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. 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