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19-1512; Rev 0; 7/99
SOT23, 1.8V, Nanopower, Beyond-the-Rails Comparators With/Without Reference
General Description
The MAX917-MAX920 nanopower comparators in space-saving SOT23 packages feature Beyond-theRailsTM inputs and are guaranteed to operate down to +1.8V. The MAX917/MAX918 feature an on-board 1.245V 1.5% reference and draw an ultra-low supply current of only 750nA, while the MAX919/MAX920 (without reference) require just 380nA of supply current. These features make the MAX917-MAX920 family of comparators ideal for all 2-cell battery applications, including monitoring/management. The unique design of the output stage limits supply-current surges while switching, virtually eliminating the supply glitches typical of many other comparators. This design also minimizes overall power consumption under dynamic conditions. The MAX917/MAX919 have a push/pull output stage that sinks and sources current. Large internal output drivers allow Rail-to-Rail(R) output swing with loads up to 8mA. The MAX918/MAX920 have an open-drain output stage that makes them suitable for mixed-voltage system design.
Features
o Ultra-Low Supply Current 380nA per Comparator (MAX919/MAX920) 750nA per Comparator with Reference (MAX917/MAX918) o Guaranteed to Operate Down to +1.8V o Internal 1.245V 1.5% Reference (MAX917/MAX918) o Input Voltage Range Extends 200mV Beyond-the-Rails o CMOS Push/Pull Output with 8mA Drive Capability (MAX917/MAX919) o Open-Drain Output Versions Available (MAX918/MAX920) o Crowbar-Current-Free Switching o Internal Hysteresis for Clean Switching o No Phase Reversal for Overdriven Inputs o Space-Saving SOT23 Package
MAX917-MAX920
Applications
2-Cell Battery Monitoring/Management Ultra-Low-Power Systems Mobile Communications Notebooks and PDAs Threshold Detectors/Discriminators Sensing at Ground or Supply Line Telemetry and Remote Systems Medical Instruments
PART MAX917EUK-T MAX917ESA MAX918EUK-T MAX918ESA MAX919EUK-T MAX919ESA MAX920EUK-T MAX920ESA
Ordering Information
TEMP. RANGE -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C PINSOT PACKAGE TOP MARK 5 SOT23-5 8 SO 5 SOT23-5 8 SO 5 SOT23-5 8 SO 5 SOT23-5 8 SO ADIQ -- ADIR -- ADIS -- ADIT --
Selector Guide
PART MAX917 MAX918 MAX919 MAX920 INTERNAL REFERENCE Yes Yes No No OUTPUT TYPE Push/Pull Open-Drain Push/Pull Open-Drain SUPPLY CURRENT (nA) 750 750 380 380
VEE 2
Pin Configurations
TOP VIEW
OUT 1 5 VCC
MAX917 MAX918 MAX919 MAX920
4 IN- (REF)
Typical Application Circuit appears at end of data sheet. Beyond-the-Rails is a trademark of Maxim Integrated Products. Rail-to-Rail is a registered trademark of Nippon Motorola, Ltd.
IN+ 3
( ) ARE FOR MAX917/MAX918.
SOT23-5
Pin Configurations continue at end of data sheet.
1
________________________________________________________________ Maxim Integrated Products
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800. For small orders, phone 1-800-835-8769.
SOT23, 1.8V, Nanopower, Beyond-the-Rails Comparators With/Without Reference MAX917-MAX920
ABSOLUTE MAXIMUM RATINGS
Supply Voltage (VCC to VEE)..................................................+6V Voltage Inputs (IN+, IN-, REF) .........(VEE - 0.3V) to (VCC + 0.3V) Output Voltage MAX917/MAX919 ........................(VEE - 0.3V) to (VCC + 0.3V) MAX918/MAX920 ......................................(VEE - 0.3V) to +6V Output Current..................................................................50mA Output Short-Circuit Duration .............................................10sec Continuous Power Dissipation (TA = +70C) 5-Pin SOT23 (derate 7.31mW/C above +70C).........571mW 8-Pin SO (derate 5.88mW/C above +70C)...............471mW Operating Temperature Range ...........................-40C to +85C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10sec) .............................+300C
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--MAX917/MAX918
(VCC = +5V, VEE = 0, VIN+ = VREF, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1) PARAMETER Supply Voltage Range Supply Current IN+ Voltage Range Input Offset Voltage Input-Referred Hysteresis Input Bias Current Power-Supply Rejection Ratio SYMBOL VCC ICC VIN+ VOS VHB IB PSRR VCC = 1.8V VCC = 5V TA = +25C TA = TMIN to TMAX VEE - 0.2 1 4 0.15 0.1 TA = +25C TA = TMIN to TMAX TA = +25C TA = TMIN to TMAX TA = +25C TA = TMIN to TMAX TA = +25C TA = TMIN to TMAX 0.001 95 8 98 10 mA VCC = 5V VCC = 1.8V VCC = 5V VCC = 1.8V 55 190 55 190 1 2 1 400 500 200 300 400 500 200 300 1 A mV mV TA = +25C TA = TMIN to TMAX CONDITIONS Inferred from the PSRR test MIN 1.8 0.75 0.80 1.30 1.60 VCC + 0.2 5 10 V mV mV nA mV/V A TYP MAX 5.5 UNITS V
Inferred from the output swing test (Note 2) (Note 3) TA = +25C TA = TMIN to TMAX VCC = 1.8V to 5.5V MAX917 only, VCC = 5V, ISOURCE = 8mA
Output Voltage Swing High
VCC - VOH MAX917 only, VCC = 1.8V, ISOURCE = 1mA VCC = 5V, ISINK = 8mA
Output Voltage Swing Low
VOL VCC = 1.8V, ISINK = 1mA
Output Leakage Current
ILEAK
MAX918 only, VO = 5.5V Sourcing, VO = VEE
Output Short-Circuit Current
ISC Sinking, VO = VCC
2
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SOT23, 1.8V, Nanopower, Beyond-the-Rails Comparators With/Without Reference
ELECTRICAL CHARACTERISTICS--MAX917/MAX918 (continued)
(VCC = +5V, VEE = 0, VIN+ = VREF, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1) PARAMETER High-to-Low Propagation Delay (Note 4) SYMBOL tPDVCC = 1.8V VCC = 5V MAX917 only Low-to-High Propagation Delay (Note 4) tPD+ MAX918 only VCC = 1.8V VCC = 5V VCC = 1.8V, RPULL-UP = 100k VCC = 5V, RPULL-UP = 100k Rise Time Fall Time Power-Up Time Reference Voltage Reference Voltage Temperature Coefficient Reference Output Voltage Noise Reference Line Regulation Reference Load Regulation tRISE tFALL tON VREF TCREF en VREF/ VCC VREF/ IOUT BW = 10Hz to 100kHz BW = 10Hz to 100kHz, CREF = 1nF 1.8V VCC 5.5V IOUT = 10nA TA = +25C TA = TMIN to TMAX 1.227 1.200 95 600 215 0.1 0.2 MAX917 only, CL = 15pF CL = 15pF CONDITIONS MIN TYP 17 22 30 95 35 120 6 4 1.2 1.245 1.263 1.290 s s ms V ppm/C VRMS mV/V mV/nA s MAX UNITS s
MAX917-MAX920
ELECTRICAL CHARACTERISTICS--MAX919/MAX920
(VCC = +5V, VEE = 0, VCM = 0, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1) PARAMETER Supply Voltage Range Supply Current Input Common-Mode Voltage Range Input Offset Voltage Input-Referred Hysteresis Input Bias Current SYMBOL VCC ICC VCC = 1.8V VCC = 5V TA = +25C TA = TMIN to TMAX VEE - 0.2 1 4 0.15 1 2 CONDITIONS Inferred from the PSRR test MIN 1.8 0.38 0.45 0.80 1.2 VCC + 0.2 5 10 V mV mV nA A TYP MAX 5.5 UNITS V
VCM VOS VHB IB
Inferred from the CMRR test -0.2V VCM (VCC + 0.2V) (Note 2) TA = +25C TA = TMIN to TMAX TA = +25C TA = TMIN to TMAX
-0.2V VCM (VCC + 0.2V) (Note 3)
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3
MAX917-MAX920
SOT23, 1.8V, Nanopower, Beyond-the-Rails Comparators With/Without Reference
ELECTRICAL CHARACTERISTICS--MAX919/MAX920 (continued)
(VCC = +5V, VEE = 0, VCM = 0, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1) PARAMETER Input Offset Current Power-Supply Rejection Ratio Common-Mode Rejection Ratio SYMBOL IOS PSRR CMRR VCC = 1.8V to 5.5V (VEE - 0.2V) VCM (VCC + 0.2V) MAX919 only, VCC = 5V, ISOURCE = 8mA MAX919 only, VCC = 1.8V, ISOURCE = 1mA VCC = 5V, ISINK = 8mA VCC = 1.8V, ISINK = 1mA TA = +25C TA = TMIN to TMAX TA = +25C TA = TMIN to TMAX TA = +25C TA = TMIN to TMAX TA = +25C TA = TMIN to TMAX 0.001 95 8 98 10 17 22 30 95 35 120 6 4 1.2 s s ms s s mA VCC = 5V VCC = 1.8V VCC = 5V VCC = 1.8V VCC = 1.8V VCC = 5V MAX919 only Low-to-High Propagation Delay (Note 4) tPD+ MAX920 only VCC = 1.8V VCC = 5V VCC = 1.8V RPULL-UP = 100k VCC = 5V RPULL-UP = 100k Rise Time Fall Time Power-Up Time tRISE tFALL tON MAX919 only, CL = 15pF CL = 15pF 55 190 55 CONDITIONS MIN TYP 10 0.1 0.5 190 1 3 400 500 200 300 400 500 200 300 1 A mV mV MAX UNITS pA mV/V mV/V
Output Voltage Swing High,
VCC - VOH
Output Voltage Swing Low
VOL
Output Leakage Current
ILEAK
MAX920 only, VO = 5.5V Sourcing, VO = VEE
Output Short-Circuit Current
ISC Sinking, VO = VCC
High-to-Low Propagation Delay (Note 4)
tPD-
Note 1: All specifications are 100% tested at TA = +25C. Specification limits over temperature (TA = TMIN to TMAX) are guaranteed by design, not production tested. Note 2: VOS is defined as the center of the hysteresis band at the input. Note 3: The hysteresis-related trip points are defined as the edges of the hysteresis band, measured with respect to the center of the band (i.e., VOS) (Figure 2). Note 4: Specified with an input overdrive (VOVERDRIVE) of 100mV, and load capacitance of CL = 15pF. VOVERDRIVE is defined above and beyond the offset voltage and hysteresis of the comparator input. For the MAX917/MAX918, reference voltage error should also be added.
4
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SOT23, 1.8V, Nanopower, Beyond-the-Rails Comparators With/Without Reference
Typical Operating Characteristics
(VCC = +5V, VEE = 0, CL = 15pF, VOVERDRIVE = 100mV, TA = +25C, unless otherwise noted.)
MAX917/MAX918 SUPPLY CURRENT vs. SUPPLY VOLTAGE AND TEMPERATURE
TA = +85C SUPPLY CURRENT (nA) 800 TA = +25C 700
MAX917-920 toc01
MAX917-MAX920
MAX919/MAX920 SUPPLY CURRENT vs. SUPPLY VOLTAGE AND TEMPERATURE
MAX917-920 toc02
MAX917/MAX918 SUPPLY CURRENT vs. TEMPERATURE
850 SUPPLY CURRENT (nA) 800 750 700 650 600 550 VCC = 3V VCC = 1.8V VCC = 5V
MAX917-920 toc03
900
600
900
SUPPLY CURRENT (nA)
TA = +85C 500 TA = +25C 400 TA = -40C
600
TA = -40C
500 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V)
300 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V)
500 -40 -15 10 35 60 85 TEMPERATURE (C)
MAX919/MAX920 SUPPLY CURRENT vs. TEMPERATURE
MAX917-920 toc04
MAX917/MAX918 SUPPLY CURRENT vs. OUTPUT TRANSITION FREQUENCY
MAX917-920 toc05
MAX919/MAX920 SUPPLY CURRENT vs. OUTPUT TRANSITION FREQUENCY
VCC = 5V
MAX917-920 toc06
550
16 14 SUPPLY CURRENT (A) 12 10 8 6 4 2 VCC = 1.8V 0 VCC = 3V VCC = 5V
14 12 SUPPLY CURRENT (A) 10 8 6 4 2 0 1 10 100 1k VCC = 1.8V 10k VCC = 3V
500 SUPPLY CURRENT (nA) VCC = 5V 450 VCC = 3V 400 VCC = 1.8V
350
300 -40 -15 10 35 60 85 TEMPERATURE (C)
1
10
100
1k
10k
100k
100k
OUTPUT TRANSITION FREQUENCY (Hz)
OUTPUT TRANSITION FREQUENCY (Hz)
OUTPUT VOLTAGE LOW vs. SINK CURRENT
MAX917-920 toc07
OUTPUT VOLTAGE LOW vs. SINK CURRENT AND TEMPERATURE
MAX917-920 toc08
MAX917/MAX919 OUTPUT VOLTAGE HIGH vs. SOURCE CURRENT
VCC = 1.8V VCC = 5V
MAX917-920 toc09
450 400 350 300 VOL (mV) 250 200 150 100 50 0 0 2 4 6 8 10 12 14 VCC = 5V VCC = 1.8V VCC = 3V
600 500 400 VOL (mV) 300 200 TA = -40C 100 0 TA = +85C TA = +25C
0.6 0.5
VCC = 3V VCC - VOH (V) 0.4 0.3 0.2 0.1 0
16
0
2
4
6
8
10
12
14
16
0
2
4
6
8
10 12 14 16 18 20
SINK CURRENT (mA)
SINK CURRENT (mA)
SOURCE CURRENT (mA)
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5
SOT23, 1.8V, Nanopower, Beyond-the-Rails Comparators With/Without Reference MAX917-MAX920
Typical Operating Characteristics (continued)
(VCC = +5V, VEE = 0, CL = 15pF, VOVERDRIVE = 100mV, TA = +25C, unless otherwise noted.)
MAX917/MAX919 OUTPUT VOLTAGE HIGH vs. SOURCE CURRENT AND TEMPERATURE
MAX917-920 toc10
SHORT-CIRCUIT SINK CURRENT vs. TEMPERATURE
MAX917-920 toc11
MAX917/MAX919 SHORT-CIRCUIT SOURCE CURRENT vs. TEMPERATURE
MAX917-920 toc12
0.6 0.5 0.4 0.3 0.2 0.1 0 0 2 4 6 8 TA = -40C TA = +85C TA = +25C
120 VCC = 5V 100 SINK CURRENT (mA) 80 60 VCC = 3V 40 20 0 VCC = 1.8V -40 -15 10 35 60
140 120 SOURCE CURRENT (mA) VCC = 5V 100 80 60 40 20 0 -40 -15 VCC = 3V
VCC - VOH (V)
VCC = 1.8V 10 35 60 85
10 12 14 16 18 20
85
SOURCE CURRENT (mA)
TEMPERATURE (C)
TEMPERATURE (C)
OFFSET VOLTAGE vs. TEMPERATURE
MAX917-920 toc13
HYSTERESIS VOLTAGE vs. TEMPERATURE
MAX917-920 toc14
MAX917/MAX918 REFERENCE VOLTAGE vs. TEMPERATURE
VCC = 5V REFERENCE VOLTAGE (V) 1.245 VCC = 3V 1.244 VCC = 1.8V 1.243
MAX917-920 toc15
0.10 0.09 0.08 VOS (mV) 0.07 VCC = 3V 0.06 0.05 VCC = 1.8V
5.0
1.246
4.5
VHB (mV)
4.0
3.5
3.0 0.04 0.03 -40 -15 10 35 VCC = 5V 60 85 2.5 -40 -15 10 35 60 85
1.242
1.241 -40
-15
10
35
60
85
TEMPERATURE (C)
TEMPERATURE (C)
TEMPERATURE (C)
MAX917/MAX918 REFERENCE VOLTAGE vs. SUPPLY VOLTAGE
MAX917-920 toc16
MAX917/MAX918 REFERENCE OUTPUT VOLTAGE vs. REFERENCE SOURCE CURRENT
MAX917-920 toc17
MAX917/MAX918 REFERENCE OUTPUT VOLTAGE vs. REFERENCE SINK CURRENT
VCC = 1.8V 1.2455
MAX917-920 toc18
1.2460
1.2440 VCC = 3V 1.2435 VCC = 1.8V
1.2460
REFERENCE VOLTAGE (V)
1.2455
VREF (V)
1.2450
1.2425 1.2445
VCC = 5V
VREF (V)
1.2430
1.2450
VCC = 3V
1.2445 VCC = 5V
1.2420
1.2440
1.2440 1.5
1.2415 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 0 1 2 3 4 5 6 7 8 9 10 SUPPLY VOLTAGE (V) SOURCE CURRENT (nA)
1.2435 0 1 2 3 4 5 6 7 8 9 10 SINK CURRENT (nA)
6
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SOT23, 1.8V, Nanopower, Beyond-the-Rails Comparators With/Without Reference
Typical Operating Characteristics (continued)
(VCC = +5V, VEE = 0, CL = 15pF, VOVERDRIVE = 100mV, TA = +25C, unless otherwise noted.)
PROPAGATION DELAY (tPD-) vs. TEMPERATURE
MAX917-920 toc19
MAX917-MAX920
MAX917-920 toc20
25 20 tPD- (s) 15 10 5 0 -40 -15 10 VCC = 3V
VCC = 1.8V VCC = 5V
120 100 tPD+ (s) 80 60 40 20 0 VCC = 1.8V VCC = 3V VCC = 5V
VCC = 1.8V 100 80 tPD- (s) 60 40 20 0 0.01 VCC = 3V
VCC = 5V
35
60
85
-40
-15
10
35
60
85
0.1
1
10
100
1000
TEMPERATURE (C)
TEMPERATURE (C)
CAPACITIVE LOAD (nF)
MAX917/MAX919 PROPAGATION DELAY (tPD+) vs. CAPACITIVE LOAD
MAX917-920 toc22
PROPAGATION DELAY (tPD-) vs. INPUT OVERDRIVE
VCC = 3V VCC = 1.8V
MAX917-920 toc23
140 120 tPD+ (s) 100 80 60 40 20 0 0.01 VCC = 1.8V VCC = 3V VCC = 5V
90 80 70
60 50 tPD- (s)
VCC = 5V
tPD+ (s)
60 50 40 VCC = 3V
40 30 20 10 VCC = 5V
30 20 10 0
VCC = 1.8V
0.1
1
10
100
1000
0
10
20
30
40
50
0
10
20
30
40
50
CAPACITIVE LOAD (nF)
INPUT OVERDRIVE (mV)
INPUT OVERDRIVE (mV)
MAX918/MAX920 PROPAGATION DELAY (tPD-) vs. PULL-UP RESISTANCE
MAX917-920 toc25
MAX918/MAX920 PROPAGATION DELAY (tPD+) vs. PULL-UP RESISTANCE
MAX917-920 toc26
PROPAGATION DELAY (tPD-) (VCC = 5V)
MAX917-920 toc27
20 VCC = 1.8V 19 18 tPD- (s) 17 16 15 14 10 100 RPULL-UP (k) 1k VCC = 5V
250
200
tPD- (s)
VCC = 3V
150
VCC = 5V
100
VCC = 3V
50 VCC = 1.8V 0 10k 10 100 RPULL-UP (k) 1k 10k 20s/div
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7
MAX917-920 toc24
160
70
100
MAX917/MAX919 PROPAGATION DELAY (tPD+) vs. INPUT OVERDRIVE
MAX917-920 toc21
30
140
MAX917/MAX919 PROPAGATION DELAY (tPD+) vs. TEMPERATURE
120
PROPAGATION DELAY (tPD-) vs. CAPACITIVE LOAD
IN+ (50mV/ div)
OUT (2V/div)
SOT23, 1.8V, Nanopower, Beyond-the-Rails Comparators With/Without Reference MAX917-MAX920
Typical Operating Characteristics (continued)
(VCC = +5V, VEE = 0, CL = 15pF, VOVERDRIVE = 100mV, TA = +25C, unless otherwise noted.)
MAX917/MAX919 PROPAGATION DELAY (tPD+) (VCC = 5V)
MAX917-920 toc28
PROPAGATION DELAY (tPD-) (VCC = 3V)
MAX917-920 toc29
MAX917/MAX919 PROPAGATION DELAY (tPD+) (VCC = 3V)
MAX917-920 toc30
IN+ (50mV/ div)
IN+ (50mV/ div)
IN+ (50mV/ div)
OUT (2V/div)
OUT (2V/div)
OUT (2V/div)
20s/div
20s/div
20s/div
PROPAGATION DELAY (tPD-) (VCC = 1.8V)
MAX917-920 toc31
MAX917/MAX919 PROPAGATION DELAY (tPD+) (VCC = 1.8V)
MAX917-920 toc32
MAX917/MAX919 10kHz RESPONSE (VCC = 1.8V)
MAX917-920 toc33
IN+ (50mV/ div)
IN+ (50mV/ div)
IN+ (50mV/ div)
OUT (1V/div)
OUT (1V/div)
OUT (1V/div)
20s/div
20s/div
20s/div
MAX917/MAX919 1kHz RESPONSE (VCC = 5V)
MAX917-920 toc34
POWER-UP/DOWN RESPONSE
MAX917-920 toc35
IN+ (50mV/div)
VCC (2V/div)
OUT (2V/div)
OUT (2V/div)
200s/div
40s/div
8
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SOT23, 1.8V, Nanopower, Beyond-the-Rails Comparators With/Without Reference
Functional Diagrams
MAX917-MAX920
VCC
VCC
IN+ OUT REF
IN+ OUT IN-
MAX917 MAX918
REF 1.245V VEE VEE
MAX919 MAX920
Pin Description
PIN MAX917/MAX918 SOT23-5 1 2 3 -- 4 5 -- SO 6 4 3 -- 2 7 1, 5, 8 MAX919/MAX920 SOT23-5 1 2 3 4 -- 5 -- SO 6 4 3 2 -- 7 1, 5, 8 OUT VEE IN+ INREF VCC N.C. Comparator Output Negative Supply Voltage Comparator Noninverting Input Comparator Inverting Input 1.245V Reference Output and Comparator Inverting Input Positive Supply Voltage No Connection. Not internally connected. NAME FUNCTION
Detailed Description
The MAX917/MAX918 feature an on-board 1.245V 1.5% reference, yet draw an ultra-low supply current of 750nA. The MAX919/MAX920 (without reference) consume just 380nA of supply current. All four devices are guaranteed to operate down to +1.8V. Their common-mode input voltage range extends 200mV beyond-the-rails. Internal hysteresis ensures clean output switching, even with slow-moving input signals. Large internal output drivers allow rail-to-rail output swing with up to 8mA loads. The output stage employs a unique design that minimizes supply-current surges while switching, virtually eliminating the supply glitches typical of many other comparators. The MAX917/MAX919 have a push/pull
output stage that sinks as well as sources current. The MAX918/MAX920 have an open-drain output stage that can be pulled beyond VCC to an absolute maximum of 6V above VEE. These open-drain versions are ideal for implementing wire-Or output logic functions.
Input Stage Circuitry
The input common-mode voltage range extends from VEE - 0.2V to VCC + 0.2V. These comparators operate at any differential input voltage within these limits. Input bias current is typically 0.15nA if the input voltage is between the supply rails. Comparator inputs are protected from overvoltage by internal ESD protection diodes connected to the supply rails. As the input voltage exceeds the supply rails, these ESD protection diodes become forward biased and begin to conduct.
9
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SOT23, 1.8V, Nanopower, Beyond-the-Rails Comparators With/Without Reference MAX917-MAX920
Output Stage Circuitry
The MAX917-MAX920 contain a unique break-beforemake output stage capable of rail-to-rail operation with up to 8mA loads. Many comparators consume orders of magnitude more current during switching than during steady-state operation. However, with this family of comparators, the supply-current change during an output transition is extremely small. In the Typical Operating Characteristics, the Supply Current vs. Output Transition Frequency graphs show the minimal supplycurrent increase as the output switching frequency approaches 1kHz. This characteristic reduces the need for power-supply filter capacitors to reduce glitches created by comparator switching currents. In batterypowered applications, this characteristic results in a substantial increase in battery life.
VCC
120nA REF
VEE
Figure 1. MAX917/MAX918 Voltage Reference Output Equivalent Circuit
Reference (MAX917/MAX918)
The internal reference in the MAX917/MAX918 has an output voltage of +1.245V with respect to VEE. Its typical temperature coefficient is 95ppm/C over the full -40C to +85C temperature range. The reference is a PNP emitter-follower driven by a 120nA current source (Figure 1). The output impedance of the voltage reference is typically 200k, preventing the reference from driving large loads. The reference can be bypassed with a low-leakage capacitor. The reference is stable for any capacitive load. For applications requiring a lower output impedance, buffer the reference with a low-input-leakage op amp, such as the MAX406.
Internal Hysteresis
Many comparators oscillate in the linear region of operation because of noise or undesired parasitic feedback. This tends to occur when the voltage on one input is equal or very close to the voltage on the other input. The MAX917-MAX920 have internal hysteresis to counter parasitic effects and noise. The hysteresis in a comparator creates two trip points: one for the rising input voltage (VTHR) and one for the falling input voltage (VTHF) (Figure 2). The difference between the trip points is the hysteresis (VHB). When the comparator's input voltages are equal, the hysteresis effectively causes one comparator input to move quickly past the other, thus taking the input out of the region where oscillation occurs. Figure 2 illustrates the case in which IN- has a fixed voltage applied, and IN+ is varied. If the inputs were reversed, the figure would be the same, except with an inverted output.
Applications Information
Low-Voltage, Low-Power Operation
The MAX917-MAX920 are ideally suited for use with most battery-powered systems. Table 1 lists a variety of battery types, capacities, and approximate operating times for the MAX917-MAX920, assuming nominal conditions.
Table 1. Battery Applications Using MAX917-MAX920
BATTERY TYPE Alkaline (2 Cells) Nickel-Cadmium (2 Cells) Lithium-Ion (1 Cell) Nickel-MetalHydride (2 Cells) 10 RECHARGEABLE VFRESH (V) 3.0 2.4 3.5 VEND-OF-LIFE (V) 1.8 1.8 2.7 CAPACITY, AA SIZE (mA-h) 2000 750 1000 MAX917/MAX918 OPERATING TIME (hr) 2.5 x 106 937,500 1.25 x 106 MAX919/MAX920 OPERATING TIME (hr) 5 x 106 1.875 x 106 2.5 x 106
No Yes Yes
Yes
2.4
1.8
1000
1.25 x 106
2.5 x 106
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SOT23, 1.8V, Nanopower, Beyond-the-Rails Comparators With/Without Reference MAX917-MAX920
IN+ VTHR INVHB VTHF HYSTERESIS BAND R2 VEE VIN VCC OUT THRESHOLDS VCC R3
R1
VREF OUT
MAX917 MAX919
Figure 2. Threshold Hysteresis Band
Figure 3. MAX917/MAX919 Additional Hysteresis
Additional Hysteresis (MAX917/MAX919)
The MAX917/MAX919 have a 4mV internal hysteresis band (VHB). Additional hysteresis can be generated with three resistors using positive feedback (Figure 3). Unfortunately, this method also slows hysteresis response time. Use the following procedure to calculate resistor values. 1) Select R3. Leakage current at IN is under 2nA, so the current through R3 should be at least 0.2A to minimize errors caused by leakage current. The current through R3 at the trip point is (VREF - VOUT)/R3. Considering the two possible output states in solving for R3 yields two formulas: R3 = VREF/IR3 or R3 = (VCC - VREF)/IR3. Use the smaller of the two resulting resistor values. For example, when using the MAX917 (VREF = 1.245V) and VCC = 5V, and if we choose IR3 = 1A, then the two resistor values are 1.2M and 3.8M. Choose a 1.2M standard value for R3. 2) Choose the hysteresis band required (VHB). For this example, choose 50mV. 3) Calculate R1 according to the following equation: R1 = R3 (VHB / VCC) For this example, insert the values R1 = 1.2M (50mV/5V) = 12k 4) Choose the trip point for VIN rising (VTHR) such that VTHR > VREF * (R1 + R3)/R3 (VTHF is the trip point for VIN falling). This is the threshold voltage at which the comparator switches its output from low to high as V IN rises above the trip point. For this example, choose 3V. 5) Calculate R2 as follows: R2 = 1/[VTHR/(VREF * R1) - (1 / R1) - (1 / R3)]
R2 = 1/[3.0V/(1.2V * 12k) - (1 / 12k) (1/1.2M)] = 8.05k For this example, choose an 8.2k standard value. 6) Verify the trip voltages and hysteresis as follows: VIN rising: VTHR = VREF * R1 [(1 / R1) + (1 / R2) + (1 / R3)] VIN falling: VTHF = VTHR - (R1 * VCC / R3) Hysteresis = VTHR - VTHF
Additional Hysteresis (MAX918/MAX920)
The MAX918/MAX920 have a 4mV internal hysteresis band. They have open-drain outputs and require an external pull-up resistor (Figure 4). Additional hysteresis can be generated using positive feedback, but the formulas differ slightly from those of the MAX917/ MAX919. Use the following procedure to calculate resistor values. 1) Select R3 according to the formulas R3 = VREF / 1A or R3 = (VCC - VREF)/1A - R4. Use the smaller of the two resulting resistor values. 2) Choose the hysteresis band required (VHB). 3) Calculate R1 according to the following equation: R1 = (R3 + R4) (VHB/VCC) 4) Choose the trip point for VIN rising (VTHR) (VTHF is the trip point for VIN falling). This is the threshold voltage at which the comparator switches its output from low to high as VIN rises above the trip point. 5) Calculate R2 as follows: 1 1 R2 = 1/ VTHR / VREF R1 - - R1 R3
(
)
______________________________________________________________________________________
11
SOT23, 1.8V, Nanopower, Beyond-the-Rails Comparators With/Without Reference MAX917-MAX920
6) Verify the trip voltages and hysteresis as follows: VIN rising:VTHR = VREF VIN falling:VTHF = VREF
Zero-Crossing Detector
Figure 5 shows a zero-crossing detector application. The MAX919's inverting input is connected to ground, and its noninverting input is connected to a 100mVp-p signal source. As the signal at the noninverting input crosses 0V, the comparator's output changes state.
R1
1
1 1 1 + + R1 R2 R3
R1
1
R1 R2
+
1
+
R1 - R3 + R4 R3 + R4
VCC
Logic-Level Translator
The Typical Application Circuit shows an application that converts 5V logic to 3V logic levels. The MAX920 is powered by the +5V supply voltage, and the pull-up resistor for the MAX920's open-drain output is connected to the +3V supply voltage. This configuration allows the full 5V logic swing without creating overvoltage on the 3V logic inputs. For 3V to 5V logic-level translations, simply connect the +3V supply voltage to VCC and the +5V supply voltage to the pull-up resistor.
VCC
Hysteresis = VTHR - VTHF
Board Layout and Bypassing
Power-supply bypass capacitors are not typically needed, but use 100nF bypass capacitors close to the device's supply pins when supply impedance is high, supply leads are long, or excessive noise is expected on the supply lines. Minimize signal trace lengths to reduce stray capacitance. A ground plane and surface-mount components are recommended.
VCC R3
100mVp-p IN+
VCC
OUT R1 VIN VCC R2 VEE OUT VEE R4 IN-
MAX919
VREF
MAX918 MAX920
Figure 5. Zero-Crossing Detector Figure 4. MAX918/MAX920 Additional Hysteresis
Typical Application Circuit
+5V (+3V) +3V (+5V)
Pin Configurations (continued)
TOP VIEW
100k IN-
VCC
RPULL-UP 3V (5V) LOGIC OUT
N.C. 1 IN- (REF) 2 IN+ 3 VEE 4
8
N.C. VCC OUT N.C.
VEE 100k IN+
OUT
MAX917 MAX918 MAX919 MAX920
7 6 5
MAX920
SO
( ) ARE FOR MAX917/MAX918.
5V (3V) LOGIC IN
LOGIC LEVEL TRANSLATOR
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.
12 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 1999 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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