MAXIM MAX977EEE

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.