19-0431; Rev 1; 7/97 Ultra-Low-Power, Single-Supply Op Amp + Comparator + Reference The comparator output stage of these devices continuously sources as much as 40mA. The comparators eliminate power-supply glitches that commonly occur when changing logic states, minimizing parasitic feedback and making the devices easier to use. In addition, they contain ±3mV internal hysteresis to ensure clean output switching, even with slow-moving input signals. ____________________Selection Table PART INTERNAL OP-AMP SUPPLY 2% GAIN COMPARATOR CURRENT PRECISION STABILITY (µA) REFERENCE (V/V) MAX951 Yes 1 Yes 7 MAX952 Yes 10 Yes 7 MAX953 No 1 Yes 5 MAX954 No 10 Yes 5 ____________________________Features ♦ Op Amp + Comparator + Reference in an 8-Pin µMAX Package (MAX951/MAX952) ♦ 7µA Typical Supply Current (Op Amp + Comparator + Reference) ♦ Comparator and Op-Amp Input Range Includes Ground ♦ Outputs Swing Rail to Rail ♦ +2.4V to +7V Supply Voltage Range ♦ Unity-Gain Stable and 125kHz Decompensated AV ≥ 10V/V Op-Amp Options ♦ Internal 1.2V ±2% Bandgap Reference ♦ Internal Comparator Hysteresis ♦ Op Amp Capable of Driving up to 1000pF Load ________________________Applications Instruments, Terminals, and Bar-Code Readers Battery-Powered Systems Automotive Keyless Entry Low-Frequency, Local-Area Alarms/Detectors Photodiode Preamps Smart Cards Infrared Receivers for Remote Controls Smoke Detectors and Safety Sensors __________________Pin Configuration TOP VIEW AMPOUT 1 8 VDD AMPIN- 2 7 COMPOUT 6 REF (COMPIN-) 5 COMPIN+ MAX951 MAX952 MAX953 MAX954 AMPIN+ 3 VSS 4 DIP/SO/µMAX ( ) ARE FOR MAX953/MAX954 Typical Operating Circuit and Ordering Information appear at end of data sheet. ________________________________________________________________ Maxim Integrated Products 1 For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800. For small orders, phone 408-737-7600 ext. 3468. MAX951–MAX954 _______________General Description The MAX951–MAX954 feature combinations of a micropower operational amplifier, comparator, and reference in an 8-pin package. In the MAX951 and MAX952, the comparator’s inverting input is connected to an internal 1.2V ±2% bandgap reference. The MAX953 and MAX954 are offered without an internal reference. The MAX951/MAX952 operate from a single +2.7V to +7V supply with a typical supply current of 7µA, while the MAX953/MAX954 operate from +2.4V to +7V with a 5µA typical supply current. Both the op amp and comparator feature a common-mode input voltage range that extends from the negative supply rail to within 1.6V of the positive rail, as well as output stages that swing rail to rail. The op amps in the MAX951/MAX953 are internally compensated to be unity-gain stable, while the op amps in the MAX952/MAX954 feature 125kHz typical bandwidth, 66V/ms slew rate, and stability for gains of 10V/V or greater. These op amps have a unique output stage that enables them to operate with an ultra-low supply current while maintaining linearity under loaded conditions. In addition, they have been designed to exhibit good DC characteristics over their entire operating temperature range, minimizing input referred errors. MAX951–MAX954 Ultra-Low-Power, Single-Supply Op Amp + Comparator + Reference ABSOLUTE MAXIMUM RATINGS Supply Voltage (VDD to VSS) ....................................................9V Inputs Current (AMPIN_, COMPIN_)..........................................20mA Voltage (AMPIN_, COMPIN_).......(VDD + 0.3V) to (VSS - 0.3V) Outputs Current (AMPOUT, COMPOUT)......................................50mA Current (REF) ..................................................................20mA Voltage (AMPOUT, COMPOUT, REF) ..............(VDD + 0.3V) to (VSS - 0.3V) Short-Circuit Duration (REF, AMPOUT)..................Continuous Short-Circuit Duration (COMPOUT, VDD to VSS ≤ 7V) ......1min Continuous Power Dissipation (TA = +70°C) Plastic DIP (derate 9.09mW/°C above +70°C) ............727mW SO (derate 5.88mW/°C above +70°C) .........................471mW µMAX (derate 4.10mW/°C above +70°C) ....................330mW CERDIP (derate 8.00mW/°C above +70°C) .................640mW Operating Temperature Ranges MAX95_E_A .....................................................-40°C to +85°C MAX95_MJA ..................................................-55°C to +125°C Maximum Junction Temperatures MAX95_E_A .................................................................+150°C MAX95_MJA.................................................................+175°C Storage Temperature Range .............................-65°C to +165°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 (VDD = 2.8V to 7V for MAX951/MAX952, VDD = 2.4V to 7V for MAX953/MAX954, VSS = 0V, VCM COMP = 0V for the MAX953/MAX954, VCM OPAMP = 0V, AMPOUT = (VDD + VSS) / 2, COMPOUT = low, TA = TMIN to TMAX, typical values are at TA = +25°C, unless otherwise noted.) PARAMETER Supply Voltage Range SYMBOL VDD CONDITIONS MAX951/MAX952 TA = -10°C to +85°C MIN TYP 2.8 7.0 TA = -10°C to +85°C 2.7 7.0 MAX953/MAX954 2.4 TA = +25°C, MAX951/MAX952 IS UNITS V 7.0 7 MAX951E/MAX952E Supply Current (Note 1) MAX TA = TMIN to TMAX 10 11 MAX951M/MAX952M 13 TA = +25°C, MAX953/MAX954 5 8 MAX953E/MAX954E 9 MAX953M/MAX954M 11 µA COMPARATOR TA = +25°C Input Offset Voltage (Note 2) VOS 1 4 MAX95_EUA (µMAX) 14 MAX95_MJA Trip Point (Note 3) Input Leakage Current (Note 4) CMVR Common-Mode Rejection Ratio CMRR 4 MAX95_EUA (µMAX) 17 MAX95_EPA/ESA 5 MAX95_MJA 7 TA = +25°C 0.003 MAX95_E 0.003 2 mV 0.050 5 nA 40 VSS VSS to (VDD - 1.6V), MAX953/MAX954 mV 6 TA = +25°C MAX95_M Common-Mode Range 3 MAX95_EPA/ESA VDD -1.6V 0.1 _______________________________________________________________________________________ 1 V mV/V Ultra-Low-Power, Single-Supply Op Amp + Comparator + Reference (VDD = 2.8V to 7V for MAX951/MAX952, VDD = 2.4V to 7V for MAX953/MAX954, VSS = 0V, VCM COMP = 0V for the MAX953/MAX954, VCM OPAMP = 0V, AMPOUT = (VDD + VSS) / 2, COMPOUT = low, TA = TMIN to TMAX, typical values are at TA = +25°C, unless otherwise noted.) PARAMETER Power-Supply Rejection Ratio SYMBOL PSRR TYP MAX MAX951/MAX952, VDD = 2.8V to 7V CONDITIONS 0.05 1 MAX953/MAX954, VDD = 2.4V to 7V 0.05 1 Response Time Tpd VOD = 10mV CL = 100pF, TA = +25°C, VDD - VSS = 5V VOD = 100mV Output High Voltage VOH ISOURCE = 2mA Output Low Voltage VOL ISINK = 1.8mA MIN 22 UNITS mV/V µs 4 VDD - 0.4V V VSS + 0.4V V REFERENCE Reference Voltage (Note 5) VREF MAX95_EPA/ESA 1.176 1.200 1.224 MAX95_EUA (µMAX) 1.130 1.200 1.270 MAX95_MJA 1.164 1.200 1.236 IOUT = ±20µA, TA = +25°C Load Regulation Voltage Noise en V 0.1 IOUT = ±6µA, MAX95_E 1.5 IOUT = ±3µA, MAX95_M 1.5 0.1Hz to 10Hz 16 TA = +25°C 1 % µVp-p OP AMP Input Offset Voltage VOS 4 MAX95_EUA (µMAX) 5 MAX95_MJA Input Bias Current IB Large-Signal Gain (no load) AVOL Large-Signal Gain (100kΩ load to VSS) Gain Bandwidth AVOL GBW Slew Rate SR Common-Mode Input Range CMVR Common-Mode Rejection Ratio CMRR Power-Supply Rejection Ratio PSRR Input Noise Voltage en 3 MAX95_EPA/ESA 5 TA = +25°C 0.003 MAX95_E 0.003 5 MAX95_M 0.003 40 AMPOUT = 0.5V to 4.5V, VDD - VSS = 5V AMPOUT = 0.5V to 4.5V, VDD - VSS = 5V mV TA = +25°C 100 MAX95_E 50 MAX95_M 10 TA = +25°C 40 MAX95_E 25 MAX95_M 5 0.050 nA 1000 V/mV 150 V/mV AV = +1V/V, MAX951/MAX953, VDD - VSS = 5V 20 AV = +10V/V, MAX952/MAX954, VDD - VSS = 5V 125 AV = +1V/V, MAX951/MAX953, VDD - VSS = 5V 12.5 AV = +10V/V, MAX952/MAX954, VDD - VSS = 5V 66 VSS kHz V/ms VDD - 1.6 VCM OPAMP = VSS to (VDD - 1.6V) 0.03 1 VDD = 2.8V to 7V, MAX951/MAX952 0.07 1.0 VDD = 2.4V to 7V, MAX953/MAX954 0.07 1.0 V mV/V mV/V fo = 1kHz 80 nV√Hz fo = 0.1Hz to 10Hz 1.2 µVp-p _______________________________________________________________________________________ 3 MAX951–MAX954 ELECTRICAL CHARACTERISTICS (continued) MAX951–MAX954 Ultra-Low-Power, Single-Supply Op Amp + Comparator + Reference ELECTRICAL CHARACTERISTICS (continued) (VDD = 2.8V to 7V for MAX951/MAX952, VDD = 2.4V to 7V for MAX953/MAX954, VSS = 0V, VCM COMP = 0V for the MAX953/MAX954, VCM OPAMP = 0V, AMPOUT = (VDD + VSS) / 2, COMPOUT = low, TA = TMIN to TMAX, typical values are at TA = +25°C, unless otherwise noted.) PARAMETER SYMBOL CONDITIONS Output High Voltage VOH RL = 100kΩ to VSS Output Low Voltage VOL RL = 100kΩ to VSS Output Source Current Output Sink Current ISRC ISNK MIN TYP MAX VDD - 500mV V VSS + 50mV TA = +25°C 70 TA = +25°C, VDD - VSS = 5V 300 MAX95_E 60 MAX95_M 40 TA = +25°C 70 TA = +25°C, VDD - VSS = 5V 200 MAX95_E 50 MAX95_M 30 UNITS 820 570 V µA µA µA Note 1: Supply current is tested with COMPIN+ = (REF - 100mV) for MAX951/MAX952, and COMPIN+ = 0V for MAX953/MAX954. Note 2: Input Offset Voltage is defined as the center of the input-referred hysteresis. VCM COMP = REF for MAX951/MAX952, and VCM COMP = 0V for MAX953/MAX954. Note 3: Trip Point is defined as the differential input voltage required to make the comparator output change. The difference between upper and lower trip points is equal to the width of the input-referred hysteresis. VCM COMP = REF for MAX951/MAX952, and VCM COMP = 0V for MAX953/MAX954. Note 4: For MAX951/MAX952, input leakage current is measured for COMPIN- at the reference voltage. For MAX953/MAX954, input leakage current is measured for both COMPIN+ and COMPIN- at VSS. Note 5: Reference voltage is measured with respect to VSS. Contact factory for availability of a 3% accurate reference voltage in the µMAX package. 4 _______________________________________________________________________________________ Ultra-Low-Power, Single-Supply Op Amp + Comparator + Reference MAX951–MAX954 __________________________________________Typical Operating Characteristics (TA = +25°C, unless otherwise noted.) SUPPLY CURRENT vs. TEMPERATURE 5 MAX953/MAX954 4 3 VCM OPAMP = 0V AMPOUT = (VDD + VSS)/2 COMP- = 1.2V or REF COMP+ = 1.1V 5 MAX953/MAX954 4 3 VDD = 2.8V (MAX951/2), VDD = 2.4V (MAX953/4), VSS = 0V, VCM OPAMP = 0V AMPOUT = 1/2 VDD, COMP- = 1.2V or REF COMP+ = 1.1V 2 1 0 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 1.200 1.195 1.190 VDD = 5V 1.185 1.180 -60 -40 -20 0 20 40 60 80 100 120 140 20 40 60 80 100 120 140 TEMPERATURE (°C) REFERENCE OUTPUT VOLTAGE vs. LOAD CURRENT POWER-SUPPLY REJECTION RATIO vs. FREQUENCY DC OPEN-LOOP GAIN vs. SUPPLY VOLTAGE VDD = 2.0 to 3.0V, VSS = -2.5V NONINVERTING AMPIN+ = 0V ACL = 1V/V (MAX951/2) ACL = 10V/V (MAX953/4), COMP- = 1.2V or REF COMP+ = 1.1V from VSS 70 SINKING CURRENT 60 50 PSRR (dB) 1.22 1.20 1.18 40 C 1.16 1.14 B 20 A: MAX951/952 REF B: MAX951/953 OP AMP C: MAX952/954 OP AMP 10 1.12 1.10 1 10 1x106 A 30 SOURCING CURRENT 1x107 1x105 1x104 1x103 1x102 1x101 1mHz INPUT SIGNAL RL = 100kΩ 1x100 0 1x100 1x101 1x102 1x103 1x104 1x105 1x106 100 MAX951-06 80 1.24 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 LOAD CURRENT (µA) FREQUENCY (Hz) SUPPLY VOLTAGE (V) DC OPEN-LOOP GAIN vs. TEMPERATURE MAX951/MAX953 OPEN-LOOP GAIN AND PHASE vs. FREQUENCY MAX952/MAX954 OPEN-LOOP GAIN AND PHASE vs. FREQUENCY 1x104 1x103 1x102 VDD = 5V 1mHz INPUT SIGNAL RL = 100kΩ PHASE 60 -120 GAIN 40 -180 20 -240 0 -300 20 40 60 80 100 120 140 TEMPERATURE (°C) -360 1 10 100 1k 10k FREQUENCY (Hz) 100k 1M MAX951-09 0 -60 60 PHASE -120 40 -180 GAIN 20 -240 0 -300 -20 RL = 100kΩ RL = 100kΩ -20 -60 -40 -20 0 80 -60 OPEN-LOOP GAIN (dB) OPEN-LOOP GAIN (dB) 80 100 0 PHASE SHIFT (Degrees) 1x105 100 MAX951-08 MAX951-07 1x106 1x100 1.205 TEMPERATURE (°C) 1.26 1x101 1.210 SUPPLY VOLTAGE (V) VSUPPLY = 5V 1.28 -60 -40 -20 0 7 MAX951–954-04 1.30 REFERENCE VOLTAGE (V) MAX951/MAX952 6 0 DC OPEN-LOOP GAIN (V/V) MAX951–954-02 7 1.215 DC OPEN-LOOP GAIN (V/V) 1 8 MAX951–954-05 2 9 -360 -40 1 10 100 1k 10k 100k 1M FREQUENCY (Hz) _______________________________________________________________________________________ 5 PHASE SHIFT (Degrees) MAX951/MAX952 6 1.220 REFERENCE VOLTAGE (V) 7 SUPPLY CURRENT (µA) SUPPLY CURRENT (µA) 8 REFERENCE VOLTAGE vs. TEMPERATURE 10 MAX951–954-01 9 MAX951-03 SUPPLY CURRENT vs. SUPPLY VOLTAGE ____________________________Typical Operating Characteristics (continued) (TA = +25°C, unless otherwise noted.) OP-AMP SHORT-CIRCUIT CURRENT vs. SUPPLY VOLTAGE OP-AMP OUTPUT VOLTAGE vs. LOAD CURRENT 0.04 SINKING CURRENT 0.02 0.10 -0.02 SOURCING CURRENT -0.04 E D -0.06 F 1000 SHORT TO VSS 500 0 SHORT TO VDD -500 NONINVERTING AMPIN+ = GND -0.08 NONINVERTING AMPIN+ =(VDD - VSS)/2 1500 -1000 -0.10 1 10 100 LOAD CURRENT (µA) 2.5 1000 2000 3 60 50 40 MAX951/3 A = 1V/V MAX952/4 A = 10V/V AMPOUT = 1VPP VCM = (VDD - VSS/2) F C E D B A 30 4.5 6.5 2.0 1.5 0 104 105 SOURCING CURRENT 2.5 0.5 0 106 VSUPPLY = 5V SINKING CURRENT 0.01 0.1 CAPACITIVE LOAD (pF) 1 10 100 200 LOAD CURRENT (mA) COMPARATOR SHORT-CIRCUIT CURRENT vs. SUPPLY VOLTAGE MAX951-4 TOC-22 SHORT-CIRCUIT CURRENT (mA) 250 200 150 SOURCING CURRENT 100 50 0 SINKING CURRENT -50 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 SUPPLY VOLTAGE (V) 6 7 3.0 1.0 103 6 3.5 10 102 5.5 4.0 20 101 5 5.0 MAX951–4 TOC-12 PARTS VSUPPLY A: MAX951/2 3V B: MAX951/3 5V D: MAX952/4 3V E: MAX952/4 5V OUTPUT VOLTAGE (V) 70 4.5 COMPARATOR OUTPUT VOLTAGE vs. LOAD CURRENT 100 80 4 SUPPLY VOLTAGE (V) OP AMP PERCENT OVERSHOOT vs. CAPACITIVE LOAD 90 3.5 MAX951–4 TOC-15 OUTPUT VOLTAGE (V) 0.06 B C A MAX951–4 TOC-11 0.08 2000 OUTPUT CURRENT (µA) A, D: VSUPPLY = ±1.5V B, E: VSUPPLY = ±2.5V C, F: VSUPPLY = ±3.5V MAX951–4 TOC-10A 0.10 OVERSHOOT (%) MAX951–MAX954 Ultra-Low-Power, Single-Supply Op Amp + Comparator + Reference _______________________________________________________________________________________ Ultra-Low-Power, Single-Supply Op Amp + Comparator + Reference COMPARATOR RESPONSE TIME FOR VARIOUS INPUT OVERDRIVES (FALLING) COMPARATOR RESPONSE TIME FOR VARIOUS INPUT OVERDRIVES (RISING) OUTPUT 1V/div INPUT 100mV/div 0V 50mV 10mV INPUT 100mV/div 20mV 0V OUTPUT 1V/div 100mV 100mV 50mV 20mV 10mV 0V 0V 2µs/div 2µs/div MAX953, LOAD = 100kΩ || 100pF, VSUPPLY = 5V MAX953, LOAD = 100kΩ || 100pF, VSUPPLY = 5V MAX951/MAX953 OP-AMP LARGE-SIGNAL TRANSIENT RESPONSE INPUT 2V/div 2.5V 2.5V OUTPUT 50mV/div OUTPUT 1V/div INPUT 200mV/div MAX951/MAX953 OP-AMP SMALL-SIGNAL TRANSIENT RESPONSE 200µs/div 100µs/div NONINVERTING, AVCL = 1V/V, LOAD = 100kΩ || 100pF to VSS, VSUPPLY = 5V NONINVERTING, AVCL = 1V/V, LOAD = 100kΩ || 100pF to VSS, VSUPPLY = 5V MAX952/MAX954 OP-AMP LARGE-SIGNAL TRANSIENT RESPONSE INPUT 20mV/div INPUT 200mV/div MAX952/MAX954 OP-AMP SMALL-SIGNAL TRANSIENT RESPONSE 2.5V OUTPUT 1V/div OUTPUT 50mV/div 2.5V 100µs/div NONINVERTING, AVCL = 10V/V, LOAD = 100kΩ || 100pF to VSS, VSUPPLY = 5V 100µs/div NONINVERTING, AVCL = 10V/V, LOAD = 100kΩ || 100pF to VSS, VSUPPLY = 5V _______________________________________________________________________________________ 7 MAX951–MAX954 ____________________________Typical Operating Characteristics (continued) (TA = +25°C, unless otherwise noted.) MAX951–MAX954 Ultra-Low-Power, Single-Supply Op Amp + Comparator + Reference ______________________________________________________________Pin Description PIN NAME FUNCTION MAX951 MAX952 1 MAX953 MAX954 1 AMPOUT 2 2 AMPIN- Inverting Op-Amp Input 3 3 AMPIN+ Noninverting Op-Amp Input 4 4 VSS Negative Supply or Ground 5 5 COMPIN+ 6 — REF — 6 COMPIN- 7 7 COMPOUT 8 8 VDD Op-Amp Output Noninverting Comparator Input 1.200V Reference Output. Also connected to inverting comparator input. Inverting Comparator Input Comparator Output Positive Supply AMPOUT 1 OP AMP 2 AMPIN- 3 AMPIN+ 4 VSS VDD 8 COMPOUT 7 AMPOUT 1 OP AMP VDD x1 1.20V REF 6 COMPIN+ 5 COMP MAX951 MAX952 2 AMPIN- 3 AMPIN+ 4 8 MAX953 MAX954 COMPOUT 7 COMPIN- 6 COMPIN+ 5 COMP VSS Figure 1. MAX951–MAX954 Functional Diagrams _______________Detailed Description The MAX951–MAX954 are combinations of a micropower op amp, comparator, and reference in an 8-pin package, as shown in Figure 1. In the MAX951/MAX952, the comparator’s negative input is connected to a 1.20V ±2% bandgap reference. All four devices are optimized to operate from a single supply. Supply current is less than 10µA (7µA typical) for the MAX951/MAX952 and less than 8µA (5µA typical) for the MAX953/MAX954. high-impedance differential inputs and a commonmode input voltage range that extends from the negative supply rail to within 1.6V of the positive rail. They have a CMOS output stage that swings rail to rail and is driven by a proprietary high gain stage, which enables them to operate with an ultra-low supply current while maintaining linearity under loaded conditions. Careful design results in good DC characteristics over their entire operating temperature range, minimizing input referred errors. Op Amp The op amps in the MAX951/MAX953 are internally compensated to be unity-gain stable, while the op amps in the MAX952/MAX954 feature 125kHz typical gain bandwidth, 66V/ms slew rate, and stability for gains of 10V/V or greater. All these op amps feature 8 Comparator The comparator in the MAX951–MAX954 has a highimpedance differential input stage with a commonmode input voltage range that extends from the negative supply rail to within 1.6V of the positive rail. Their CMOS output stage swings rail to rail and can _______________________________________________________________________________________ Ultra-Low-Power, Single-Supply Op Amp + Comparator + Reference RA R1 VS VIN COMPOUT COMPOUT RB REF REF Figure 2. External Hysteresis continuously source as much as 40mA. The comparators eliminate power-supply glitches that commonly occur when changing logic states, minimizing parasitic feedback and making them easier to use. In addition, they include internal hysteresis (±3mV) to ensure clean output switching, even with slow-moving input signals. The inputs can be taken above and below the supply rails up to 300mV without damage. Input voltages beyond this range can forward bias the ESD-protection diodes and should be avoided. The MAX951–MAX954 comparator outputs swing rail to rail (from VDD to VSS). TTL compatibility is assured by using a +5V ±10% supply. The MAX951–MAX954 comparator continuously outputs source currents as high as 40mA and sink currents of over 5mA, while keeping quiescent currents in the microampere range. The output can source 100mA (at VDD = 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; this minimizes feedback through the supplies and helps ensure stability without bypassing. Reference The internal reference in the MAX951/MAX952 has an output of 1.20V with respect to VSS. Its accuracy is ±2% in the -40°C to +85°C temperature range. It is comprised of a trimmed bandgap reference fed by a proportionalto-absolute-temperature (PTAT) current source and buffered by a micropower unity-gain amplifier. The REF output is typically capable of sourcing and sinking 20µA. Do not bypass the reference output. The reference is stable for capacitive loads less than 100pF. __________Applications Information The micropower MAX951–MAX954 are designed to extend battery life in portable instruments and add functionality in power-limited industrial controls. Following are some practical considerations for circuit design and layout. Comparator Hysteresis Hysteresis increases the comparator’s noise immunity by increasing the upper threshold and decreasing the lower threshold. The comparator in these devices contain a ±3mV wide internal hysteresis band to ensure clean output switching, even with slow-moving signals. When necessary, hysteresis can be increased by using external resistors to add positive feedback, as shown in Figure 2. This circuit increases hysteresis at the expense of more supply current and a slower response. The design procedure is as follows: 1) Set R2. The leakage current in COMPIN+ is less than 5nA (up to +85°C), so current through R2 can be as little as 500nA and still maintain good accuracy. If R2 = 2.4MΩ, the current through R2 at the upper trip point is VREF / R2 or 500nA. 2) Choose the width of the hysteresis band. In this example choose VEHYST = 50mV. R1 = R2 [VEHYST − 2VIHYST ] (VDD + 2VIHYST ) where the internal hysteresis is VIHYST = 3mV. 3) Determine R1. If the supply voltage is 5V, then R1 = 24kΩ. 4) Check the hysteresis trip points. The upper trip point is VIN(H) = (R1 + R2) ( ) VREF + VIHYST R2 or 1.22V in our example. The lower trip point is 50mV less, or 1.17V in our example. If a resistor divider is used for R1, the calculations should be modified using a Thevenin equivalent model. 5) Determine RA: _______________________________________________________________________________________ 9 MAX951–MAX954 R2 R2 MAX951–MAX954 Ultra-Low-Power, Single-Supply Op Amp + Comparator + Reference VCC = 5V ANTENNA AMPIN+ 0.1µF AMPOUT L1 330mH R2 C1A 390pF C1B C1C 330pF 20-60pF 0.1µF MAX952 20k 1.0M 100k 1 L1 x C1 = (2π fC) 2 2pF to 10pF Figure 3. Compensation for Feedback-Node Capacitance 7) Calculate RB. (R2) VS(H) + VIHYST ( − VREF + ) (R2)(R A ) VIHSYT )(R A LAYOUT-SENSITIVE AREA, METAL RFI SHIELDING ADVISED Op-Amp Stability and Board Layout Considerations In the example, RA is again 24kΩ. 6) Select the upper trip point VS(H). Our example is set at 4.75V. (VREF REF Figure 4. Low-Frequency Radio Receiver Application V R A ≈ R2 SHYST , for VSHYST >> VIHYST VDD ) + R2 RB is 8.19kΩ, or approximately 8.2kΩ. Input Noise Considerations Because low power requirements often demand highimpedance circuits, effects from radiated noise are more significant. Thus, traces between the op-amp or comparator inputs and any resistor networks attached should be kept as short as possible. Crosstalk Reference Internal crosstalk to the reference from the comparator is package dependent. Typical values (VDD = 5V) are 45mV for the plastic DIP package and 32mV for the SO package. Applications using the reference for the op amp or external circuitry can eliminate this crosstalk by using a simple RC lowpass filter, as shown in Figure 5. Op Amp Internal crosstalk to the op amp from the comparator is package dependent, but not input referred. Typical values (VDD = 5V) are 4mV for the plastic DIP package and 280µV for the SO package. 10 1.2V COMP 5.1M R1 RB = 10M AMP Unlike other industry-standard micropower CMOS op amps, the op amps in the MAX951–MAX954 maintain stability in their minimum gain configuration while driving heavy capacitive loads, as demonstrated in the MAX951/MAX953 Op-Amp Percent Overshoot vs. Capacitive Load graph in the Typical Operating Characteristics. Although this family is primarily designed for low-frequency applications, good layout is extremely important. Low-power, high-impedance circuits may increase the effects of board leakage and stray capacitance. For example, the combination of a 10MΩ resistance (from leakage between traces on a contaminated, poorly designed PC board) and a 1pF stray capacitance provides a pole at approximately 16kHz, which is near the amplifier’s bandwidth. Board routing and layout should minimize leakage and stray capacitance. In some cases, stray capacitance may be unavoidable and it may be necessary to add a 2pF to 10pF capacitor across the feedback resistor to compensate; select the smallest capacitor value that ensures stability. Input Overdrive With 100mV overdrive, comparator propagation delay is typically 6µs. The Typical Operating Characteristics show propagation delay for various overdrive levels. Supply current can increase when the op amp in the MAX951–MAX954 is overdriven to the negative supply rail. For example, when connecting the op amp as a comparator and applying a -100mV input overdrive, supply current rises by around 15µA and 32µA for supply voltages of 2.8V and 7V, respectively. ______________________________________________________________________________________ Ultra-Low-Power, Single-Supply Op Amp + Comparator + Reference NEC SE307-C 51Ω C2 15pF, 5% MAX953 NEC PH302B R1A 49.9k R1 1% 49.9kB 1% R2 1.0M, 1% VCC 0.1µF 30k C1 150pF, 5% 100k MAX952 10M AMP 4.7M RADIOACTIVE IONIZATION CHAMBER SMOKE SENSOR AMP COMP COMP 1.2V LAYOUT-SENSITIVE AREA 0.1µF REF 5.1M LAYOUT-SENSITIVE AREA 1 R1 x C1 = R2 x C2 = 2π fC Figure 5. Infrared Receiver Application Power-Supply Bypassing Power-supply bypass capacitors are not required if the supply impedance is low. For single-supply applications, it is good general practice to bypass VDD with a. 0.1µF capacitor to ground. Do not bypass the reference output. ________________Application Circuits Low-Frequency Radio Receiver for Alarms and Detectors Figure 4’s circuit is useful as a front end for low-frequency RF alarms. The unshielded inductor (M7334-ND from Digikey) is used with capacitors C1A, C1B, and C1C in a resonant circuit to provide frequency selectivity. The op amp from a MAX952 amplifies the signal received. The comparator improves noise immunity, provides a signal strength threshold, and translates the received signal into a pulse train. Carrier frequencies are limited to around 10kHz. 10kHz is used in the example in Figure 4. The layout and routing of components for the amplifier should be tight to minimize 60Hz interference and crosstalk from the comparator. Metal shielding is recommended to prevent RFI from the comparator or digital circuitry from exciting the receiving antenna. The transmitting antenna can be long parallel wires spaced about 7.2cm apart, with equal but opposite currents. Radio waves from this antenna will be detectable when the receiver is brought within close proximity, but cancel out at greater distances. Infrared Receiver Front End for Remote Controls and Data Links The circuit in Figure 5 uses the MAX952 as a PIN photodiode preamplifier and discriminator for an infrared receiver. The op amp is configured as a Delyiannis- Figure 6. Sensor Preamp and Alarm Trigger Application Friend bandpass filter to reduce disturbances from noise and eliminate low-frequency interference from sunlight, fluorescent lights, etc. This circuit is applicable for TV remote controls and low-frequency data links up to 20kbps. Carrier frequencies are limited to around 10kHz. 10kHz is used in the example circuit. Component layout and routing for the amplifier should be tight to reduce stray capacitance, 60Hz interference, and RFI from the comparator. Crosstalk from comparator edges will distort the amplifier signal. In order to minimize the effect, a lowpass RC filter is added to the connection from the reference to the noninverting input of the op amp. Sensor Preamp and Alarm Trigger for Smoke Detectors The high-impedance CMOS inputs of the MAX951– MAX954 op amp are ideal for buffering high-impedance sensors, such as smoke detector ionization chambers, piezoelectric transducers, gas detectors, and pH sensors. Input bias currents are typically less than 3pA at room temperature. A 5µA typical quiescent current for the MAX953 will minimize battery drain without resorting to complex sleep schemes, allowing continuous monitoring and immediate detection. Ionization-type smoke detectors use a radioactive source, such as Americium, to ionize smoke particles. A positive voltage on a plate attached to the source repels the positive smoke ions and accelerates them toward an outer electrode connected to ground. Some ions collect on an intermediate plate. With careful design, the voltage on this plate will stabilize at a little less than one-half the supply voltage under normal conditions, but rise higher when smoke increases the ion current. This voltage is buffered ______________________________________________________________________________________ 11 MAX951–MAX954 VCC = 5V 10kHz, 5Vp-p MAX951–MAX954 Ultra-Low-Power, Single-Supply Op Amp + Comparator + Reference by the high input impedance op amp of a MAX951 (Figure 6). The comparator and resistor voltage divider set an alarm threshold to indicate a fire. Design and fabrication of the connection from the intermediate plate of the ionization chamber to the noninverting input of the op amp is critical, since the impedance of this node must be well above 50MΩ. This connection must be as short and direct as possible to prevent charge leakage and 60Hz interference. Where possible, the grounded outer electrode or chassis of the ionization chamber should shield this connection to reduce 60Hz interference. Pay special attention to board cleaning, to prevent leakage due to ionic compounds such as chlorides, flux, and other contaminants from the manufacturing process. Where applicable, a coating of high-purity wax may be used to insulate this connection and prevent leakage due to surface moisture or an accumulation of dirt. ______________Ordering Information PART TEMP. RANGE ___________________Chip Topography V DD AMPOUT AMPIN- COMPOUT 0.084" (2.134mm) AMPIN+ REF(COMPIN-) COMPIN+ V SS 0.058" (1.473mm) ( ) ARE FOR MAX953/MAX954 PIN-PACKAGE MAX951C/D 0°C to +70°C Dice* MAX951EPA -40°C to +85°C 8 Plastic DIP MAX951ESA -40°C to +85°C 8 SO MAX951EUA -40°C to +85°C 8 µMAX MAX951MJA -55°C to +125°C 8 CERDIP** MAX952C/D 0°C to +70°C MAX952EPA -40°C to +85°C 8 Plastic DIP MAX952ESA -40°C to +85°C 8 SO MAX952EUA -40°C to +85°C 8 µMAX MAX952MJA -55°C to +125°C 8 CERDIP** MAX953C/D 0°C to +70°C MAX953EPA -40°C to +85°C 8 Plastic DIP MAX953ESA -40°C to +85°C 8 SO MAX953EUA -40°C to +85°C 8 µMAX MAX953MJA -55°C to +125°C 8 CERDIP** Dice* TRANSISTOR COUNT: 163 SUBSTRATE CONNECTED TO VDD __________Typical Operating Circuit 8 0.1µF 3 INPUT Dice* MAX954C/D 0°C to +70°C Dice* MAX954EPA -40°C to +85°C 8 Plastic DIP MAX954ESA -40°C to +85°C 8 SO MAX954EUA -40°C to +85°C 8 µMAX MAX954MJA -55°C to +125°C 8 CERDIP** VCC AMPIN+ MAX951 MAX952 2 1 1M 5 COMPOUT R2 R1 7 6 REF 4 1.20V VSS * Dice are tested at TA = +25°C, DC parameters only. ** Contact factory for availability and processing to MIL-STD-883. 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. 12 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 1997 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.