Rainbow Electronics MAX977 User Manual

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 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.

________________________Applications

Battery-Powered Systems
RF ID Tags
Keyless Entry
Threshold Detectors/Discriminators
3V Systems
IR Receivers
Digital-Line Receivers

____________________________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)

MAX975/MAX977

Single/Dual, +3V/+5V Dual-Speed

Comparators with Auto-Standby

________________________________________________________________

Maxim Integrated Products

1

Functional Diagram

19-1141; Rev 1; 11/98

PART

MAX975ESA

MAX975EUA
MAX977ESD

-40°C to +85°C

-40°C to +85°C

-40°C to +85°C

TEMP. RANGE PIN-PACKAGE

8 SO
8 µMAX
14 SO

Ordering Information

Pin Configurations appear at end of data sheet.

MAX977EEE -40°C to +85°C

16 QSOP

MAX975

V

CC

IN+

LP

OUT

GND

STO

HIGH SPEED

LOW POWER

ENABLE

IN-

STAT

TIMING

CIRCUIT

ENABLE

TRANSITION

MONITOR

For free samples & the latest literature: http://www.maxim-ic.com, or phone [phone].
For small orders, phone [phone].

MAX975/MAX977

Single/Dual, +3V/+5V Dual-Speed
Comparators with Auto-Standby

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

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
T

A

= +25°C.) (Note 1)

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.

Supply Voltage (V

CC

)

............................................................+6V

All Other Pins..............................................-0.3V to (V

CC

+ 0.3V)

Duration of Output Short Circuit to GND_ or V

CC

......Continuous

Continuous Power Dissipation (T

A

= +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

250 500

µA

36

I

CC

Supply Current
Per Comparator

35

dB

77

PSRR

Power-Supply
Rejection Ratio

63 90

V2.7 5.25V

CC

Supply-Voltage
Operating Range

UNITSMIN TYP MAXSYMBOLPARAMETER

High-speed mode

µMAX/QSOP

SO

CONDITIONS

Low-power mode

High-speed mode

Auto-standby/low-power modes

VCM= 1V,

2.7V ≤ VCC≤ 5.25V

Common-Mode
Voltage Range

V

CMR

(Note 2) -0.2 VCC- 1.2 V

High-speed mode, TA= +25°C +0.2 ±2

±3High-speed mode, TA= T

MIN

to T

MAX

±1 ±5

Input Offset Voltage
(Note 3)

VCM= 1V,
VCC= 5V

Auto-standby/
low-power modes,
TA= T

MIN

to T

MAX

mV

SO 0.5 2 4

Input-Referred Hysteresis V

HYS

VCM= 1V, VCC= 5V (Note 4)

µMAX/QSOP 0.3 2 4

mV

I

B

SO -100 -300

High-speed mode

µMAX/QSOP -100 -400Input Bias Current

Auto-standby/low-power modes -5

nA

Input Offset Current I

OS

±20 ±100 nA

Input Capacitance C

IN

3 pF

SO 66 90

High-speed mode

µMAX/QSOP 54

Common-Mode
Rejection Ratio

CMRR

-0.2V ≤ V

CM

≤ VCC- 1.2V

Low-power mode 82

dB

SO

V

OS

POWER SUPPLY

COMPARATOR INPUTS

±1 ±7

µMAX/QSOP

MAX975/MAX977

Single/Dual, +3V/+5V Dual-Speed

Comparators with Auto-Standby

_______________________________________________________________________________________ 3

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
T

A

= +25°C.) (Note 1)

C

LOAD

= 10pF,

VCC= 5V

I

SINK

= 2mA, all modes

High-speed mode,
overdrive = 5mV

Low-power mode,
overdrive = 10mV

I

SOURCE

= 2mA, all modes

CONDITIONS

µs0.82 1.6

ns28 50

t

PD+

Propagation Delay, Low to High
(Note 6)

V0.1 0.4V

OL

OUT_ Output Voltage Low

V0.7xVCCVCC/2V

LPIH

LP Input Voltage High

VVCC- 0.4 VCC- 0.1V

OH

OUT_ Output Voltage High

UNITSMIN TYP MAXSYMBOLPARAMETER

VVCC/ 2 0.3xV

CC

V

LPIL

LP Input Voltage Low

µA

(Note 5)

0.01 ±1I

LPB

LP Input Current

µs10t

LP

LP Fall Time

V

CC

= 3V µA0.15I

STO

STO_ Source Current

VVCC/ 2 0.3 x V

CC

V

CIL

STO_ Input Voltage Low

C

LOAD

= 10pF,

VCC= 5V

High-speed mode,
overdrive = 5mV

Low-power mode,
overdrive = 10mV

µs0.48 1.6

ns28 50

t

PD-

Propagation Delay, High to Low
(Note 6)

C

LOAD

= 10pF ns2t

SKEW

Propagation-Delay Skew (Note 6)

MAX977 only, C

LOAD

= 10pF ns1

∆t

PD

Propagation-Delay Matching

C

LOAD

= 10pF,

VCC= 5.0V

High-speed mode
Low-power mode 1.6

ns

1.6

Rise/Fall Time

I

SOURCE

= 3mA, all modes VV

CC

- 0.4V

SH

STAT_ Output Voltage High

I

SINK

= 400µA, all modes V0.4V

SL

STAT_ Output Voltage Low

DIGITAL INPUTS

DIGITAL OUTPUTS

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: V

OS

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, V

OS

is added to the overdrive. The following

equation defines propagation-delay skew: t

SKEW

= t

PD+

- t

PD-.

MAX975/MAX977

Single/Dual, +3V/+5V Dual-Speed
Comparators with Auto-Standby

4 _______________________________________________________________________________________

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
T

A

= +25°C.) (Note 1)

CONDITIONS

(Note 9)
10mV overdrive (Note 10)

µs

(Note 8)

3

t

ASB

Auto-Standby Timeout

t

ASBE

UNITSMIN TYP MAXSYMBOLPARAMETER

Auto-Standby Enable Time

µs24t

ASD

Auto-Standby Wake-Up Time

10mV overdrive (Note 11)

(Note 12)

µs1.6t

PWD

Auto-Standby Wake-Up Input
or LP Pulse Width

µs0.8t

ASCD

Auto-Standby Comparator
Disable

(Note 13) µs3t

LPE

Low-Power Enable Time

(Note 14) µs1.1 4t

HSE

High-Speed Enable Time

(Note 15) µs0.7t

LPCD

Low-Power Comparator Disable

(Note 16) ns20t

LPSH

Low-Power STAT_ High

AUTO-STANDBY/LOW-POWER TIMING (Note 7; Figure 2)

Note 7: Timing specifications are guaranteed by design.
Note 8: Set by 1000pF external capacitor at the STO_ pin. t

ASB

is defined as the time from last input transition to STAT_ = high.

Does not include time to go into standby condition (t

ASBE)

.

Note 9: t

ASBE

is defined as the time from when STAT_ goes high to when the supply current drops to 5µA.

Note 10: t

ASD

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.

Note 11: t

PWD

is defined as the minimum input or LP pulse width to trigger fast-mode operation from auto-standby.

Note 12: t

ASCD

is defined as the time from the last input transition to when the supply current increases to 300µA.

Note 13: t

LPE

is defined as the time from when LP is driven high to when the supply current drops to 5µA.

Note 14: t

HSE

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.

Note 15: t

LPCD

is defined as the time from when LP goes low to when the supply current increases to 300µA.

Note 16: t

LPSH

is defined as the time from when LP goes high to when STAT_ goes high.

ms51016

MAX975/MAX977

Single/Dual, +3V/+5V Dual-Speed

Comparators with Auto-Standby

_______________________________________________________________________________________

5

-1.20

-1.15

-1.10

-1.05

-1.00

-0.95

-0.90

-0.85

-0.80

-0.75

-0.70

-0.65

-0.60

-60 -40 -20 0 20 40 60 80 100

LOW-POWER OFFSET VOLTAGE

vs. TEMPERATURE

MAX977-01

TEMPERATURE (°C)

OFFSET VOLTAGE (mV)

VCC = 3V

1

0.01k 10k1k0.1k 100k 1M 10M 100M

SUPPLY CURRENT PER COMPARATOR

vs. OUTPUT TRANSITION FREQUENCY

10

MAX977-02

TRANSITION FREQUENCY (kHz)

SUPPLY CURRENT

PER COMPARATOR (µA)

100

1000

10000

HIGH-SPEED MODE

LOW-POWER MODE

-170

-150

-130

-110

-90

-70

-50

-60 -40 -20 0 20 40 60 80 100

HIGH-SPEED INPUT BIAS CURRENT

vs. TEMPERATURE

MAX977-03

TEMPERATURE (°C)

INPUT BIAS CURRENT (nA)

VCC = 3V

VCC = 5V

7.0

6.5

6.0

5.5

5.0

4.5

4.0

3.0

3.5

-60 -40 -20 0 20 40 60 80 100

LOW-POWER INPUT BIAS CURRENT

vs. TEMPERATURE

MAX977-04

TEMPERATURE (°C)

INPUT BIAS CURRENT (nA)

VCC = 3V

VCC = 5V

200

250

300

350

400

450

500

550

600

0 50 100 150 200 250

LOW-POWER PROPAGATION DELAY

vs. CAPACITIVE LOAD

MAX977-07

CAPACITIVE LOAD (pF)

PROPAGATION DELAY (ns)

VCC = 3V

VCC = 3V

VCC = 5V

VCC = 5V

t

PD-

50mV OVERDRIVE

tPD+

-1.0

-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 80 100

HIGH-SPEED VOLTAGE TRIP POINTS/INPUT

OFFSET VOLTAGE vs. TEMPERATURE

MAX977-05

TEMPERATURE (°C)

TRIP POINTS/OFFSET VOLTAGE (mV)

VCC = 5V

V

TRIP+

V

TRIP-

V

OS

-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 40 60 80 100

HIGH-SPEED VOLTAGE TRIP POINTS/INPUT

OFFSET VOLTAGE vs. TEMPERATURE

MAX977-06

TEMPERATURE (°C)

TRIP POINTS/OFFSET VOLTAGE (mV)

V

TRIP-

V

OS

V

TRIP+

VCC = 3V

200
150

250

300

350

400

450

500

550

600

650

700

0 40 80 120 160 240200

LOW-POWER PROPAGATION DELAY

vs. INPUT OVERDRIVE

MAX977-08

INPUT OVERDRIVE (mV)

PROPAGATION DELAY (ns)

VCC = 3V

VCC = 3V

VCC = 5V

VCC = 5V

C

LOAD

=15pF

t

PD-

t

PD+

10.2

10.1

10.0

9.9

9.8

9.7

9.6

9.5

9.4

9.3

-60 -40 -20 0 20 40 60 80 100

AUTO-STANDBY TIMEOUT

vs. TEMPERATURE

MAX977-09

TEMPERATURE (°C)

TIMEOUT (ms)

VCC = 3V

VCC = 5V

__________________________________________Typical Operating Characteristics

(VCC= 3.0V, TA = +25°C, unless otherwise noted.)

MAX975/MAX977

Single/Dual, +3V/+5V Dual-Speed
Comparators with Auto-Standby

6 _______________________________________________________________________________________

____________________________Typical Operating Characteristics (continued)

(V

CC

= 3.0V, TA= +25°C, unless otherwise noted.)

100000

1

1 10 100 1000 10000

AUTO-STANDBY TIMEOUT
vs. TIMEOUT CAPACITOR

10

MAX977-10

CAPACITANCE (pF)

TIMEOUT (µs)

100

1000

10000

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0 5 10 15 20 25 30 35

OUTPUT HIGH VOLTAGE

vs. OUTPUT SOURCE CURRENT

MAX977-11

SOURCE CURRENT (mA)

OUTPUT VOLTAGE (V)

V

CC

= 3V

TA = +85°C

TA = -40°C

TA = +25°C

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0 5 10 15 20 25 30 35 40

OUTPUT LOW VOLTAGE

vs. OUTPUT SINK CURRENT

MAX977-12

SINK CURRENT (mA)

OUTPUT VOLTAGE (V)

V

CC

= 3V

TA = +85°C

TA = +25°C

TA = -40°C

10

14

18

22

26

30

-60 -40 -20 0 20 40 60 80 100

HIGH-SPEED PROPAGATION DELAY

vs. TEMPERATURE (V

CC

= 5V)

MAX977-13

TEMPERATURE (°C)

PROPAGATION DELAY (ns)

C

LOAD

= 15pF

V

OD

= 50mV

t

PD+

t

PD-

100

120

140

160

180

200

220

240

260

280

300

-60 -40 -20 0 20 40 60 80 100

HIGH-SPEED SUPPLY CURRENT

PER COMPARATOR

vs. TEMPERATURE (V

CC

= 3V)

MAX977-16

TEMPERATURE (°C)

SUPPLY CURRENT (µA)

OUT_ = HIGH

OUT_ = LOW

15

17

19

21

23

25

27

29

31

33

35

-60 -40 -20 0 20 40 60 80 100

HIGH-SPEED PROPAGATION DELAY

vs. TEMPERATURE (V

CC

= 3V)

MAX977-14

TEMPERATURE (°C)

PROPAGATION DELAY (ns)

C

LOAD

= 15pF

t

PD+

t

PD-

VOD = 50mV

100

125

150

175

200

225

250

275

300

325

350

375

400

-60 -40 -20 0 20 40 60 80 100

HIGH-SPEED SUPPLY CURRENT

PER COMPARATOR

vs. TEMPERATURE (V

CC

= 5V)

MAX977-15

TEMPERATURE (°C)

SUPPLY CURRENT (µA)

OUT_ = HIGH

OUT_ = LOW

1.5

2.0

2.5

3.0

3.5

4.0

4.5

-60 -40 -20 0 20 40 60 80 100

STANDBY/LOW-POWER SUPPLY

CURRENT PER COMPARATOR

vs. TEMPERATURE (V

CC

= 5V)

MAX977-17

TEMPERATURE (°C)

SUPPLY CURRENT (µA)

OUT_ = HIGH

OUT_ = LOW

1.8

2.0

2.2

2.4

2.6

2.8

3.0

3.2

3.4

3.6

3.8

-60 -40 -20 0 20 40 60 80 100

STANDBY/LOW POWER-SUPPLY

CURRENT PER COMPARATOR

vs. TEMPERATURE (V

CC

= 3V)

MAX977-18

TEMPERATURE (°C)

SUPPLY CURRENT (µA)

OUT = HIGH

OUT = LOW

MAX975/MAX977

Single/Dual, +3V/+5V Dual-Speed

Comparators with Auto-Standby

_______________________________________________________________________________________

7

15.0

17.5

20.0

22.5

25.0

27.5

30.0

32.5

35.0

37.5

40.0

42.5

45.0

0 50 100 150 200 250

HIGH-SPEED PROPAGATION DELAY

vs. CAPACITIVE LOAD

MAX977-19

CAPACITIVE LOAD (pF)

PROPAGATION DELAY (ns)

VCC = +3V

VCC = +5V

t

PD+

t

PD-

t

PD+

t

PD-

C

LOAD

= 15pF

V

OD

= 50mV

0

5

10

15

20

25

30

0 20 40 60 80 100 120 140 160 180 200

HIGH-SPEED PROPAGATION DELAY

vs. INPUT OVERDRIVE

MAX977-20

INPUT OVERDRIVE (mV)

PROPAGATION DELAY (ns)

t

PD-

C

LOAD

= 15pF

VCC = +3V

t

PD+

VCC = +5V

200

240

280

320

360

400

440

480

520

560

600

-60 -40 -20 0 20 40 60 80 100

LOW-POWER PROPAGATION DELAY

vs. TEMPERATURE (V

CC

= 3V)

MAX977-21

TEMPERATURE (°C)

PROPAGATION DELAY (ns)

C

LOAD

= 15pF

V

OD

= 50mV

t

PD+

t

PD-

150

200

250

300

350

400

450

500

550

600

650

700

750

-60 -40 -20 0 20 40 60 80 100

LOW-POWER PROPAGATION DELAY

vs. TEMPERATURE (V

CC

= 5V)

MAX977-22

TEMPERATURE (°C)

PROPAGATION DELAY (ns)

C

LOAD

= 15pF

V

OD

= 50mV

t

PD+

t

PD-

PROPAGATION DELAY tPD+

HIGH-SPEED MODE (V

CC

= +3V)

t

PD+

INPUT
5mV/div

5ns/div

OUTPUT
1V/div

V

OS

V

CC

VCC/2

GND

MAX975/977 TOC23

PROPAGATION DELAY t

PD-

HIGH-SPEED MODE (VCC = +3V)

t

PD-

INPUT
5mV/div

5ns/div

OUTPUT
1V/div

V

OS

V

CC

VCC/2

GND

MAX975/977 TOC24

PROPAGATION DELAY t

PD-

HIGH-SPEED MODE (VCC = +5V)

t

PD-

INPUT
5mV/div

5ns/div

OUTPUT
2V/div

V

OS

V

CC

VCC/2

GND

MAX975/977 TOC25

____________________________Typical Operating Characteristics (continued)

(V

CC

= 3.0V, TA= +25°C, unless otherwise noted.)

MAX975/MAX977

Single/Dual, +3V/+5V Dual-Speed
Comparators with Auto-Standby

8 _______________________________________________________________________________________

____________________________Typical Operating Characteristics (continued)

(VCC= 3.0V, TA= +25°C, unless otherwise noted.)

PROPAGATION DELAY t

PD-

LOW-POWER MODE (VCC = +3V)

t

PD-

INPUT
5mV/div

100ns/div

OUTPUT
1V/div

V

OS

V

CC

VCC/2

GND

MAX975/977 TOC27

PROPAGATION DELAY t

PD+

LOW-POWER MODE (VCC = +3V)

t

PD+

INPUT
5mV/div

100ns/div

OUTPUT
1V/div

V

OS

V

CC

VCC/2

GND

MAX975/977 TOC28

PROPAGATION DELAY t

PD+

LOW-POWER MODE (VCC = +5V)

t

PD+

INPUT
5mV/div

100ns/div

OUTPUT
2V/div

V

OS

V

CC

VCC/2

GND

MAX975/977 TOC29

PROPAGATION DELAY t

PD-

LOW-POWER MODE (VCC = +3V)

t

PD-

INPUT
5mV/div

100ns/div

OUTPUT
2V/div

V

OS

V

CC

VCC/2

GND

MAX975/977 TOC30

PROPAGATION DELAY t

PD+

HIGH-SPEED MODE (VCC = +5V)

t

PD+

INPUT
5mV/div

5ns/div

OUTPUT
2V/div

V

OS

V

CC

VCC/2

GND

MAX975/977 TOC26

MAX975/MAX977

Single/Dual, +3V/+5V Dual-Speed

Comparators with Auto-Standby

_______________________________________________________________________________________

9

____________________________Typical Operating Characteristics (continued)

(VCC= 3.0V, TA= +25°C, unless otherwise noted.)

10MHz RESPONSE

HIGH-SPEED MODE (V

CC

= +3V)

INPUT
5mV/div

20ns/div

OUTPUT
1V/div

V

OS

V

CC

GND

MAX975/977 TOC33

100kHz RESPONSE

LOW-POWER MODE (V

CC

= +3V)

INPUT
5mV/div

2µs/div

OUTPUT
1V/div

V

OS

V

CC

GND

MAX975/977 TOC31

10MHz RESPONSE

HIGH-SPEED MODE (V

CC

= +5V)

INPUT
5mV/div

20ns/div

OUTPUT
2V/div

V

OS

V

CC

GND

MAX975/977 TOC34

MAX975

AUTO-STANDBY OPERATION

1ms/div

C

STO_

= 100pF

I

np

I

CC

OUT

0µA

250µA

3V
0V

+100mV

-100mV

MAX975/977 TOC35

100kHz RESPONSE

LOW-POWER MODE (V

CC

= +5V)

INPUT
5mV/div

2µs/div

OUTPUT
2V/div

V

OS

V

CC

GND

MAX975/977 TOC32

MAX975/MAX977

Single/Dual, +3V/+5V Dual-Speed
Comparators with Auto-Standby

10 ______________________________________________________________________________________

_____________________________________________________________Pin Descriptions

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.

STO5

GroundGND6
Comparator OutputOUT7

LP8

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.

STAT4

Inverting Comparator InputIN-3

PIN

Noninverting Comparator InputIN+2

Positive Supply Voltage, +2.7V to +5.25VV

CC

1

FUNCTIONNAME

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 VCCif high-speed mode will not be used.

FUNCTION

QSOP

1, 9

2, 10
3, 11

4, 5

8, 16

7, 15

6, 14

13

12

NAME

1, 8

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: t

ASB

= 10 x C µs, where C is in pF.

2, 9

GNDA, GNDB

Ground for Comparator A/B

3, 10

OUTA, OUTB

Output for Comparator A/B

4 V

CC

Positive Supply Voltage, +2.7V to +5.25V. For QSOP, connect pin 4 to pin 5.

7, 14

STATB,

STATA

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.

6, 13 INB-, INA- Inverting Input for Comparator B/A

5, 12 INB+, INA+ Noninverting Input for Comparator B/A

11 LP

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 VCCif
high-speed mode will not be used.

— N.C. No connection. Not internally connected.

SO

MAX975

MAX977

_______________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

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

MAX975/MAX977

Single/Dual, +3V/+5V Dual-Speed

Comparators with Auto-Standby

______________________________________________________________________________________ 11

INPUTS

LP STO_ IDLE TIME

MODE

STAT

OUTPUT

L t

ASB

= C

STO

x 10µs/pF <t

ASB

High speed
(Auto-standby enabled)

L

L t

ASB

= C

STO

x 10µs/pF ≥t

ASB

Auto-standby H

↓

(falling edge)

L X

High speed
(Auto-standby mode disabled)

L

H X X Low power H

Table 1. Programming

V

OL

V

OH

V

IN-

= 0

V

OS

=

V

TRIP+

+ V

TRIP-

2

COMPARATOR

OUTPUT

V

TRIP+

V

IN+

V

HYST

V

TRIP-

Figure 1. Input and Output Waveforms, Noninverting Input
Varied

MAX975/MAX977

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, C

STO

, 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.

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 VCCand 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

12 ______________________________________________________________________________________

t

PWD

t

ASB

t

ASD

t

PD-

t

PD+

t

LPSH

t

ASBE

t

LPCD

t

LPE

t

HSE

V

CC

V

OL

V

OH

V

OS

DIFFERENTIAL

INPUT

VOLTAGE

OUT_

STAT_

I

CC (TYP)

LP

0V

300µA

3µA

t

ASCD

V

CC

A

Figure 2. Timing Diagram

__________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.

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.

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 t

ASB

= 10 x C

STO

_ µs, where C

STO

_
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’shigh gain bandwidth requires
design precautions to realize the comparator’s full high­speed capability. The following precautions are recom­mended:

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 V

CC

as pos-

sible.

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 RD. 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.

MAX975/MAX977

Single/Dual, +3V/+5V Dual-Speed

Comparators with Auto-Standby

______________________________________________________________________________________ 13

STO_

CMOS
LOGIC

Figure 3. Driving STO_with CMOS Logic

GND

STAT

V

CC

V

CC

V

CC

R

D

R1 R2

R3

OUT

LOSS OF SIGNAL

MAX975

V

CC

Figure 4. IR Receiver

MAX975/MAX977

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 (V

OTH

) when V

IN

is rising, and calculate R2 and R3 with the following
formula:

R2 + R3 = R1 x [V

OTH

/ (V

REF

+ VH) - 1]

where VH= 1/2V

HYST

.

3) Choose the undervoltage threshold (V

UTH

) when V

IN

is

falling, and calculate R2 with the following formula:

R2 = (R1 + R2 + R3) x [(V

REF

- VH) / V

UTH

] - R1

where VH= 1/2V

HYST

.

4) Calculate R3 with the following formula:
R3 = (R2 + R3) - R2

5) Verify the resistor values. The equations are as

follows:

V

OTH

= (V

REF

+ VH) x (R1 + R2 + R3) / R1

V

UTH

= (V

REF

- 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

14 ______________________________________________________________________________________

6

1

3

7

10

R3

V

CC

V

CC

V

IN

5

R2

R1

82.1k, 1%

24.9k, 1%

100k, 1%

2

11

9

OVERVOLTAGE

(PIN NUMBERS SHOWN ARE FOR QSOP PACKAGE)

UNDERVOLTAGE

POWER GOOD

C

STOB

1/2

MAX977

MAX6120

14

15

2

V

CC

4

3

1

C

STOA

0.1µF

1/2

MAX977

Figure 5. Window Comparator

I/0

I/0

WAKE-UP IRQ

3V

3V

0.1µF

µP

0.1µF

1M4.7k

GND

STAT
LP

STO

C

STO

V

CC

50Ω

X-BAND
DETECTOR

MAX975

Figure 6. Toll-Tag Reader

MAX975/MAX977

Single/Dual, +3V/+5V Dual-Speed

Comparators with Auto-Standby

______________________________________________________________________________________ 15

TRANSISTOR COUNT: 522 (MAX975)

1044 (MAX977)

___________________Chip Information

1
2
3
4

8
7
6
5

LP
OUT
GND
STOSTAT

IN-

IN+

V

CC

MAX975

SO/µMAX

TOP VIEW

14
13
12
11
10
9
8

1
2
3
4
5
6
7

STATA
INA­INA+
LPV

CC

OUTA

GNDA

STOA

MAX977

OUTB
GNDB
STOBSTATB

INB-

INB+

SO QSOP

16
15
14
13
12
11
10

9

1
2
3
4
5
6
7
8

STATA
INA­INA+
LP
N.C.
OUTB
GNDB
STOB

STOA

GNDA

OUTA

V

CC

V

CC

INB+
INB-

STATB

MAX977

__________________________________________________________Pin Configurations

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.

________________________________________________________Package Information

8LUMAXD.EPS

QSOP.EPS