19-1141; Rev 1; 11/98 Single/Dual, +3V/+5V Dual-Speed Comparators with Auto-Standby The MAX975/MAX977 single/dual comparators feature three different operating modes, and are optimized for +3V and +5V single-supply applications. The operating modes are as follows: high speed, high speed with auto-standby, and low power. Propagation delay is 28ns in high-speed mode, while supply current is only 250µA. Supply current is reduced to 3µA in low-power mode. The auto-standby feature allows the comparator to automatically change from low-power mode to highspeed mode upon receipt of an input signal. In the absence of an input signal, the comparator reverts back to low-power mode after an adjustable timeout period. The timeout period for the MAX975 to enter standby is set by a single capacitor. The dual MAX977 features independently adjustable timeout periods for each comparator using separate capacitors. The MAX975/MAX977’s inputs have a common-mode voltage range of -0.2V to (VCC - 1.2V). The differential input voltage range extends rail to rail. The outputs are capable of rail-to-rail operation without external pull-up circuitry, making these devices ideal for interface with CMOS/TTL logic. All inputs and outputs can tolerate a continuous short-circuit fault condition to either rail. The comparator’s internal hysteresis in high-speed mode ensures clean output switching, even with slow-moving input signals. The single MAX975 is available in 8-pin SO and 8-pin µMAX packages, while the dual MAX977 is available in 14-pin SO and 16-pin QSOP packages. ____________________________Features ♦ Three Operating Modes: High Speed High Speed with Auto-Standby Low Power ♦ 28ns Propagation Delay (high-speed mode) ♦ 5µA Max Supply Current in Low-Power/ Auto-Standby Modes ♦ +3V/+5V Single-Supply Operation ♦ Rail-to-Rail Outputs ♦ Ground-Sensing Input ♦ Internal Hysteresis (high-speed mode) ♦ Adjustable Timeout Period ♦ µMAX Package (MAX975) QSOP-16 Package (MAX977) Ordering Information TEMP. RANGE PIN-PACKAGE MAX975ESA PART -40°C to +85°C 8 SO MAX975EUA MAX977ESD MAX977EEE -40°C to +85°C -40°C to +85°C -40°C to +85°C 8 µMAX 14 SO 16 QSOP Functional Diagram VCC ________________________Applications Battery-Powered Systems RF ID Tags Keyless Entry Threshold Detectors/Discriminators 3V Systems IR Receivers Digital-Line Receivers MAX975 IN+ LP HIGH SPEED OUT ENABLE TRANSITION MONITOR GND LOW POWER ENABLE IN- STAT TIMING CIRCUIT STO Pin Configurations 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 1-800-835-8769. MAX975/MAX977 General Description MAX975/MAX977 Single/Dual, +3V/+5V Dual-Speed Comparators with Auto-Standby ABSOLUTE MAXIMUM RATINGS Supply Voltage (VCC) ............................................................+6V All Other Pins..............................................-0.3V to (VCC + 0.3V) Duration of Output Short Circuit to GND_ or VCC ......Continuous Continuous Power Dissipation (TA = +70°C) 8-Pin SO (derate 5.88mW/°C above +70°C)..................471mW 8-Pin µMAX (derate 4.10mW/°C above +70°C) .............330mW 14-Pin SO (derate 8.33mW/°C above +70°C)................667mW 16-Pin QSOP (derate 8.33mW/°C above +70°C)...........667mW Operating Temperature Range ...........................-40°C to +85°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 (VCC = +2.7V to +5.25V, specifications are for high-speed mode, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 5.25 V POWER SUPPLY Supply-Voltage Operating Range VCC 2.7 High-speed mode Supply Current Per Comparator Power-Supply Rejection Ratio ICC Auto-standby/low-power modes PSRR VCM = 1V, 2.7V ≤ VCC ≤ 5.25V VCMR (Note 2) 250 500 SO 3 5 µMAX/QSOP 3 6 High-speed mode 63 Low-power mode 90 µA dB 77 COMPARATOR INPUTS Common-Mode Voltage Range -0.2 High-speed mode, TA = +25°C Input Offset Voltage (Note 3) Input-Referred Hysteresis Input Bias Current VOS VHYS IB VCM = 1V, VCC = 5V VCC - 1.2 +0.2 High-speed mode, TA = TMIN to TMAX Auto-standby/ low-power modes, TA = TMIN to TMAX VCM = 1V, VCC = 5V (Note 4) High-speed mode SO ±1 ±5 µMAX/QSOP ±1 ±7 0.5 2 4 µMAX/QSOP 0.3 2 4 SO -100 -300 µMAX/QSOP -100 -400 nA ±100 nA Auto-standby/low-power modes Input Capacitance CIN 3 2 High-speed mode Low-power mode mV -5 ±20 -0.2V ≤ VCM ≤ VCC - 1.2V mV SO IOS CMRR ±2 ±3 Input Offset Current Common-Mode Rejection Ratio V SO 66 µMAX/QSOP 54 pF 90 dB 82 _______________________________________________________________________________________ Single/Dual, +3V/+5V Dual-Speed Comparators with Auto-Standby (VCC = +2.7V to +5.25V, specifications are for high-speed mode, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP 0.7 x VCC VCC / 2 MAX UNITS DIGITAL INPUTS LP Input Voltage High VLPIH LP Input Voltage Low VLPIL VCC / 2 LP Fall Time tLP LP Input Current ILPB STO_ Input Voltage Low VCIL STO_ Source Current ISTO VCC = 3V OUT_ Output Voltage High VOH ISOURCE = 2mA, all modes OUT_ Output Voltage Low VOL ISINK = 2mA, all modes tPD+ CLOAD = 10pF, VCC = 5V V 0.3 x VCC V 10 µs 0.01 ±1 µA VCC / 2 0.3 x VCC (Note 5) 0.15 V µA DIGITAL OUTPUTS Propagation Delay, Low to High (Note 6) Propagation Delay, High to Low (Note 6) Propagation-Delay Skew (Note 6) Propagation-Delay Matching tPD- tSKEW ∆tPD CLOAD = 10pF, VCC = 5V V 0.1 0.4 V High-speed mode, overdrive = 5mV 28 50 ns Low-power mode, overdrive = 10mV 0.82 1.6 µs High-speed mode, overdrive = 5mV 28 50 ns Low-power mode, overdrive = 10mV 0.48 1.6 µs CLOAD = 10pF 2 ns MAX977 only, CLOAD = 10pF 1 ns CLOAD = 10pF, VCC = 5.0V Rise/Fall Time VCC - 0.4 VCC - 0.1 High-speed mode 1.6 Low-power mode 1.6 STAT_ Output Voltage High VSH ISOURCE = 3mA, all modes STAT_ Output Voltage Low VSL ISINK = 400µA, all modes ns VCC - 0.4 V 0.4 V Note 1: The MAX975EUA is 100% production tested at TA = +25°C; all temperature specifications are guaranteed by design. Note 2: Inferred by CMRR. Either input can be driven to the absolute maximum limit without false output inversion, as long as the other input is within the specified common-mode input voltage range. Note 3: VOS is defined as the mean of trip points. The trip points are the extremities of the differential input voltage required to make the comparator output change state (Figure 1). Note 4: The difference between the upper and lower trip points is equal to the width of the input-referred hysteresis zone (Figure 1). Note 5: Guaranteed by design. The LP pin is sensitive to noise. If fall times larger than 10µs are expected, bypass LP to ground using a 0.1µF capacitor. Note 6: Propagation delay is guaranteed by design. For low-overdrive conditions, VOS is added to the overdrive. The following equation defines propagation-delay skew: tSKEW = tPD+ - tPD-. _______________________________________________________________________________________ 3 MAX975/MAX977 ELECTRICAL CHARACTERISTICS (continued) MAX975/MAX977 Single/Dual, +3V/+5V Dual-Speed Comparators with Auto-Standby ELECTRICAL CHARACTERISTICS (continued) (VCC = +2.7V to +5.25V, specifications are for high-speed mode, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 5 10 16 ms AUTO-STANDBY/LOW-POWER TIMING (Note 7; Figure 2) Auto-Standby Timeout tASB (Note 8) Auto-Standby Enable Time tASBE (Note 9) 3 Auto-Standby Wake-Up Time tASD 10mV overdrive (Note 10) 2 Auto-Standby Wake-Up Input or LP Pulse Width tPWD 10mV overdrive (Note 11) Auto-Standby Comparator Disable tASCD (Note 12) 0.8 µs tLPE (Note 13) 3 µs High-Speed Enable Time tHSE (Note 14) 1.1 Low-Power Comparator Disable tLPCD (Note 15) 0.7 µs Low-Power STAT_ High tLPSH (Note 16) 20 ns Low-Power Enable Time Note 7: Note 8: Note 9: Note 10: Note 11: Note 12: Note 13: Note 14: Note 15: Note 16: 4 µs 4 1.6 µs µs 4 µs Timing specifications are guaranteed by design. Set by 1000pF external capacitor at the STO_ pin. tASB is defined as the time from last input transition to STAT_ = high. Does not include time to go into standby condition (tASBE). tASBE is defined as the time from when STAT_ goes high to when the supply current drops to 5µA. tASD is defined as the time from the last input transition to when STAT_ goes low. The comparator is in high-speed mode before STAT_ is low. tPWD is defined as the minimum input or LP pulse width to trigger fast-mode operation from auto-standby. tASCD is defined as the time from the last input transition to when the supply current increases to 300µA. tLPE is defined as the time from when LP is driven high to when the supply current drops to 5µA. tHSE is defined as the time from when LP goes low to when STAT goes low. The comparator is in high-speed mode before STAT_ is low. tLPCD is defined as the time from when LP goes low to when the supply current increases to 300µA. tLPSH is defined as the time from when LP goes high to when STAT_ goes high. _______________________________________________________________________________________ Single/Dual, +3V/+5V Dual-Speed Comparators with Auto-Standby -0.85 -0.90 -0.95 -1.00 -1.05 -1.10 -1.15 -1.20 0 20 40 60 80 100 LOW-POWER MODE 10 1 0.01k 0.1k 100 -70 VCC = 3V -90 -110 VCC = 5V -130 -170 1k 10k 100k 1M 10M 100M -60 -40 -20 20 40 60 80 100 LOW-POWER INPUT BIAS CURRENT vs. TEMPERATURE HIGH-SPEED VOLTAGE TRIP POINTS/INPUT OFFSET VOLTAGE vs. TEMPERATURE HIGH-SPEED VOLTAGE TRIP POINTS/INPUT OFFSET VOLTAGE vs. TEMPERATURE 5.5 VCC = 5V 5.0 4.5 VCC = 3V 4.0 3.5 MAX977-05 TRIP POINTS/OFFSET VOLTAGE (mV) MAX977-04 6.0 1.0 VCC = 5V 0.8 0.6 VTRIP+ 0.4 0.2 0 VOS -0.2 VTRIP- -0.4 -0.6 -0.8 -1.0 3.0 -60 -40 -20 0 20 40 60 80 -60 -40 -20 100 0 20 40 60 80 1.2 1.0 0.8 0.6 0.4 MAX977-06 TEMPERATURE (°C) TRIP POINTS/OFFSET VOLTAGE (mV) TRANSITION FREQUENCY (kHz) 6.5 VCC = 3V VTRIP+ 0.2 0 -0.2 -0.4 VOS -0.6 VTRIP- -0.8 -1.0 -1.2 100 -60 -40 -20 0 20 40 60 TEMPERATURE (°C) TEMPERATURE (°C) TEMPERATURE (°C) LOW-POWER PROPAGATION DELAY vs. CAPACITIVE LOAD LOW-POWER PROPAGATION DELAY vs. INPUT OVERDRIVE AUTO-STANDBY TIMEOUT vs. TEMPERATURE tPD+ 500 450 VCC = 3V 400 350 VCC = 3V 300 tPD- tPD+ 450 VCC = 3V 350 300 50mV OVERDRIVE 200 VCC = 3V VCC = 5V 100 150 CAPACITIVE LOAD (pF) 200 250 100 MAX977-09 VCC = 3V 9.8 9.7 9.6 VCC = 5V 9.4 150 50 9.9 9.5 tPD- 200 80 10.0 500 400 100 10.1 VCC = 5V 550 80 10.2 600 250 VCC = 5V 250 CLOAD =15pF TIMEOUT (ms) VCC = 5V PROPAGATION DELAY (ns) 550 650 MAX977-08 700 MAX977-07 600 0 0 TEMPERATURE (°C) 7.0 INPUT BIAS CURRENT (nA) HIGH-SPEED MODE 1000 -150 -60 -40 -20 PROPAGATION DELAY (ns) -50 MAX977-03 10000 INPUT BIAS CURRENT (nA) VCC = 3V MAX977-02 MAX977-01 -0.60 -0.65 -0.70 -0.75 -0.80 HIGH-SPEED INPUT BIAS CURRENT vs. TEMPERATURE SUPPLY CURRENT PER COMPARATOR vs. OUTPUT TRANSITION FREQUENCY SUPPLY CURRENT PER COMPARATOR (µA) OFFSET VOLTAGE (mV) LOW-POWER OFFSET VOLTAGE vs. TEMPERATURE 9.3 0 40 80 120 160 INPUT OVERDRIVE (mV) 200 240 -60 -40 -20 0 20 40 60 TEMPERATURE (°C) _______________________________________________________________________________________ 5 MAX975/MAX977 __________________________________________Typical Operating Characteristics (VCC = 3.0V, TA = +25°C, unless otherwise noted.) ____________________________Typical Operating Characteristics (continued) (VCC = 3.0V, TA = +25°C, unless otherwise noted.) OUTPUT HIGH VOLTAGE vs. OUTPUT SOURCE CURRENT VCC = 3V 3.0 1000 100 TA = -40°C 2.5 2.0 1.5 VCC = 3V 3.0 OUTPUT VOLTAGE (V) OUTPUT VOLTAGE (V) TIMEOUT (µs) 10000 3.5 MAX977-11 3.5 MAX977-10 100000 OUTPUT LOW VOLTAGE vs. OUTPUT SINK CURRENT TA = +85°C 1.0 MAX977-12 AUTO-STANDBY TIMEOUT vs. TIMEOUT CAPACITOR TA = +25°C TA = +85°C 2.5 2.0 TA = -40°C 1.5 1.0 10 0.5 0.5 TA = +25°C 0.0 1 10 100 1000 10000 5 10 15 20 25 30 35 0 15 20 25 30 35 SINK CURRENT (mA) HIGH-SPEED PROPAGATION DELAY vs. TEMPERATURE (VCC = 5V) HIGH-SPEED PROPAGATION DELAY vs. TEMPERATURE (VCC = 3V) HIGH-SPEED SUPPLY CURRENT PER COMPARATOR vs. TEMPERATURE (VCC = 5V) PROPAGATION DELAY (ns) 26 tPD22 tPD+ 18 14 31 CLOAD = 15pF VOD = 50mV 29 27 25 23 tPDtPD+ 21 19 -60 -40 -20 0 20 40 60 80 -60 -40 -20 100 OUT_ = HIGH 275 250 225 200 OUT_ = LOW 175 150 125 100 15 10 400 375 350 325 300 0 20 40 60 80 100 -60 -40 -20 0 20 40 60 80 TEMPERATURE (°C) TEMPERATURE (°C) TEMPERATURE (°C) HIGH-SPEED SUPPLY CURRENT PER COMPARATOR vs. TEMPERATURE (VCC = 3V) STANDBY/LOW-POWER SUPPLY CURRENT PER COMPARATOR vs. TEMPERATURE (VCC = 5V) STANDBY/LOW POWER-SUPPLY CURRENT PER COMPARATOR vs. TEMPERATURE (VCC = 3V) SUPPLY CURRENT (µA) 4.0 OUT_ = HIGH 240 220 200 180 OUT_ = LOW 160 140 OUT_ = LOW 3.5 3.0 OUT_ = HIGH 2.5 3.6 3.4 3.2 3.0 OUT = LOW 2.8 2.6 2.4 2.2 2.0 2.0 120 100 1.5 -60 -40 -20 0 20 40 TEMPERATURE (°C) 60 80 100 100 MAX977-18 3.8 SUPPLY CURRENT (µA) 280 MAX977-17 4.5 MAX977-16 300 40 MAX977-15 33 SUPPLY CURRENT (µA) MAX977-13 35 17 6 10 SOURCE CURRENT (mA) CLOAD = 15pF VOD = 50mV 260 5 CAPACITANCE (pF) 30 PROPAGATION DELAY (ns) 0.0 0 MAX977-14 1 SUPPLY CURRENT (µA) MAX975/MAX977 Single/Dual, +3V/+5V Dual-Speed Comparators with Auto-Standby OUT = HIGH 1.8 -60 -40 -20 0 20 40 TEMPERATURE (°C) 60 80 100 -60 -40 -20 0 20 40 TEMPERATURE (°C) _______________________________________________________________________________________ 60 80 100 Single/Dual, +3V/+5V Dual-Speed Comparators with Auto-Standby tPDtPD+ 32.5 30.0 27.5 25.0 tPDVCC = +5V tPD+ 22.5 20.0 17.5 15.0 25 VCC = +3V 20 tPD+ VCC = +5V 15 10 5 50 100 150 200 250 520 480 440 tPD+ 400 360 tPD- 320 280 200 0 -60 -40 -20 20 40 60 80 100 120 140 160 180 200 CAPACITIVE LOAD (pF) INPUT OVERDRIVE (mV) 0 20 40 60 80 100 TEMPERATURE (°C) PROPAGATION DELAY tPD+ HIGH-SPEED MODE (VCC = +3V) MAX977-22 LOW-POWER PROPAGATION DELAY vs. TEMPERATURE (VCC = 5V) 750 700 650 600 550 CLOAD = 15pF VOD = 50mV 560 240 CLOAD = 15pF 0 0 600 PROPAGATION DELAY (ns) tPDPROPAGATION DELAY (ns) VCC = +3V MAX977-21 30 LOW-POWER PROPAGATION DELAY vs. TEMPERATURE (VCC = 3V) MAX977-20 CLOAD = 15pF VOD = 50mV HIGH-SPEED PROPAGATION DELAY vs. INPUT OVERDRIVE MAX977-19 45.0 42.5 40.0 37.5 35.0 PROPAGATION DELAY (ns) PROPAGATION DELAY (ns) HIGH-SPEED PROPAGATION DELAY vs. CAPACITIVE LOAD CLOAD = 15pF VOD = 50mV INPUT 5mV/div VOS VCC tPD+ 500 450 400 350 VCC/2 tPD- 300 OUTPUT 1V/div GND 250 200 150 MAX975/977 TOC23 -60 -40 -20 0 20 40 60 80 5ns/div 100 tPD+ TEMPERATURE (°C) PROPAGATION DELAY tPDHIGH-SPEED MODE (VCC = +3V) VOS PROPAGATION DELAY tPDHIGH-SPEED MODE (VCC = +5V) INPUT 5mV/div VOS OUTPUT 1V/div VCC INPUT 5mV/div VCC VCC/2 OUTPUT 2V/div VCC/2 GND GND MAX975/977 TOC24 5ns/div tPD- MAX975/977 TOC25 5ns/div tPD- _______________________________________________________________________________________ 7 MAX975/MAX977 ____________________________Typical Operating Characteristics (continued) (VCC = 3.0V, TA = +25°C, unless otherwise noted.) MAX975/MAX977 Single/Dual, +3V/+5V Dual-Speed Comparators with Auto-Standby ____________________________Typical Operating Characteristics (continued) (VCC = 3.0V, TA = +25°C, unless otherwise noted.) PROPAGATION DELAY tPDLOW-POWER MODE (VCC = +3V) PROPAGATION DELAY tPD+ HIGH-SPEED MODE (VCC = +5V) INPUT 5mV/div VOS INPUT 5mV/div VOS VCC VCC/2 VCC OUTPUT 2V/div VCC/2 OUTPUT 1V/div GND GND MAX975/977 TOC27 MAX975/977 TOC26 5ns/div 100ns/div tPD+ tPD- PROPAGATION DELAY tPD+ LOW-POWER MODE (VCC = +3V) INPUT 5mV/div VOS VCC VCC/2 OUTPUT 1V/div GND MAX975/977 TOC28 100ns/div tPD+ PROPAGATION DELAY tPD+ LOW-POWER MODE (VCC = +5V) PROPAGATION DELAY tPDLOW-POWER MODE (VCC = +3V) INPUT 5mV/div VOS VCC INPUT 5mV/div VOS VCC OUTPUT 2V/div VCC/2 GND OUTPUT 2V/div VCC/2 GND MAX975/977 TOC29 100ns/div 8 tPD+ MAX975/977 TOC30 100ns/div tPD- _______________________________________________________________________________________ Single/Dual, +3V/+5V Dual-Speed Comparators with Auto-Standby 100kHz RESPONSE LOW-POWER MODE (VCC = +3V) 100kHz RESPONSE LOW-POWER MODE (VCC = +5V) INPUT 5mV/div VOS INPUT 5mV/div VOS VCC VCC OUTPUT 2V/div OUTPUT 1V/div GND GND MAX975/977 TOC32 2µs/div MAX975/977 TOC31 2µs/div 10MHz RESPONSE HIGH-SPEED MODE (VCC = +5V) INPUT 5mV/div VOS VCC OUTPUT 2V/div GND MAX975/977 TOC34 20ns/div MAX975 AUTO-STANDBY OPERATION 10MHz RESPONSE HIGH-SPEED MODE (VCC = +3V) +100mV INPUT 5mV/div VOS Inp VCC -100mV 3V OUTPUT 1V/div GND OUT 0V ICC 250µA 0µA MAX975/977 TOC33 20ns/div MAX975/977 TOC35 1ms/div CSTO_ = 100pF _______________________________________________________________________________________ 9 MAX975/MAX977 ____________________________Typical Operating Characteristics (continued) (VCC = 3.0V, TA = +25°C, unless otherwise noted.) MAX975/MAX977 Single/Dual, +3V/+5V Dual-Speed Comparators with Auto-Standby _____________________________________________________________Pin Descriptions MAX975 PIN NAME FUNCTION 1 VCC Positive Supply Voltage, +2.7V to +5.25V 2 IN+ Noninverting Comparator Input 3 IN- Inverting Comparator Input 4 STAT Mode Status Pin. Indicates the operating mode. STAT is high for auto-standby mode or low-power mode, and during the transition to high-speed mode. STAT = low indicates that the comparator is in high-speed mode. STAT can source 3mA to power additional circuitry. 5 STO Set Timeout Input. Connect a capacitor from STO to GND to program the time the comparator may remain idle before entering standby mode. Connect STO to GND to disable the auto-standby feature. Calculate timeout with the following relationship: tASB = 10 x C µs, where C is in pF. 6 GND Ground 7 OUT Comparator Output 8 LP Low Power Mode Input. Drive LP high for low-power mode. Drive LP low for high-speed mode (STO = GND) or for high-speed mode with auto-standby. Connect to GND if low-power mode will not be used. Connect to VCC if high-speed mode will not be used. MAX977 QSOP NAME FUNCTION 1, 8 1, 9 STOA, STOB Set Idle Timeout Input A/B. Connect a capacitor from STOA/STOB to GND to program the time in which comparator A/B may remain idle before entering standby mode. Connect STOA/STOB to GND to disable the auto-standby feature for comparator A/B. Calculate timeout with the following relationship: tASB = 10 x C µs, where C is in pF. 2, 9 2, 10 GNDA, GNDB Ground for Comparator A/B 3, 10 3, 11 OUTA, OUTB Output for Comparator A/B 4 4, 5 VCC 5, 12 6, 14 INB+, INA+ 6, 13 7, 15 INB-, INA- SO 7, 14 8, 16 STATB, STATA — 12 N.C. 11 10 13 LP Positive Supply Voltage, +2.7V to +5.25V. For QSOP, connect pin 4 to pin 5. Noninverting Input for Comparator B/A Inverting Input for Comparator B/A Mode Status Pin B/A. Indicates the operating mode of comparator B/A. STATB/STATA is high for auto-standby mode or for low-power mode, and during the transition to high-speed mode. STATB/STATA = low indicates that comparator B/A is in high-speed mode. STATB/STATA can source 3mA to power additional circuitry. No connection. Not internally connected. Low Power Mode Input for both comparators. Drive LP high for low-power mode. Drive LP low for high-speed mode (STO_ = GND) or for high-speed mode with autostandby. Connect to GND if low-power mode will not be used. Connect to VCC if high-speed mode will not be used. ______________________________________________________________________________________ Single/Dual, +3V/+5V Dual-Speed Comparators with Auto-Standby MAX975/MAX977 Table 1. Programming INPUTS STAT OUTPUT MODE LP STO_ IDLE TIME L tASB = CSTO x 10µs/pF <tASB High speed (Auto-standby enabled) L L tASB = CSTO x 10µs/pF ≥tASB Auto-standby H ↓ (falling edge) L X High speed (Auto-standby mode disabled) L H X X Low power H _______________Detailed Description The MAX975/MAX977 single/dual comparators have three operating modes, and use a +2.7V to +5.25V single supply. The operating modes are as follows: high speed, high speed with auto-standby, and low power. Propagation delay is typically 28ns in highspeed mode, while typical supply current is 250µA. In low-power mode, propagation delay is typically 480ns and power consumption is only 3µA. The auto-standby feature switches into low-power standby for each comparator with unchanging outputs in high-speed mode. The timeout period, or the time that OUT_ must be idle (unchanged state) for the MAX975/ MAX977 to enter auto-standby, is adjustable by means of an external capacitor. All inputs and outputs can tolerate a continuous short-circuit fault condition to either rail. Internal hysteresis in high-speed mode ensures clean output switching, even with slow-moving input signals. The MAX975 functional diagram shows two paralleled comparators, a timing circuit, a transition detector, and logic gates. The upper comparator is high speed, while the lower comparator is a slower low-power comparator. The dual MAX977 features independent timeout adjustment. The following sections discuss the details of operation. Hysteresis (High-Speed Mode Only) Most high-speed comparators can oscillate in the linear operating region because of noise or undesired parasitic feedback. This tends to occur when the voltage on one input is equal to or very close to the voltage on the other input. The MAX975/MAX977 have internal hysteresis to counter parasitic effects and noise. The hysteresis in a comparator creates two trip points: one for the rising input voltage and one for the falling VHYST VTRIP+ VIN+ VTRIP- COMPARATOR OUTPUT VOS = VTRIP+ + VTRIP2 VIN- = 0 VOH VOL Figure 1. Input and Output Waveforms, Noninverting Input Varied input voltage (Figure 1). The difference between the trip points is the hysteresis. When the comparators’ input voltages are equal, the hysteresis effectively causes one comparator input voltage to move quickly past the other, taking the input out of the region where oscillation occurs. Figure 1 illustrates the case where IN- has a fixed voltage applied and IN+ is varied. If the inputs were reversed, the figure would be the same, except with an inverted output. Auto-Standby Mode The MAX975/MAX977’s auto-standby function operates only in high-speed mode. The device enters autostandby when OUT_ remains unchanged for a preprogrammed timeout period. In auto-standby mode, the low-power comparator is enabled while the high-speed comparator is disabled and STAT_ goes high. The logic state and sink/source capabilities of OUT_ remain unchanged, but propagation delay increases to 480ns. In this mode, the timing circuitry is powered down, and the transition detector monitors the low-power comparator for a transition. When an output transition occurs (OUT_ changes state), the timing circuitry is ______________________________________________________________________________________ 11 MAX975/MAX977 Single/Dual, +3V/+5V Dual-Speed Comparators with Auto-Standby tASB DIFFERENTIAL INPUT VOLTAGE OUT_ VOS VOH VCC A VOL tPD+ STAT_ tPWD tPD- tASD VCC 0V ICC (TYP) tLPSH tASCD 300µA 3µA tLPCD tASBE LP tLPE tHSE Figure 2. Timing Diagram powered up, the high-speed comparator is enabled, the low-power comparator is disabled, and STAT goes high, placing the MAX975 back into high-speed mode (Figure 2). Use an external capacitor, CSTO, to program the timeout period required for the comparator to enter autostandby mode. Determine the capacitor required for a particular timeout period by the relationship t ASB = 10 x Cµs, where C is in pF. For example, connecting a 0.1µF capacitor to STO_ results in a timeout period of 1sec. The propagation delay of OUT_ when exiting auto standby mode is equivalent to the low-power-mode propagation delay. When STAT_ goes low, the lowpower comparator is disabled and the high-speed comparator is ready for operation. To bring the comparator out of auto-standby mode without a transition occurring on OUT_, toggle LP low-high-low. The LP pin is sensitive to noise. If fall times larger than 10µs are expected, bypass LP with a 0.1µF capacitor to GND. To disable auto-standby mode, drive STO_ low or connect it to ground. Note that driving STO_ low while in autostandby mode will not bring the comparator out of autostandby mode. Also, if driving STO_ with an open drain, leakage must be less than 1nA. On power-up, the device is in high-speed mode unless LP is high. The MAX977 operates in the same manner as the MAX975. 12 Low-Power Mode Driving LP high switches the MAX975/MAX977 to lowpower mode. In this mode, the supply current drops to a maximum of 5µA, and propagation delay increases typically to 480ns. The high-speed comparator is disabled and the low-power comparator is enabled for continuous operation. Return to high-speed mode by driving LP low. The LP pin is sensitive to noise. If fall times larger than 10µs are expected, bypass LP with a 0.1µF capacitor to GND. The logic state and sink/ source capabilities of OUT_ remain unchanged in lowpower mode. Input-Stage Circuitry The MAX975/MAX977 input common-mode range is from -0.2V to (VCC - 1.2V). But the voltage range for each comparator input extends to both VCC and GND rails. The output remains in the correct logic state while one or both of the inputs are within the common-mode range. If both input levels are out of the common-mode range, input-stage current saturation occurs and the output becomes unpredictable. ______________________________________________________________________________________ Single/Dual, +3V/+5V Dual-Speed Comparators with Auto-Standby Powering Circuitry with STAT STAT’s function is to indicate the comparator’s operating mode. When STAT is low, the comparator is in highspeed mode and will meet the guaranteed propagation delay. When STAT is high, the comparator is in autostandby mode, in low-power mode, or in transition to high-speed mode. An additional feature of this pin is that it can source 3mA of current. When STAT is high, additional circuitry can be powered. This circuitry can be automatically powered up or powered down, depending on the input signal or lack of input signal received by the MAX975/MAX977. CMOS LOGIC Board layout can create timing errors due to parasitic effects. Make the STO_ traces as short as possible to reduce capacitance and coupling effects. When driving STO_ to disable auto-standby mode, use standard CMOS logic isolated with a low-leakage (<1nA) diode, such as National’s FJT1100 (Figure 3). 15nA leakage typically results in 10% error. The MAX977 has separate timing inputs (STOA and STOB). These pins must have separate capacitors. The timing circuits will not operate correctly if a single capacitor is used with STOA and STOB connected together. The relationship between the timeout period and the STO_ capacitor is tASB = 10 x CSTO_ µs, where CSTO_ is in pF. This equation is for larger capacitance values, and does not take into account variations due to board capacitance and board leakage. If less than 1ms is desired, subtract the ~3pF STO_ parasitic capacitance from the calculated value. Circuit Layout and Bypassing The MAX975/MAX977’s high gain bandwidth requires design precautions to realize the comparator’s full highspeed capability. The following precautions are recommended: STO_ Figure 3. Driving STO_ with CMOS Logic R3 VCC VCC VCC STO_ Considerations The charge currents for the capacitor connected to STO_ are on the order of 100nA. This necessitates caution in capacitor type selection and board layout. Capacitor leakage currents must be less than 1nA to prevent timing errors. Ceramic capacitors are available in values up to 1µF, and are an excellent choice for this application. If a larger capacitance value is needed, use parallel ceramic capacitors to get the required capacitance. Aluminum and tantalum electrolytic capacitors are not recommended due to their higher leakage currents. MAX975/MAX977 __________Applications Information RD OUT STAT LOSS OF SIGNAL GND R1 VCC R2 MAX975 Figure 4. IR Receiver 1) Use a printed circuit board with an unbroken, lowinductance ground plane. 2) Place a decoupling capacitor (a 0.1µF ceramic capacitor is a good choice) as close to VCC as possible. 3) Keep lead lengths short on the inputs and outputs, to avoid unwanted parasitic feedback around the comparators. 4) Solder the devices directly to the printed circuit board instead of using a socket. 5) Minimize input impedance. 6) For slowly varying inputs, use a small capacitor (~1000pF) across the inputs to improve stability. IR Receiver Figure 4 shows an application using the MAX975 as an infrared receiver. The infrared photodiode creates a current relative to the amount of infrared light present. This current creates a voltage across R D. When this voltage level crosses the voltage applied by the voltage divider to the inverting input, the output transitions. If the photodiode is not receiving enough signal to cause transitions on the MAX975’s output, STAT is used as a loss-of-signal indicator. R3 adds additional hysteresis for noise immunity. ______________________________________________________________________________________ 13 MAX975/MAX977 Single/Dual, +3V/+5V Dual-Speed Comparators with Auto-Standby VCC R3 14 VIN 82.1k, 1% 0.1µF 4 1/2 MAX977 3V 0.1µF UNDERVOLTAGE 3 1 15 VCC 2 VCC R2 1 24.9k, 1% MAX6120 2 µP STO 50Ω 6 5 11 GND X-BAND DETECTOR 9 10 CSTO OVERVOLTAGE 3V CSTOB 4.7k (PIN NUMBERS SHOWN ARE FOR QSOP PACKAGE) Figure 5. Window Comparator 1M 0.1µF Figure 6. Toll-Tag Reader Window Comparator The MAX977 is ideal for making a window detector (undervoltage/overvoltage detector). The schematic shown in Figure 5 uses a MAX6120 reference and component values selected for a 2.0V undervoltage threshold and a 2.5V overvoltage threshold. Choose different thresholds by changing the values of R1, R2, and R3. OUTA provides an active-low undervoltage indication, and OUTB gives an active-low overvoltage indication. ANDing the two outputs provides an active-high, power-good signal. The design procedure is as follows: 1) Select R1. The leakage current into INB- is normally 100nA, so the current through R1 should exceed 10µA for the thresholds to be accurate. R1 values in the 50kΩ to 100kΩ range are typical. 2) Choose the overvoltage threshold (VOTH) when VIN is rising, and calculate R2 and R3 with the following formula: R2 + R3 = R1 x [VOTH / (VREF + VH) - 1] where VH = 1/2VHYST. 3) Choose the undervoltage threshold (VUTH) when VIN is falling, and calculate R2 with the following formula: R2 = (R1 + R2 + R3) x [(VREF - VH) / VUTH] - R1 where VH = 1/2VHYST. 14 LP I/0 VCC 7 R1 100k, 1% I/0 MAX975 POWER GOOD 1/2 MAX977 3 WAKE-UP IRQ STAT CSTOA 4) Calculate R3 with the following formula: R3 = (R2 + R3) - R2 5) Verify the resistor values. The equations are as follows: VOTH = (VREF + VH) x (R1 + R2 + R3) / R1 VUTH = (VREF - VH) x (R1 + R2 + R3) / (R1 + R2) Toll-Tag Circuit The circuit shown in Figure 6 uses a MAX975 in a very low standby-power AM demodulator circuit that wakes up a toll tag (part of an automated roadway tollcollection system). This application requires very long standby times with brief and infrequent interrogations. In the awake state, it is capable of demodulating the typical 600kHz AM carrier riding on the 2.4GHz RF signal. In this state, the comparator draws its 250µA highspeed current. After communications have ceased, or when instructed by the microcontroller, the comparator returns to its low-power state. The comparator draws only 3µA in this state, while monitoring for RF activity. Typically, this application requires two comparators and a discrete power-management and signalswitchover circuit. The MAX975 circuit is smaller, simpler, less costly, and saves design time. ______________________________________________________________________________________ Single/Dual, +3V/+5V Dual-Speed Comparators with Auto-Standby TOP VIEW VCC 1 IN+ 2 IN- 3 8 MAX975 STAT 4 LP STOA 1 16 STATA STOA 1 14 STATA GNDA 2 15 INA- GNDA 2 13 INA- OUTA 3 14 INA+ OUTA 3 12 INA+ VCC 4 7 OUT 6 GND VCC 4 5 STO SO/µMAX MAX977 MAX977 13 LP 11 LP VCC 5 12 N.C. INB+ 5 10 OUTB INB+ 6 11 OUTB INB- 6 9 GNDB INB- 7 10 GNDB STATB 7 8 STOB STATB 8 SO 9 STOB QSOP ___________________Chip Information TRANSISTOR COUNT: 522 (MAX975) 1044 (MAX977) ______________________________________________________________________________________ 15 MAX975/MAX977 __________________________________________________________Pin Configurations 8LUMAXD.EPS ________________________________________________________Package Information QSOP.EPS MAX975/MAX977 Single/Dual, +3V/+5V Dual-Speed Comparators with Auto-Standby 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 © 1998 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.