MAXIM MAX921ESA

19-0115; Rev 6; 4/09
Ultra Low-Power,
Single/Dual-Supply Comparators
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.
INTERNAL 1%
PRECISION
REFERENCE
COMPARATORS
PER
PACKAGE
INTERNAL
HYSTERESIS
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
PACKAGE
PART
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.
____________________________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
PART
TEMP RANGE
PIN-PACKAGE
MAX921CPA
0°C to +70°C
8 Plastic DIP
MAX921CSA
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
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+
3 IN+
OUT 8
4 IN-
________________________Applications
Battery-Powered Systems
Threshold Detectors
Window Comparators
Oscillator Circuits
µMAX is a registered trademark of Maxim Integrated Products, Inc.
5 HYST
MAX921
6 REF
V2
GND
1
THRESHOLD DETECTOR
________________________________________________________________ Maxim Integrated Products
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.
1
MAX921–MAX924
_______________General Description
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
UNITS
11
V
2.5
3.2
POWER REQUIREMENTS
Supply Voltage Range
(Note 1)
2.5
TA = +25°C
MAX921,
C/E temp. ranges
HYST = REF
M temp. range
4
5
TA = +25°C
MAX922
Supply Current
2.5
C/E temp. ranges
4
M temp. range
IN+ = IN- + 100mV
5
TA = +25°C
3.1
4.5
5.5
6
7.5
6.5
8.5
11
±0.01
±10
±5
±40
MAX923,
C/E temp. ranges
HYST = REF
M temp. range
TA = +25°C
C/E temp. ranges
MAX924
M temp. range
COMPARATOR
Input Offset Voltage
VCM = 2.5V
Input Leakage Current (IN-, IN+)
IN+ = IN- = 2.5V
Input Leakage Current (HYST)
Input Common-Mode Voltage Range
Common-Mode Rejection Ratio
Power-Supply Rejection Ratio
Voltage Noise
Hysteresis Input Voltage Range
MAX921, MAX923
Response Time
2
C/E temp. ranges
M temp. range
±0.02
V-
V- to (V+ – 1.3V)
V+ = 2.5V to 11V
100Hz to 100kHz
MAX921, MAX923
TA = +25°C, 100pF load
3.2
0.1
0.1
20
REF- 0.05V
Overdrive = 10mV
Overdrive = 100mV
V+ – 1.3
1.0
1.0
REF
12
4
_______________________________________________________________________________________
µA
mV
nA
nA
V
mV/V
mV/V
µVRMS
V
µs
Ultra Low-Power,
Single/Dual-Supply Comparators
MAX921–MAX924
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
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
V+ – 0.4
UNITS
V
V
REFERENCE (MAX921/MAX923/MAX924 ONLY)
X
C temp. range
E temp. range
M temp. range
TA = +25°C
C/E temp. ranges
M temp. range
TA = +25°C
C/E temp. ranges
M temp. range
Reference Voltage
Source Current
Sink Current
Voltage Noise
1.170
1.158
1.147
15
6
4
8
4
2
100Hz to 100kHz
1.182
1.194
1.206
1.217
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
UNITS
POWER REQUIREMENTS
TA = +25°C
MAX921
2.4
C/E temp. ranges
M temp. range
TA = +25°C
MAX922
Supply Current
C/E temp. ranges
TA = +25°C
MAX923
MAX924
COMPARATOR
Input Offset Voltage
4.8
2.4
C/E temp. ranges
M temp. range
TA = +25°C
C/E temp. ranges
M temp. range
4.8
3.4
4.3
5.2
5.8
7.2
6.2
8.0
10.5
±0.01
±10
±5
±40
VCM = 1.5V
Input Leakage Current (IN-, IN+)
IN+ = IN- = 1.5V
Input Leakage Current (HYST)
MAX921, MAX923
C/E temp. ranges
M temp. range
3.0
3.8
M temp. range
HYST = REF,
IN+ = (IN- + 100mV)
3.0
3.8
±0.02
µA
mV
nA
nA
_______________________________________________________________________________________
3
ELECTRICAL CHARACTERISTICS: 3V OPERATION (continued)
(V+ = 3V, V- = GND = 0V, TA = TMIN to TMAX, unless otherwise noted.)
PARAMETER
CONDITIONS
Input Common-Mode Voltage Range
Common-Mode Rejection Ratio
Power-Supply Rejection Ratio
Voltage Noise
Hysteresis Input Voltage Range
MIN
TYP
VV- to (V+ – 1.3V)
V+ = 2.5V to 11V
100Hz to 100kHz
MAX921, MAX923
0.2
0.1
20
MAX
UNITS
V+ – 1.3
1
1
V
mV/V
mV/V
µVRMS
V
REF- 0.05V
Overdrive = 10mV
Overdrive = 100mV
REF
14
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
µs
V+ – 0.4
V
V
REFERENCE
C temp. range
E temp. range
M temp. range
TA = +25°C
C/E temp. ranges
M temp. range
TA = +25°C
C/E temp. ranges
M temp. range
Reference Voltage
Source Current
Sink Current
Voltage Noise
1.170
1.158
1.147
15
6
4
8
4
2
1.182
1.194
1.206
1.217
V
25
µA
15
µA
100Hz to 100kHz
100
µVRMS
Typical Operating Characteristics
(V+ = 5V, V- = GND, TA = +25°C, unless otherwise noted).
2.0
MAX921/924-TOC2
V+ = 5V
V+ = 5V
4.5
4.0
V+ = 3V
VOH (V)
1.5
1.0
3.5
3.0
2.5
V+ = 3V
0.5
2.0
0.0
4
8
12
LOAD CURRENT (mA)
4
16
20
SINK
1.185
1.180
SOURCE
1.175
1.170
1.165
V+ = 5V
OR
V+ = 3V
1.160
1.155
1.5
0
1.190
REFERENCE OUTPUT VOLTAGE (V)
5.0
MAX921/4-TOC1
2.5
REFERENCE OUTPUT VOLTAGE vs.
OUTPUT LOAD CURRENT
OUTPUT VOLTAGE HIGH vs.
LOAD CURRENT
MAX921/924-TOC3
OUTPUT VOLTAGE LOW
vs. LOAD CURRENT
VOL (V)
MAX921–MAX924
Ultra Low-Power,
Single/Dual-Supply Comparators
0
10
20
30
LOAD CURRENT (mA)
40
50
0
5
10
15
20
25
OUTPUT LOAD CURRENT (μA)
_______________________________________________________________________________________
30
Ultra Low-Power,
Single/Dual-Supply Comparators
MAX921
SUPPLY CURRENT vs.
TEMPERATURE
COMMERCIAL
TEMP. RANGE
1.19
1.18
1.17
1.16
4.0
V+ = 5V, V- = - 5V
3.5
3.0
V+ = 3V, V- = 0V
IN+ = (IN- + 100mV)
4.0
3.5
V+ = 10V, V- = 0V
3.0
2.5
V+ = 5V, V- = 0V
2.5
2.0
1.15
V+ = 3V, V- = 0V
V+ = 5V, V- = 0V
2.0
1.14
-60 -40 -20 0
-20
20
60
100
140
-60
-20
20
100
60
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
MAX923
SUPPLY CURRENT vs. TEMPERATURE
MAX924
SUPPLY CURRENT vs. TEMPERATURE
MAX924
SUPPLY CURRENT vs.
LOW SUPPLY VOLTAGES
4.0
V+ = 5V, V- = 0V
3.5
3.0
2.5
8
V+ = 5V, V- = -5V
6
V+ = 5V, V- = 0V
5
4
140
MAX921/924-TOC9
9
7
10
MAX921/924-TOC8
IN+ = (IN- + 100mV)
SUPPLY CURRENT (μA)
4.5
10
SUPPLY CURRENT (μA)
MAX921/924-TOC7
5.0
SUPPLY CURRENT (μA)
1.5
-60
20 40 60 80 100 120 140
MAX921/924-TOC6
IN+ = (IN- + 100mV)
SUPPLY CURRENT (μA)
REFERENCE VOLTAGE (V)
EXTENDED TEMP. RANGE
1.20
4.5
MAX921/924-TOC5
MILITARY TEMP. RANGE
1.21
4.5
MAX921/924-TOC4
1.22
MAX922
SUPPLY CURRENT vs. TEMPERATURE
SUPPLY CURRENT (μA)
REFERENCE VOLTAGE
vs. TEMPERATURE
1
0.1
V+ = 3V, V- = 0V
V+ = 3V, V- = 0V
3
2.0
-20
20
60
100
20
60
100
140
2.0
1.5
2.5
SINGLE-SUPPLY VOLTAGE (V)
HYSTERESIS CONTROL
TRANSFER FUNCTION
RESPONSE TIME vs.
LOAD CAPACITANCE
NO CHANGE
-20
-40
4.0
V0
10μF
3.5
3.0
2.5
2.0
1.5
1.0
OUTPUT LOW
0
10
20
30
VREF -VHYST (mV)
40
50
V- = 0V
16
14
VOHL
12
10
8
VOLH
6
4
0.5
-80
18
MAX921/924 TOC12
100k
MAX921/924-TOC11
4.5
OUTPUT VOLTAGE (V)
20
0
5.0
MAX921/924 TOC10
OUTPUT HIGH
40
0
1.0
TEMPERATURE (°C)
60
IN+ – IN- (mV)
-20
TEMPERATURE (°C)
80
-60
0.01
-60
140
RESPONSE TIME (μs)
-60
2
-0.3
0.2
0.1
-0.2 -0.1
0
IN+ INPUT VOLTAGE (mV)
0.3
0
20
40
60
80
100
LOAD CAPACITANCE (nF)
_______________________________________________________________________________________
5
MAX921-MAX924
Typical Operating Characteristics (continued)
(V+ = 5V, V- = GND, TA = +25°C, unless otherwise noted).
Typical Operating Characteristics (continued)
(V+ = 5V, V- = GND, TA = +25°C, unless otherwise noted).
50mV
1
10mV
0
-2
2
6
10
10mV
100mV
2
20mV
1
50mV
14
18
RESPONSE TIME (μs)
100
0.01
-2
1
2
6
10
14
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
200
OUT CONNECTED TO V-
160
140
120
100
80
60
2.5
OUT CONNECTED TO V+
GND CONNECTED TO VSINK CURRENT (mA)
MAX921/924-TOC16
10
±20mV OVERDRIVE
0.1
±100mV
OVERDRIVE
180
SOURCE CURRENT (mA)
SOURCE CURRENT INTO 0.75V LOAD
1
0
MAX924 RESPONSE TIME
AT LOW SUPPLY VOLTAGES
100
MAX921/924-TOC15
MAX921/924-TOC14
4
3
0
100
10
MAX121/124-TOC18
2
5
RESPONSE TIME (ms)
20mV
MAX924 RESPONSE TIME
AT LOW SUPPLY VOLTAGES
MAX121/124-TOC17
100mV
INPUT VOLTAGE (mV)
4
3
OUTPUT VOLTAGE (V)
5
0
INPUT VOLTAGE (mV)
RESPONSE TIME FOR VARIOUS
INPUT OVERDRIVES
MAX921/924-TOC13
OUTPUT VOLTAGE (V)
RESPONSE TIME FOR VARIOUS
INPUT OVERDRIVES
CURRENT (mA)
MAX921–MAX924
Ultra Low-Power,
Single/Dual-Supply Comparators
20
10
40
20
SINK CURRENT AT VOUT = 0.4V
0
0.1
1.0
2.0
1.5
2.5
0
0
1.0
2.0
3.0
4.0
5.0
0
TOTAL SUPPLY VOLTAGE (V)
SINGLE-SUPPLY VOLTAGE (V)
5
10
TOTAL SUPPLY VOLTAGE (V)
____________________________________________________________Pin Descriptions
PIN
NAME
FUNCTION
–
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-
MAX921
MAX922
MAX923
1
–
–
6
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
_______________________________________________________________________________________
Ultra Low-Power,
Single/Dual-Supply Comparators
PIN
NAME
FUNCTION
MAX921
MAX922
MAX923
–
5
4
INB-
Inverting input of comparator B
5
–
5
HYST
Hysteresis input. Connect to REF if not used. Input voltage range is from
VREF to VREF - 50mV.
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-.
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.
3
V+
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-
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.
FUNCTION
Positive supply
Negative supply. Connect to ground for single-supply operation.
_______________________________________________________________________________________
7
MAX921–MAX924
_______________________________________________Pin Descriptions (continued)
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
MAX922
1 OUTA
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
OUTB 8
V+ 7
2 V-
1 OUTB
3 INA+
INB+ 6
4 INA-
INB- 5
MAX924
2 OUTA
Figure 1a. MAX922 Functional Diagram
MAX923
1 OUTA
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
OUTB 8
V+ 7
2 V3 INA+
REF 6
4 INB-
HYST 5
V-
Figure 1b. MAX923 Functional Diagram
8
OUTC 16
Figure 1c. MAX924 Functional Diagram
_______________________________________________________________________________________
Ultra Low-Power,
Single/Dual-Supply Comparators
INVREF - VHYST
HYSTERESIS
VHB
BAND
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.
OUT
Figure 2. Threshold Hysteresis Band
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.
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
IREF
6
REF
2.5V TO 11V
7
V+
R1
5
R2
MAX921
MAX923
HYST
V2
Figure 3. Programming the HYST Pin
_______________________________________________________________________________________
9
MAX921–MAX924
THRESHOLDS
IN+
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.
MAX921–MAX924
Ultra Low-Power,
Single/Dual-Supply Comparators
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:
VHB
R1 =
(2 × IREF )
VHB ⎞
⎛
⎜1.182 –
⎟
⎝
2 ⎠
R2 =
IREF
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 (IREF =
0.5µA), the equation for R1 and V HB 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 the MAX921 and MAX923, and the high
10
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 (V HB), the voltage
between the upper and lower thresholds. In this
example, choose VHB = 50mV.
3. Calculate R1.
V
R1 = R3 × HB
V+
0.05
= 10M ×
5
= 100kΩ
4. Choose the threshold voltage for VIN rising (VTHR).
In this example, choose VTHR = 3V.
5. Calculate R2.
1
R2 =
⎡⎛
⎞ 1
VTHR
1 ⎤
⎢⎜
⎥
−
⎟−
⎢⎝ (VREF × R1) ⎠ R1 R3 ⎥
⎣
⎦
1
=
⎡⎛
⎞
3
1
1 ⎤
−
−
⎢⎜
⎥
⎟
⎢⎣⎝ (1.182 × 100k) ⎠ 100k 10M ⎥⎦
= 65.44kΩ
A 1% preferred value is 64.9kΩ.
V+
R3
R1
VIN
V+
R2
MAX924 VGND
VREF
Figure 4. External Hysteresis
______________________________________________________________________________________
OUT
Ultra Low-Power,
Single/Dual-Supply Comparators
Auto-Off Power Source
MOMENTARY
SWITCH
4.5V TO 6.0V
7
V+
6
MAX921
IN+ 3
REF
47k
C
5
R
HYST
1.1M
OUT 8
VBATT -0.15V
10mA
4 IN100k
V2
GND
1
Figure 5. Auto-off power switch operates on 2.5µA quiescent
current.
6. Verify the threshold voltages with these formulas:
VIN rising :
1
1 ⎞
⎛ 1
VTHR = VREF × R1 × ⎜
+
+
⎟
⎝ R1
R2
R3 ⎠
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.
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 (VH = VHB/2). This means that the
hysteresis apparent at VIN will be larger because of
the input resistor divider.
______________________________________________________________________________________
11
MAX921–MAX924
_______________Typical Applications
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.
3. Calculate R2 + R3. The overvoltage threshold
should be 5.5V when V IN is rising. The design
equation is as follows:
⎛
⎞
VOTH
R2 + R3 = R1 × ⎜
− 1⎟
V
+
V
⎝ REF
⎠
H
VIN
VOTH = 5.5V
VUTH = 4.5V
+5V
R3
V+
INA+
OUTA
UNDERVOLTAGE
HYST
10k
R5
R2
⎛
⎞
5.5
= 294k × ⎜
− 1⎟
⎝ (1.182 + 0.005)
⎠
POWER GOOD
REF
R4
2.4M
= 1.068MΩ
OUTB
OVERVOLTAGE
INB-
4. Calculate R2. The undervoltage threshold should
be 4.5V when VIN is falling. The design equation is
as follows:
VR1
MAX923
(VREF − VH )
− R1
VUTH
R2 = (R1 + R2 + R3) ×
= (294k + 1.068M) ×
(1.182 − 0.005)
− 294k
4.5
Figure 6. Window Detector
= 62.2kΩ
Choose R2 = 61.9kΩ (1% standard value).
Bar-Graph Level Gauge
5. Calculate R3.
R3 = (R2 + R3) − R2
= 1.068M − 61.9k
= 1.006MΩ
Choose R3 = 1MΩ (1% standard value)
6. Verify the resistor values. The equations are as
follows, evaluated for the above example.
(R1 + R2 + R3)
R1
= 5.474V.
Undervoltage threshold :
VUTH = (VREF − VH ) ×
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 :
VOTH = (VREF + VH ) ×
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.
(R1 + R2 + R3)
(R1 + R2)
= 4.484V,
where the hysteresis voltage VH = VREF ×
12
R5
.
R4
______________________________________________________________________________________
Ultra Low-Power,
Single/Dual-Supply Comparators
MAX921–MAX924
R2
R1
VIN
1.182V 8
+5V
+5V
3
V+
V+
REF
MAX924
10k
MAX924
INA+
VINA
OUTA
V- 9
INA-
5 INA+
182k
0 FOR VINA < 0V
1 FOR VINB > 0V
OUTA 2
10k
1V
330Ω
4 INA-
INB+
VINB
OUTB
250k
INB-
7 INB+
OUTB 1
750mV 6
330Ω
INB-
10k
VINC
INC+
OUTC
250k
INC-
11 INC+
OUTC 16
330Ω
500mV 10 INC-
10k
VIND
IND+
OUTD
250k
IND-
13 IND+
REF
OUTD 15
330Ω
250mV 12 IND-
250k
N.C.
GND
GND
14
Figure 7. Bar-Graph Level Gauge
V-
-5V
Figure 8. Level Shifter: ±5V Input to CMOS Output
______________________________________________________________________________________
13
MAX921–MAX924
Ultra Low-Power,
Single/Dual-Supply Comparators
_________________Pin Configurations
_Ordering Information (continued)
PART
TOP VIEW
TEMP RANGE
-55°C to +125°C
8 SO**
-55°C to +125°C
8 SO**
GND
1
8
OUT
MAX921MSA/PR-T
V-
2
7
V+
MAX922CPA
0°C to +70°C
8 Plastic DIP
6
REF
MAX922CSA
0°C to +70°C
8 SO
5
HYST
IN+ 3
MAX921
IN- 4
DIP/SO/μMAX
MAX922CUA
0°C to +70°C
8 µMAX
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**
OUTA
1
8
OUTB
MAX922MSA/PR
-55°C to +125°C
8 SO**
V-
2
7
V+
MAX922MSA/PR-T
-55°C to +125°C
8 SO**
6
INB+
MAX923CPA
0°C to +70°C
8 Plastic DIP
INB-
MAX923CSA
0°C to +70°C
8 SO
INA+ 3
MAX922
INA- 4
5
DIP/SO/μMAX
OUTA
1
V-
2
INA+ 3
8
MAX923
INB- 4
OUTB
7
V+
6
REF
5
HYST
DIP/SO/μMAX
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
MAX923ESA
-40°C to +85°C
8 SO
MAX923MJA
-55°C to +125°C
8 CERDIP**
MAX923MSA/PR
-55°C to +125°C
8 SO**
MAX923MSA/PR-T
-55°C to +125°C
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
MAX924EPE
-40°C to +85°C
16 Plastic DIP
Dice*
OUTB 1
16 OUTC
MAX924ESE
-40°C to +85°C
16 Narrow SO
OUTA 2
15 OUTD
MAX924MJE
-55°C to +125°C
16 CERDIP**
14 GND
MAX924MSE/PR
-55°C to +125°C
16 Narrow SO**
MAX924MSE/PR-T
-55°C to +125°C
16 Narrow SO**
V+ 3
INA- 4
MAX924
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
14
PIN-PACKAGE
MAX921MSA/PR
______________________________________________________________________________________
Ultra Low-Power,
Single/Dual-Supply Comparators
MAX921/MAX922/MAX923
MAX924
OUTB
OUTA
10
1
OUTC
OUTD
V+
9
2
8
3
GND
0.075"
(1.91mm)
4
7
5
0.108"
(2.74mm)
6
IND+
INA-
IND-
INA+
0.059"
(1.50mm)
DIE PAD
1
2
3
4
5
6
7
8
9
10
MAX921
GND
VVIN+
INHYST
REF
V+
V+
OUT
INC+
INB-
MAX922
OUTA
VVINA+
INAINBINB+
V+
V+
OUTB
MAX923
OUTA
VVINA+
INBHYST
REF
V+
V+
OUTB
INB+
REF
V-
INC-
0.069"
(1.75mm)
TRANSISTOR COUNT: 267
SUBSTRATE CONNECTED TO V+
TRANSISTOR COUNT: 164
SUBSTRATE CONNECTED TO V+
______________________________________________________________________________________
15
MAX921–MAX924
__________________________________________________________Chip Topographies
MAX921–MAX924
Ultra Low-Power,
Single/Dual-Supply Comparators
Package Information
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages.
16
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
______________________________________________________________________________________
Ultra Low-Power,
Single/Dual-Supply Comparators
REVISION
NUMBER
REVISION
DATE
4
8/08
5
8/08
Adding information for rugged plastic product
6
4/09
Updated Ordering Information
DESCRIPTION
Updated TOCs 5 and 10
PAGES
CHANGED
5
1, 14
1, 14, 16
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.
MAX921/MAX924
Revision History