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19-0431; Rev 1; 7/97
Ultra-Low-Power, Single-Supply Op Amp + Comparator + Reference
_______________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 7A, while the MAX953/MAX954 operate from +2.4V to +7V with a 5A 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. 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.
____________________________Features
o Op Amp + Comparator + Reference in an 8-Pin MAX Package (MAX951/MAX952) o 7A Typical Supply Current (Op Amp + Comparator + Reference) o Comparator and Op-Amp Input Range Includes Ground o Outputs Swing Rail to Rail o +2.4V to +7V Supply Voltage Range o Unity-Gain Stable and 125kHz Decompensated AV 10V/V Op-Amp Options o Internal 1.2V 2% Bandgap Reference o Internal Comparator Hysteresis o Op Amp Capable of Driving up to 1000pF Load
MAX951-MAX954
________________________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
____________________Selection Table
PART INTERNAL OP-AMP SUPPLY 2% GAIN COMPARATOR CURRENT PRECISION STABILITY (A) REFERENCE (V/V) Yes Yes No No 1 10 1 10 Yes Yes Yes Yes 7 7 5 5
__________________Pin Configuration
TOP VIEW
MAX951 MAX952 MAX953 MAX954
AMPOUT 1 AMPIN- 2 AMPIN+ 3 VSS 4
8
VDD COMPOUT REF (COMPIN-) COMPIN+
MAX951 MAX952 MAX953 MAX954
DIP/SO/MAX
7 6 5
( ) ARE FOR MAX953/MAX954
Typical Operating Circuit and Ordering Information appear at end of data sheet.
________________________________________________________________ Maxim Integrated Products 1
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Ultra-Low-Power, Single-Supply Op Amp + Comparator + Reference MAX951-MAX954
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 = +70C) Plastic DIP (derate 9.09mW/C above +70C) ............727mW SO (derate 5.88mW/C above +70C) .........................471mW MAX (derate 4.10mW/C above +70C) ....................330mW CERDIP (derate 8.00mW/C above +70C) .................640mW Operating Temperature Ranges MAX95_E_A .....................................................-40C to +85C MAX95_MJA ..................................................-55C to +125C Maximum Junction Temperatures MAX95_E_A .................................................................+150C MAX95_MJA.................................................................+175C Storage Temperature Range .............................-65C to +165C 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
(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 = +25C, unless otherwise noted.) PARAMETER Supply Voltage Range SYMBOL VDD CONDITIONS MAX951/MAX952 TA = -10C to +85C MAX953/MAX954 TA = +25C, MAX951/MAX952 MAX951E/MAX952E Supply Current (Note 1) IS MAX951M/MAX952M TA = +25C, MAX953/MAX954 MAX953E/MAX954E MAX953M/MAX954M COMPARATOR TA = +25C Input Offset Voltage (Note 2) VOS MAX95_EPA/ESA MAX95_EUA (MAX) MAX95_MJA TA = +25C Trip Point (Note 3) MAX95_EUA (MAX) MAX95_EPA/ESA MAX95_MJA Input Leakage Current (Note 4) Common-Mode Range Common-Mode Rejection Ratio CMVR CMRR VSS to (VDD - 1.6V), MAX953/MAX954 TA = +25C MAX95_E MAX95_M VSS 0.1 4 17 5 7 0.003 0.003 0.050 5 40 VDD -1.6V 1 V mV/V nA mV 1 3 4 14 6 mV 5 TA = TMIN to TMAX TA = -10C to +85C MIN 2.8 2.7 2.4 7 TYP MAX 7.0 7.0 7.0 10 11 13 8 9 11 A V UNITS
2
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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 = +25C, unless otherwise noted.) PARAMETER Power-Supply Rejection Ratio Response Time Output High Voltage Output Low Voltage REFERENCE MAX95_EPA/ESA Reference Voltage (Note 5) VREF MAX95_EUA (MAX) MAX95_MJA IOUT = 20A, TA = +25C Load Regulation Voltage Noise OP AMP TA = +25C Input Offset Voltage VOS MAX95_EPA/ESA MAX95_EUA (MAX) MAX95_MJA TA = +25C Input Bias Current IB MAX95_E MAX95_M Large-Signal Gain (no load) AVOL AMPOUT = 0.5V to 4.5V, VDD - VSS = 5V TA = +25C MAX95_E MAX95_M TA = +25C MAX95_E MAX95_M 100 50 10 40 25 5 20 125 12.5 66 VSS VCM OPAMP = VSS to (VDD - 1.6V) VDD = 2.8V to 7V, MAX951/MAX952 VDD = 2.4V to 7V, MAX953/MAX954 fo = 1kHz fo = 0.1Hz to 10Hz 0.03 0.07 0.07 80 1.2 VDD - 1.6 1 1.0 1.0 kHz V/ms V mV/V mV/V nVHz Vp-p 150 V/mV 0.003 0.003 0.003 1000 V/mV 1 3 4 5 5 0.050 5 40 nA mV en IOUT = 6A, MAX95_E IOUT = 3A, MAX95_M 0.1Hz to 10Hz 16 1.176 1.130 1.164 1.200 1.200 1.200 0.1 1.5 1.5 Vp-p % 1.224 1.270 1.236 V SYMBOL PSRR Tpd VOH VOL CONDITIONS MAX951/MAX952, VDD = 2.8V to 7V MAX953/MAX954, VDD = 2.4V to 7V VOD = 10mV CL = 100pF, TA = +25C, VDD - VSS = 5V VOD = 100mV ISOURCE = 2mA ISINK = 1.8mA VDD - 0.4V VSS + 0.4V MIN TYP 0.05 0.05 22 4 MAX 1 1 UNITS mV/V s V V
MAX951-MAX954
Large-Signal Gain (100k load to VSS) Gain Bandwidth Slew Rate Common-Mode Input Range Common-Mode Rejection Ratio Power-Supply Rejection Ratio Input Noise Voltage
AVOL
AMPOUT = 0.5V to 4.5V, VDD - VSS = 5V
GBW SR CMVR CMRR PSRR en
AV = +1V/V, MAX951/MAX953, VDD - VSS = 5V AV = +10V/V, MAX952/MAX954, VDD - VSS = 5V AV = +1V/V, MAX951/MAX953, VDD - VSS = 5V AV = +10V/V, MAX952/MAX954, VDD - VSS = 5V
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3
Ultra-Low-Power, Single-Supply Op Amp + Comparator + Reference MAX951-MAX954
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 = +25C, unless otherwise noted.) PARAMETER Output High Voltage Output Low Voltage SYMBOL VOH VOL CONDITIONS RL = 100k to VSS RL = 100k to VSS TA = +25C Output Source Current ISRC TA = +25C, VDD - VSS = 5V MAX95_E MAX95_M TA = +25C Output Sink Current ISNK TA = +25C, VDD - VSS = 5V MAX95_E MAX95_M 70 300 60 40 70 200 50 30 570 A A 820 A MIN TYP MAX UNITS V VSS + 50mV V VDD - 500mV
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 MAX package.
4
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Ultra-Low-Power, Single-Supply Op Amp + Comparator + Reference
__________________________________________Typical Operating Characteristics
(TA = +25C, unless otherwise noted.)
MAX951-MAX954
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX951-954-01
SUPPLY CURRENT vs. TEMPERATURE
9 SUPPLY CURRENT (A) 8 7 6 5 4 3 2 1 0 7 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 -60 -40 -20 0 20 40 60 80 100 120 140 MAX953/MAX954 MAX951/MAX952
MAX951-954-02
REFERENCE VOLTAGE vs. TEMPERATURE
1.215 REFERENCE VOLTAGE (V) 1.210 1.205 1.200 1.195 1.190 1.185 1.180 -60 -40 -20 0 20 40 60 80 100 120 140 TEMPERATURE (C) VDD = 5V
MAX951-03
9 8 SUPPLY CURRENT (A) 7 6 5 4 3 2 1 0 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 SUPPLY VOLTAGE (V) VCM OPAMP = 0V AMPOUT = (VDD + VSS)/2 COMP- = 1.2V or REF COMP+ = 1.1V MAX953/MAX954 MAX951/MAX952
10
1.220
TEMPERATURE (C)
REFERENCE OUTPUT VOLTAGE vs. LOAD CURRENT
MAX951-954-04
POWER-SUPPLY REJECTION RATIO vs. FREQUENCY
70 60 PSRR (dB) 50 40 30 20 10 A: MAX951/952 REF B: MAX951/953 OP AMP C: MAX952/954 OP AMP
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
MAX951-954-05
DC OPEN-LOOP GAIN vs. SUPPLY VOLTAGE
1x106 DC OPEN-LOOP GAIN (V/V) 1x105 1x104 1x103 1x102 1x101 1x100 2 1mHz INPUT SIGNAL RL = 100k 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 SUPPLY VOLTAGE (V)
MAX951-06
1.30 1.28 REFERENCE VOLTAGE (V) 1.26 1.24 1.22 1.20 1.18 1.16 1.14 1.12 1.10 1
VSUPPLY = 5V SINKING CURRENT
80
1x107
A C B
SOURCING CURRENT
10 LOAD CURRENT (A)
100
0 1x100 1x101 1x102 1x103 1x104 1x105 1x106 FREQUENCY (Hz)
DC OPEN-LOOP GAIN vs. TEMPERATURE
MAX951-07
MAX951/MAX953 OPEN-LOOP GAIN AND PHASE vs. FREQUENCY
MAX951-08
MAX952/MAX954 OPEN-LOOP GAIN AND PHASE vs. FREQUENCY
MAX951-09
1x106 1x105 1x104 1x103 1x102 1x101 1x100 VDD = 5V 1mHz INPUT SIGNAL RL = 100k -60 -40 -20 0
100 80 OPEN-LOOP GAIN (dB) 60 GAIN 40 20 0 RL = 100k -20 PHASE
0 -60 PHASE SHIFT (Degrees)
100 80 OPEN-LOOP GAIN (dB) 60 40 PHASE
0 -60 -120 -180 PHASE SHIFT (Degrees)
DC OPEN-LOOP GAIN (V/V)
-120 -180 -240 -300 -360
20 0 -20 -40 1 10 100
GAIN -240 -300 RL = 100k -360 1k 10k 100k 1M FREQUENCY (Hz)
20 40 60 80 100 120 140
1
10
100
1k
10k
100k
1M
TEMPERATURE (C)
FREQUENCY (Hz)
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5
Ultra-Low-Power, Single-Supply Op Amp + Comparator + Reference MAX951-MAX954
____________________________Typical Operating Characteristics (continued)
(TA = +25C, unless otherwise noted.)
OP-AMP OUTPUT VOLTAGE vs. LOAD CURRENT
MAX951-4 TOC-10A
OP-AMP SHORT-CIRCUIT CURRENT vs. SUPPLY VOLTAGE
NONINVERTING AMPIN+ =(VDD - VSS)/2
MAX951-4 TOC-11
0.10 0.08 0.06 OUTPUT VOLTAGE (V) 0.04 0.02 0.10 -0.02 -0.04 -0.06 -0.08 -0.10 1 10 100 LOAD CURRENT (A) NONINVERTING AMPIN+ = GND D SOURCING CURRENT E F A, D: VSUPPLY = 1.5V B, E: VSUPPLY = 2.5V C, F: VSUPPLY = 3.5V SINKING CURRENT A BC
2000 1500 OUTPUT CURRENT (A) 1000 SHORT TO VSS 500 0 SHORT TO VDD -500 -1000
1000 2000
2.5
3
3.5
4
4.5
5
5.5
6
6.5
7
SUPPLY VOLTAGE (V)
OP AMP PERCENT OVERSHOOT vs. CAPACITIVE LOAD
MAX951-4 TOC-12
COMPARATOR OUTPUT VOLTAGE vs. LOAD CURRENT
4.5 4.0 OUTPUT VOLTAGE (V) 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 SINKING CURRENT 0.1 1 10 100 200 VSUPPLY = 5V SOURCING CURRENT
MAX951-4 TOC-15
100 90 80 OVERSHOOT (%) 70 60 50 40 30 20 10 0 101 102 103 104 105 PARTS VSUPPLY A: MAX951/2 3V B: MAX951/3 5V D: MAX952/4 3V E: MAX952/4 5V MAX951/3 A = 1V/V MAX952/4 A = 10V/V AMPOUT = 1VPP VCM = (VDD - VSS/2)
E D A B
5.0
F C
106
0.01
CAPACITIVE LOAD (pF)
LOAD CURRENT (mA)
COMPARATOR SHORT-CIRCUIT CURRENT vs. SUPPLY VOLTAGE
MAX951-4 TOC-22
250 SHORT-CIRCUIT CURRENT (mA) 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
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Ultra-Low-Power, Single-Supply Op Amp + Comparator + Reference
____________________________Typical Operating Characteristics (continued)
(TA = +25C, unless otherwise noted.) COMPARATOR RESPONSE TIME FOR VARIOUS INPUT OVERDRIVES (FALLING)
INPUT 100mV/div
MAX951-MAX954
COMPARATOR RESPONSE TIME FOR VARIOUS INPUT OVERDRIVES (RISING)
0V
OUTPUT 1V/div
100mV OUTPUT 1V/div 100mV
50mV INPUT 100mV/div
20mV
10mV 0V 0V
50mV
20mV
10mV 0V
2s/div MAX953, LOAD = 100k || 100pF, VSUPPLY = 5V
2s/div MAX953, LOAD = 100k || 100pF, VSUPPLY = 5V
MAX951/MAX953 OP-AMP SMALL-SIGNAL TRANSIENT RESPONSE
INPUT 200mV/div
MAX951/MAX953 OP-AMP LARGE-SIGNAL TRANSIENT RESPONSE
2.5V OUTPUT 50mV/div
OUTPUT 1V/div
INPUT 2V/div 2.5V
100s/div NONINVERTING, AVCL = 1V/V, LOAD = 100k || 100pF to VSS, VSUPPLY = 5V
200s/div NONINVERTING, AVCL = 1V/V, LOAD = 100k || 100pF to VSS, VSUPPLY = 5V
MAX952/MAX954 OP-AMP SMALL-SIGNAL TRANSIENT RESPONSE
INPUT 200mV/div 2.5V OUTPUT 1V/div 100s/div NONINVERTING, AVCL = 10V/V, LOAD = 100k || 100pF to VSS, VSUPPLY = 5V
MAX952/MAX954 OP-AMP LARGE-SIGNAL TRANSIENT RESPONSE
OUTPUT 50mV/div
INPUT 20mV/div 2.5V
100s/div NONINVERTING, AVCL = 10V/V, LOAD = 100k || 100pF to VSS, VSUPPLY = 5V
_______________________________________________________________________________________
7
Ultra-Low-Power, Single-Supply Op Amp + Comparator + Reference MAX951-MAX954
______________________________________________________________Pin Description
PIN MAX951 MAX952 1 2 3 4 5 6 -- 7 8 MAX953 MAX954 1 2 3 4 5 -- 6 7 8 NAME AMPOUT AMPINAMPIN+ VSS COMPIN+ REF COMPINCOMPOUT VDD Op-Amp Output Inverting Op-Amp Input Noninverting Op-Amp Input Negative Supply or Ground Noninverting Comparator Input 1.200V Reference Output. Also connected to inverting comparator input. Inverting Comparator Input Comparator Output Positive Supply FUNCTION
AMPOUT 1 OP AMP
VDD COMPOUT
8 7 AMPOUT 1 OP AMP VDD
8
MAX953 MAX954
COMPOUT 7
2 3 4
AMPINx1 AMPIN+ VSS 1.20V COMP REF 6 2 3 4 COMPIN+ 5 AMPINAMPIN+ COMP VSS
COMPIN-
6
MAX951 MAX952
COMPIN+
5
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 10A (7A typical) for the MAX951/MAX952 and less than 8A (5A 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 MAX951-MAX954
R2 R1 VIN COMPOUT VS COMPOUT RA R2
REF
RB
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.
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 +85C), so current through R2 can be as little as 500nA and still maintain good accuracy. If R2 = 2.4M, 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 )
Reference
The internal reference in the MAX951/MAX952 has an output of 1.20V with respect to VSS. Its accuracy is 2% in the -40C to +85C 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 20A. Do not bypass the reference output. The reference is stable for capacitive loads less than 100pF.
where the internal hysteresis is VIHYST = 3mV. 3) Determine R1. If the supply voltage is 5V, then R1 = 24k. 4) Check the hysteresis trip points. The upper trip point is 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: VIN(H) =
(R1 + R2)
(
)
__________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.
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9
Ultra-Low-Power, Single-Supply Op Amp + Comparator + Reference MAX951-MAX954
ANTENNA AMPIN+ AMPOUT L1 330mH 0.1F 20k AMP 1.0M 100k R1 2pF to 10pF 1 L1 x C1 = (2 fC) 2 5.1M REF LAYOUT-SENSITIVE AREA, METAL RFI SHIELDING ADVISED 1.2V COMP 10M VCC = 5V
0.1F C1A 390pF C1B C1C 330pF 20-60pF
MAX952
R2
Figure 3. Compensation for Feedback-Node Capacitance
Figure 4. Low-Frequency Radio Receiver Application
V R A R2 SHYST , for VSHYST >> VIHYST VDD In the example, RA is again 24k. 6) Select the upper trip point VS(H). Our example is set at 4.75V. 7) Calculate RB. RB =
Op-Amp Stability and Board Layout Considerations
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 10M 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.
(R2) VS(H)
(VREF
+ VIHYST
- VREF +
(
) (R2)(R A ) VIHSYT )(R A
+ R2
)
RB is 8.19k, or approximately 8.2k.
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 280V for the SO package.
10
Input Overdrive
With 100mV overdrive, comparator propagation delay is typically 6s. 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 15A and 32A for supply voltages of 2.8V and 7V, respectively.
______________________________________________________________________________________
Ultra-Low-Power, Single-Supply Op Amp + Comparator + Reference MAX951-MAX954
VCC = 5V 10kHz, 5Vp-p NEC SE307-C 51 C2 15pF, 5% NEC PH302B R2 1.0M, 1% C1 150pF, 5% AMP 0.1F 30k 10M RADIOACTIVE IONIZATION CHAMBER SMOKE SENSOR 4.7M AMP COMP
MAX953
VCC
R1A 49.9k R1 B 1% 49.9k 1%
100k
1.2V
COMP LAYOUT-SENSITIVE AREA REF 5.1M
MAX952
LAYOUT-SENSITIVE AREA 1 R1 x C1 = R2 x C2 = 2 fC
0.1F
Figure 5. Infrared Receiver Application
Figure 6. Sensor Preamp and Alarm Trigger 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. 0.1F 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.
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 5A 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
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-
______________________________________________________________________________________
Ultra-Low-Power, Single-Supply Op Amp + Comparator + Reference MAX951-MAX954
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 50M. 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.
___________________Chip Topography
AMPOUT V DD
AMPIN-
COMPOUT 0.084" (2.134mm)
AMPIN+
REF(COMPIN-)
V SS 0.058" (1.473mm)
COMPIN+
______________Ordering Information
PART MAX951C/D MAX951EPA MAX951ESA MAX951EUA MAX951MJA MAX952C/D MAX952EPA MAX952ESA MAX952EUA MAX952MJA MAX953C/D MAX953EPA MAX953ESA MAX953EUA MAX953MJA MAX954C/D MAX954EPA MAX954ESA MAX954EUA MAX954MJA TEMP. RANGE 0C to +70C -40C to +85C -40C to +85C -40C to +85C -55C to +125C 0C to +70C -40C to +85C -40C to +85C -40C to +85C -55C to +125C 0C to +70C -40C to +85C -40C to +85C -40C to +85C -55C to +125C 0C to +70C -40C to +85C -40C to +85C -40C to +85C -55C to +125C PIN-PACKAGE Dice* 8 Plastic DIP 8 SO 8 MAX 8 CERDIP** Dice* 8 Plastic DIP 8 SO 8 MAX 8 CERDIP** Dice* 8 Plastic DIP 8 SO 8 MAX 8 CERDIP** Dice* 8 Plastic DIP 8 SO 8 MAX 8 CERDIP**
( ) ARE FOR MAX953/MAX954
TRANSISTOR COUNT: 163 SUBSTRATE CONNECTED TO VDD
__________Typical Operating Circuit
8 0.1F INPUT AMPIN+ 3 2 1 1M R2 R1 6 REF 4 VCC
MAX951 MAX952
5 COMPOUT 7
1.20V
VSS
* Dice are tested at TA = +25C, 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 (c) 1997 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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