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19-0115; Rev 3; 3/95
Ultra Low-Power, Single/Dual-Supply Comparators
_______________General Description
The MAX921-MAX924 single, dual, and quad micropower, low-voltage comparators feature the lowest power consumption available. These comparators draw less than 4A supply current over temperature (MAX921/MAX922), and include an internal 1.182V 1% voltage reference, programmable hysteresis, and TTL/CMOS outputs that sink and source current. Ideal for 3V or 5V single-supply applications, the MAX921-MAX924 operate from a single +2.5V to +11V supply (or a 1.25V to 5V dual supply), and each comparator's input voltage range swings from the negative supply rail to within 1.3V of the positive supply. The MAX921-MAX924's unique output stage continuously sources as much as 40mA. And by eliminating power-supply glitches that commonly occur when comparators change logic states, the MAX921-MAX924 minimize parasitic feedback, which makes them easier to use. The single MAX921 and dual MAX923 provide a unique and simple method for adding hysteresis without feedback and complicated equations, simply by using the HYST pin and two resistors.
COMPARATORS PER PACKAGE
____________________________Features
o MAX Package--Smallest 8-Pin SO (MAX921/MAX922/MAX923) o Ultra-Low 4A Max Quiescent Current Over Extended Temp. Range (MAX921) 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 1% 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
MAX921-MAX924
______________Ordering Information
PART MAX921CPA MAX921CSA MAX921CUA MAX921C/D MAX921EPA MAX921ESA MAX921MJA TEMP. RANGE 0C to +70C 0C to +70C 0C to +70C 0C to +70C -40C to +85C -40C to +85C -55C to +125C PIN-PACKAGE 8 Plastic DIP 8 SO 8 MAX Dice* 8 Plastic DIP 8 SO 8 CERDIP**
INTERNAL 1% PRECISION REFERENCE
INTERNAL HYSTERESIS
PACKAGE
PART
MAX921 MAX922 MAX923 MAX924
Yes No Yes Yes
1 2 2 4
Yes No Yes No
8-Pin DIP/SO/MAX 8-Pin DIP/SO/MAX 8-Pin DIP/SO/MAX 16-Pin DIP/SO/MAX
Ordering Information continued at end of data sheet. * Dice are tested at TA = +25C, DC parameters only. ** Contact factory for availability and processing to MIL-STD-883.
__________Typical Operating Circuit
VIN 7 V+ 3 IN+ OUT 8 4 IN-
________________________Applications
Battery-Powered Systems Threshold Detectors Window Comparators Oscillator Circuits
5 HYST 6 REF V2
MAX921
GND 1
THRESHOLD DETECTOR ________________________________________________________________ Maxim Integrated Products 1
Call toll free 1-800-998-8800 for free samples or literature.
Ultra Low-Power, Single/Dual-Supply Comparators MAX921-MAX924
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_ (MAX921/924) .....(V+ + 0.3V) to (GND - 0.3V) Voltage OUT_ (MAX922/923)...........(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 8-Pin CERDIP (derate 8.00mW/C above +70C)........640mW 16-Pin Plastic DIP (derate 10.53mW/C above +70C)..842mW 16-Pin SO (derate 8.70mW/C above +70C) ................696mW 16-Pin CERDIP (derate 10.00mW/C above +70C) ......800mW Operating Temperature Ranges: MAX92_C_ _ .......................................................0C to +70C MAX92_E_ _.....................................................-40C to +85C MAX92_MJ_ ..................................................-55C to +125C 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) MAX921, C/E temp. ranges HYST = REF M temp. range TA = +25C MAX922 Supply Current IN+ = IN- + 100mV C/E temp. ranges M temp. range MAX923, C/E temp. ranges HYST = REF M temp. range TA = +25C C/E temp. ranges MAX924 M temp. range 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 MAX921, MAX923 VV- to (V+ - 1.3V) V+ = 2.5V to 11V 100Hz to 100kHz MAX921, MAX923 TA = +25C, 100pF load Overdrive = 10mV Overdrive = 100mV 0.1 0.1 20 REF- 0.05V 12 4 C/E temp. ranges M temp. range 0.01 0.02 V+ - 1.3 1.0 1.0 REF TA = +25C 3.1 2.5 TA = +25C 2.5 2.5 11 3.2 4 5 3.2 4 5 4.5 6 7.5 6.5 8.5 11 10 5 40 mV nA nA V mV/V mV/V VRMS V s A V CONDITIONS MIN TYP MAX UNITS
5.5
2
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Ultra Low-Power, Single/Dual-Supply Comparators
ELECTRICAL CHARACTERISTICS: 5V OPERATION (continued)
(V+ = 5V, V- = GND = 0V, TA = TMIN to TMAX, unless otherwise noted.) PARAMETER Output High Voltage MAX92_ MAX922/ MAX923 MAX921/ MAX924 CONDITIONS C/E temp. ranges: IOUT = 17mA; M temp. range: IOUT = 10mA C/E temp. ranges: IOUT = 1.8mA; M temp. range: IOUT = 1.2mA C/E temp. ranges: IOUT = 1.8mA; M temp. range: IOUT = 1.2mA C temp. range E temp. range M temp. range TA = +25C C/E temp. ranges M temp. range TA = +25C C/E temp. ranges M temp. range 100Hz to 100kHz 1.170 1.158 1.147 15 6 4 8 4 2 MIN V+ - 0.4 V- + 0.4 V GND + 0.4 TYP MAX UNITS V
MAX921-MAX924
Output Low Voltage
REFERENCE (MAX921/MAX923/MAX924 ONLY) X 1.182 Reference Voltage 1.194 1.206 1.217 V
25 A 15 A 100 VRMS
Source Current
Sink Current Voltage Noise
Note 1: MAX924 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 TA = +25C MAX921 C/E temp. ranges M temp. range TA = +25C MAX922 Supply Current HYST = REF, IN+ = (IN- + 100mV) MAX923 C/E temp. ranges M temp. range TA = +25C C/E temp. ranges M temp. range TA = +25C C/E temp. ranges M temp. range 3.4 2.4 2.4 3.0 3.8 4.8 3.0 3.8 4.8 4.3 5.8 7.2 6.2 8.0 10.5 10 5 40 mV nA nA A CONDITIONS MIN TYP MAX UNITS
5.2
MAX924 COMPARATOR Input Offset Voltage Input Leakage Current (IN-, IN+) Input Leakage Current (HYST)
VCM = 1.5V IN+ = IN- = 1.5V MAX921, MAX923 C/E temp. ranges M temp. range 0.01 0.02
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3
Ultra Low-Power, Single/Dual-Supply Comparators MAX921-MAX924
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 CONDITIONS V- to (V+ - 1.3V) V+ = 2.5V to 11V 100Hz to 100kHz MAX921, MAX923 TA = +25C, 100pF load MAX92_ MAX922/ MAX923 MAX921/ MAX924 Overdrive = 10mV Overdrive = 100mV V+ - 0.4 V- + 0.4 V GND + 0.4 MIN V0.2 0.1 20 REF- 0.05V 14 5 TYP MAX V+ - 1.3 1 1 REF UNITS V mV/V mV/V VRMS V s V
C/E temp. ranges: IOUT = 10mA; M temp. range: IOUT = 6mA C/E temp. ranges: IOUT = 0.8mA; M temp. range: IOUT = 0.6mA C/E temp. ranges: IOUT = 0.8mA; M temp. range: IOUT = 0.6mA C temp. range E temp. range M temp. range TA = +25C C/E temp. ranges M temp. range TA = +25C C/E temp. ranges M temp. range
Output Low Voltage
REFERENCE Reference Voltage 1.170 1.158 1.147 15 6 4 8 4 2 1.182 1.194 1.206 1.217 V
25 A 15 A 100 VRMS
Source Current
Sink Current Voltage Noise 100Hz to 100kHz
__________________________________________Typical Operating Characteristics
(V+ = 5V, V- = GND, TA = +25C, unless otherwise noted).
OUTPUT VOLTAGE LOW vs. LOAD CURRENT
MAX921/4-TOC1
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)
4
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Ultra Low-Power, Single/Dual-Supply Comparators
__________________________________________Typical Operating Characteristics
(V+ = 5V, V- = GND, TA = +25C, unless otherwise noted).
REFERENCE VOLTAGE vs. TEMPERATURE
MAX921/924-TOC4
MAX921-MAX924
MAX921 SUPPLY CURRENT vs. TEMPERATURE
MAX921/924-TOC5
MAX922 SUPPLY CURRENT vs. TEMPERATURE
IN+ = (IN- + 100mV) 4.0 SUPPLY CURRENT (A) 3.5 V+ = 10V, V- = 0V 3.0 2.5 V+ = 5V, V- = 0V 2.0 V+ = 3V, V- = 0V 1.5
MAX921/924-TOC6
1.22 1.21 REFERENCE VOLTAGE (V) 1.20 1.19 1.18 1.17 1.16 1.15 MILITARY TEMP. RANGE EXTENDED TEMP. RANGE COMMERCIAL TEMP. RANGE
4.5 IN+ = IN- + 100mV SUPPLY CURRENT (A) 4.0 V+ = 5V, V- = - 5V
4.5
3.5
3.0 V+ = 3V, V- = 0V 2.5 V+ = 5V, V- = 0V
1.14 -60 -40 -20 0 20 40 60 80 100 120 140 TEMPERATURE (C)
2.0 -60 -20 20 60 100 140 TEMPERATURE (C)
-60
-20
20
60
100
140
TEMPERATURE (C)
MAX923 SUPPLY CURRENT vs. TEMPERATURE
MAX921/924-TOC7
MAX924 SUPPLY CURRENT vs. TEMPERATURE
MAX921/924-TOC8
MAX924 SUPPLY CURRENT vs. LOW SUPPLY VOLTAGES
MAX921/924-TOC9
5.0 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
SUPPLY CURRENT (A) 140
1
0.1
0.01 -60 -20 20 60 100 1.0 1.5 2.0 2.5 TEMPERATURE (C) SINGLE-SUPPLY VOLTAGE (V)
140
TEMPERATURE (C)
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 V- = 0V
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
VOHL
50
-0.3
VREF -VHYST (mV)
0.2 0.1 -0.2 -0.1 0 IN+ INPUT VOLTAGE (mV)
0.3
0
20
40
60
80
100
LOAD CAPACITANCE (nF)
_______________________________________________________________________________________
5
Ultra Low-Power, Single/Dual-Supply Comparators MAX921-MAX924
__________________________________________Typical Operating Characteristics
(V+ = 5V, V- = GND, TA = +25C, unless otherwise noted). RESPONSE TIME FOR VARIOUS INPUT OVERDRIVES
MAX921/924-TOC13
RESPONSE TIME FOR VARIOUS INPUT OVERDRIVES
MAX921/924-TOC14
MAX924 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)
MAX924 RESPONSE TIME 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
____________________________________________________________Pin Descriptions
PIN MAX921 1 - 2 3 - 4 - 6 MAX922 - 1 2 - 3 - 4 MAX923 - 1 2 - 3 - - NAME GND OUTA VIN+ INA+ ININAFUNCTION 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 (MAX921). Noninverting comparator input Noninverting input of comparator A Inverting comparator input Inverting input of comparator A
_______________________________________________________________________________________
Ultra Low-Power, Single/Dual-Supply Comparators
_______________________________________________Pin Descriptions (continued)
PIN MAX921 - 5 6 - 7 8 - MAX922 5 - - 6 7 - 8 MAX923 4 5 6 - 7 - 8 NAME INBHYST REF INB+ V+ OUT OUTB 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-. Noninverting input of comparator B 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-. FUNCTION
MAX921-MAX924
PIN MAX924 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.
_______________________________________________________________________________________
7
Ultra Low-Power, Single/Dual-Supply Comparators MAX921-MAX924
_______________Detailed Description
The MAX921-MAX924 comprise various combinations of a micropower 1.182V reference and a micropower comparator. The Typical Operating Circuit shows the MAX921 configuration, and Figures 1a-1c show the MAX922-MAX924 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 circuit-board layout is not optimal. Internal hysteresis in the MAX921 and MAX923 provides the easiest method for implementing hysteresis. It also produces faster hysteresis action and consumes much less current than circuits using external positive feedback. 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 MAX921 and the MAX924 from a single supply. The maximum supply voltage in this case is still 11V. For proper comparator operation, the input signal can swing 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 MAX921 and MAX924 at 5V provides TTL/CMOS compatibility when monitoring bipolar input signals. TTL compatibility for the MAX922 and MAX923 is achieved by operation from a single +5V supply.
Power-Supply and Input Signal Ranges
This family of devices operates from a single +2.5V to +11V power supply. The MAX921 and MAX924 have a
Low-Voltage Operation: V+ = 1V (MAX924 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 current falls. The reference will not function below
1 OUTA 2 V3 INA+ 4 INA-
MAX922
OUTB 8 V+ 7 1 OUTB INB+ 6 2 OUTA INB- 5 3 V+ 4 INAGND 14 IND+ 13 IND- 12 OUTD 15
MAX924
OUTC 16
Figure 1a. MAX922 Functional Diagram
5 INA+
1 OUTA 2 V3 INA+ 4 INBV-
MAX923
6 INBOUTB 8 7 INB+ V+ 7 8 REF REF 6 HYST 5
INC+ 11 INC- 10 V- 9
Figure 1b. MAX923 Functional Diagram
8
Figure 1c. MAX924 Functional Diagram
_______________________________________________________________________________________
Ultra Low-Power, Single/Dual-Supply Comparators
The MAX921-MAX924'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.
MAX921-MAX924
IN+
THRESHOLDS
INVREF - VHYST
HYSTERESIS VHB BAND
Voltage Reference
OUT
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 1% in the range 0C to +70C. The REF output is typically capable of sourcing 15A and sinking 8A. Do not bypass the REF output.
Figure 2. Threshold Hysteresis Band
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). 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
about 2.2V, although the comparators will continue to operate with a total supply voltage as low as 1V. While the MAX924 has comparators that may be used at supply voltages below 2V, the MAX921, MAX922, and MAX923 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.
IREF R1
6 REF
2.5V TO 11V 7 V+
Comparator Output
With 100mV of overdrive, propagation delay is typically 3s. The Typical Operating Characteristics show the propagation delay for various overdrive levels. The MAX921 and MAX924 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 MAX922 and MAX923 have no GND pin, and their outputs swing from V+ to V-. Connect V- to ground and V+ to a +5V supply to achieve TTL compatibility.
5 R2
MAX921 MAX923
HYST V2
Figure 3. Programming the HYST Pin
_______________________________________________________________________________________
9
Ultra Low-Power, Single/Dual-Supply Comparators MAX921-MAX924
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. 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. 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.
__________Applications Information
Hysteresis
Hysteresis increases the comparators' noise margin by increasing the upper threshold and decreasing the lower threshold (see Figure 2).
Hysteresis (MAX921/MAX923) To add hysteresis to the MAX921 or MAX923, 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 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 V HB can be approximated as: R1 (k) = VHB (mV) When hysteresis is obtained in this manner for the MAX923, the same hysteresis applies to both comparators.
V+ R3
R1 VIN R2
MAX924 VGND
V+
OUT
VREF
Hysteresis (MAX922/MAX924) 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 MAX921 and MAX923, and the high
10
Figure 4. External Hysteresis
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Ultra Low-Power, Single/Dual-Supply Comparators
_______________Typical Applications
4.5V TO 6.0V 7 V+ MOMENTARY SWITCH
MAX921-MAX924
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 (V BATT - 0.12V), but draws only 3.5A quiescent current. This circuit takes advantage of the four key features of the MAX921: 2.5A supply current, an internal reference, hysteresis, and high current output. Using the component values shown, the threeresistor 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 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.
6 47k 5 1.1M
MAX921
REF
IN+ 3 C R
HYST OUT 8
4 IN100k V2 GND 1
VBATT -0.15V 10mA
Figure 5. Auto-off power switch operates on 2.5A quiescent current.
Window Detector
The MAX923 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 (MAX921/MAX923) section. In this example, 5mV of hysteresis has been added at the comparator input (VH = VHB/2). This means that the hysteresis apparent at VIN will be larger because of the input resistor divider.
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 -
(R1
x V +) R3
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.
______________________________________________________________________________________
11
Ultra Low-Power, Single/Dual-Supply Comparators MAX921-MAX924
2. Select R1. The leakage current into INB- is normally under 1nA, so the current through R1 should exceed 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:
R2 = (R1 + R2 + R3) x = (294k + 1.068M) x (VREF - VH ) - R1 VUTH (1.182 - 0.005) - 294k 4.5
R1 VIN R3 INA+ V+ OUTA UNDERVOLTAGE VOTH = 5.5V VUTH = 4.5V
+5V
HYST R2 10k R5 REF R4 2.4M INBVOUTB POWER GOOD
OVERVOLTAGE
MAX923
Figure 6. Window Detector
= 62.2k Choose R2 = 61.9k (1% standard value).
Bar-Graph Level Gauge
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 : VOTH = (VREF + VH ) x = 5.474V. Undervoltage threshold : VUTH = (VREF - VH ) x = 4.484V, where the hysteresis voltage VH = VREF x R5 . R4 (R1 + R2 + R3) (R1 + R2) (R1 + R2 + R3) R1
The high output source capability of the MAX921 series is useful for driving LEDs. An example of this is the simple four-stage level detector shown in Figure 7. 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.
12
______________________________________________________________________________________
Ultra Low-Power, Single/Dual-Supply Comparators MAX921-MAX924
R1 +5V 3 V+ 1.182V 8 R2 V IN +5V
V+ 10k VINA V- 9 INA+ OUTA 0 FOR VINA < 0V 1 FOR VINB > 0V
MAX924
REF
MAX924
182k
5 INA+ OUTA 2 10k 1V 4 INA330 VINB
INA-
INB+ OUTB
250k
7 INB+ OUTB 1 750mV 6 INB330 10k VINC
INB-
INC+ OUTC
250k
11 INC+ OUTC 16 500mV 10 INC330 10k VIND
INC-
IND+ OUTD
250k
13 IND+ OUTD 15 250mV 12 INDGND 14 330
INDREF VN.C.
GND
250k
-5V
Figure 7. Bar-Graph Level Gauge
Figure 8. Level Shifter: 5V Input to CMOS Output
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13
Ultra Low-Power, Single/Dual-Supply Comparators MAX921-MAX924
_________________Pin Configurations
TOP VIEW
GND V1 2 8 7 OUT V+ REF HYST
_Ordering Information (continued)
PART MAX922CPA MAX922CSA MAX922CUA MAX922C/D MAX922EPA MAX922ESA MAX922MJA MAX923CPA MAX923CSA MAX923CUA MAX923C/D MAX923EPA MAX923ESA MAX923MJA MAX924CPE MAX924CSE MAX924C/D MAX924EPE MAX924ESE MAX924MJE TEMP. RANGE 0C to +70C 0C to +70C 0C to +70C 0C to +70C -40C to +85C -40C to +85C -55C to +125C 0C to +70C 0C to +70C 0C to +70C 0C to +70C -40C to +85C -40C to +85C -55C to +125C 0C to +70C 0C to +70C 0C to +70C -40C to +85C -40C to +85C -55C to +125C PIN-PACKAGE 8 Plastic DIP 8 SO 8 MAX Dice* 8 Plastic DIP 8 SO 8 CERDIP** 8 Plastic DIP 8 SO 8 MAX Dice* 8 Plastic DIP 8 SO 8 CERDIP** 16 Plastic DIP 16 Narrow SO Dice* 16 Plastic DIP 16 Narrow SO 16 CERDIP**
IN+ 3 IN- 4
MAX921
6 5
DIP/SO/MAX
OUTA V-
1 2
8 7
OUTB V+ INB+ INB-
INA+ 3 INA- 4
MAX922
6 5
DIP/SO/MAX
OUTA V-
1 2
8 7
OUTB V+ REF HYST
INA+ 3 INB- 4
MAX923
6 5
* Dice are tested at TA = +25C, DC parameters only. ** Contact factory for availability and processing to MIL-STD-883.
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
MAX924
13 IND+ 12 IND11 INC+ 10 INC9 V-
DIP/Narrow SO
14
______________________________________________________________________________________
Ultra Low-Power, Single/Dual-Supply Comparators
__________________________________________________________Chip Topographies
MAX921/MAX922/MAX923
OUTA
MAX921-MAX924
MAX924
OUTB OUTC OUTD
1
10
V+
9 2 8 3 4 7 0.108" (2.74mm) INAINA+ 0.059" (1.50mm) INBIND+ INDINC+ 0.075" (1.91mm) GND
5
6
DIE PAD 1 2 3 4 5 6 7 8 9 10
MAX921 GND VVIN+ INHYST REF V+ V+ OUT
MAX922 OUTA VVINA+ INAINBINB+ V+ V+ OUTB
MAX923 OUTA VVINA+ INBHYST REF V+ V+ OUTB
INB+
REF
V-
INC-
0.069" (1.75mm)
TRANSISTOR COUNT: 267 SUBSTRATE CONNECTED TO V+
TRANSISTOR COUNT: 164 SUBSTRATE CONNECTED TO V+
______________________________________________________________________________________
15
Ultra Low-Power, Single/Dual-Supply Comparators MAX921-MAX924
_______________________________________________________Package Information
DIM
C A 0.101mm 0.004 in B A1 L
e
A A1 B C D E e H L
INCHES MAX MIN 0.044 0.036 0.008 0.004 0.014 0.010 0.007 0.005 0.120 0.116 0.120 0.116 0.0256 0.198 0.188 0.026 0.016 6 0
MILLIMETERS MIN MAX 0.91 1.11 0.10 0.20 0.25 0.36 0.13 0.18 2.95 3.05 2.95 3.05 0.65 4.78 5.03 0.41 0.66 0 6
21-0036D
E
H
8-PIN MAX MICROMAX SMALL-OUTLINE PACKAGE
D
DIM
D A e B
0.101mm 0.004in.
0-8
A1
C
L
A A1 B C E e H L
INCHES MAX MIN 0.069 0.053 0.010 0.004 0.019 0.014 0.010 0.007 0.157 0.150 0.050 0.244 0.228 0.050 0.016
MILLIMETERS MIN MAX 1.35 1.75 0.10 0.25 0.35 0.49 0.19 0.25 3.80 4.00 1.27 5.80 6.20 0.40 1.27
E
H
Narrow SO SMALL-OUTLINE PACKAGE (0.150 in.)
DIM PINS D D D 8 14 16
INCHES MILLIMETERS MIN MAX MIN MAX 0.189 0.197 4.80 5.00 0.337 0.344 8.55 8.75 0.386 0.394 9.80 10.00
21-0041A
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) 1995 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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