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19-1141; Rev 1; 11/98
Single/Dual, +3V/+5V Dual-Speed Comparators with Auto-Standby
General Description
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 250A. Supply current is reduced to 3A 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 MAX 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) 5A 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 MAX Package (MAX975) QSOP-16 Package (MAX977)
MAX975/MAX977
Ordering Information
PART MAX975ESA MAX975EUA MAX977ESD MAX977EEE TEMP. RANGE -40C to +85C -40C to +85C -40C to +85C -40C to +85C PIN-PACKAGE 8 SO 8 MAX 14 SO 16 QSOP
Functional Diagram
________________________Applications
Battery-Powered Systems RF ID Tags Keyless Entry Threshold Detectors/Discriminators 3V Systems IR Receivers Digital-Line Receivers
IN+
VCC
MAX975
LP HIGH SPEED ENABLE TRANSITION MONITOR
OUT
LOW POWER ENABLE IN-
GND
STAT
TIMING CIRCUIT
STO
Pin Configurations appear at end of data sheet.
________________________________________________________________ Maxim Integrated Products
1
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Single/Dual, +3V/+5V Dual-Speed Comparators with Auto-Standby MAX975/MAX977
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 = +70C) 8-Pin SO (derate 5.88mW/C above +70C)..................471mW 8-Pin MAX (derate 4.10mW/C above +70C) .............330mW 14-Pin SO (derate 8.33mW/C above +70C)................667mW 16-Pin QSOP (derate 8.33mW/C above +70C)...........667mW Operating Temperature Range ...........................-40C to +85C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10sec) .............................+300C
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VCC = +2.7V to +5.25V, specifications are for high-speed mode, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1) PARAMETER POWER SUPPLY Supply-Voltage Operating Range Supply Current Per Comparator Power-Supply Rejection Ratio COMPARATOR INPUTS Common-Mode Voltage Range VCMR (Note 2) High-speed mode, TA = +25C Input Offset Voltage (Note 3) VOS VCM = 1V, VCC = 5V High-speed mode, TA = TMIN to TMAX Auto-standby/ low-power modes, TA = TMIN to TMAX SO MAX/QSOP SO MAX/QSOP SO MAX/QSOP 0.5 0.3 1 1 2 2 -100 -100 -5 20 3 -0.2V VCM VCC - 1.2V High-speed mode Low-power mode SO MAX/QSOP 66 54 82 90 dB 100 nA pF -0.2 +0.2 VCC - 1.2 2 3 5 7 4 4 -300 -400 nA mV mV V VCC High-speed mode ICC Auto-standby/low-power modes VCM = 1V, 2.7V VCC 5.25V SO MAX/QSOP 63 2.7 250 3 3 90 77 5.25 500 5 6 dB A V SYMBOL CONDITIONS MIN TYP MAX UNITS
PSRR
High-speed mode Low-power mode
Input-Referred Hysteresis
VHYS
VCM = 1V, VCC = 5V (Note 4) High-speed mode Auto-standby/low-power modes
Input Bias Current Input Offset Current Input Capacitance Common-Mode Rejection Ratio
IB IOS CIN CMRR
2
_______________________________________________________________________________________
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 = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1) PARAMETER DIGITAL INPUTS LP Input Voltage High LP Input Voltage Low LP Fall Time LP Input Current STO_ Input Voltage Low STO_ Source Current DIGITAL OUTPUTS OUT_ Output Voltage High OUT_ Output Voltage Low Propagation Delay, Low to High (Note 6) VOH VOL ISOURCE = 2mA, all modes ISINK = 2mA, all modes CLOAD = 10pF, VCC = 5V High-speed mode, overdrive = 5mV Low-power mode, overdrive = 10mV High-speed mode, overdrive = 5mV Low-power mode, overdrive = 10mV VCC - 0.4 VCC - 0.1 0.1 28 0.82 28 0.48 2 1 1.6 1.6 VCC - 0.4 0.4 High-speed mode Low-power mode 0.4 50 1.6 50 1.6 V V ns s ns s ns ns ns V V VLPIH VLPIL tLP ILPB VCIL ISTO VCC = 3V (Note 5) 0.01 VCC / 2 0.15 0.7 x VCC VCC / 2 VCC / 2 0.3 x VCC 10 1 0.3 x VCC V V s A V A SYMBOL CONDITIONS MIN TYP MAX UNITS
MAX975/MAX977
tPD+
Propagation Delay, High to Low (Note 6) Propagation-Delay Skew (Note 6) Propagation-Delay Matching Rise/Fall Time STAT_ Output Voltage High STAT_ Output Voltage Low
tPD-
CLOAD = 10pF, VCC = 5V CLOAD = 10pF
tSKEW tPD
MAX977 only, CLOAD = 10pF CLOAD = 10pF, VCC = 5.0V
VSH VSL
ISOURCE = 3mA, all modes ISINK = 400A, all modes
Note 1: The MAX975EUA is 100% production tested at TA = +25C; 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 10s are expected, bypass LP to ground using a 0.1F 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-.
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3
Single/Dual, +3V/+5V Dual-Speed Comparators with Auto-Standby MAX975/MAX977
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +2.7V to +5.25V, specifications are for high-speed mode, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1) PARAMETER Auto-Standby Timeout Auto-Standby Enable Time Auto-Standby Wake-Up Time Auto-Standby Wake-Up Input or LP Pulse Width Auto-Standby Comparator Disable Low-Power Enable Time High-Speed Enable Time Low-Power Comparator Disable Low-Power STAT_ High SYMBOL tASB tASBE tASD tPWD tASCD tLPE tHSE tLPCD tLPSH (Note 8) (Note 9) 10mV overdrive (Note 10) 10mV overdrive (Note 11) (Note 12) (Note 13) (Note 14) (Note 15) (Note 16) 1.6 0.8 3 1.1 0.7 20 4 CONDITIONS MIN 5 TYP 10 3 2 4 MAX 16 UNITS ms s s s s s s s ns AUTO-STANDBY/LOW-POWER TIMING (Note 7; Figure 2)
Note 7: Note 8: Note 9: Note 10: Note 11: Note 12: Note 13: Note 14: Note 15: Note 16:
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 5A. 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 300A. tLPE is defined as the time from when LP is driven high to when the supply current drops to 5A. 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 300A. tLPSH is defined as the time from when LP goes high to when STAT_ goes high.
4
_______________________________________________________________________________________
Single/Dual, +3V/+5V Dual-Speed Comparators with Auto-Standby
__________________________________________Typical Operating Characteristics
(VCC = 3.0V, TA = +25C, unless otherwise noted.)
MAX975/MAX977
LOW-POWER OFFSET VOLTAGE vs. TEMPERATURE
-0.60 -0.65 -0.70 -0.75 -0.80 -0.85 -0.90 -0.95 -1.00 -1.05 -1.10 -1.15 -1.20 -60 -40 -20 0 20 40 60 80 100 TEMPERATURE (C)
MAX977-01
SUPPLY CURRENT PER COMPARATOR vs. OUTPUT TRANSITION FREQUENCY
MAX977-02
HIGH-SPEED INPUT BIAS CURRENT vs. TEMPERATURE
MAX977-03
10000
-50 -70 VCC = 3V -90 -110 -130 -150
VCC = 3V
OFFSET VOLTAGE (mV)
SUPPLY CURRENT PER COMPARATOR (A)
1000
HIGH-SPEED MODE
100
INPUT BIAS CURRENT (nA)
VCC = 5V
10
LOW-POWER MODE
1 0.01k 0.1k
-170 1k 10k 100k 1M 10M 100M -60 -40 -20 0 20 40 60 80 100 TEMPERATURE (C)
TRANSITION FREQUENCY (kHz)
LOW-POWER INPUT BIAS CURRENT vs. TEMPERATURE
MAX977-04
HIGH-SPEED VOLTAGE TRIP POINTS/INPUT OFFSET VOLTAGE vs. TEMPERATURE
MAX977-05
HIGH-SPEED VOLTAGE TRIP POINTS/INPUT OFFSET VOLTAGE vs. TEMPERATURE
TRIP POINTS/OFFSET VOLTAGE (mV) 1.2 1.0 0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0 -1.2 -60 -40 -20 0 20 VCC = 3V VTRIP+
MAX977-06
7.0 6.5 INPUT BIAS CURRENT (nA) 6.0 5.5 VCC = 5V 5.0 4.5 VCC = 3V 4.0 3.5 3.0 -60 -40 -20 0 20 40 60 80
1.0 TRIP POINTS/OFFSET VOLTAGE (mV) 0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0 -60 -40 -20 0 20 40 60 80 VTRIPVOS VCC = 5V VTRIP+
VOS
VTRIP-
100
100
40
60
80
100
TEMPERATURE (C)
TEMPERATURE (C)
TEMPERATURE (C)
LOW-POWER PROPAGATION DELAY vs. CAPACITIVE LOAD
MAX977-07
LOW-POWER PROPAGATION DELAY vs. INPUT OVERDRIVE
MAX977-08
AUTO-STANDBY TIMEOUT vs. TEMPERATURE
10.1 10.0
MAX977-09
600 550 PROPAGATION DELAY (ns) 500 450 400 350 300 250 200 0 50 100 150 200 VCC = 3V tPDVCC = 5V 50mV OVERDRIVE VCC = 3V VCC = 5V tPD+
700 650 PROPAGATION DELAY (ns) 600 550 500 450 400 350 300 250 200 150 0 40 80 VCC = 5V 120 160 200 VCC = 3V tPDVCC = 3V VCC = 5V tPD+ CLOAD =15pF
10.2
TIMEOUT (ms)
9.9 9.8 9.7 9.6 9.5 9.4 9.3 VCC = 5V
VCC = 3V
250
240
-60 -40 -20
0
20
40
60
80
100
CAPACITIVE LOAD (pF)
INPUT OVERDRIVE (mV)
TEMPERATURE (C)
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5
Single/Dual, +3V/+5V Dual-Speed Comparators with Auto-Standby MAX975/MAX977
____________________________Typical Operating Characteristics (continued)
(VCC = 3.0V, TA = +25C, unless otherwise noted.)
AUTO-STANDBY TIMEOUT vs. TIMEOUT CAPACITOR
MAX977-10
OUTPUT HIGH VOLTAGE vs. OUTPUT SOURCE CURRENT
MAX977-11
OUTPUT LOW VOLTAGE vs. OUTPUT SINK CURRENT
VCC = 3V 3.0 OUTPUT VOLTAGE (V) 2.5 2.0 1.5 1.0 0.5 TA = -40C TA = +85C TA = +25C
MAX977-12
100000
3.5 VCC = 3V 3.0 OUTPUT VOLTAGE (V) 2.5 2.0 1.5 1.0 0.5 TA = +25C TA = -40C
3.5
10000 TIMEOUT (s)
1000
100
TA = +85C
10
1 1 10 100 1000 10000 CAPACITANCE (pF)
0.0 0 5 10 15 20 25 30 35 SOURCE CURRENT (mA)
0.0 0 5 10 15 20 25 30 35 40 SINK CURRENT (mA)
HIGH-SPEED PROPAGATION DELAY vs. TEMPERATURE (VCC = 5V)
MAX977-13
HIGH-SPEED PROPAGATION DELAY vs. TEMPERATURE (VCC = 3V)
MAX977-14
HIGH-SPEED SUPPLY CURRENT PER COMPARATOR vs. TEMPERATURE (VCC = 5V)
400 375 350 325 300 275 250 225 200 175 150 125 100
MAX977-15
30 CLOAD = 15pF VOD = 50mV PROPAGATION DELAY (ns) 26 tPD22 tPD+ 18
35 33 PROPAGATION DELAY (ns) 31 29 27 25 23 21 19 17 tPDtPD+ CLOAD = 15pF VOD = 50mV
SUPPLY CURRENT (A)
OUT_ = HIGH
OUT_ = LOW
14
10 -60 -40 -20 0 20 40 60 80 100 TEMPERATURE (C)
15 -60 -40 -20 0 20 40 60 80 100 TEMPERATURE (C)
-60 -40 -20
0
20
40
60
80
100
TEMPERATURE (C)
HIGH-SPEED SUPPLY CURRENT PER COMPARATOR vs. TEMPERATURE (VCC = 3V)
MAX977-16
STANDBY/LOW-POWER SUPPLY CURRENT PER COMPARATOR vs. TEMPERATURE (VCC = 5V)
MAX977-17
STANDBY/LOW POWER-SUPPLY CURRENT PER COMPARATOR vs. TEMPERATURE (VCC = 3V)
3.6 SUPPLY CURRENT (A) 3.4 3.2 3.0 2.8 2.6 2.4 2.2 2.0 OUT = HIGH -60 -40 -20 0 20 40 60 80 100 OUT = LOW
MAX977-18
300 280 SUPPLY CURRENT (A) 260 240 220 200 180 OUT_ = LOW 160 140 120 100 -60 -40 -20 0 20 40 60 80 OUT_ = HIGH
4.5 4.0 SUPPLY CURRENT (A) 3.5 3.0 2.5 2.0 1.5
3.8
OUT_ = LOW
OUT_ = HIGH
1.8 -60 -40 -20 0 20 40 60 80 100 TEMPERATURE (C) TEMPERATURE (C)
100
TEMPERATURE (C)
6
_______________________________________________________________________________________
Single/Dual, +3V/+5V Dual-Speed Comparators with Auto-Standby
____________________________Typical Operating Characteristics (continued)
(VCC = 3.0V, TA = +25C, unless otherwise noted.)
MAX975/MAX977
HIGH-SPEED PROPAGATION DELAY vs. CAPACITIVE LOAD
45.0 42.5 40.0 37.5 35.0 32.5 30.0 27.5 25.0 22.5 20.0 17.5 15.0 0 50 100
MAX977-19
HIGH-SPEED PROPAGATION DELAY vs. INPUT OVERDRIVE
MAX977-20
LOW-POWER PROPAGATION DELAY vs. TEMPERATURE (VCC = 3V)
560 PROPAGATION DELAY (ns) 520 480 440 400 360 320 280 240 200 -60 -40 -20 0 20 40 60 80 100 tPDtPD+ CLOAD = 15pF VOD = 50mV
MAX977-21
30 tPDPROPAGATION DELAY (ns) 25 20 15 10 5 CLOAD = 15pF 0 tPD+ VCC = +5V VCC = +3V
600
PROPAGATION DELAY (ns)
CLOAD = 15pF VOD = 50mV tPD-
VCC = +3V
tPD+ tPDVCC = +5V tPD+
150
200
250
0
20 40 60 80 100 120 140 160 180 200 INPUT OVERDRIVE (mV)
CAPACITIVE LOAD (pF)
TEMPERATURE (C)
LOW-POWER PROPAGATION DELAY vs. TEMPERATURE (VCC = 5V)
750 700 650 600 550 500 450 400 350 300 250 200 150 -60 -40 -20 0 20 40 60 80 100 CLOAD = 15pF VOD = 50mV
MAX977-22
PROPAGATION DELAY tPD+ HIGH-SPEED MODE (VCC = +3V)
PROPAGATION DELAY (ns)
VOS VCC
INPUT 5mV/div
tPD+ VCC/2 tPDOUTPUT 1V/div
GND
MAX975/977 TOC23
5ns/div
tPD+
TEMPERATURE (C)
PROPAGATION DELAY tPDHIGH-SPEED MODE (VCC = +3V)
PROPAGATION DELAY tPDHIGH-SPEED MODE (VCC = +5V)
VOS VCC VCC/2
INPUT 5mV/div
VOS
INPUT 5mV/div
OUTPUT 1V/div
VCC VCC/2 GND OUTPUT 2V/div
GND
MAX975/977 TOC24
MAX975/977 TOC25
5ns/div
tPD-
5ns/div
tPD-
_______________________________________________________________________________________
7
Single/Dual, +3V/+5V Dual-Speed Comparators with Auto-Standby MAX975/MAX977
____________________________Typical Operating Characteristics (continued)
(VCC = 3.0V, TA = +25C, unless otherwise noted.)
PROPAGATION DELAY tPD+ HIGH-SPEED MODE (VCC = +5V)
INPUT 5mV/div
PROPAGATION DELAY tPDLOW-POWER MODE (VCC = +3V)
INPUT 5mV/div
VOS
VOS VCC
VCC VCC/2 GND
MAX975/977 TOC26
VCC/2 OUTPUT 2V/div OUTPUT 1V/div
GND
MAX975/977 TOC27
5ns/div
tPD+
100ns/div
tPD-
PROPAGATION DELAY tPD+ LOW-POWER MODE (VCC = +3V)
VOS VCC VCC/2 GND
INPUT 5mV/div
OUTPUT 1V/div
MAX975/977 TOC28
100ns/div
tPD+
PROPAGATION DELAY tPD+ LOW-POWER MODE (VCC = +5V)
PROPAGATION DELAY tPDLOW-POWER MODE (VCC = +3V)
VOS
INPUT 5mV/div
VOS
INPUT 5mV/div
VCC VCC/2 GND OUTPUT 2V/div
VCC VCC/2 GND OUTPUT 2V/div
MAX975/977 TOC29
MAX975/977 TOC30
100ns/div
tPD+
100ns/div
tPD-
8
_______________________________________________________________________________________
Single/Dual, +3V/+5V Dual-Speed Comparators with Auto-Standby
____________________________Typical Operating Characteristics (continued)
(VCC = 3.0V, TA = +25C, unless otherwise noted.) 100kHz RESPONSE LOW-POWER MODE (VCC = +3V)
100kHz RESPONSE LOW-POWER MODE (VCC = +5V)
MAX975/MAX977
VOS VCC
INPUT 5mV/div
VOS
INPUT 5mV/div
VCC
OUTPUT 1V/div GND
GND
OUTPUT 2V/div
MAX975/977 TOC32
MAX975/977 TOC31
2s/div
2s/div
10MHz RESPONSE HIGH-SPEED MODE (VCC = +5V)
VOS
INPUT 5mV/div
VCC OUTPUT 2V/div GND
MAX975/977 TOC34
20ns/div
10MHz RESPONSE HIGH-SPEED MODE (VCC = +3V)
+100mV VOS VCC OUTPUT 1V/div GND OUT 0V ICC 250A 0A
MAX975/977 TOC33
MAX975 AUTO-STANDBY OPERATION
INPUT 5mV/div
Inp -100mV 3V
MAX975/977 TOC35
20ns/div
1ms/div CSTO_ = 100pF
_______________________________________________________________________________________
9
Single/Dual, +3V/+5V Dual-Speed Comparators with Auto-Standby MAX975/MAX977
_____________________________________________________________Pin Descriptions
MAX975
PIN 1 2 3 4 NAME VCC IN+ INSTAT Positive Supply Voltage, +2.7V to +5.25V Noninverting Comparator Input Inverting Comparator Input 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. 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 s, where C is in pF. Ground Comparator Output 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. FUNCTION
5 6 7 8
STO GND OUT LP
MAX977
SO QSOP NAME STOA, STOB GNDA, GNDB OUTA, OUTB VCC INB+, INA+ INB-, INAFUNCTION 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 s, where C is in pF. Ground for Comparator A/B Output for Comparator A/B 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.
1, 8
1, 9
2, 9 3, 10 4 5, 12 6, 13
2, 10 3, 11 4, 5 6, 14 7, 15
7, 14
8, 16
STATB, STATA
--
12
N.C.
11
13
LP
10
______________________________________________________________________________________
Single/Dual, +3V/+5V Dual-Speed Comparators with Auto-Standby MAX975/MAX977
Table 1. Programming
INPUTS LP L L (falling edge) H STO_ tASB = CSTO x 10s/pF tASB = CSTO x 10s/pF L X IDLE TIME High speed (Auto-standby enabled) Auto-standby High speed (Auto-standby mode disabled) Low power
L H L 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 250A. In low-power mode, propagation delay is typically 480ns and power consumption is only 3A. 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.
VHYST VTRIP+ VIN+ VTRIPVOS = VTRIP+ + VTRIP2 VIN- = 0
COMPARATOR OUTPUT
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
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
______________________________________________________________________________________
Single/Dual, +3V/+5V Dual-Speed Comparators with Auto-Standby MAX975/MAX977
tASB tPWD
DIFFERENTIAL INPUT VOLTAGE OUT_
VOS
VOH VOL
VCC A tPD+ tPDtASD tLPSH
STAT_
VCC 0V 300A 3A tASBE tLPCD tASCD
ICC (TYP)
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 Cs, where C is in pF. For example, connecting a 0.1F 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 10s are expected, bypass LP with a 0.1F 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.
Low-Power Mode
Driving LP high switches the MAX975/MAX977 to lowpower mode. In this mode, the supply current drops to a maximum of 5A, 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 10s are expected, bypass LP with a 0.1F 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.
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______________________________________________________________________________________
Single/Dual, +3V/+5V Dual-Speed Comparators with Auto-Standby
__________Applications Information
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 STO_
MAX975/MAX977
Figure 3. Driving STO_ with CMOS Logic
VCC
R3
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 1F, 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. 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_ s, 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.
VCC RD GND R1 VCC R2 STAT
OUT LOSS OF SIGNAL
MAX975
Figure 4. IR Receiver
1) Use a printed circuit board with an unbroken, lowinductance ground plane. 2) Place a decoupling capacitor (a 0.1F 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.
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:
______________________________________________________________________________________
13
Single/Dual, +3V/+5V Dual-Speed Comparators with Auto-Standby MAX975/MAX977
VCC R3 VIN 82.1k, 1% 15 2 R2 1 24.9k, 1% VCC 14 4 0.1F UNDERVOLTAGE 3 1 VCC CSTOA POWER GOOD VCC 6 50 5 STAT WAKE-UP IRQ I/0 LP I/0 STO 0.1F 3V
1/2 MAX977
MAX975
P
MAX6120
2
1/2 MAX977
3 R1 100k, 1% 7 10 9
11
OVERVOLTAGE X-BAND DETECTOR
CSTO GND
CSTOB
3V
4.7k (PIN NUMBERS SHOWN ARE FOR QSOP PACKAGE)
1M 0.1F
Figure 5. Window Comparator
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 10A for the thresholds to be accurate. R1 values in the 50k to 100k 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.
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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 250A highspeed current. After communications have ceased, or when instructed by the microcontroller, the comparator returns to its low-power state. The comparator draws only 3A 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
__________________________________________________________Pin Configurations
TOP VIEW
STOA 1 STOA 1 VCC 1 IN+ 2 IN- 3 STAT 4 8 LP OUT GND STO GNDA 2 OUTA 3 VCC 4 INB+ 5 INB- 6 STATB 7 14 STATA 13 INA12 INA+ GNDA 2 OUTA 3 VCC 4 VCC 5 INB+ 6 INB- 7 STATB 8 16 STATA 15 INA14 INA+
MAX975/MAX977
MAX975
7 6 5
MAX977
13 LP 12 N.C. 11 OUTB 10 GNDB 9 STOB
MAX977
11 LP 10 OUTB 9 8 GNDB STOB
SO/MAX
SO
QSOP
___________________Chip Information
TRANSISTOR COUNT: 522 (MAX975) 1044 (MAX977)
______________________________________________________________________________________
15
Single/Dual, +3V/+5V Dual-Speed Comparators with Auto-Standby MAX975/MAX977
________________________________________________________Package Information
8LUMAXD.EPS
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
16 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 1998 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
QSOP.EPS

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