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19-0194; Rev 1; 2/97
Ultra Low-Power, Low-Cost Comparators with 2% Reference
_______________General Description
The MAX931-MAX934 single, dual, and quad micropower, low-voltage comparators plus an on-board 2% accurate reference feature the lowest power consumption available. These comparators draw less than 4A supply current over temperature (MAX931), and include an internal 1.182V 2% voltage reference, programmable hysteresis, and TTL/CMOS outputs that sink and source current. Ideal for 3V or 5V single-supply applications, the MAX931-MAX934 operate from a single +2.5V to +11V supply (or a 1.25V to 5V dual supply), and each comparator's input voltage range extends from the negative supply rail to within 1.3V of the positive supply. The MAX931-MAX934's unique output stage continuously sources as much as 40mA. And by eliminating powersupply glitches that commonly occur when comparators change logic states, the MAX931-MAX934 minimize parasitic feedback, which makes them easier to use. The single MAX931 and dual MAX932/MAX933 provide a unique and simple method for adding hysteresis without feedback and complicated equations, using the HYST pin and two resistors. For applications that require increased precision with similar power requirements, see the MAX921-MAX924 data sheet. These devices include a 1% precision reference.
INTERNAL COMPARATORS INTERNAL 2% PER HYSTERESIS REFERENCE PACKAGE PACKAGE
____________________________Features
o Ultra-Low 4A Max Quiescent Current Over Extended Temp. Range (MAX931) o Power Supplies: Single +2.5V to +11V Dual 1.25V to 5.5V o Input Voltage Range Includes Negative Supply o Internal 1.182V 2% Bandgap Reference o Adjustable Hysteresis o TTL-/CMOS-Compatible Outputs o 12s Propagation Delay (10mV Overdrive) o No Switching Crowbar Current o 40mA Continuous Source Current o Available in Space-Saving MAX Package
MAX931-MAX934
______________Ordering Information
PART MAX931CPA MAX931CSA MAX931CUA MAX931EPA MAX931ESA TEMP. RANGE 0C to +70C 0C to +70C 0C to +70C -40C to +85C -40C to +85C PIN-PACKAGE 8 Plastic DIP 8 SO 8 MAX 8 Plastic DIP 8 SO
PART
MAX931
Yes
1
Yes
8-Pin DIP/SO/ MAX 8-Pin DIP/SO/ MAX 8-Pin DIP/SO/ MAX 16-Pin DIP/SO
Ordering Information continued on last page. For similar devices guaranteed over the military temp. range, see the MAX921-MAX924 data sheet. The MAX931, MAX933, and MAX934 are pin-compatible with the 1% accurate MAX921, MAX923, and MAX924, respectively. The MAX932 and MAX922 are not pin-compatible.
MAX932
Yes
2
Yes
__________Typical Operating Circuit
VIN 7 3 IN+ V+ OUT 8 4 IN-
MAX933
Yes
2
Yes
MAX934
Yes
4
No
________________________Applications
Battery-Powered Systems Threshold Detectors Window Comparators Oscillator Circuits Alarm Circuits
5 HYST
6 REF V2
MAX931
GND 1
THRESHOLD DETECTOR 1
________________________________________________________________ Maxim Integrated Products
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800
Ultra Low-Power, Low-Cost Comparators with 2% Reference MAX931-MAX934
ABSOLUTE MAXIMUM RATINGS
V+ to V-, V+ to GND, GND to V-................................-0.3V, +12V Inputs Current, IN_+, IN_-, HYST...............................................20mA Voltage, IN_+, IN_-, HYST................(V+ + 0.3V) to (V- - 0.3V) Outputs Current, REF....................................................................20mA Current, OUT_ .................................................................50mA Voltage, REF ....................................(V+ + 0.3V) to (V- - 0.3V) Voltage, OUT_ (MAX931/934) .....(V+ + 0.3V) to (GND - 0.3V) Voltage, OUT_ (MAX932/933)..........(V+ + 0.3V) to (V- - 0.3V) OUT_ Short-Circuit Duration (V+ 5.5V) ...............Continuous Continuous Power Dissipation (TA = +70C) 8-Pin Plastic DIP (derate 9.09mW/C above +70C) ...727mW 8-Pin SO (derate 5.88mW/C above +70C)................471mW 8-Pin MAX (derate 4.1mW/C above +70C) .............330mW 16-Pin Plastic DIP (derate 10.53mW/C above +70C)..842mW 16-Pin SO (derate 8.70mW/C above +70C) ................696mW Operating Temperature Ranges: MAX93_C_ _ .......................................................0C to +70C MAX93_E_ _.....................................................-40C to +85C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10sec) .............................+300C
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS--5V Operation
(V+ = 5V, V- = GND = 0V, TA = TMIN to TMAX, unless otherwise noted.) PARAMETER POWER REQUIREMENTS Supply Voltage Range (Note 1) MAX931, HYST = REF MAX932, HYST = REF Supply Current IN+ = IN- + 100mV MAX933, HYST = REF TA = +25C C/E temp. ranges TA = +25C MAX934 C/E temp. ranges COMPARATOR Input Offset Voltage Input Leakage Current (IN-, IN+) Input Leakage Current (HYST) Input Common-Mode Voltage Range Common-Mode Rejection Ratio Power-Supply Rejection Ratio Voltage Noise Hysteresis Input Voltage Range Response Time VCM = 2.5V IN+ = IN- = 2.5V, C/E temp. ranges MAX931, MAX932, MAX933 VV- to (V+ - 1.3V) V+ = 2.5V to 11V 100Hz to 100kHz MAX931, MAX932, MAX933 TA = +25C, 100pF load Overdrive = 10mV Overdrive = 100mV 0.1 0.1 20 REF - 0.05 12 4 0.01 0.02 V+ - 1.3 1.0 1.0 REF 8.5 10 5 mV nA nA V mV/V mV/V VRMS V s 5.5 3.1 4.5 6 6.5 TA = +25C C/E temp. ranges TA = +25C C/E temp. ranges 3.1 2.5 2.5 11 3.2 4 4.5 6 A V CONDITIONS MIN TYP MAX UNITS
2
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Ultra Low-Power, Low-Cost Comparators with 2% Reference
ELECTRICAL CHARACTERISTICS--5V Operation (continued)
(V+ = 5V, V- = GND = 0V, TA = TMIN to TMAX, unless otherwise noted.) PARAMETER Output High Voltage CONDITIONS C/E temp. ranges, IOUT = 17mA MAX932, MAX933 MAX931, MAX934 MIN V+ - 0.4 V- + 0.4 V GND + 0.4 TYP MAX UNITS V
MAX931-MAX934
Output Low Voltage
C/E temp. ranges, IOUT = 1.8mA
REFERENCE X C temp. range Reference Voltage E temp. range TA = +25C Source Current C/E temp. ranges TA = +25C Sink Current C/E temp. ranges Voltage Noise 100Hz to 100kHz 4 100 VRMS 6 8 15 A 1.147 15 25 A 1.217 1.158 1.182 1.206 V
Note 1: MAX934 comparators work below 2.5V, see Low-Voltage Operation section for more details.
ELECTRICAL CHARACTERISTICS--3V Operation
(V+ = 3V, V- = GND = 0V, TA = TMIN to TMAX, unless otherwise noted.) PARAMETER POWER REQUIREMENTS MAX931,
HYST = REF
CONDITIONS
MIN
TYP
MAX
UNITS
TA = +25C C/E temp. ranges TA = +25C C/E temp. ranges TA = +25C C/E temp. ranges TA = +25C
2.4
3.0 3.8
MAX932,
HYST = REF
3.4
4.3 5.8 A
Supply Current
IN+ = (IN- + 100mV) MAX933,
HYST = REF
3.4
4.3 5.8
5.2
6.2 8.0
MAX934 C/E temp. ranges COMPARATOR Input Offset Voltage Input Leakage Current (IN-, IN+) Input Leakage Current (HYST)
VCM = 1.5V IN+ = IN- = 1.5V, C/E temp. ranges MAX931, MAX932, MAX933
0.01 0.02
10 1
mV nA nA
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Ultra Low-Power, Low-Cost Comparators with 2% Reference MAX931-MAX934
ELECTRICAL CHARACTERISTICS--3V Operation (continued)
(V+ = 3V, V- = GND = 0V, TA = TMIN to TMAX, unless otherwise noted.) PARAMETER Input Common-Mode Voltage Range Common-Mode Rejection Ratio Power-Supply Rejection Ratio Voltage Noise Hysteresis Input Voltage Range Response Time Output High Voltage V- to (V+ - 1.3V) V+ = 2.5V to 11V 100Hz to 100kHz MAX931, MAX932, MAX933 TA = +25C, 100pF load Overdrive = 10mV Overdrive = 100mV V+ - 0.4 MAX932, MAX933 MAX931 REFERENCE C temp. range Reference Voltage E temp. range TA = +25C Source Current C/E temp. ranges TA = +25C Sink Current C/E temp. ranges Voltage Noise 100Hz to 100kHz 4 100 VRMS 6 8 15 A 1.147 15 25 A 1.217 1.158 1.182 1.206 V V- + 0.4 V GND + 0.4 REF - 0.05 14 5 CONDITIONS MIN V0.2 0.1 20 REF TYP MAX V+ - 1.3 1 1 UNITS V mV/V mV/V VRMS V s V
C/E temp. ranges, IOUT = 10mA
Output Low Voltage
C/E temp. ranges, IOUT = 0.8mA
4
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Ultra Low-Power, Low-Cost Comparators with 2% Reference
__________________________________________Typical Operating Characteristics
(V+ = 5V, V- = GND, TA = +25C, unless otherwise noted.)
OUTPUT VOLTAGE LOW vs. LOAD CURRENT
MAX921/4-TOC1
MAX931-MAX934
OUTPUT VOLTAGE HIGH vs. LOAD CURRENT
MAX921/924-TOC2
REFERENCE OUTPUT VOLTAGE vs. OUTPUT LOAD CURRENT
REFERENCE OUTPUT VOLTAGE (V) SINK 1.185 1.180 SOURCE 1.175 1.170 1.165 1.160 1.155 V+ = 5V OR V+ = 3V 0 5 10 15 20 25 30
MAX921/924-TOC3
2.5
V+ = 5V
5.0 4.5 4.0 VOH (V) 3.5 3.0 2.5 V+ = 5V
1.190
2.0 V+ = 3V VOL (V) 1.5
1.0
0.5 2.0 0.0 0 4 8 12 16 20 LOAD CURRENT (mA) 1.5 0 10 20 30
V+ = 3V
40
50
LOAD CURRENT (mA)
OUTPUT LOAD CURRENT (A)
REFERENCE VOLTAGE vs. TEMPERATURE
MAX921/924-TOC4
MAX931 SUPPLY CURRENT vs. TEMPERATURE
MAX921/924-TOC5
MAX932 SUPPLY CURRENT vs. TEMPERATURE
IN+ = IN- +100mV 4.5 SUPPLY CURRENT (A) 4.0 V+ = 5V, V- = 0V 3.5 3.0 2.5
MAX921/924-TOC6
1.22 1.21 REFERENCE VOLTAGE (V) 1.20 1.19 1.18 1.17 1.16 1.15 EXTENDED TEMP. RANGE COMMERCIAL TEMP. RANGE
4.5 IN+ = IN- + 100mV SUPPLY CURRENT (A) 4.0 V+ = 5V, V- = - 5V
5.0
3.5
3.0 V+ = 3V, V- = 0V 2.5 V+ = 5V, V- = 0V
V+ = 3V, V- = 0V 2.0 60 100 140 -60 -20 20 60 100 140
1.14 -60 -40 -20 0 20 40 60 80 100 120 140 TEMPERATURE (C)
2.0 -60 -20 20 TEMPERATURE (C)
TEMPERATURE (C)
MAX933 SUPPLY CURRENT vs. TEMPERATURE
MAX921/924-TOC7
MAX934 SUPPLY CURRENT vs. TEMPERATURE
MAX921/924-TOC8
MAX934 SUPPLY CURRENT vs. LOW SUPPLY VOLTAGES
IN+ = IN- +100mV SUPPLY CURRENT (A)
MAX921/924-TOC9
5.0 IN+ = IN- +100mV 4.5 SUPPLY CURRENT (A) 4.0 V+ = 5V, V- = 0V 3.5 3.0 2.5 V+ = 3V, V- = 0V 2.0 -60 -20 20 60 100
10 IN+ = (IN- + 100mV) 9 SUPPLY CURRENT (A) 8 7 6 5 4 3 V+ = 5V, V- = 0V V+ = 3V, V- = 0V V+ = 5V, V- = -5V
10
1
0.1
0.01 -60 -20 20 60 100 140 1.0 1.5 2.0 2.5 TEMPERATURE (C) SINGLE-SUPPLY VOLTAGE (V)
140
TEMPERATURE (C)
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5
Ultra Low-Power, Low-Cost Comparators with 2% Reference MAX931-MAX934
____________________________Typical Operating Characteristics (continued)
(V+ = 5V, V- = GND, TA = +25C, unless otherwise noted.)
HYSTERESIS CONTROL
MAX921/924 TOC10
TRANSFER FUNCTION
MAX921/924-TOC11
RESPONSE TIME vs. LOAD CAPACITANCE
16 RESPONSE TIME (s) 14 12 10 8 6 4 2 VOLH VOHL
MAX921/924 TOC12
80 60 OUTPUT HIGH 40 IN+ - IN- (V) 20 0 -20 -40 -60 -80 0 10 20 30 40 OUTPUT LOW NO CHANGE
5.0 4.5 4.0 OUTPUT VOLTAGE (V) 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0
100k 10F V0
18
50
-0.3
VREF -VHYST (mV)
0.1 0.2 -0.2 -0.1 0 IN+ INPUT VOLTAGE (mV)
0.3
0
20
40
60
80
100
LOAD CAPACITANCE (nF)
RESPONSE TIME FOR VARIOUS INPUT OVERDRIVES
MAX921/924-TOC13
RESPONSE TIME FOR VARIOUS INPUT OVERDRIVES
MAX921/924-TOC14
MAX934 RESPONSE TIME AT LOW SUPPLY VOLTAGES
MAX921/924-TOC15
10
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
5 4 3 2 1 0 100mV 20mV 50mV 10mV
5 4 3 2 1 0 50mV 100mV 20mV 10mV
RESPONSE TIME (ms)
1
INPUT VOLTAGE (mV)
INPUT VOLTAGE (mV)
100 0
0.1 100mV OVERDRIVE 0.01
20mV OVERDRIVE
0 100 -2 2 6 10 14 18
-2
2
6
10
14
18
1.0
1.5
2.0
2.5
RESPONSE TIME (s)
RESPONSE TIME (s)
SINGLE-SUPPLY VOLTAGE (V)
MAX934 OUTPUT DRIVE AT LOW SUPPLY VOLTAGES
MAX921/924-TOC16
SHORT-CIRCUIT SOURCE CURRENT vs. SUPPLY VOLTAGE
MAX121/124-TOC17
SHORT-CIRCUIT SINK CURRENT vs. SUPPLY VOLTAGE
OUT CONNECTED TO V+ GND CONNECTED TO VSINK CURRENT (mA) 20
MAX121/124-TOC18
100 SOURCE CURRENT INTO 0.75V LOAD CURRENT (mA) 10
200 180 SOURCE CURRENT (mA) 160 140 120 100 80 60 40 OUT CONNECTED TO V-
1
10
SINK CURRENT AT VOUT = 0.4V 0.1 1.0 1.5 2.0 2.5 SINGLE-SUPPLY VOLTAGE (V)
20 0 0 1.0 2.0 3.0 4.0 5.0 TOTAL SUPPLY VOLTAGE (V) 0 0 5 TOTAL SUPPLY VOLTAGE (V) 10
6
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Ultra Low-Power, Low-Cost Comparators with 2% Reference
____________________________________________________________Pin Descriptions
PIN MAX931 1 - 2 3 - 4 - - 5 6 7 8 - MAX932 - 1 2 - 3 - 4 - 5 6 7 - 8 MAX933 - 1 2 - 3 - - 4 5 6 7 - 8 NAME GND OUTA VIN+ INA+ ININB+ INBHYST REF V+ OUT OUTB FUNCTION Ground. Connect to V- for single-supply operation. Output swings from V+ to GND. Comparator A output. Sinks and sources current. Swings from V+ to V-. Negative supply. Connect to ground for single-supply operation (MAX931). Noninverting comparator input Noninverting input of comparator A Inverting comparator input Noninverting input of comparator B Inverting input of comparator B Hysteresis input. Connect to REF if not used. Input voltage range is from VREF to VREF - 50mV. Reference output. 1.182V with respect to V-. Positive supply Comparator output. Sinks and sources current. Swings from V+ to GND. Comparator B output. Sinks and sources current. Swings from V+ to V-.
MAX931-MAX934
PIN MAX934 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
NAME OUTB OUTA V+ INAINA+ INBINB+ REF VINCINC+ INDIND+ GND OUTD OUTC
FUNCTION Comparator B output. Sinks and sources current. Swings from V+ to GND. Comparator A output. Sinks and sources current. Swings from V+ to GND. Positive supply Inverting input of comparator A Noninverting input of comparator A Inverting input of comparator B Noninverting input of comparator B Reference output. 1.182V with respect to V-. Negative supply. Connect to ground for single-supply operation. Inverting input of comparator C Noninverting input of comparator C Inverting input of comparator D Noninverting input of comparator D Ground. Connect to V- for single-supply operation. Comparator D output. Sinks and sources current. Swings from V+ to GND. Comparator C output. Sinks and sources current. Swings from V+ to GND.
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7
Ultra Low-Power, Low-Cost Comparators with 2% Reference MAX931-MAX934
_______________Detailed Description
The MAX931-MAX934 comprise various combinations of a micropower 1.182V reference and a micropower comparator. The Typical Operating Circuit shows the MAX931 configuration, and Figures 1a-1c show the MAX932/MAX933/MAX934 configurations. Each comparator continuously sources up to 40mA, and the unique output stage eliminates crowbar glitches during output transitions. This makes them immune to parasitic feedback (which can cause instability) and provides excellent performance, even when circuitboard layout is not optimal. Internal hysteresis in the MAX931/MAX932/MAX933 provides the easiest method for implementing hysteresis. It also produces faster hysteresis action and consumes much less current than circuits using external positive feedback. a separate ground for the output driver, allowing operation with dual supplies ranging from 1.25V to 5.5V. Connect V- to GND when operating the MAX931 and the MAX934 from a single supply. The maximum supply voltage in this case is still 11V. For proper comparator operation, the input signal can be driven from the negative supply (V-) to within one volt of the positive supply (V+ - 1V). The guaranteed common-mode input voltage range extends from V- to (V+ - 1.3V). The inputs can be taken above and below the supply rails by up to 300mV without damage. Operating the MAX931 and MAX934 at 5V provides TTL/CMOS compatibility when monitoring bipolar input signals. TTL compatibility for the MAX932 and MAX933 is achieved by operation from a single +5V supply.
Low-Voltage Operation: V+ = 1V (MAX934 Only)
The guaranteed minimum operating voltage is 2.5V (or 1.25V). As the total supply voltage is reduced below 2.5V, the performance degrades and the supply
Power-Supply and Input Signal Ranges
This family of devices operates from a single +2.5V to +11V power supply. The MAX931 and MAX934 have
1 OUTA 2 V-
MAX932
OUTB
8
V+ 7 1 OUTB OUTA V+ INAINA+ REF HYST V4 5 6 2 5
MAX934
OUTC OUTD 16 15
3 INA+ 4 INB+
3
A
D
GND 14 IND+
Figure 1a. MAX932 Functional Diagram
13
IND-
12
1 OUTA 2 V-
MAX933
OUTB
B 8 6 INB-
C INC+ INCV11 10 9
V+ 7 7 REF HYST V6 8 5
INB+ REF
3 INA+ 4 INB-
Figure 1b. MAX933 Functional Diagram
8
Figure 1c. MAX934 Functional Diagram
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Ultra Low-Power, Low-Cost Comparators with 2% Reference
current falls. The reference will not function below about 2.2V, although the comparators will continue to operate with a total supply voltage as low as 1V. While the MAX934 has comparators that may be used at supply voltages below 2V, the MAX931, MAX932, and MAX933 may not be used with supply voltages significantly below 2.5V. At low supply voltages, the comparators' output drive is reduced and the propagation delay increases (see Typical Operating Characteristics). The useful input voltage range extends from the negative supply to a little under 1V below the positive supply, which is slightly closer to the positive rail than the device operating from higher supply voltages. Test your prototype over the full temperature and supply-voltage range if operation below 2.5V is anticipated. As the input voltage approaches the comparator's offset, the output begins to bounce back and forth; this peaks when VIN = VOS. (The lowpass filter shown on the graph averages out the bouncing, making the transfer function easy to observe.) Consequently, the comparator has an effective wideband peak-to-peak noise of around 0.3mV. The voltage reference has peak-to peak noise approaching 1mV. Thus, when a comparator is used with the reference, the combined peak-to-peak noise is about 1mV. This, of course, is much higher than the RMS noise of the individual components. Care should be taken in the layout to avoid capacitive coupling from any output to the reference pin. Crosstalk can significantly increase the actual noise of the reference.
MAX931-MAX934
__________Applications Information
Hysteresis
Hysteresis increases the comparators' noise margin by increasing the upper threshold and decreasing the lower threshold (see Figure 2).
Comparator Output
With 100mV of overdrive, propagation delay is typically 3s. The Typical Operating Characteristics show the propagation delay for various overdrive levels. The MAX931 and MAX934 output swings from V+ to GND, so TTL compatibility is assured by using a +5V 10% supply. The negative supply does not affect the output swing, and can range from 0V to -5V 10%. The MAX932 and MAX933 do not have a GND pin, and their outputs swing from V+ to V-. Connect V- to ground and V+ to a +5V supply to achieve TTL compatibility. The MAX931-MAX934's unique design achieves an output source current of more than 40mA and a sink current of over 5mA, while keeping quiescent currents in the microampere range. The output can source 100mA (at V+ = 5V) for short pulses, as long as the package's maximum power dissipation is not exceeded. The output stage does not generate crowbar switching currents during transitions, which minimizes feedback through the supplies and helps ensure stability without bypassing.
Hysteresis (MAX931/MAX932/MAX933) To add hysteresis to the MAX931/MAX932/MAX933, connect resistor R1 between REF and HYST, and connect resistor R2 between HYST and V- (Figure 3). If no hysteresis is required, connect HYST to REF. When hysteresis is added, the upper threshold increases by the same amount that the lower threshold decreases. The hysteresis band (the difference between the upper and lower thresholds, VHB) is approximately equal to twice the voltage between REF and HYST. The HYST input can be adjusted to a maximum voltage of REF and to a minimum voltage of (REF - 50mV). The
IN+
THRESHOLDS
Voltage Reference
The internal bandgap voltage reference has an output of 1.182V above V-. Note that the REF voltage is referenced to V-, not to GND. Its accuracy is 2% in the range 0C to +70C. The REF output is typically capable of sourcing 15A and sinking 8A. Do not bypass the REF output. For applications that require a 1% precision reference, see the MAX921-MAX924 data sheet.
INVREF - VHYST HYSTERESIS VHB BAND
OUT
Noise Considerations
Although the comparators have a very high gain, useful gain is limited by noise. This is shown in the Transfer Function graph (see Typical Operating Characteristics).
Figure 2. Threshold Hysteresis Band
9
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Ultra Low-Power, Low-Cost Comparators with 2% Reference MAX931-MAX934
maximum difference between REF and HYST (50mV) will therefore produce a 100mV max hysteresis band. Use the following equations to determine R1 and R2: VHB R1 = 2 x IREF ) ( VHB 1.182 - 2 R2 = IREF Where I REF (the current sourced by the reference) should not exceed the REF source capability, and should be significantly larger than the HYST input current. I REF values between 0.1A and 4A are usually appropriate. If 2.4M is chosen for R2 (IREF = 0.5A), the equation for R1 and VHB can be approximated as: R1 (k) = VHB (mV) When hysteresis is obtained in this manner for the MAX932/MAX933, the same hysteresis applies to both comparators. 2. Choose the hysteresis voltage (V HB), the voltage between the upper and lower thresholds. In this example, choose VHB = 50mV. 3. Calculate R1. V R1 = R3 x HB V+ 0.05 = 10M x 5 = 100k 4. Choose the threshold voltage for VIN rising (VTHR). In this example, choose VTHR = 3V. 5. Calculate R2. 1 R2 = 1 VTHR 1 - - (VREF x R1) R1 R3 1 = 3 1 1 - 100k - 10M (1.182 x 100k) = 65.44k A 1% preferred value is 64.9k. 6. Verify the threshold voltages with these formulas: VIN rising : 1 1 1 + + VTHR = VREF x R1 x R1 R2 R3 VIN falling : VTHF = VTHR -
Hysteresis (MAX934) Hysteresis can be set with two resistors using positive feedback, as shown in Figure 4. This circuit generally draws more current than the circuits using the HYST pin on the MAX931/MAX932/MAX933, and the high feedback impedance slows hysteresis. The design procedure is as follows: 1. Choose R3. The leakage current of IN+ is under 1nA (up to +85C), so the current through R3 can be around 100nA and still maintain good accuracy. The current through R3 at the trip point is VREF/R3, or 100nA for R3 = 11.8M. 10M is a good practical value.
(R1
x V +) R3
2.5V TO 11V IREF 7 6 REF V+ R1 VIN V+ R3
R1
5 R2
MAX931 MAX932 MAX933
HYST V2
R2
MAX934 VGND VREF
V+
OUT
Figure 3. Programming the HYST Pin
10
Figure 4. External Hysteresis
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Ultra Low-Power, Low-Cost Comparators with 2% Reference
Board Layout and Bypassing
Power-supply bypass capacitors are not needed if the supply impedance is low, but 100nF bypass capacitors should be used when the supply impedance is high or when the supply leads are long. Minimize signal lead lengths to reduce stray capacitance between the input and output that might cause instability. Do not bypass the reference output. For example: 2M x 10F x 4.6 = 92sec. The actual time will vary with both the leakage current of the capacitor and the voltage applied to the circuit.
MAX931-MAX934
Window Detector
The MAX933 is ideal for making window detectors (undervoltage/overvoltage detectors). The schematic is shown in Figure 6, with component values selected for an 4.5V undervoltage threshold, and a 5.5V overvoltage threshold. Choose different thresholds by changing the values of R1, R2, and R3. To prevent chatter at the output when the supply voltage is close to a threshold, hysteresis has been added using R4 and R5. OUTA provides an active-low undervoltage indication, and OUTB gives an active-low overvoltage indication. ANDing the two outputs provides an activehigh, power-good signal. The design procedure is as follows: 1. Choose the required hysteresis level and calculate values for R4 and R5 according to the formulas in the Hysteresis (MAX931/MAX932/MAX933) section. In this example, 5mV of hysteresis has been added at the comparator input (VH = VHB/2). This means that the hysteresis apparent at V IN will be larger because of the input resistor divider. 2. Select R1. The leakage current into INB- is normally under 1nA, so the current through R1 should exceed
_______________Typical Applications
Auto-Off Power Source
Figure 5 shows the schematic for a 40mA power supply that has a timed auto power-off function. The comparator output is the switched power-supply output. With a 10mA load, it typically provides a voltage of (VBATT - 0.12V), but draws only 3.5A quiescent current. This circuit takes advantage of the four key features of the MAX931: 2.5A supply current, an internal reference, hysteresis, and high current output. Using the component values shown, the three-resistor voltage divider programs the maximum 50mV of hysteresis and sets the IN- voltage at 100mV. This gives an IN+ trip threshold of approximately 50mV for IN+ falling. The RC time constant determines the maximum poweron time of the OUT pin before power-down occurs. This period can be approximated by: R x C x 4.6sec
MOMENTARY SWITCH VIN 4.5V TO 6.0V 7 V+ VOTH = 5.5V VUTH = 4.5V +5V
R3 INA+
V+ OUTA HYST UNDERVOLTAGE
6 47k 5 1.1M 4 100k
MAX931
REF
IN+
3 C R R2 R5 10k
POWER GOOD REF OUTB INBOVERVOLTAGE
HYST OUT INV2 GND 1 R1 8 VBATT -0.15V 10mA
R4 2.4M
V-
MAX933
Figure 5. Auto-off power switch operates on 2.5A quiescent current.
Figure 6. Window Detector
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11
Ultra Low-Power, Low-Cost Comparators with 2% Reference MAX931-MAX934
100nA for the thresholds to be accurate. R1 values up to about 10M can be used, but values in the 100k to 1M range are usually easier to deal with. In this example, choose R1 = 294k. 3. Calculate R2 + R3. The overvoltage threshold should be 5.5V when V IN is rising. The design equation is as follows: VOTH R2 + R3 = R1 x - 1 VREF + VH 5.5 = 294k x - 1 (1.182 + 0.005) = 1.068M 4. Calculate R2. The undervoltage threshold should be 4.5V when VIN is falling. The design equation is as follows: (VREF - VH ) - R1 VUTH (1.182 - 0.005) = (294k + 1.068M) x - 294k 4.5 = 62.2k Choose R2 = 61.9k (1% standard value). R2 = (R1 + R2 + R3) x 5. Calculate R3. R3 = (R2 + R3) - R2 = 1.068M - 61.9k = 1.006M Choose R3 = 1M (1% standard value). 6. Verify the resistor values. The equations are as follows, evaluated for the above example. Overvoltage threshold : (R1 + R2 + R3) VOTH = (VREF + VH ) x R1 = 5.474V. Undervoltage threshold : (R1 + R2 + R3) VUTH = (VREF - VH ) x (R1 + R2) = 4.484V, R5 . where the hysteresis voltage VH = VREF x R4
250k
The full-scale threshold (all LEDs on) is given by VIN = (R1 + R2)/R1 volts. The other thresholds are at 3/4 full scale, 1/2 full scale, and 1/4 full scale. The output resistors limit the current into the LEDs.
Level Shifter
Figure 8 shows a circuit to shift from bipolar 5V inputs to TTL signals. The 10k resistors protect the comparator inputs, and do not materially affect the operation of the circuit.
Two-Stage Low-Voltage Detector
Figure 9 shows the MAX932 monitoring an input voltage in two steps. When VIN is higher than the LOW and FAIL thresholds, outputs are high. Threshold calculations are similar to those for the windowdetector application.
R1 +5V 3 V+
R2 V IN
1.182V
MAX934
8 REF V9
182k 1V
5 4
INA+ OUTA INA-
2 330
7
INB+ OUTB
1 330
750mV
6
INB-
250k 500mV
11 10
INC+ OUTC INC-
16 330
250k 250mV
13
IND+ OUTD 15 330 GND 14
12 IND-
250k
Bar-Graph Level Gauge
The high output source capability of the MAX931 series is useful for driving LEDs. An example of this is the simple four-stage level detector shown in Figure 7.
12
Figure 7. Bar-Graph Level Gauge
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Ultra Low-Power, Low-Cost Comparators with 2% Reference MAX931-MAX934
+5V V+
10k VINA
MAX934
INA+ OUTA INA0 FOR VINA < 0V 1 FOR VINB > 0V R3 INA+ VIN +5V V+
10k VINB
REF INB+ OUTB INBR2 R5 HYST
INPUT VOLTAGE FAIL
R4 10k VINC INC+ OUTC INCR1
INB+
INPUT VOLTAGE LOW
MAX932
V-
10k VIND
IND+ OUTD INDREF GND VN.C.
-5V
Figure 8. Level Shifter: 5V Input to CMOS Output
Figure 9. Two-Stage Low-Voltage Detector
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13
Ultra Low-Power, Low-Cost Comparators with 2% Reference MAX931-MAX934
_________________Pin Configurations
TOP VIEW
GND V1 2 8 7 OUT V+ REF HYST
_Ordering Information (continued)
PART MAX932CPA MAX932CSA MAX932CUA MAX932EPA MAX932ESA MAX933CPA MAX933CSA MAX933CUA MAX933EPA MAX933ESA MAX934CPE MAX934CSE MAX934EPE MAX934ESE TEMP. RANGE 0C to +70C 0C to +70C 0C to +70C -40C to +85C -40C to +85C 0C to +70C 0C to +70C 0C to +70C -40C to +85C -40C to +85C 0C to +70C 0C to +70C -40C to +85C -40C to +85C PIN-PACKAGE 8 Plastic DIP 8 SO 8 MAX 8 Plastic DIP 8 SO 8 Plastic DIP 8 SO 8 MAX 8 Plastic DIP 8 SO 16 Plastic DIP 16 Narrow SO 16 Plastic DIP 16 Narrow SO
IN+ 3 IN- 4
MAX931
6 5
DIP/SO/MAX
OUTA V-
1 2
8 7
OUTB V+ REF HYST
INA+ 3 INB+ 4
MAX932
6 5
DIP/SO/MAX
OUTA V-
1 2
8 7
OUTB V+ REF HYST
For similar devices guaranteed over the military temp. range, see the MAX921-MAX924 data sheet. The MAX931, MAX933, and MAX934 are pin-compatible with the 1% accurate MAX921, MAX923, and MAX924, respectively. The MAX932 and MAX922 are not pin-compatible.
INA+ 3 INB- 4
MAX933
6 5
DIP/SO/MAX
OUTB 1 OUTA 2 V+ 3 INA- 4 INA+ 5 INB- 6 INB+ 7 REF 8
16 OUTC 15 OUTD 14 GND
MAX934
13 12 11 10 9
IND+ INDINC+ INCV-
DIP/Narrow SO
14
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Ultra Low-Power, Low-Cost Comparators with 2% Reference
________________________________________________________Package Information
PDIPN.EPS
MAX931-MAX934
______________________________________________________________________________________
SOICN.EPS
15
Ultra Low-Power, Low-Cost Comparators with 2% Reference MAX931-MAX934
__________________________________________Package Information (continued)
8LUMAXD.EPS
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
16 __________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600 (c) 1997 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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