19-0115; Rev 3; 3/95 Ultra Low-Power, Single/Dual-Supply Comparators PACKAGE INTERNAL HYSTERESIS COMPARATORS PER PACKAGE INTERNAL 1% PRECISION REFERENCE PART MAX921 Yes 1 Yes 8-Pin DIP/SO/µMAX MAX922 No 2 No 8-Pin DIP/SO/µMAX MAX923 Yes 2 Yes 8-Pin DIP/SO/µMAX No 16-Pin DIP/SO/µMAX MAX924 Yes 4 ____________________________Features ♦ µMAX Package—Smallest 8-Pin SO (MAX921/MAX922/MAX923) ♦ Ultra-Low 4µA Max Quiescent Current Over Extended Temp. Range (MAX921) ♦ Power Supplies: Single +2.5V to +11V Dual ±1.25V to ±5.5V ♦ Input Voltage Range Includes Negative Supply ♦ Internal 1.182V ±1% Bandgap Reference ♦ Adjustable Hysteresis ♦ TTL/CMOS-Compatible Outputs ♦ 12µs Propagation Delay (10mV Overdrive) ♦ No Switching Crowbar Current ♦ 40mA Continuous Source Current ______________Ordering Information PART TEMP. RANGE MAX921CPA 0°C to +70°C MAX921CSA 0°C to +70°C MAX921CUA MAX921C/D MAX921EPA MAX921ESA MAX921MJA 0°C to +70°C 0°C to +70°C -40°C to +85°C -40°C to +85°C -55°C to +125°C PIN-PACKAGE 8 Plastic DIP 8 SO 8 µMAX Dice* 8 Plastic DIP 8 SO 8 CERDIP** Ordering Information continued at end of data sheet. * Dice are tested at TA = +25°C, 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 MAX921 6 REF V2 GND 1 THRESHOLD DETECTOR ________________________________________________________________ Maxim Integrated Products Call toll free 1-800-998-8800 for free samples or literature. 1 MAX921–MAX924 _______________General Description The MAX921–MAX924 single, dual, and quad micropower, low-voltage comparators feature the lowest power consumption available. These comparators draw less than 4µA 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. MAX921–MAX924 Ultra Low-Power, Single/Dual-Supply Comparators 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 = +70°C) 8-Pin Plastic DIP (derate 9.09mW/°C above +70°C) ...727mW 8-Pin SO (derate 5.88mW/°C above +70°C)................471mW 8-Pin µMAX (derate 4.1mW/°C above +70°C) .............330mW 8-Pin CERDIP (derate 8.00mW/°C above +70°C)........640mW 16-Pin Plastic DIP (derate 10.53mW/°C above +70°C)..842mW 16-Pin SO (derate 8.70mW/°C above +70°C) ................696mW 16-Pin CERDIP (derate 10.00mW/°C above +70°C) ......800mW Operating Temperature Ranges: MAX92_C_ _ .......................................................0°C to +70°C MAX92_E_ _.....................................................-40°C to +85°C MAX92_MJ_ ..................................................-55°C to +125°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10sec) .............................+300°C 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 CONDITIONS MIN TYP MAX UNITS 11 V 2.5 3.2 POWER REQUIREMENTS Supply Voltage Range (Note 1) 2.5 TA = +25°C MAX921, C/E temp. ranges HYST = REF M temp. range 4 5 TA = +25°C MAX922 Supply Current 2.5 C/E temp. ranges 4 M temp. range IN+ = IN- + 100mV 5 TA = +25°C 3.1 4.5 5.5 6 7.5 6.5 8.5 11 ±0.01 ±10 ±5 ±40 MAX923, C/E temp. ranges HYST = REF M temp. range TA = +25°C C/E temp. ranges MAX924 M temp. range COMPARATOR Input Offset Voltage VCM = 2.5V Input Leakage Current (IN-, IN+) IN+ = IN- = 2.5V Input Leakage Current (HYST) Input Common-Mode Voltage Range Common-Mode Rejection Ratio Power-Supply Rejection Ratio Voltage Noise Hysteresis Input Voltage Range MAX921, MAX923 Response Time 2 C/E temp. ranges M temp. range ±0.02 V- V- to (V+ – 1.3V) V+ = 2.5V to 11V 100Hz to 100kHz MAX921, MAX923 TA = +25°C, 100pF load 3.2 0.1 0.1 20 REF- 0.05V Overdrive = 10mV Overdrive = 100mV V+ – 1.3 1.0 1.0 REF 12 4 _______________________________________________________________________________________ µA mV nA nA V mV/V mV/V µVRMS V µs Ultra Low-Power, Single/Dual-Supply Comparators MAX921–MAX924 ELECTRICAL CHARACTERISTICS: 5V OPERATION (continued) (V+ = 5V, V- = GND = 0V, TA = TMIN to TMAX, unless otherwise noted.) PARAMETER Output High Voltage Output Low Voltage CONDITIONS MIN TYP MAX MAX92_ C/E temp. ranges: IOUT = 17mA; M temp. range: IOUT = 10mA MAX922/ MAX923 C/E temp. ranges: IOUT = 1.8mA; M temp. range: IOUT = 1.2mA V- + 0.4 MAX921/ MAX924 C/E temp. ranges: IOUT = 1.8mA; M temp. range: IOUT = 1.2mA GND + 0.4 V+ – 0.4 UNITS V V REFERENCE (MAX921/MAX923/MAX924 ONLY) X C temp. range E temp. range M temp. range TA = +25°C C/E temp. ranges M temp. range TA = +25°C C/E temp. ranges M temp. range Reference Voltage Source Current Sink Current Voltage Noise 1.170 1.158 1.147 15 6 4 8 4 2 100Hz to 100kHz 1.182 1.194 1.206 1.217 V 25 µA 15 µA 100 µVRMS 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 CONDITIONS MIN TYP MAX UNITS POWER REQUIREMENTS TA = +25°C MAX921 2.4 C/E temp. ranges M temp. range TA = +25°C MAX922 C/E temp. ranges TA = +25°C MAX923 MAX924 COMPARATOR Input Offset Voltage 4.8 2.4 C/E temp. ranges M temp. range TA = +25°C C/E temp. ranges M temp. range 4.8 3.4 4.3 5.2 5.8 7.2 6.2 8.0 10.5 ±0.01 ±10 ±5 ±40 VCM = 1.5V Input Leakage Current (IN-, IN+) IN+ = IN- = 1.5V Input Leakage Current (HYST) MAX921, MAX923 C/E temp. ranges M temp. range 3.0 3.8 M temp. range HYST = REF, IN+ = (IN- + 100mV) Supply Current 3.0 3.8 ±0.02 µA mV nA nA _______________________________________________________________________________________ 3 ELECTRICAL CHARACTERISTICS: 3V OPERATION (continued) (V+ = 3V, V- = GND = 0V, TA = TMIN to TMAX, unless otherwise noted.) PARAMETER CONDITIONS Input Common-Mode Voltage Range Common-Mode Rejection Ratio Power-Supply Rejection Ratio Voltage Noise Hysteresis Input Voltage Range MIN TYP VV- to (V+ – 1.3V) V+ = 2.5V to 11V 100Hz to 100kHz MAX921, MAX923 0.2 0.1 20 MAX UNITS V+ – 1.3 1 1 V mV/V mV/V µVRMS V REF- 0.05V Overdrive = 10mV Overdrive = 100mV REF 14 5 Response Time TA = +25°C, 100pF load Output High Voltage MAX92_ C/E temp. ranges: IOUT = 10mA; M temp. range: IOUT = 6mA MAX922/ MAX923 C/E temp. ranges: IOUT = 0.8mA; M temp. range: IOUT = 0.6mA V- + 0.4 MAX921/ MAX924 C/E temp. ranges: IOUT = 0.8mA; M temp. range: IOUT = 0.6mA GND + 0.4 Output Low Voltage µs V+ – 0.4 V V REFERENCE C temp. range E temp. range M temp. range TA = +25°C C/E temp. ranges M temp. range TA = +25°C C/E temp. ranges M temp. range Reference Voltage Source Current Sink Current Voltage Noise 1.170 1.158 1.147 15 6 4 8 4 2 1.182 1.194 1.206 1.217 V 25 µA 15 µA 100Hz to 100kHz 100 µVRMS __________________________________________Typical Operating Characteristics (V+ = 5V, V- = GND, TA = +25°C, unless otherwise noted). 2.0 MAX921/924-TOC2 V+ = 5V V+ = 5V 4.5 4.0 V+ = 3V VOH (V) 1.5 1.0 3.5 3.0 2.5 V+ = 3V 0.5 2.0 0.0 4 8 12 LOAD CURRENT (mA) 4 16 20 SINK 1.185 1.180 SOURCE 1.175 1.170 1.165 V+ = 5V OR V+ = 3V 1.160 1.155 1.5 0 1.190 REFERENCE OUTPUT VOLTAGE (V) 5.0 MAX921/4-TOC1 2.5 REFERENCE OUTPUT VOLTAGE vs. OUTPUT LOAD CURRENT OUTPUT VOLTAGE HIGH vs. LOAD CURRENT MAX921/924-TOC3 OUTPUT VOLTAGE LOW vs. LOAD CURRENT VOL (V) MAX921–MAX924 Ultra Low-Power, Single/Dual-Supply Comparators 0 10 20 30 LOAD CURRENT (mA) 40 50 0 5 10 15 20 25 OUTPUT LOAD CURRENT (µA) _______________________________________________________________________________________ 30 Ultra Low-Power, Single/Dual-Supply Comparators MAX921 SUPPLY CURRENT vs. TEMPERATURE COMMERCIAL TEMP. RANGE 1.19 1.18 1.17 1.16 4.0 V+ = 5V, V- = - 5V 3.5 3.0 V+ = 3V, V- = 0V IN+ = (IN- + 100mV) 4.0 3.5 V+ = 10V, V- = 0V 3.0 2.5 V+ = 5V, V- = 0V 2.5 2.0 1.15 V+ = 3V, V- = 0V V+ = 5V, V- = 0V 2.0 1.14 -60 -40 -20 0 -20 20 60 100 140 -60 -20 20 100 60 TEMPERATURE (°C) TEMPERATURE (°C) TEMPERATURE (°C) MAX923 SUPPLY CURRENT vs. TEMPERATURE MAX924 SUPPLY CURRENT vs. TEMPERATURE MAX924 SUPPLY CURRENT vs. LOW SUPPLY VOLTAGES 4.0 V+ = 5V, V- = 0V 3.5 3.0 2.5 8 7 V+ = 5V, V- = -5V 6 V+ = 5V, V- = 0V 5 4 140 MAX921/924-TOC9 10 MAX921/924-TOC8 IN+ = (IN- + 100mV) 9 SUPPLY CURRENT (µA) MAX921/924-TOC7 4.5 10 SUPPLY CURRENT (µA) 5.0 SUPPLY CURRENT (µA) 1.5 -60 20 40 60 80 100 120 140 MAX921/924-TOC6 IN+ = IN- + 100mV SUPPLY CURRENT (µA) REFERENCE VOLTAGE (V) EXTENDED TEMP. RANGE 1.20 4.5 MAX921/924-TOC5 MILITARY TEMP. RANGE 1.21 4.5 MAX921/924-TOC4 1.22 MAX922 SUPPLY CURRENT vs. TEMPERATURE SUPPLY CURRENT (µA) REFERENCE VOLTAGE vs. TEMPERATURE 1 0.1 V+ = 3V, V- = 0V V+ = 3V, V- = 0V 3 2.0 -20 20 60 100 20 60 100 140 2.0 1.5 2.5 SINGLE-SUPPLY VOLTAGE (V) HYSTERESIS CONTROL TRANSFER FUNCTION RESPONSE TIME vs. LOAD CAPACITANCE 20 NO CHANGE -20 -40 4.0 V0 10µF 3.5 3.0 2.5 2.0 1.5 1.0 OUTPUT LOW 0 10 20 30 VREF -VHYST (mV) 40 50 V- = 0V 16 14 VOHL 12 10 8 VOLH 6 4 0.5 -80 18 MAX921/924 TOC12 100k MAX921/924-TOC11 4.5 OUTPUT VOLTAGE (V) 40 0 5.0 MAX921/924 TOC10 OUTPUT HIGH 0 1.0 TEMPERATURE (°C) 60 IN+ – IN- (V) -20 TEMPERATURE (°C) 80 -60 0.01 -60 140 RESPONSE TIME (µs) -60 2 -0.3 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 MAX921-MAX924 __________________________________________Typical Operating Characteristics (V+ = 5V, V- = GND, TA = +25°C, unless otherwise noted). __________________________________________Typical Operating Characteristics (V+ = 5V, V- = GND, TA = +25°C, unless otherwise noted). 2 50mV 1 10mV 0 -2 2 6 10 10mV 100mV 2 20mV 1 50mV 14 18 RESPONSE TIME (µs) 100 0.01 -2 1 2 6 10 14 18 1.0 2.0 1.5 RESPONSE TIME (µs) SINGLE-SUPPLY VOLTAGE (V) SHORT-CIRCUIT SOURCE CURRENT vs. SUPPLY VOLTAGE SHORT-CIRCUIT SINK CURRENT vs. SUPPLY VOLTAGE 200 OUT CONNECTED TO V- 160 140 120 100 80 60 2.5 OUT CONNECTED TO V+ GND CONNECTED TO VSINK CURRENT (mA) MAX921/924-TOC16 10 ±20mV OVERDRIVE 0.1 ±100mV OVERDRIVE 180 SOURCE CURRENT (mA) SOURCE CURRENT INTO 0.75V LOAD 1 0 MAX924 RESPONSE TIME AT LOW SUPPLY VOLTAGES 100 MAX921/924-TOC15 MAX921/924-TOC14 4 3 0 100 10 MAX121/124-TOC18 20mV 5 RESPONSE TIME (ms) 100mV MAX924 RESPONSE TIME AT LOW SUPPLY VOLTAGES MAX121/124-TOC17 MAX921/924-TOC13 4 3 OUTPUT VOLTAGE (V) 5 0 INPUT VOLTAGE (mV) RESPONSE TIME FOR VARIOUS INPUT OVERDRIVES INPUT VOLTAGE (mV) OUTPUT VOLTAGE (V) RESPONSE TIME FOR VARIOUS INPUT OVERDRIVES CURRENT (mA) MAX921–MAX924 Ultra Low-Power, Single/Dual-Supply Comparators 20 10 40 20 SINK CURRENT AT VOUT = 0.4V 0 0.1 1.0 2.0 1.5 2.5 0 0 1.0 2.0 3.0 4.0 5.0 0 TOTAL SUPPLY VOLTAGE (V) SINGLE-SUPPLY VOLTAGE (V) 5 10 TOTAL SUPPLY VOLTAGE (V) ____________________________________________________________Pin Descriptions PIN NAME FUNCTION – GND Ground. Connect to V- for single-supply operation. Output swings from V+ to GND. 1 1 OUTA Comparator A output. Sinks and sources current. Swings from V+ to V-. 2 2 2 V- 3 – – IN+ MAX921 MAX922 MAX923 1 – – 6 – 3 3 INA+ 4 – – IN- – 4 – INA- 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 NAME FUNCTION MAX921 MAX922 MAX923 – 5 4 INB- Inverting input of comparator B 5 – 5 HYST Hysteresis input. Connect to REF if not used. Input voltage range is from VREF to VREF - 50mV. 6 – 6 REF Reference output. 1.182V with respect to V-. – 6 – INB+ Noninverting input of comparator B 7 7 7 V+ 8 – – OUT Comparator output. Sinks and sources current. Swings from V+ to GND. – 8 8 OUTB Comparator B output. Sinks and sources current. Swings from V+ to V-. Positive supply PIN MAX924 NAME 1 OUTB Comparator B output. Sinks and sources current. Swings from V+ to GND. 2 OUTA Comparator A output. Sinks and sources current. Swings from V+ to GND. FUNCTION 3 V+ 4 INA- Positive supply Inverting input of comparator A 5 INA+ Noninverting input of comparator A 6 INB- Inverting input of comparator B 7 INB+ Noninverting input of comparator B 8 REF Reference output. 1.182V with respect to V-. 9 V- Negative supply. Connect to ground for single-supply operation. 10 INC- Inverting input of comparator C 11 INC+ Noninverting input of comparator C 12 IND- Inverting input of comparator D 13 IND+ Noninverting input of comparator D 14 GND Ground. Connect to V- for single-supply operation. 15 OUTD Comparator D output. Sinks and sources current. Swings from V+ to GND. 16 OUTC Comparator C output. Sinks and sources current. Swings from V+ to GND. _______________________________________________________________________________________ 7 MAX921–MAX924 _______________________________________________Pin Descriptions (continued) MAX921–MAX924 Ultra Low-Power, Single/Dual-Supply Comparators _______________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. 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 MAX922 1 OUTA 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. 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 OUTB 8 V+ 7 2 V- 1 OUTB 3 INA+ INB+ 6 4 INA- INB- 5 MAX924 2 OUTA Figure 1a. MAX922 Functional Diagram MAX923 1 OUTA OUTD 15 3 V+ GND 14 4 INA- IND+ 13 5 INA+ IND- 12 6 INB- INC+ 11 7 INB+ INC- 10 8 REF V- 9 OUTB 8 V+ 7 2 V- REF 6 3 INA+ HYST 5 4 INBV- Figure 1b. MAX923 Functional Diagram 8 OUTC 16 Figure 1c. MAX924 Functional Diagram _______________________________________________________________________________________ Ultra Low-Power, Single/Dual-Supply Comparators INVREF - VHYST HYSTERESIS VHB BAND 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 ±1% in the range 0°C to +70°C. The REF output is typically capable of sourcing 15µA and sinking 8µA. Do not bypass the REF output. OUT Figure 2. Threshold Hysteresis Band 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. Comparator Output With 100mV of overdrive, propagation delay is typically 3µs. 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. 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 IREF 6 REF 2.5V TO 11V 7 V+ R1 5 R2 MAX921 MAX923 HYST V2 Figure 3. Programming the HYST Pin _______________________________________________________________________________________ 9 MAX921–MAX924 THRESHOLDS IN+ 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 Ultra Low-Power, Single/Dual-Supply Comparators 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. __________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 × 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 0.1µA and 4µA are usually appropriate. If 2.4MΩ is chosen for R2 (IREF = 0.5µA), the equation for R1 and V HB can be approximated as: R1 (kΩ) = VHB (mV) When hysteresis is obtained in this manner for the MAX923, the same hysteresis applies to both comparators. 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 feedback impedance slows hysteresis. The design procedure is as follows: 1. Choose R3. The leakage current of IN+ is under 1nA (up to +85°C), 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 = 11.8MΩ. 10MΩ 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 × HB V+ 0.05 = 10M × 5 = 100kΩ 4. Choose the threshold voltage for VIN rising (VTHR). In this example, choose VTHR = 3V. 5. Calculate R2. 1 R2 = 1 VTHR 1 − − (VREF × R1) R1 R3 1 = 3 1 1 − − (1.182 × 100k) 100k 10M = 65.44kΩ A 1% preferred value is 64.9kΩ. V+ R3 R1 VIN V+ R2 MAX924 VGND VREF Figure 4. External Hysteresis ______________________________________________________________________________________ OUT Ultra Low-Power, Single/Dual-Supply Comparators Auto-Off Power Source MOMENTARY SWITCH 4.5V TO 6.0V 7 V+ 6 MAX921 IN+ 3 REF 47k C 5 R HYST 1.1M OUT 8 VBATT -0.15V 10mA 4 IN100k V2 GND 1 Figure 5. Auto-off power switch operates on 2.5µA quiescent current. 6. Verify the threshold voltages with these formulas: VIN rising : 1 1 1 + + VTHR = VREF × R1 × R1 R2 R3 VIN falling : VTHF = VTHR − (R1 × 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. 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 3.5µA quiescent current. This circuit takes advantage of the four key features of the MAX921: 2.5µA 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: 2MΩ x 10µF x 4.6 = 92sec. The actual time will vary with both the leakage current of the capacitor and the voltage applied to the circuit. 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. ______________________________________________________________________________________ 11 MAX921–MAX924 _______________Typical Applications MAX921–MAX924 Ultra Low-Power, Single/Dual-Supply Comparators 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 10MΩ can be used, but values in the 100kΩ to 1MΩ range are usually easier to deal with. In this example, choose R1 = 294kΩ. 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 × − 1 VREF + VH VIN VOTH = 5.5V VUTH = 4.5V +5V R3 V+ INA+ OUTA UNDERVOLTAGE HYST 10k R5 R2 5.5 = 294k × − 1 (1.182 + 0.005) POWER GOOD REF R4 2.4M = 1.068MΩ OUTB OVERVOLTAGE INB- 4. Calculate R2. The undervoltage threshold should be 4.5V when VIN is falling. The design equation is as follows: VR1 MAX923 (VREF − VH ) − R1 VUTH R2 = (R1 + R2 + R3) × = (294k + 1.068M) × (1.182 − 0.005) − 294k 4.5 Figure 6. Window Detector = 62.2kΩ Choose R2 = 61.9kΩ (1% standard value). Bar-Graph Level Gauge 5. Calculate R3. R3 = (R2 + R3) − R2 = 1.068M − 61.9k = 1.006MΩ Choose R3 = 1MΩ (1% standard value) 6. Verify the resistor values. The equations are as follows, evaluated for the above example. (R1 + R2 + R3) R1 = 5.474V. Undervoltage threshold : VUTH = (VREF − VH ) × Level Shifter Figure 8 shows a circuit to shift from bipolar ±5V inputs to TTL signals. The 10kΩ resistors protect the comparator inputs, and do not materially affect the operation of the circuit. Overvoltage threshold : VOTH = (VREF + VH ) × 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. (R1 + R2 + R3) (R1 + R2) = 4.484V, where the hysteresis voltage VH = VREF × 12 R5 . R4 ______________________________________________________________________________________ Ultra Low-Power, Single/Dual-Supply Comparators MAX921–MAX924 R2 R1 V IN 1.182V 8 +5V +5V 3 V+ V+ REF MAX924 10k MAX924 INA+ VINA OUTA V- 9 INA- 5 INA+ 182k 0 FOR VINA < 0V 1 FOR VINB > 0V OUTA 2 10k 1V 330Ω 4 INA- INB+ VINB OUTB 250k INB- 7 INB+ OUTB 1 750mV 6 330Ω INB- 10k VINC INC+ OUTC 250k INC- 11 INC+ OUTC 16 330Ω 500mV 10 INC- 10k VIND IND+ OUTD 250k IND- 13 IND+ REF OUTD 15 330Ω 250mV 12 IND- 250k N.C. GND GND 14 Figure 7. Bar-Graph Level Gauge V- -5V Figure 8. Level Shifter: ±5V Input to CMOS Output ______________________________________________________________________________________ 13 MAX921–MAX924 Ultra Low-Power, Single/Dual-Supply Comparators _________________Pin Configurations _Ordering Information (continued) PART TOP VIEW MAX922CPA GND V- 1 8 2 IN+ 3 MAX921 IN- 4 OUT 7 V+ 6 REF 5 HYST DIP/SO/µMAX OUTA 1 V- 2 INA+ 3 MAX922 INA- 4 8 OUTB 7 V+ 6 INB+ 5 INB- DIP/SO/µMAX OUTA 1 8 OUTB V- 2 7 V+ 6 REF 5 HYST INA+ 3 MAX923 INB- 4 TEMP. RANGE 0°C to +70°C MAX922CSA 0°C to +70°C MAX922CUA MAX922C/D MAX922EPA MAX922ESA MAX922MJA MAX923CPA 0°C to +70°C 0°C to +70°C -40°C to +85°C -40°C to +85°C -55°C to +125°C 0°C to +70°C 16 OUTC OUTA 2 15 OUTD V+ 3 INA- 4 MAX923CSA 0°C to +70°C 0°C to +70°C 0°C to +70°C -40°C to +85°C -40°C to +85°C -55°C to +125°C 0°C to +70°C 8 µMAX Dice* 8 Plastic DIP 8 SO 8 CERDIP** 16 Plastic DIP MAX924CSE MAX924C/D MAX924EPE MAX924ESE MAX924MJE 0°C to +70°C 0°C to +70°C -40°C to +85°C -40°C to +85°C -55°C to +125°C 16 Narrow SO Dice* 16 Plastic DIP 16 Narrow SO 16 CERDIP** 13 IND+ INA+ 5 12 IND- INB- 6 11 INC+ INB+ 7 10 INC- REF 8 9 V- DIP/Narrow SO 14 8 SO * Dice are tested at TA = +25°C, DC parameters only. ** Contact factory for availability and processing to MIL-STD-883. 14 GND MAX924 8 SO 8 µMAX Dice* 8 Plastic DIP 8 SO 8 CERDIP** 8 Plastic DIP MAX923CUA MAX923C/D MAX923EPA MAX923ESA MAX923MJA MAX924CPE DIP/SO/µMAX OUTB 1 PIN-PACKAGE 8 Plastic DIP ______________________________________________________________________________________ Ultra Low-Power, Single/Dual-Supply Comparators MAX921/MAX922/MAX923 MAX924 OUTB OUTA 10 1 OUTC OUTD V+ 9 2 8 3 GND 0.075" (1.91mm) 4 7 5 6 0.108" (2.74mm) IND+ INA- IND- INA+ 0.059" (1.50mm) DIE PAD 1 2 3 4 5 6 7 8 9 10 MAX921 GND VVIN+ INHYST REF V+ V+ OUT INC+ INB- 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 MAX921–MAX924 __________________________________________________________Chip Topographies MAX921–MAX924 Ultra Low-Power, Single/Dual-Supply Comparators _______________________________________________________Package Information DIM C α A 0.101mm 0.004 in e B A1 L A A1 B C D E e H L α 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 µMAX MICROMAX SMALL-OUTLINE PACKAGE D DIM D 0°-8° A 0.101mm 0.004in. e B A1 E C L Narrow SO SMALL-OUTLINE PACKAGE (0.150 in.) H 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 DIM PINS D D D 8 14 16 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 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 © 1995 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.