCILLC assume any liability
arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages.
“Typical” parameters which may be provided in SCILLC data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. All
operating parameters, including “Typicals” must be validated for each customer application by customer’s technical experts. SCILLC does not convey any license under its patent rights
nor the rights of others. SCILLC products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applications
intended to support or sustain life, or for any other application in which the failure of the SCILLC product could create a situation where personal injury or death may occur. Should
Buyer purchase or use SCILLC products for any such unintended or unauthorized application, Buyer shall indemnify and hold SCILLC and its officers, employees, subsidiaries, affiliates,
and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death
associated with such unintended or unauthorized use, even if such claim alleges that SCILLC was negligent regarding the design or manufacture of the part. SCILLC is an Equal
Opportunity/Affirmative Action Employer. This literature is subject to all applicable copyright laws and is not for resale in any manner.
PUBLICATION ORDERING INFORMATION
LITERATURE FULFILLMENT:
Literature Distribution Center for ON Semiconductor
P.O. Box 5163, Denver, Colorado 80217 USA
Phone: 303−675−2175 or 800−344−3860 Toll Free USA/Canada
Fax: 303−675−2176 or 800−344−3867 Toll Free USA/Canada
Email: [email protected]
N. American Technical Support: 800−282−9855 Toll Free
USA/Canada
Europe, Middle East and Africa Technical Support:
Phone: 421 33 790 2910
Japan Customer Focus Center
Phone: 81−3−5773−3850
http://onsemi.com
9
ON Semiconductor Website: www.onsemi.com
Order Literature: http://www.onsemi.com/orderlit
For additional information, please contact your local
Sales Representative
AND8426/D