MAXIM MAX921, MAX924 Technical data

_______________General Description

The MAX921–MAX924 single, dual, and quad micro­power, low-voltage comparators feature the lowest
power consumption available. These comparators draw
less than 4µA supply current over temperature
(MAX921/MAX922), and include an internal 1.182V
±1% voltage reference, programmable hysteresis, and
TTL/CMOS outputs that sink and source current.

Ideal for 3V or 5V single-supply applications, the
MAX921–MAX924 operate from a single +2.5V to +11V
supply (or a ±1.25V to ±5V dual supply), and each
comparator’s input voltage range swings from the
negative supply rail to within 1.3V of the positive
supply.

The MAX921–MAX924’s unique output stage con­tinuously sources as much as 40mA. And by eliminating
power-supply glitches that commonly occur when com­parators change logic states, the MAX921–MAX924
minimize parasitic feedback, which makes them easier to
use.

The single MAX921 and dual MAX923 provide a unique
and simple method for adding hysteresis without
feedback and complicated equations, simply by using
the HYST pin and two resistors.

________________________Applications

Battery-Powered Systems
Threshold Detectors
Window Comparators
Oscillator Circuits

____________________________Features

♦ µMAX®Package—Smallest 8-Pin SO

(MAX921/MAX922/MAX923)

♦ Ultra-Low 4µA Max Quiescent Current

Over Extended Temp. Range (MAX921)

♦ Power Supplies:

Single +2.5V to +11V
Dual ±1.25V to ±5.5V

♦ Input Voltage Range Includes Negative Supply

♦ Internal 1.182V ±1% Bandgap Reference

♦ Adjustable Hysteresis

♦ TTL/CMOS-Compatible Outputs

♦ 12µs Propagation Delay (10mV Overdrive)

♦ No Switching Crowbar Current

♦ 40mA Continuous Source Current

Ordering Information continued at end of data sheet.

*Dice are tested at T

A

= +25°C, DC parameters only.

**Contact factory for availability.

MAX921–MAX924

Ultra Low-Power,

Single/Dual-Supply Comparators

________________________________________________________________ Maxim Integrated Products 1

MAX921

OUT

IN+

HYST

REF

V-

GND

V+

21

4

5

6

8

3

7

IN-

THRESHOLD DETECTOR

V

IN

__________Typical Operating Circuit

19-0115; Rev 6; 4/09

PART TEMP RANGE PIN-PACKAGE

MAX921CPA

0°C to +70°C 8 Plastic DIP

MAX921CSA 0°C to +70°C 8 SO

MAX921C/D 0°C to +70°C Dice*

PART

INTERNAL 1%

PRECISION

REFERENCE

COMPARATORS

PER

PACKAGE

INTERNAL

HYSTERESIS

PACKAGE

MAX921 Yes 1 Yes

8-Pin
DIP/SO/µMAX

MAX922 No 2 No

8-Pin
DIP/SO/µMAX

MAX923 Yes 2 Yes

8-Pin
DIP/SO/µMAX

MAX924 Yes 4 No

16-Pin
DIP/SO/µMAX

MAX921EPA -40°C to +85°C 8 Plastic DIP
MAX921ESA -40°C to +85°C 8 SO
MAX921MJA -55°C to +125°C 8 CERDIP

MAX921CUA 0°C to +70°C 8 µMAX

For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim's website at www.maxim-ic.com.

Ordering Information

µMAX is a registered trademark of Maxim Integrated Products, Inc.

MAX921–MAX924

Ultra Low-Power,
Single/Dual-Supply Comparators

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

V+ to V-, V+ to GND, GND to V-................................-0.3V, +12V

Inputs

Current, IN_+, IN_-, HYST...............................................20mA

Voltage, IN_+, IN_-, HYST................(V+ + 0.3V) to (V- – 0.3V)

Outputs

Current, REF....................................................................20mA

Current, OUT_ .................................................................50mA

Voltage, REF ....................................(V+ + 0.3V) to (V- – 0.3V)

Voltage, OUT_ (MAX921/924) .....(V+ + 0.3V) to (GND – 0.3V)

Voltage OUT_ (MAX922/923)...........(V+ + 0.3V) to (V- – 0.3V)

OUT_ Short-Circuit Duration (V+ ≤ 5.5V) ...............Continuous

Continuous Power Dissipation (TA= +70°C)

8-Pin Plastic DIP (derate 9.09mW/°C above +70°C) ...727mW

8-Pin SO (derate 5.88mW/°C above +70°C)................471mW

8-Pin µMAX (derate 4.1mW/°C above +70°C) .............330mW

8-Pin CERDIP (derate 8.00mW/°C above +70°C)........640mW

16-Pin Plastic DIP (derate 10.53mW/°C above +70°C)..842mW

16-Pin SO (derate 8.70mW/°C above +70°C) ................696mW

16-Pin CERDIP (derate 10.00mW/°C above +70°C) ......800mW

Operating Temperature Ranges:

MAX92_C_ _ .......................................................0°C to +70°C

MAX92_E_ _.....................................................-40°C to +85°C

MAX92_MJ_ ..................................................-55°C to +125°C

Storage Temperature Range .............................-65°C to +150°C

Lead Temperature (soldering, 10s) .................................+300°C

ELECTRICAL CHARACTERISTICS: 5V OPERATION

(V+ = 5V, V- = GND = 0V, TA= T

MIN

to T

MAX

, unless otherwise noted.)

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.

PARAMETER

MAX923,
HYST = REF

MIN TYP MAX UNITS

MAX924

7.5

VV- V+ – 1.3

5.5 6.5

MAX921,
HYST = REF

8.5

Supply Current IN+ = IN- + 100mV

IN+ = IN- = 2.5V

11

µA

Supply Voltage Range

TA= +25°C, 100pF load

2.5 11 V

2.5 3.2

MAX922

4

5

2.5 3.2

Input Offset Voltage

CONDITIONS

M temp. range

±10 mV

TA= +25°C

C/E temp. ranges

M temp. range

±0.01 ±5

nAInput Leakage Current (IN-, IN+)

(Note 1)

±40

Input Leakage Current (HYST)

TA= +25°C

C/E temp. ranges

M temp. range

±0.02 nA

Input Common-Mode Voltage Range

TA= +25°C

VCM= 2.5V

C/E temp. ranges

Common-Mode Rejection Ratio

M temp. range

MAX921, MAX923

0.1 1.0 mV/V

Power-Supply Rejection Ratio

V- to (V+ – 1.3V)

V+ = 2.5V to 11V

100Hz to 100kHz

0.1 1.0 mV/V

Voltage Noise

MAX921, MAX923

Overdrive = 10mV
Overdrive = 100mV

20 µV

RMS

Hysteresis Input Voltage Range REF- 0.05V REF V

C/E temp. ranges

M temp. range

TA= +25°C

12

µsResponse Time

C/E temp. ranges

4

4

5

3.1 4.5

6

POWER REQUIREMENTS

COMPARATOR

MAX921–MAX924

Ultra Low-Power,

Single/Dual-Supply Comparators

_______________________________________________________________________________________ 3

PARAMETER

Voltage Noise

C/E temp. ranges: I

OUT

= 17mA;

M temp. range: I

OUT

= 10mA

MIN TYP MAX UNITS

100Hz to 100kHz 100 µV

RMS

MAX922/
MAX923

C/E temp. ranges: I

OUT

= 1.8mA;

M temp. range: I

OUT

= 1.2mA

C/E temp. ranges: I

OUT

= 1.8mA;

M temp. range: I

OUT

= 1.2mA

CONDITIONS

C temp. range

VOutput High Voltage

E temp. range

MAX92_

M temp. range

V+ – 0.4

TA= +25°C

V- + 0.4

V

15 25

µAC/E temp. ranges 6Source Current

M temp. range 4

TA= +25°C

GND + 0.4

Output Low Voltage

815

MAX921/
MAX924

µA

X

C/E temp. ranges 4

Sink Current

1.170 1.182 1.194

V

M temp. range

1.158 1.206Reference Voltage

2

1.147 1.217

ELECTRICAL CHARACTERISTICS: 5V OPERATION (continued)

(V+ = 5V, V- = GND = 0V, TA= T

MIN

to T

MAX

, unless otherwise noted.)

ELECTRICAL CHARACTERISTICS: 3V OPERATION

(V+ = 3V, V- = GND = 0V, TA= T

MIN

to T

MAX

, unless otherwise noted.)

PARAMETER

MAX923

MIN TYP MAX UNITS

MAX924

7.2

5.2 6.2

MAX921

8.0

Supply Current

HYST = REF,
IN+ = (IN- + 100mV)

IN+ = IN- = 1.5V

10.5

µA

2.4 3.0

MAX922

3.8

4.8

2.4 3.0

Input Offset Voltage

CONDITIONS

M temp. range

±10 mV

TA= +25°C

C/E temp. ranges

M temp. range

±0.01 ±5

nAInput Leakage Current (IN-, IN+)

±40

Input Leakage Current (HYST)

TA= +25°C

C/E temp. ranges

M temp. range

±0.02 nA

TA= +25°C

VCM= 1.5V

C/E temp. ranges

M temp. range

MAX921, MAX923

C/E temp. ranges

M temp. range

TA= +25°C

C/E temp. ranges

3.8

4.8

3.4 4.3

5.8

REFERENCE (MAX921/MAX923/MAX924 ONLY)

POWER REQUIREMENTS

COMPARATOR

Note 1: MAX924 comparators work below 2.5V, see Low-Voltage Operation section for more details.

MAX921–MAX924

Ultra Low-Power,
Single/Dual-Supply Comparators

4 _______________________________________________________________________________________

Typical Operating Characteristics

(V+ = 5V, V- = GND, TA = +25°C, unless otherwise noted).

0.0
020

OUTPUT VOLTAGE LOW

vs. LOAD CURRENT

0.5

2.5

MAX921/4-TOC1

LOAD CURRENT (mA)

V

OL

(V)

12

1.5

1.0

48 16

2.0

V+ = 5V

V+ = 3V

1.5
010 30 50

OUTPUT VOLTAGE HIGH vs.

LOAD CURRENT

2.5

4.5

MAX921/924-TOC2

LOAD CURRENT (mA)

V

OH

(V)

20 40

3.5

5.0

2.0

4.0

3.0

V+ = 5V

V+ = 3V

1.155
0 5 15 25

REFERENCE OUTPUT VOLTAGE vs.

OUTPUT LOAD CURRENT

1.165

1.185

MAX921/924-TOC3

OUTPUT LOAD CURRENT (μA)

REFERENCE OUTPUT VOLTAGE (V)

10 20

1.175

1.190

1.160

1.180

1.170

V+ = 5V

OR

V+ = 3V

30

SINK

SOURCE

ELECTRICAL CHARACTERISTICS: 3V OPERATION (continued)

(V+ = 3V, V- = GND = 0V, TA= T

MIN

to T

MAX

, unless otherwise noted.)

PARAMETER

Voltage Noise

C/E temp. ranges: I

OUT

= 10mA;

M temp. range: I

OUT

= 6mA

MIN TYP MAX UNITS

100Hz to 100kHz 100 µV

RMS

Input Common-Mode Voltage Range VV- V+ – 1.3

MAX922/
MAX923

TA= +25°C, 100pF load

C/E temp. ranges: I

OUT

= 0.8mA;

M temp. range: I

OUT

= 0.6mA

C/E temp. ranges: I

OUT

= 0.8mA;

M temp. range: I

OUT

= 0.6mA

CONDITIONS

Common-Mode Rejection Ratio 0.2 1 mV/V

Power-Supply Rejection Ratio

V- to (V+ – 1.3V)

V+ = 2.5V to 11V

100Hz to 100kHz

0.1 1 mV/V

Voltage Noise

MAX921, MAX923

Overdrive = 10mV

Overdrive = 100mV

20 µV

RMS

Hysteresis Input Voltage Range REF- 0.05V REF V

14

µsResponse Time

5

C temp. range

VOutput High Voltage

E temp. range

MAX92_

M temp. range

V+ – 0.4

TA= +25°C

V- + 0.4

V

15 25

µA

C/E temp. ranges 6

Source Current

M temp. range 4

TA= +25°C

GND + 0.4

Output Low Voltage

815

MAX921/
MAX924

µA

C/E temp. ranges 4

Sink Current

1.170 1.182 1.194

V

M temp. range

1.158 1.206Reference Voltage

2

1.147 1.217

REFERENCE

MAX921-MAX924

Ultra Low-Power,

Single/Dual-Supply Comparators

_______________________________________________________________________________________ 5

1.22

1.14

-60 -20 60 140

REFERENCE VOLTAGE

vs. TEMPERATURE

1.16

1.20

MAX921/924-TOC4

TEMPERATURE (°C)

REFERENCE VOLTAGE (V)

20 100

1.18

1.21

1.15

1.19

1.17

-40 0 8040 120

MILITARY TEMP. RANGE

EXTENDED TEMP. RANGE

COMMERCIAL
TEMP. RANGE

2.0

-60 140

MAX921

SUPPLY CURRENT vs.

TEMPERATURE

2.5

4.5

MAX921/924-TOC5

TEMPERATURE (°C)

SUPPLY CURRENT (μA)

60

3.5

3.0

-20 20 100

4.0

V+ = 5V, V- = - 5V

V+ = 3V, V- = 0V

V+ = 5V, V- = 0V

IN+ = (IN- + 100mV)

4.5

1.5

-60 140

MAX922

SUPPLY CURRENT vs. TEMPERATURE

2.0

4.0

MAX921/924-TOC6

TEMPERATURE (°C)

SUPPLY CURRENT (μA)

60

3.0

2.5

-20 20 100

3.5

IN+ = (IN- + 100mV)

V+ = 5V, V- = 0V

V+ = 3V, V- = 0V

V+ = 10V, V- = 0V

4.5

5.0

-60 140

MAX923

SUPPLY CURRENT vs. TEMPERATURE

2.0

4.0

MAX921/924-TOC7

TEMPERATURE (°C)

SUPPLY CURRENT (μA)

60

3.0

2.5

-20 20 100

3.5

V+ = 5V, V- = 0V

V+ = 3V, V- = 0V

80

-80
010 30 50

HYSTERESIS CONTROL

-40

40

MAX921/924 TOC10

V

REF

-V

HYST

(mV)

IN+ – IN- (mV)

20 40

0

60

-60

20

-20

NO CHANGE

OUTPUT LOW

OUTPUT HIGH

10

3

-60 140

MAX924

SUPPLY CURRENT vs. TEMPERATURE

4

8

MAX921/924-TOC8

TEMPERATURE (°C)

SUPPLY CURRENT (μA)

60

6

5

-20 20 100

7

9

IN+ = (IN- + 100mV)

V+ = 5V, V- = 0V

V+ = 3V, V- = 0V

V+ = 5V, V- = -5V

10

0.01

1.0 2.0 2.5

MAX924

SUPPLY CURRENT vs.

LOW SUPPLY VOLTAGES

0.1

1

MAX921/924-TOC9

SINGLE-SUPPLY VOLTAGE (V)

SUPPLY CURRENT (μA)

1.5

5.0

0

-0.3 -0.1 0.3

TRANSFER FUNCTION

1.0

4.0

MAX921/924-TOC11

IN+ INPUT VOLTAGE (mV)

OUTPUT VOLTAGE (V)

0.1

3.0

2.0

4.5

0.5

3.5

2.5

1.5

-0.2 0

0.2

100k

V

0

10μF

18

2

0 20 60 100

RESPONSE TIME vs.
LOAD CAPACITANCE

6

14

MAX921/924 TOC12

LOAD CAPACITANCE (nF)

RESPONSE TIME (μs)

40 80

10

16

4

12

8

V

OLH

V- = 0V

V

OHL

Typical Operating Characteristics (continued)

(V+ = 5V, V- = GND, TA = +25°C, unless otherwise noted).

MAX921–MAX924

Ultra Low-Power,
Single/Dual-Supply Comparators

6 _______________________________________________________________________________________

Typical Operating Characteristics (continued)

(V+ = 5V, V- = GND, TA = +25°C, unless otherwise noted).

-2 2 10 18

RESPONSE TIME FOR VARIOUS

INPUT OVERDRIVES

0

4

MAX921/924-TOC13

RESPONSE TIME (μs)

OUTPUT VOLTAGE (V)

614

2

0

5

100

3

1

50mV

100mV

20mV

10mV

INPUT VOLTAGE (mV)

-2 2 10 18

RESPONSE TIME FOR VARIOUS

INPUT OVERDRIVES

0

4

MAX921/924-TOC14

RESPONSE TIME (μs)

OUTPUT VOLTAGE (V)

614

2

0

5

100

3

1

50mV

100mV

20mV

10mV

INPUT VOLTAGE (mV)

10

0.01

1.0 2.0 2.5

MAX924 RESPONSE TIME

AT LOW SUPPLY VOLTAGES

0.1

1

MAX921/924-TOC15

SINGLE-SUPPLY VOLTAGE (V)

RESPONSE TIME (ms)

1.5

±20mV OVERDRIVE

±100mV

OVERDRIVE

100

0.1

1.0 2.0 2.5

MAX924 RESPONSE TIME

AT LOW SUPPLY VOLTAGES

1

10

MAX921/924-TOC16

SINGLE-SUPPLY VOLTAGE (V)

CURRENT (mA)

1.5

SINK CURRENT AT V

OUT

= 0.4V

SOURCE CURRENT INTO 0.75V LOAD

200

0

0 1.0 3.0 5.0

SHORT-CIRCUIT SOURCE CURRENT

vs. SUPPLY VOLTAGE

40

160

MAX121/124-TOC17

TOTAL SUPPLY VOLTAGE (V)

SOURCE CURRENT (mA)

2.0 4.0

120

80

20

60

180

140

100

OUT CONNECTED TO V-

20

0

010

SHORT-CIRCUIT SINK CURRENT

vs. SUPPLY VOLTAGE

MAX121/124-TOC18

TOTAL SUPPLY VOLTAGE (V)

SINK CURRENT (mA)

5

10

OUT CONNECTED TO V+
GND CONNECTED TO V-

PIN

MAX921 MAX922 MAX923

NAME FUNCTION

1 – – GND Ground. Connect to V- for single-supply operation. Output swings from V+ to GND.

– 1 OUTA Comparator A output. Sinks and sources current. Swings from V+ to V-.

2 2 2 V- Negative supply. Connect to ground for single-supply operation (MAX921).

1

3 – – IN+ Noninverting comparator input

– 3 3 INA+ Noninverting input of comparator A

4 – – IN- Inverting comparator input

____________________________________________________________Pin Descriptions

– 4 – INA- Inverting input of comparator A

MAX921–MAX924

Ultra Low-Power,

Single/Dual-Supply Comparators

_______________________________________________________________________________________ 7

PIN

–

– 6 –

MAX921 MAX922 MAX923

NAME FUNCTION

– 5 4 INB- Inverting input of comparator B

INB+

5 5 HYST

Hysteresis input. Connect to REF if not used. Input voltage range is from
V

REF

to V

REF

- 50mV.

6 – 6 REF Reference output. 1.182V with respect to V-.

Noninverting input of comparator B

7 7 7 V+ Positive supply

8 – – OUT Comparator output. Sinks and sources current. Swings from V+ to GND.

– 8 8 OUTB Comparator B output. Sinks and sources current. Swings from V+ to V-.

_______________________________________________Pin Descriptions (continued)

PIN

MAX924

NAME FUNCTION

1 OUTB Comparator B output. Sinks and sources current. Swings from V+ to GND.

2 OUTA Comparator A output. Sinks and sources current. Swings from V+ to GND.

3 V+ Positive supply

4 INA- Inverting input of comparator A

5 INA+ Noninverting input of comparator A

6 INB- Inverting input of comparator B

7 INB+ Noninverting input of comparator B

8 REF Reference output. 1.182V with respect to V-.

9 V- Negative supply. Connect to ground for single-supply operation.

10 INC- Inverting input of comparator C

11 INC+ Noninverting input of comparator C

12 IND- Inverting input of comparator D

13 IND+ Noninverting input of comparator D

14 GND Ground. Connect to V- for single-supply operation.

15 OUTD Comparator D output. Sinks and sources current. Swings from V+ to GND.

16 OUTC Comparator C output. Sinks and sources current. Swings from V+ to GND.

MAX921–MAX924

Ultra Low-Power,
Single/Dual-Supply Comparators

8 _______________________________________________________________________________________

_______________Detailed Description

The MAX921–MAX924 comprise various combinations
of a micropower 1.182V reference and a micropower
comparator. The Typical Operating Circuit shows the
MAX921 configuration, and Figures 1a-1c show the
MAX922–MAX924 configurations.

Each comparator continuously sources up to 40mA,
and the unique output stage eliminates crowbar
glitches during output transitions. This makes them
immune to parasitic feedback (which can cause
instability) and provides excellent performance, even
when circuit-board layout is not optimal.

Internal hysteresis in the MAX921 and MAX923 provides
the easiest method for implementing hysteresis. It also
produces faster hysteresis action and consumes much
less current than circuits using external positive feedback.

Power-Supply and Input Signal Ranges

This family of devices operates from a single +2.5V to
+11V power supply. The MAX921 and MAX924 have a

separate ground for the output driver, allowing
operation with dual supplies ranging from ±1.25V to
±5.5V. Connect V- to GND when operating the
MAX921 and the MAX924 from a single supply. The
maximum supply voltage in this case is still 11V.

For proper comparator operation, the input signal can
swing from the negative supply (V-) to within one volt of
the positive supply (V+ – 1V). The guaranteed
common-mode input voltage range extends from V- to
(V+ - 1.3V). The inputs can be taken above and below
the supply rails by up to 300mV without damage.

Operating the MAX921 and MAX924 at ±5V provides
TTL/CMOS compatibility when monitoring bipolar input
signals. TTL compatibility for the MAX922 and MAX923
is achieved by operation from a single +5V supply.

Low-Voltage Operation: V+ = 1V (MAX924 Only)

The guaranteed minimum operating voltage is 2.5V (or
±1.25V). As the total supply voltage is reduced below

2.5V, the performance degrades and the supply
current falls. The reference will not function below

OUTA

V-

INA+

INA-

OUTB

V+

INB+

INB-

MAX922

1

2

3

4

8

7

6

5

Figure 1a. MAX922 Functional Diagram

OUTA

V-

INA+

INB-

OUTB

V+

REF

HYST

MAX923

1

2

3

4

8

7

6

5

V-

Figure 1b. MAX923 Functional Diagram

OUTA

V+

INA-

INA+

OUTD

GND

IND+

IND-

MAX924

2

3

4

5

15

14

13

12

16

11

10

9

1

6

7

8

OUTB

INB-

INB+

REF

OUTC

INC+

INC-

V-

Figure 1c. MAX924 Functional Diagram

about 2.2V, although the comparators will continue to
operate with a total supply voltage as low as 1V. While
the MAX924 has comparators that may be used at
supply voltages below 2V, the MAX921, MAX922, and
MAX923 may not be used with supply voltages sig­nificantly below 2.5V.

At low supply voltages, the comparators’ output drive is
reduced and the propagation delay increases (see
Typical Operating Characteristics). The useful input
voltage range extends from the negative supply to a
little under 1V below the positive supply, which is
slightly closer to the positive rail than the device
operating from higher supply voltages. Test your
prototype over the full temperature and supply-voltage
range if operation below 2.5V is anticipated.

Comparator Output

With 100mV of overdrive, propagation delay is typically
3µs. The Typical Operating Characteristics show the
propagation delay for various overdrive levels.

The MAX921 and MAX924 output swings from V+ to
GND, so TTL compatibility is assured by using a +5V
±10% supply. The negative supply does not affect the
output swing, and can range from 0V to -5V ±10%.

The MAX922 and MAX923 have no GND pin, and their
outputs swing from V+ to V-. Connect V- to ground and
V+ to a +5V supply to achieve TTL compatibility.

The MAX921–MAX924’s unique design achieves an
output source current of more than 40mA and a sink
current of over 5mA, while keeping quiescent currents in
the microampere range. The output can source 100mA
(at V+ = 5V) for short pulses, as long as the package's
maximum power dissipation is not exceeded. The
output stage does not generate crowbar switching
currents during transitions, which minimizes feedback
through the supplies and helps ensure stability without
bypassing.

Voltage Reference

The internal bandgap voltage reference has an output
of 1.182V above V-. Note that the REF voltage is
referenced to V-, not to GND. Its accuracy is ±1% in
the range 0°C to +70°C. The REF output is typically
capable of sourcing 15µA and sinking 8µA. Do not
bypass the REF output.

Noise Considerations

Although the comparators have a very high gain, useful
gain is limited by noise. This is shown in the Transfer
Function graph (see Typical Operating Characteristics).
As the input voltage approaches the comparator's
offset, the output begins to bounce back and forth; this
peaks when VIN= VOS. (The lowpass filter shown on
the graph averages out the bouncing, making the
transfer function easy to observe.) Consequently, the
comparator has an effective wideband peak-to-peak
noise of around 0.3mV. The voltage reference has
peak-to peak noise approaching 1mV. Thus, when a

MAX921–MAX924

Ultra Low-Power,

Single/Dual-Supply Comparators

_______________________________________________________________________________________ 9

THRESHOLDS

OUT

IN-

IN+

V

HB

HYSTERESIS

BAND

VREF - VHYST

Figure 2. Threshold Hysteresis Band

7

2

5

6

HYST

REF

V-

V+

R1

R2

MAX921
MAX923

2.5V TO 11V

I

REF

Figure 3. Programming the HYST Pin

MAX921–MAX924

comparator is used with the reference, the combined
peak-to-peak noise is about 1mV. This, of course, is
much higher than the RMS noise of the individual
components. Care should be taken in the layout to
avoid capacitive coupling from any output to the
reference pin. Crosstalk can significantly increase the
actual noise of the reference.

__________Applications Information

Hysteresis

Hysteresis increases the comparators’ noise margin by
increasing the upper threshold and decreasing the
lower threshold (see Figure 2).

Hysteresis (MAX921/MAX923)

To add hysteresis to the MAX921 or MAX923, connect
resistor R1 between REF and HYST, and connect
resistor R2 between HYST and V- (Figure 3). If no
hysteresis is required, connect HYST to REF. When
hysteresis is added, the upper threshold increases by
the same amount that the lower threshold decreases.
The hysteresis band (the difference between the upper
and lower thresholds, VHB) is approximately equal to
twice the voltage between REF and HYST. The HYST
input can be adjusted to a maximum voltage of REF
and to a minimum voltage of (REF – 50mV). The
maximum difference between REF and HYST (50mV)
will therefore produce a 100mV max hysteresis band.
Use the following equations to determine R1 and R2:

Where I

REF

(the current sourced by the reference)
should not exceed the REF source capability, and
should be significantly larger than the HYST input
current. I

REF

values between 0.1µA and 4µA are

usually appropriate. If 2.4MΩ is chosen for R2 (I

REF

=

0.5µA), the equation for R1 and VHBcan be
approximated as:

When hysteresis is obtained in this manner for the
MAX923, the same hysteresis applies to both comparators.

Hysteresis (MAX922/MAX924)

Hysteresis can be set with two resistors using positive
feedback, as shown in Figure 4. This circuit generally
draws more current than the circuits using the HYST
pin on the MAX921 and MAX923, and the high

feedback impedance slows hysteresis. The design
procedure is as follows:

1. Choose R3. The leakage current of IN+ is under
1nA (up to +85°C), so the current through R3 can be
around 100nA and still maintain good accuracy.
The current through R3 at the trip point is V

REF

/R3,

or 100nA for R3 = 11.8MΩ. 10MΩ is a good
practical value.

2. Choose the hysteresis voltage (VHB), the voltage
between the upper and lower thresholds. In this
example, choose VHB= 50mV.

3. Calculate R1.

4. Choose the threshold voltage for VINrising (V

THR

).

In this example, choose V

THR

= 3V.

5. Calculate R2.

A 1% preferred value is 64.9kΩ.

R2 =

V

(V

1R11

R3

3

(1.182 100k)1100k110M

65.44k

THR

REF R1)

1

1

×

⎛

⎝

⎜

⎞

⎠

⎟

−−

⎡

⎣

⎢
⎢

⎤

⎦

⎥
⎥

=

×

⎛
⎝

⎜

⎞
⎠

⎟

−−

⎡

⎣

⎢
⎢

⎤

⎦

⎥
⎥

=

Ω

R1 = R3

V

V

10M

0.05
5

HB

×

+

=×

R1 (k ) = V (mV)

HB

Ω

R1 =

V

2 I

R2 =

1.182 –

V

2

I

HB

REF

HB

REF

×

()

⎛
⎝

⎜

⎞
⎠

⎟

Ultra Low-Power,
Single/Dual-Supply Comparators

10 ______________________________________________________________________________________

GND

V-

V+

MAX924

OUT

R3

R1

R2

V

REF

V

IN

V+

Figure 4. External Hysteresis

6. Verify the threshold voltages with these formulas:

Board Layout and Bypassing

Power-supply bypass capacitors are not needed if the
supply impedance is low, but 100nF bypass capacitors
should be used when the supply impedance is high or
when the supply leads are long. Minimize signal lead
lengths to reduce stray capacitance between the input
and output that might cause instability. Do not bypass
the reference output.

_______________Typical Applications

Auto-Off Power Source

Figure 5 shows the schematic for a 40mA power supply
that has a timed auto power-off function. The
comparator output is the switched power-supply
output. With a 10mA load, it typically provides a
voltage of (V

BATT

– 0.12V), but draws only 3.5µA
quiescent current. This circuit takes advantage of the
four key features of the MAX921: 2.5µA supply current,
an internal reference, hysteresis, and high current
output. Using the component values shown, the three­resistor voltage divider programs the maximum ±50mV
of hysteresis and sets the IN- voltage at 100mV. This
gives an IN+ trip threshold of approximately 50mV for
IN+ falling.

The RC time constant determines the maximum power­on time of the OUT pin before power-down occurs.
This period can be approximated by:

R x C x 4.6sec

For example: 2MΩ x 10µF x 4.6 = 92sec. The actual
time will vary with both the leakage current of the
capacitor and the voltage applied to the circuit.

Window Detector

The MAX923 is ideal for making window detectors
(undervoltage/overvoltage detectors). The schematic
is shown in Figure 6, with component values selected
for an 4.5V undervoltage threshold, and a 5.5V
overvoltage threshold. Choose different thresholds by
changing the values of R1, R2, and R3. To prevent
chatter at the output when the supply voltage is close
to a threshold, hysteresis has been added using R4
and R5. OUTA provides an active-low undervoltage
indication, and OUTB gives an active-low overvoltage
indication. ANDing the two outputs provides an active­high, power-good signal.

The design procedure is as follows:

1. Choose the required hysteresis level and calculate

values for R4 and R5 according to the formulas in
the Hysteresis (MAX921/MAX923) section. In this
example, ±5mV of hysteresis has been added at the
comparator input (V

H

= VHB/2). This means that the
hysteresis apparent at VINwill be larger because of
the input resistor divider.

V rising :

V V R1

1

R1

1

R2

1

R3

V falling :

V V

R1 V

R3

IN

THR REF

IN

THF THR

=××++

⎛
⎝

⎜

⎞
⎠

⎟

=−

×+

()

MAX921–MAX924

Ultra Low-Power,

Single/Dual-Supply Comparators

______________________________________________________________________________________ 11

MAX921

OUT

IN-

HYST

REF

V-

GND

IN+

V+

VBATT -0.15V

10mA

21

4

5

6

8

3

100k

1.1M

47k

4.5V TO 6.0V

MOMENTARY

SWITCH

7

R

C

Figure 5. Auto-off power switch operates on 2.5µA quiescent
current.

MAX921–MAX924

Ultra Low-Power,
Single/Dual-Supply Comparators

12 ______________________________________________________________________________________

2. Select R1. The leakage current into INB- is normally
under 1nA, so the current through R1 should
exceed 100nA for the thresholds to be accurate. R1
values up to about 10MΩ can be used, but values in
the 100kΩ to 1MΩ range are usually easier to deal
with. In this example, choose R1 = 294kΩ.

3. Calculate R2 + R3. The overvoltage threshold
should be 5.5V when VINis rising. The design
equation is as follows:

4. Calculate R2. The undervoltage threshold should
be 4.5V when VINis falling. The design equation is
as follows:

5. Calculate R3.

Choose R3 = 1MΩ (1% standard value)

6. Verify the resistor values. The equations are as
follows, evaluated for the above example.

Bar-Graph Level Gauge

The high output source capability of the MAX921 series
is useful for driving LEDs. An example of this is the
simple four-stage level detector shown in Figure 7.
The full-scale threshold (all LEDs on) is given by VIN=
(R1 + R2)/R1 volts. The other thresholds are at 3/4 full
scale, 1/2 full scale, and 1/4 full scale. The output
resistors limit the current into the LEDs.

Level Shifter

Figure 8 shows a circuit to shift from bipolar ±5V inputs
to TTL signals. The 10kΩ resistors protect the
comparator inputs, and do not materially affect the
operation of the circuit.

Overvoltage threshold :

V (V V )

(R1 R2 R3)

R1

5.474V.

Undervoltage threshold :

V (V V )

(R1 R2 R3)

(R1 + R2)

4.484V,

where the hysteresis voltage V V

R5
R4

OTH REF H

UTH REF H

H REF

=+×

++

=

=−×

++

=

=×

.

R3 (R2 + R3) R2

.068M 6 k

1.006M

=−
=−
=

119 .

Ω

R2 (R1 + R2 + R3)

(V V )

V

R1

(294k + 1.068M)

(1.182 0.005)

4.5

294k

62.2k

Choose R2 61.9k (1% standard value).

REF H

UTH

=×−−

=×−−

=

=

Ω

Ω

R2 R3 R1

V

V V

1

294k

5.5

(1.182 0.005)

1

1.068M

OTH

REF H

+=×

+

−

⎛
⎝

⎜

⎞
⎠

⎟

=×

+

−

⎛
⎝

⎜

⎞
⎠

⎟

=Ω

MAX923

INB-

REF

HYST

INA+

V-

V+

OUTA

OUTB

10k
R5

2.4M

R1

R2

R3

UNDERVOLTAGE

POWER GOOD

OVERVOLTAGE

V

IN

V

OTH

= 5.5V

V

UTH

= 4.5V

R4

+5V

Figure 6. Window Detector

MAX921–MAX924

Ultra Low-Power,

Single/Dual-Supply Comparators

______________________________________________________________________________________ 13

INB+

INB-

INC+

INC-

IND+

IND-

INA+

INA-

OUTA

OUTB

OUTC

OUTD

5

4

7

6

11

10

13

12

750mV

1V

500mV

250mV

250k

250k

250k

250k

182k

9

2

1

16

15

REF

8

V-

V+

GND
14

MAX924

3

+5V

V

IN

R1

R2

1.182V

330Ω

330Ω

330Ω

330Ω

Figure 7. Bar-Graph Level Gauge Figure 8. Level Shifter: ±5V Input to CMOS Output

+5V

V+

GND

MAX924

OUTA

OUTB

OUTC

OUTD

REFV-N.C.

0 FOR V
1 FOR V

< 0V

INA

> 0V

INB

10k

V

INA

10k

V

INB

10k

V

INC

10k

V

IND

INA+

INA-

INB+

INB-

INC+

INC-

IND+

IND-

-5V

MAX921–MAX924

Ultra Low-Power,
Single/Dual-Supply Comparators

14 ______________________________________________________________________________________

1

2

3

4

8

7

6

5

OUT

V+

REF

HYST

IN-

IN+

V-

GND

MAX921

DIP/SO/μMAX

TOP VIEW

1

2

3

4

8

7

6

5

OUTB

V+

INB+

INB-

INA-

INA+

V-

OUTA

MAX922

DIP/SO/μMAX

1

2

3

4

8

7

6

5

OUTB

V+

REF

HYST

INB-

INA+

V-

OUTA

MAX923

DIP/SO/μMAX

16

15

14

13

12

11

10

9

1

2

3

4

5

6

7

8

OUTC

OUTD

GND

IND+

INA-

V+

OUTA

OUTB

MAX924

IND-

INC+

INC-

V-

REF

INB+

INB-

INA+

DIP/Narrow SO

_________________Pin Configurations _Ordering Information (continued)

*Dice are tested at TA= +25°C, DC parameters only.
**Contact factory for availability.

PART

TEMP RANGE

PIN-PACKAGE

MAX921MSA/PR

8 SO**

MAX921MSA/PR-T

8 SO**

MAX922CPA 0°C to +70°C 8 Plastic DIP

MAX922CSA 0°C to +70°C 8 SO

MAX922CUA 0°C to +70°C 8 µMAX

MAX922C/D 0°C to +70°C Dice*

MAX922EPA

8 Plastic DIP

MAX922ESA

8 SO

MAX922MJA

8 CERDIP**

MAX922MSA/PR

8 SO**

MAX922MSA/PR-T

8 SO**

MAX923CPA 0°C to +70°C 8 Plastic DIP

MAX923CSA 0°C to +70°C 8 SO

MAX923CUA 0°C to +70°C 8 µMAX

MAX923C/D 0°C to +70°C Dice*

MAX923EPA

8 Plastic DIP

MAX923ESA

8 SO

MAX923MJA

8 CERDIP**

MAX923MSA/PR

8 SO**

MAX923MSA/PR-T

8 SO**

MAX924CPE 0°C to +70°C 16 Plastic DIP

MAX924CSE 0°C to +70°C 16 Narrow SO

MAX924C/D 0°C to +70°C Dice*

MAX924EPE

16 Plastic DIP

MAX924ESE

16 Narrow SO

MAX924MJE

16 CERDIP**

MAX924MSE/PR

16 Narrow SO**

MAX924MSE/PR-T

16 Narrow SO**

-55°C to +125°C

-55°C to +125°C

-40°C to +85°C

-40°C to +85°C

-55°C to +125°C

-55°C to +125°C

-55°C to +125°C

-40°C to +85°C

-40°C to +85°C

-55°C to +125°C

-55°C to +125°C

-55°C to +125°C

-40°C to +85°C

-40°C to +85°C

-55°C to +125°C

-55°C to +125°C

-55°C to +125°C

MAX921–MAX924

Ultra Low-Power,

Single/Dual-Supply Comparators

______________________________________________________________________________________ 15

__________________________________________________________Chip Topographies

9

8

6

7

1

2

3

4

0.075"

(1.91mm)

0.059"

(1.50mm)

5

10

GND

IND+

INC+

IND-

V+

INA+

INA-

INB-

OUTA

OUTB OUTC

OUTD

INC-REFINB+

V-

0.108"

(2.74mm)

0.069"

(1.75mm)

TRANSISTOR COUNT: 164
SUBSTRATE CONNECTED TO V+

TRANSISTOR COUNT: 267
SUBSTRATE CONNECTED TO V+

DIE PAD MAX921 MAX922 MAX923

1 GND OUTA OUTA

2 V-V-V-

3 V-V-V-

4 IN+ INA+ INA+

5 IN- INA- INB-

6 HYST INB- HYST

7 REF INB+ REF

8 V+V+V+

9 V+V+V+

10 OUT OUTB OUTB

MAX921/MAX922/MAX923 MAX924

MAX921–MAX924

Ultra Low-Power,
Single/Dual-Supply Comparators

16 ______________________________________________________________________________________

Package Information

For the latest package outline information and land patterns, go to www.maxim-ic.com/packages.

PACKAGE TYPE PACKAGE CODE DOCUMENT NO.

8 Plastic DIP P8-1 21-0043

16 Plastic DIP P16-1 21-0043

8 SO S8-2 21-0041

16 SO S16-3 21-0041

8 µMAX U8-1 21-0036

8 CERDIP J8-1 21-0045

16 CERDIP J16-3 21-0045

MAX921/MAX924

Ultra Low-Power,

Single/Dual-Supply Comparators

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.

Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 17

© 2009 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.

Revision History

REVISION

NUMBER

REVISION

DATE

DESCRIPTION

PAGES

CHANGED

4 8/08 Updated TOCs 5 and 10 5

5 8/08 Adding information for rugged plastic product 1, 14

6 4/09 Updated Ordering Information 1, 14, 16