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MAX921–MAX924
Ultra Low-Power,
Single/Dual-Supply Comparators
General Description
The MAX921–MAX924 single, dual, and quad micro-power,
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 powersupply glitches that commonly occur when comparators
change logic states, the MAX921–MAX924 minimize
parasitic feedback, which makes them easier to use.
●● 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
PART
TEMP RANGE
0°C to +70°C
8 SO
MAX921CUA
0°C to +70°C
8 μMAX
MAX921C/D
0°C to +70°C
Dice*
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
Yes
1
Yes
8-Pin
DIP/SO/μMAX
MAX922
No
2
No
8-Pin
DIP/SO/μMAX
Yes
8-Pin
DIP/SO/μMAX
3 IN+
No
16-Pin
DIP/SO/μMAX
4 IN-
MAX924
Yes
Yes
2
4
PACKAGE
INTERNAL
HYSTERESIS
MAX921CSA
COMPARATORS
PER
PACKAGE
8 Plastic DIP
INTERNAL 1%
PRECISION
REFERENCE
0°C to +70°C
MAX921
MAX923
Applications
●●
●●
●●
●●
Battery-Powered Systems
Threshold Detectors
Window Comparators
Oscillator Circuits
μMAX is a registered trademark of Maxim Integrated Products, Inc.
19-0115; Rev 7; 1/20
PIN-PACKAGE
MAX921CPA
PART
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.
Features
Ordering Information continued at end of data sheet.
*Dice are tested at TA = +25°C, DC parameters only.
**Contact factory for availability.
Typical Operating Circuit
VIN
7
V+
OUT 8
5 HYST
MAX921
6 REF
V-
2
GND
1
THRESHOLD DETECTOR
MAX921–MAX924
Ultra Low-Power,
Single/Dual-Supply Comparators
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
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 : 5V OPERATION
(V+ = 5V, V- = GND = 0V, TA = TMIN to TMAX, unless otherwise noted.)
PARAMETER
CONDITIONS
MIN
TYP
MAX
2.5
3.2
UNITS
POWER REQUIREMENTS
Supply Voltage Range
(Note 1)
2.5
MAX921,
HYST = REF
MAX922
Supply Current
TA = +25°C
11
C/E temp. ranges
4
M temp. range
5
TA = +25°C
2.5
3.2
C/E temp. ranges
4
M temp. range
IN+ = IN- + 100mV
MAX923,
HYST = REF
MAX924
5
TA = +25°C
3.1
V
4.5
C/E temp. ranges
6
M temp. range
7.5
TA = +25°C
5.5
6.5
C/E temp. ranges
8.5
M temp. range
11
COMPARATOR
Input Offset Voltage
VCM = 2.5V
Input Leakage Current (IN-, IN+)
IN+ = IN- = 2.5V
Input Leakage Current (HYST)
MAX921, MAX923
±10
C/E temp. ranges
±0.01
M temp. range
±5
±40
±0.02
Input Common-Mode Voltage Range
V-
mV
nA
nA
V+ – 1.3
V
Common-Mode Rejection Ratio
V- to (V+ – 1.3V)
0.1
1.0
mV/V
Power-Supply Rejection Ratio
V+ = 2.5V to 11V
0.1
1.0
mV/V
Voltage Noise
100Hz to 100kHz
Hysteresis Input Voltage Range
MAX921, MAX923
Response Time
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TA = +25°C, 100pF load
20
REF- 0.05V
REF
Overdrive = 10mV
12
Overdrive = 100mV
4
μVRMS
V
µs
Maxim Integrated │ 2
MAX921–MAX924
Ultra Low-Power,
Single/Dual-Supply Comparators
Electrical Characteristics : 5V OPERATION (continued)
(V+ = 5V, V- = GND = 0V, TA = TMIN to TMAX, unless otherwise noted.)
PARAMETER
Output High Voltage
Output Low Voltage
CONDITIONS
MIN
TYP
MAX
MAX92_
C/E temp. ranges: IOUT = 17mA;
M temp. range: IOUT = 10mA
V+ –
0.4
MAX922/
MAX923
C/E temp. ranges: IOUT = 1.8mA;
M temp. range: IOUT = 1.2mA
V- +
0.4
MAX921/
MAX924
C/E temp. ranges: IOUT = 1.8mA;
M temp. range: IOUT = 1.2mA
GND
+ 0.4
UNITS
V
V
REFERENCE (MAX921/MAX923/MAX924 ONLY)
Reference Voltage
Source Current
Sink Current
Voltage Noise
C temp. range
1.170
E temp. range
1.158
1.206
M temp. range
1.147
1.217
TA = +25°C
15
C/E temp. ranges
6
M temp. range
4
TA = +25°C
8
C/E temp. ranges
4
M temp. range
2
100Hz to 100kHz
1.182
1.194
V
25
µA
15
µA
100
μVRMS
Note 1: MAX924 comparators work below 2.5V, see Low-Voltage Operation section for more details.
Electrical Characteristics: 3V OPERATION
(V+ = 3V, V- = GND = 0V, TA = TMIN to TMAX, unless otherwise noted.)
PARAMETER
CONDITIONS
MIN
TYP
MAX
2.4
3.0
UNITS
POWER REQUIREMENTS
MAX921
TA = +25°C
C/E temp. ranges
3.8
M temp. range
MAX922
Supply Current
HYST = REF,
IN+ = (IN- + 100mV)
TA = +25°C
4.8
2.4
C/E temp. ranges
3.8
M temp. range
MAX923
MAX924
TA = +25°C
3.0
4.8
3.4
4.3
C/E temp. ranges
5.8
M temp. range
7.2
TA = +25°C
5.2
µA
6.2
C/E temp. ranges
8.0
M temp. range
10.5
COMPARATOR
Input Offset Voltage
VCM = 1.5V
Input Leakage Current (IN-, IN+)
IN+ = IN- = 2.5V
Input Leakage Current (HYST)
MAX921, MAX923
www.maximintegrated.com
±10
C/E temp. ranges
±0.01
M temp. range
±5
±40
±0.02
mV
nA
nA
Maxim Integrated │ 3
MAX921–MAX924
Ultra Low-Power,
Single/Dual-Supply Comparators
Electrical Characteristics (continued)
(V+ = 3V, V- = GND = 0V, TA = TMIN to TMAX, unless otherwise noted.)
PARAMETER
CONDITIONS
MIN
Input Common-Mode Voltage Range
TYP
V-
MAX
V+ – 1.3
Common-Mode Rejection Ratio
V- to (V+ – 1.3V)
0.2
1
Power-Supply Rejection Ratio
V+ = 2.5V to 11V
0.1
1
Voltage Noise
100Hz to 100kHz
20
Hysteresis Input Voltage Range
MAX921, MAX923
REF- 0.05V
REF
Overdrive = 10mV
14
Overdrive = 100mV
5
Response Time
TA = +25°C, 100pF load
Output High Voltage
MAX92_
C/E temp. ranges: IOUT = 10mA;
M temp. range: IOUT = 6mA
MAX922/
MAX923
C/E temp. ranges: IOUT = 0.8mA;
M temp. range: IOUT = 0.6mA
V- +
0.4
MAX921/
MAX924
C/E temp. ranges: IOUT = 0.8mA;
M temp. range: IOUT = 0.6mA
GND
+ 0.4
Output Low Voltage
UNITS
V
mV/V
mV/V
μVRMS
V
µs
V+ –
0.4
V
V
REFERENCE
Reference Voltage
Source Current
Sink Current
Voltage Noise
C temp. range
1.170
E temp. range
1.158
M temp. range
1.147
TA = +25°C
15
C/E temp. ranges
6
M temp. range
4
TA = +25°C
8
C/E temp. ranges
4
M temp. range
2
1.182
1.194
1.206
V
1.217
25
µA
15
µA
100Hz to 100kHz
100
μVRMS
Typical Operating Characteristics
(V+ = 5V, V- = GND, TA = +25°C, unless otherwise noted).
4.0
V+ = 3V
VOH (V)
1.5
1.0
3.5
3.0
2.5
0.5
0.0
V+ = 3V
2.0
0
4
8
12
LOAD CURRENT (mA)
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16
20
1.5
0
10
20
30
LOAD CURRENT (mA)
40
50
1.190
MAX921/924-TOC3
V+ = 5V
4.5
REFERENCE OUTPUT VOLTAGE vs.
OUTPUT LOAD CURRENT
MAX921/924-TOC2
V+ = 5V
2.0
VOL (V)
5.0
MAX921/4-TOC1
2.5
OUTPUT VOLTAGE HIGH vs.
LOAD CURRENT
REFERENCE OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE LOW
vs. LOAD CURRENT
SINK
1.185
1.180
SOURCE
1.175
1.170
1.165
V+ = 5V
OR
V+ = 3V
1.160
1.155
0
5
10
15
20
25
30
OUTPUT LOAD CURRENT (µA)
Maxim Integrated │ 4
MAX921–MAX924
Ultra Low-Power,
Single/Dual-Supply Comparators
Typical Operating Characteristics (continued)
(V+ = 5V, V- = GND, TA = +25°C, unless otherwise noted).
SUPPLY CURRENT (µA)
COMMERCIAL
TEMP. RANGE
1.19
1.18
1.17
1.16
V+ = 3V, V- = 0V
4.0
V+ = 5V, V- = 0V
3.5
3.0
2.5
100
140
-60
-20
MAX921/924-TOC6
20
100
60
TEMPERATURE (°C)
MAX924
SUPPLY CURRENT vs. TEMPERATURE
MAX924
SUPPLY CURRENT vs.
LOW SUPPLY VOLTAGES
IN+ = (IN- + 100mV)
7
V+ = 5V, V- = -5V
6
5
10
V+ = 5V, V- = 0V
0.1
V+ = 3V, V- = 0V
-60
-20
20
60
100
0.01
140
1.0
2.0
1.5
2.5
TRANSFER FUNCTION
RESPONSE TIME vs.
LOAD CAPACITANCE
OUTPUT VOLTAGE (V)
-20
-40
100k
4.0
V0
10µF
3.5
3.0
2.5
2.0
1.5
1.0
OUTPUT LOW
10
5.0
4.5
30
VREF -VHYST (mV)
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40
50
0
V- = 0V
16
14
VOHL
12
10
8
VOLH
6
4
0.5
20
18
MAX921/924 TOC12
HYSTERESIS CONTROL
NO CHANGE
140
1
SINGLE-SUPPLY VOLTAGE (V)
0
0
100
TEMPERATURE (°C)
20
-60
60
8
3
140
20
TEMPERATURE (°C)
OUTPUT HIGH
40
IN+ – IN- (mV)
60
V+ = 5V, V- = 0V
1.5
RESPONSE TIME (µs)
60
20
MAX921/924 TOC10
80
-20
2.5
TEMPERATURE (°C)
4
V+ = 3V, V- = 0V
-60
-20
-60
9
SUPPLY CURRENT (µA)
4.5
SUPPLY CURRENT (µA)
10
MAX921/924-TOC7
5.0
V+ = 10V, V- = 0V
3.0
V+ = 3V, V- = 0V
V+ = 5V, V- = 0V
MAX921/924-TOC8
20 40 60 80 100 120 140
3.5
2.0
SUPPLY CURRENT (µA)
-60 -40 -20 0
2.0
MAX923
SUPPLY CURRENT vs. TEMPERATURE
-80
MAX921/924-TOC5
3.0
TEMPERATURE (°C)
2.0
V+ = 5V, V- = - 5V
3.5
IN+ = (IN- + 100mV)
4.0
2.5
1.15
1.14
4.0
MAX922
SUPPLY CURRENT vs. TEMPERATURE
4.5
MAX921/924-TOC11
REFERENCE VOLTAGE (V)
EXTENDED TEMP. RANGE
1.20
IN+ = (IN- + 100mV)
SUPPLY CURRENT (µA)
MILITARY TEMP. RANGE
1.21
4.5
MAX921/924-TOC4
1.22
MAX921
SUPPLY CURRENT vs. TEMPERATURE
MAX921/924-TOC9
REFERENCE VOLTAGE
vs. TEMPERATURE
-0.3
-0.2
-0.1
0.2
0.1
0
IN+ INPUT VOLTAGE (mV)
0.3
2
0
20
40
60
80
100
LOAD CAPACITANCE (nF)
Maxim Integrated │ 5
MAX921–MAX924
Ultra Low-Power,
Single/Dual-Supply Comparators
Typical Operating Characteristics (continued)
(V+ = 5V, V- = GND, TA = +25°C, unless otherwise noted).
RESPONSE TIME FOR VARIOUS
INPUT OVERDRIVES
10mV
0
0
2
6
10
14
18
RESPONSE TIME (µs)
CURRENT (mA)
SOURCE CURRENT INTO 0.75V LOAD
MAX921/924-TOC16
MAX924 RESPONSE TIME
AT LOW SUPPLY VOLTAGES
100
50mV
10
1
MAX921/924-TOC15
MAX921/924-TOC14
20mV
1
0
100
-2
100
2
1
±20mV OVERDRIVE
0.1
0
±100mV
OVERDRIVE
-2
200
180
2
6
10
14
0.01
18
1.0
2.0
1.5
RESPONSE TIME (µs)
SINGLE-SUPPLY VOLTAGE (V)
SHORT-CIRCUIT SOURCE CURRENT
vs. SUPPLY VOLTAGE
SHORT-CIRCUIT SINK CURRENT
vs. SUPPLY VOLTAGE
OUT CONNECTED TO V-
160
140
120
100
80
60
OUT CONNECTED TO V+
GND CONNECTED TO V-
20
2.5
MAX121/124-TOC18
50mV
1
100mV
SINK CURRENT (mA)
2
10mV
RESPONSE TIME (ms)
20mV
4
3
MAX924 RESPONSE TIME
AT LOW SUPPLY VOLTAGES
10
MAX121/124-TOC17
MAX921/924-TOC13
100mV
OUTPUT VOLTAGE (V)
4
3
5
INPUT VOLTAGE (mV)
5
SOURCE CURRENT (mA)
INPUT VOLTAGE (mV)
OUTPUT VOLTAGE (V)
RESPONSE TIME FOR VARIOUS
INPUT OVERDRIVES
10
40
0.1
20
SINK CURRENT AT VOUT = 0.4V
1.0
1.5
2.0
2.5
SINGLE-SUPPLY VOLTAGE (V)
0
0
1.0
2.0
3.0
4.0
5.0
0
TOTAL SUPPLY VOLTAGE (V)
0
5
10
TOTAL SUPPLY VOLTAGE (V)
Pin Descriptions
PIN
NAME
FUNCTION
MAX921
MAX922
MAX923
1
–
–
GND
Ground. Connect to V- for single-supply operation. Output swings from V+ to GND.
–
1
1
OUTA
Comparator A output. Sinks and sources current. Swings from V+ to V-.
2
2
2
V-
3
–
–
IN+
–
3
3
INA+
4
–
–
IN-
–
4
–
INA-
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Negative supply. Connect to ground for single-supply operation (MAX921).
Noninverting comparator input
Noninverting input of comparator A
Inverting comparator input
Inverting input of comparator A
Maxim Integrated │ 6
MAX921–MAX924
Ultra Low-Power,
Single/Dual-Supply Comparators
Pin Descriptions (continued)
PIN
NAME
FUNCTION
MAX921
MAX922
MAX923
–
5
4
INB-
5
–
5
HYST
6
–
6
REF
Reference output. 1.182V with respect to V-.
–
6
–
INB+
Noninverting input of comparator B
7
7
7
V+
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-.
Inverting input of comparator B
Hysteresis input. Connect to REF if not used. Input voltage range is from
VREF to VREF - 50mV.
Positive supply
PIN
MAX924
NAME
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.
FUNCTION
3
V+
4
INA-
Positive supply
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.
www.maximintegrated.com
Maxim Integrated │ 7
MAX921–MAX924
Ultra Low-Power,
Single/Dual-Supply Comparators
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 commonmode 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 about 2.2V,
MAX922
OUTB 8
1 OUTA
V+ 7
2 V3 INA+
INB+ 6
4 INA-
INB- 5
Figure 1a. MAX922 Functional Diagram
MAX923
OUTB 8
1 OUTA
V+ 7
2 V-
1 OUTB
MAX924
2 OUTA
OUTC 16
OUTD 15
3 V+
GND 14
4 INA-
IND+ 13
5 INA+
IND- 12
6 INB-
INC+ 11
7 INB+
INC- 10
8 REF
V- 9
REF 6
3 INA+
HYST 5
4 INBV-
1b. MAX923 Functional Diagram
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1c. MAX924 Functional Diagram
Maxim Integrated │ 8
MAX921–MAX924
THRESHOLDS
IN+
INVREF - VHYST
Ultra Low-Power,
Single/Dual-Supply Comparators
HYSTERESIS
VHB
BAND
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
OUT
Figure 2. Threshold Hysteresis Band
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 supplyvoltage range if operation below 2.5V is anticipated.
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 comparator is used with the reference,
the combined peak-to-peak noise is about 1mV. This, of
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.
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IREF
6
R1
5
R2
2.5V TO 11V
7
V+
REF
MAX921
MAX923
HYST
V2
Figure 3. Programming the HYST Pin
Maxim Integrated │ 9
MAX921–MAX924
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:
R1 =
(2
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 VREF/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.
VHB
V+
0.05
= 10M ×
5
= 100kΩ
R1 = R3 ×
4) Choose the threshold voltage for VIN rising (VTHR).
In this example, choose VTHR = 3V.
5) Calculate R2.
1
V
1
1
THR
−
−
(VREF × R1) R1 R3
1
=
3
1
1
−
−
(1.182 × 100k) 100k 10M
R2 =
VHB
× IREF )
VHB
1.182 – 2
R2 =
IREF
Where IREF (the current sourced by the reference) should
not exceed the REF source capability, and should be
significantly larger than the HYST input current. IREF
values between 0.1μA and 4μA are usually appropriate. If
2.4MΩ is chosen for R2 (IREF = 0.5μA), the equation for
R1 and VHB can be approximated as:
R1 (kΩ ) = VHB (mV)
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
www.maximintegrated.com
Ultra Low-Power,
Single/Dual-Supply Comparators
= 65.44kΩ
A 1% preferred value is 64.9kΩ.
V+
R3
VIN
R1
V+
MAX924 V-
R2
OUT
GND
VREF
Figure 4. External Hysteresis
Maxim Integrated │ 10
MAX921–MAX924
Ultra Low-Power,
Single/Dual-Supply Comparators
Typical Applications
MOMENTARY
SWITCH
4.5V TO 6.0V
Auto-Off Power Source
7
V+
MAX921
6
IN+ 3
REF
47k
C
5
R
HYST
OUT 8
1.1M
VBATT -0.15V
10mA
4 IN100k
V-
GND
1
2
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 (VBATT – 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 three-resistor 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
Figure 5. Auto-off power switch operates on 2.5μA quiescent
current.
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.
6) Verify the threshold voltages with these formulas:
Window Detector
VIN rising:
VTHR=
1
1
1
VREF × R1 ×
+
+
R2
R3
R1
VIN falling:
VTHF
=
VTHR −
(R1
× V +)
R3
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.
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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 (VH = VHB/2). This means that the
hysteresis apparent at VIN will be larger because of
the input resistor divider.
Maxim Integrated │ 11
MAX921–MAX924
Ultra Low-Power,
Single/Dual-Supply Comparators
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.
VIN
Calculate R2. The undervoltage threshold should be
4.5V when VIN is falling. The design equation is as
follows:
(VREF − VH )
R2 = (R1 + R2 + R3) ×
− R1
VUTH
= (294k + 1.068M) ×
(1.182 − 0.005)
− 294k
4.5
= 62.2kΩ
Choose=
R2
61.9kΩ (1% standard value).
4) Calculate R3.
=
R3
=
=
Choose R3
=
(R2 + R3) − R2
1.068M − 61.9k
1.006MΩ
1MΩ (1% standard value).
+5V
R3
V+
INA+
3) Calculate R2 + R3. The overvoltage threshold should
be 5.5V when VIN is rising. The design equation is
as follows:
VOTH
− 1
R2 + R3 = R1 ×
VREF + VH
5.5
294k ×
=
− 1
(1.182
0.005)
+
= 1.068MΩ
VOTH = 5.5V
VUTH = 4.5V
OUTA
10k
R5
R2
R4
2.4M
UNDERVOLTAGE
HYST
POWER GOOD
REF
OUTB
INB-
R1
V-
OVERVOLTAGE
MAX923
Figure 6. Window Detector
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
Verify the resistor values. The equations are as
follows, evaluated for the above example.
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:
VOTH=
(VREF + VH ) ×
= 5.474V.
Undervoltage threshold:
VUTH=
(VREF − VH ) ×
(R1 + R2 + R3)
R1
(R1 + R2 + R3)
(R1 + R2)
= 4.484V,
where the hysteresis voltage=
VH
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VREF ×
R5
.
R4
Maxim Integrated │ 12
MAX921–MAX924
Ultra Low-Power,
Single/Dual-Supply Comparators
R2
R1
VIN
+5V
+5V
3
V+
1.182V 8 REF
V+
MAX924
10k
VINA
OUTA
V- 9
INA-
5 INA+
182k
OUTA 2
1V
330Ω
4 INA-
MAX924
INA+
10k
VINB
0 FOR VINA < 0V
1 FOR VINB > 0V
INB+
OUTB
250k
INB-
7 INB+
OUTB 1
330Ω
750mV 6 INB-
VINC
10k
INC+
OUTC
250k
INC-
11 INC+
OUTC 16
330Ω
500mV 10 INC-
VIND
10k
IND+
OUTD
250k
IND-
13 IND+
REF
OUTD 15
330Ω
250mV 12 IND250k
GND
14
Figure 7. Bar-Graph Level Gauge
www.maximintegrated.com
GND
N.C.
V-
-5V
Figure 8. Level Shifter: ±5V Input to CMOS Output
Maxim Integrated │ 13
MAX921–MAX924
Ultra Low-Power,
Single/Dual-Supply Comparators
Pin Configurations
Ordering Information (continued)
PART
TOP VIEW
TEMP RANGE
PIN-PACKAGE
MAX921MSA/PR
-55°C to +125°C
8 SO**
MAX921MSA/PR-T
-55°C to +125°C
8 SO**
8
OUT
MAX922CPA
0°C to +70°C
8 Plastic DIP
7
V+
MAX922CSA
0°C to +70°C
8 SO
IN+ 3
6
REF
MAX922CUA
0°C to +70°C
8 µMAX
IN- 4
5
HYST
MAX922C/D
0°C to +70°C
Dice*
MAX922EPA
-40°C to +85°C
8 Plastic DIP
MAX922ESA
-40°C to +85°C
8 SO
MAX922MJA
-55°C to +125°C
8 CERDIP**
GND 1
V-
2
MAX921
DIP/SO/µMAX
OUTA 1
8
OUTB
MAX922MSA/PR
-55°C to +125°C
8 SO**
7
V+
MAX922MSA/PR-T
-55°C to +125°C
8 SO**
INA+ 3
6
INB+
MAX923CPA
0°C to +70°C
8 Plastic DIP
INA- 4
5
INB-
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
-40°C to +85°C
8 Plastic DIP
V-
MAX922
2
DIP/SO/µMAX
OUTA 1
8
OUTB
MAX923ESA
-40°C to +85°C
8 SO
7
V+
MAX923MJA
-55°C to +125°C
8 CERDIP**
INA+ 3
6
REF
MAX923MSA/PR
-55°C to +125°C
8 SO**
INB- 4
5
HYST
MAX923MSA/PR-T
-55°C to +125°C
8 SO**
V-
MAX923
2
DIP/SO/µMAX
MAX924CPE
0°C to +70°C
16 Plastic DIP
MAX924CSE
0°C to +70°C
16 Narrow SO
Dice*
OUTB 1
MAX924C/D
0°C to +70°C
16 OUTC
OUTA 2
MAX924EPE
-40°C to +85°C
16 Plastic DIP
15 OUTD
MAX924ESE
-40°C to +85°C
16 Narrow SO
MAX924MJE
-55°C to +125°C
16 CERDIP**
MAX924MSE/PR
-55°C to +125°C
16 Narrow SO**
MAX924MSE/PR-T
-55°C to +125°C
16 Narrow SO**
V+ 3
MAX924
INA- 4
14 GND
13 IND+
INA+ 5
12 IND-
INB- 6
11 INC+
INB+ 7
10 INC-
REF 8
9
*Dice are tested at TA = +25°C, DC parameters only.
**Contact factory for availability.
V-
DIP/Narrow SO
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Maxim Integrated │ 14
MAX921–MAX924
Ultra Low-Power,
Single/Dual-Supply Comparators
Chip Topographies
MAX921/MAX922/MAX923
MAX924
OUTB
OUTA
OUTC
OUTD
10
1
V+
9
2
8
3
4
7
5
6
0.061"
(1.55mm)
GND
0.108"
(2.74mm)
IND+
INA-
IND-
INA+
0.058"
(1.47mm)
INC+
INB-
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
INB+
REF
V-
INC-
0.069"
(1.75mm)
TRANSISTOR COUNT: 267
SUBSTRATE CONNECTED TO V+
TRANSISTOR COUNT: 164
SUBSTRATE CONNECTED TO V+
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Maxim Integrated │ 15
MAX921–MAX924
Ultra Low-Power,
Single/Dual-Supply Comparators
Package Information
For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”,
“#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing
pertains to the package regardless of RoHS status.
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
J16-3-1
21-0045
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Maxim Integrated │ 16
MAX921–MAX924
Ultra Low-Power,
Single/Dual-Supply Comparators
Revision History
REVISION
NUMBER
REVISION
DATE
4
8/08
Updated TOCs 5 and 10
5
8/08
Adding information for rugged plastic product
6
4/09
Updated Ordering Information
7
1/20
Updated Chip Topographies
DESCRIPTION
PAGES
CHANGED
5
1, 14
1, 14, 16
15
For pricing, delivery, and ordering information, please visit Maxim Integrated’s online storefront at https://www.maximintegrated.com/en/storefront/storefront.html.
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses
are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits)
shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.
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