MAX923CUA-T_技术文档

19-0115; Rev 6; 4/09

Ultra Low-Power,

Single/Dual-Supply Comparators

_______________General Description

____________________________Features

♦ µMAX^®Package—Smallest 8-Pin SO

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

1ꢀ voltage reference, programmable hysteresis, and

TTL/CMOS outputs that sink and source current.

(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

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.

♦ Input Voltage Range Includes Negative Supply

♦ Internal 1.182V 1ꢀ ꢁandgap Reꢂerence

♦ Adjustable Hysteresis

♦ TTL/CMOS-Compatible Outputs

The MAX921–MAX924’s unique output stage con-

tinuously sources as much as 40mA. And by eliminating

power-supply glitches that commonly occur when com-

parators change logic states, the MAX921–MAX924

minimize parasitic feedback, which makes them easier to

use.

♦ 12µs Propagation Delay (10mV Overdrive)

♦ No Switching Crowbar Current

♦ 40mA Continuous Source Current

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.

Ordering Information

PART

TEMP RANGE

0°C to +70°C

-40°C to +85°C

-55°C to +125°C

PIN-PACKAGE

8 Plastic DIP

8 SO

MAX921CPA

MAX921CSA

MAX921CUA

MAX921C/D

MAX921EPA

MAX921ESA

MAX921MJA

8 µMAX

Dice*

8 Plastic DIP

8 SO

8 CERDIP

Ordering Information continued at end of data sheet.

*Dice are tested at T = +25°C, DC parameters only.

**Contact factory for availability.

A

8-Pin

DIP/SO/µMAX

MAX921

MAX922

MAX923

MAX924

Yes

No

1

2

4

Yes

No

__________Typical Operating Circuit

8-Pin

DIP/SO/µMAX

V

IN

8-Pin

DIP/SO/µMAX

Yes

No

7

V+

16-Pin

DIP/SO/µMAX

3

IN+

OUT 8

4 IN-

________________________Applications

HYST

5

Battery-Powered Systems

Threshold Detectors

Window Comparators

Oscillator Circuits

MAX921

6 REF

GND

1

V-

2

THRESHOLD DETECTOR

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

________________________________________________________________ Maxim Integrated Products

1

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.

Ultra Low-Power,

Single/Dual-Supply Comparators

AꢁSOLUTE MAXIMUM RATINGS

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

Inputs

Continuous Power Dissipation (T = +70°C)

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

A

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

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, T = T

A

to T

, unless otherwise noted.)

MIN

MAX

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

POWER REQUIREMENTS

Supply Voltage Range

(Note 1)

2.5

11

3.2

4

V

T

= +25°C

2.5

3.1

5.5

A

MAX921,

HYST = REF

C/E temp. ranges

M temp. range

5

T

A

= +25°C

3.2

4

MAX922

C/E temp. ranges

M temp. range

5

Supply Current

IN+ = IN- + 100mV

µA

T

A

= +25°C

4.5

6

MAX923,

HYST = REF

C/E temp. ranges

M temp. range

7.5

6.5

8.5

11

T

A

= +25°C

MAX924

C/E temp. ranges

M temp. range

COMPARATOR

Input Offset Voltage

V

= 2.5V

10

5

mV

nA

CM

C/E temp. ranges

M temp. range

0.01

0.02

Input Leakage Current (IN-, IN+)

Input Leakage Current (HYST)

IN+ = IN- = 2.5V

MAX921, MAX923

40

nA

V

Input Common-Mode Voltage Range

Common-Mode Rejection Ratio

Power-Supply Rejection Ratio

Voltage Noise

V-

V+ – 1.3

1.0

V- to (V+ – 1.3V)

V+ = 2.5V to 11V

100Hz to 100kHz

MAX921, MAX923

0.1

20

mV/V

1.0

µV

RMS

V

Hysteresis Input Voltage Range

REF- 0.05V

REF

Overdrive = 10mV

Overdrive = 100mV

12

4

Response Time

T

A

= +25°C, 100pF load

µs

2

_______________________________________________________________________________________

Ultra Low-Power,

Single/Dual-Supply Comparators

ELECTRICAL CHARACTERISTICS: 5V OPERATION (continued)

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

A

to T

, unless otherwise noted.)

MIN

MAX

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

C/E temp. ranges: I

= 17mA;

= 10mA

OUT

Output High Voltage

MAX92_

V+ – 0.4

V

M temp. range: I

OUT

MAX922/ C/E temp. ranges: I

MAX923 M temp. range: I

= 1.8mA;

= 1.2mA

V- + 0.4

OUT

Output Low Voltage

V

MAX921/ C/E temp. ranges: I

MAX924 M temp. range: I

= 1.8mA;

= 1.2mA

GND + 0.4

OUT

XREFERENCE (MAX921/MAX923/MAX924 ONLY)

C temp. range

E temp. range

M temp. range

1.170

1.182

25

1.194

1.206

1.217

Reference Voltage

1.158

V

1.147

T

A

= +25°C

15

6

Source Current

Sink Current

C/E temp. ranges

M temp. range

µA

4

T

A

= +25°C

8

15

C/E temp. ranges

M temp. range

4

2

Voltage Noise

100Hz to 100kHz

100

µV

RMS

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, T = T

A

to T

, unless otherwise noted.)

MIN

MAX

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

POWER REQUIREMENTS

T

= +25°C

2.4

3.0

3.8

4.8

3.0

3.8

4.8

4.3

5.8

7.2

6.2

8.0

10.5

A

MAX921 C/E temp. ranges

M temp. range

T

A

= +25°C

2.4

3.4

5.2

MAX922 C/E temp. ranges

M temp. range

HYST = REF,

IN+ = (IN- + 100mV)

Supply Current

µA

T

A

= +25°C

MAX923

C/E temp. ranges

M temp. range

T

A

= +25°C

MAX924 C/E temp. ranges

M temp. range

COMPARATOR

Input Offset Voltage

V

= 1.5V

10

mV

nA

CM

C/E temp. ranges

M temp. range

0.01

0.02

5

Input Leakage Current (IN-, IN+)

Input Leakage Current (HYST)

IN+ = IN- = 1.5V

MAX921, MAX923

40

_______________________________________________________________________________________

3

Ultra Low-Power,

Single/Dual-Supply Comparators

ELECTRICAL CHARACTERISTICS: 3V OPERATION (continued)

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

A

to T

, unless otherwise noted.)

MIN

MAX

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

Input Common-Mode Voltage Range

Common-Mode Rejection Ratio

Power-Supply Rejection Ratio

Voltage Noise

V-

V+ – 1.3

V

V- to (V+ – 1.3V)

V+ = 2.5V to 11V

100Hz to 100kHz

MAX921, MAX923

0.2

0.1

20

1

mV/V

µV

RMS

Hysteresis Input Voltage Range

REF- 0.05V

V+ – 0.4

REF

V

Overdrive = 10mV

Overdrive = 100mV

14

5

Response Time

T

A

= +25°C, 100pF load

µs

V

C/E temp. ranges: I

M temp. range: I

= 10mA;

= 6mA

OUT

Output High Voltage

MAX92_

OUT

MAX922/ C/E temp. ranges: I

MAX923 M temp. range: I

= 0.8mA;

= 0.6mA

V- + 0.4

OUT

Output Low Voltage

V

MAX921/ C/E temp. ranges: I

MAX924 M temp. range: I

= 0.8mA;

GND + 0.4

= 0.6mA

OUT

REFERENCE

C temp. range

E temp. range

M temp. range

1.170

1.182

25

1.194

1.206

1.217

Reference Voltage

1.158

V

1.147

T

A

= +25°C

15

6

Source Current

C/E temp. ranges

M temp. range

µA

4

T

A

= +25°C

8

15

Sink Current

C/E temp. ranges

M temp. range

4

2

Voltage Noise

100Hz to 100kHz

100

µV

RMS

Typical Operating Characteristics

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

A

OUTPUT VOLTAGE LOW

vs. LOAD CURRENT

OUTPUT VOLTAGE HIGH vs.

LOAD CURRENT

REFERENCE OUTPUT VOLTAGE vs.

OUTPUT LOAD CURRENT

2.5

2.0

5.0

1.190

V+ = 5V

SINK

V+ = 5V

4.5

4.0

1.185

1.180

V+ = 3V

SOURCE

1.5

1.0

3.5

3.0

2.5

2.0

1.5

1.175

1.170

1.165

1.160

1.155

V+ = 3V

V+ = 5V

OR

0.5

0.0

V+ = 3V

0

4

8

12

16

20

0

10

20

30

40

50

0

5

10

15

20

25

30

LOAD CURRENT (mA)

OUTPUT LOAD CURRENT (μA)

4

_______________________________________________________________________________________

Ultra Low-Power,

Single/Dual-Supply Comparators

Typical Operating Characteristics (continued)

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

A

MAX921

SUPPLY CURRENT vs.

TEMPERATURE

REFERENCE VOLTAGE

vs. TEMPERATURE

MAX922

SUPPLY CURRENT vs. TEMPERATURE

1.22

1.21

4.5

4.0

4.5

4.0

IN+ = (IN- + 100mV)

V+ = 10V, V- = 0V

IN+ = (IN- + 100mV)

MILITARY TEMP. RANGE

EXTENDED TEMP. RANGE

1.20

1.19

3.5

3.0

2.5

2.0

1.5

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

COMMERCIAL

TEMP. RANGE

3.5

3.0

1.18

1.17

V+ = 3V, V- = 0V

V+ = 5V, V- = 0V

V+ = 3V, V- = 0V

1.16

1.15

2.5

2.0

V+ = 5V, V- = 0V

1.14

-60 -40 -20

0

20 40 60 80 100 120 140

-60

-20

20

60

100

140

-60

-20

20

60

100

140

TEMPERATURE (°C)

MAX924

SUPPLY CURRENT vs.

LOW SUPPLY VOLTAGES

MAX924

MAX923

SUPPLY CURRENT vs. TEMPERATURE

10

9

5.0

10

IN+ = (IN- + 100mV)

4.5

4.0

8

1

V+ = 5V, V- = 0V

7

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

3.5

3.0

2.5

2.0

6

0.1

V+ = 5V, V- = 0V

V+ = 3V, V- = 0V

5

4

V+ = 3V, V- = 0V

3

0.01

-60

-20

20

60

100

140

-60

-20

20

60

100

140

1.0

1.5

2.0

2.5

TEMPERATURE (°C)

SINGLE-SUPPLY VOLTAGE (V)

RESPONSE TIME vs.

LOAD CAPACITANCE

TRANSFER FUNCTION

HYSTERESIS CONTROL

5.0

4.5

80

60

18

16

V- = 0V

100k

V

0

OUTPUT HIGH

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0

10μF

40

20

14

12

V

OHL

NO CHANGE

10

8

0

-20

V

OLH

-40

-60

6

4

OUTPUT LOW

10

-80

2

-0.3

-0.1

0.1

0.2

0.3

0

20

-V

30

(mV)

40

50

-0.2

0

20

40

60

80

100

IN+ INPUT VOLTAGE (mV)

V

LOAD CAPACITANCE (nF)

REF HYST

_______________________________________________________________________________________

5

Ultra Low-Power,

Single/Dual-Supply Comparators

Typical Operating Characteristics (continued)

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

A

RESPONSE TIME FOR VARIOUS

INPUT OVERDRIVES

RESPONSE TIME FOR VARIOUS

INPUT OVERDRIVES

MAX924 RESPONSE TIME

AT LOW SUPPLY VOLTAGES

10

5

4

3

4

3

100mV

50mV

10mV

1

20mV

100mV

2

1

2

1

20mV

50mV

10mV

0

100

0

20mV OVERDRIVE

0.1

100mV

OVERDRIVE

0

100

0.01

-2

2

6

10

14

18

1.0

1.5

2.0

2.5

-2

2

6

10

14

18

RESPONSE TIME (μs)

SINGLE-SUPPLY VOLTAGE (V)

RESPONSE TIME (μs)

SHORT-CIRCUIT SOURCE CURRENT

vs. SUPPLY VOLTAGE

SHORT-CIRCUIT SINK CURRENT

vs. SUPPLY VOLTAGE

MAX924 RESPONSE TIME

AT LOW SUPPLY VOLTAGES

200

100

OUT CONNECTED TO V+

GND CONNECTED TO V-

180

160

140

120

100

80

OUT CONNECTED TO V-

SOURCE CURRENT INTO 0.75V LOAD

20

10

1

10

0

60

40

20

SINK CURRENT AT V

1.5

= 0.4V

2.0

OUT

0

0.1

0

1.0

2.0

3.0

4.0

5.0

0

5

10

1.0

2.5

TOTAL SUPPLY VOLTAGE (V)

SINGLE-SUPPLY VOLTAGE (V)

____________________________________________________________Pin Descriptions

NAME

FUNCTION

MAX921 MAX922 MAX923

1

–

2

3

–

4

–

1

2

–

3

–

4

–

1

2

–

3

–

GND

OUTA

V-

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

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

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

Noninverting comparator input

IN+

INA+

IN-

Noninverting input of comparator A

Inverting comparator input

INA-

Inverting input of comparator A

6

_______________________________________________________________________________________

Ultra Low-Power,

Single/Dual-Supply Comparators

_______________________________________________Pin Descriptions (continued)

NAME

FUNCTION

MAX921 MAX922 MAX923

–

5

–

4

5

INB-

Inverting input of comparator B

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

5

HYST

V

REF

to V - 50mV.

REF

6

–

7

8

–

6

7

–

8

6

–

7

–

8

REF

INB+

V+

Reference output. 1.182V with respect to V-.

Noninverting input of comparator B

Positive supply

OUT

OUTB

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

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

MAX924

NAME

FUNCTION

1

2

OUTB

OUTA

V+

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

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

Positive supply

3

4

INA-

INA+

INB-

INB+

REF

Inverting input of comparator A

5

Noninverting input of comparator A

6

Inverting input of comparator B

7

Noninverting input of comparator B

8

Reference output. 1.182V with respect to V-.

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

Inverting input of comparator C

9

V-

10

11

12

13

14

15

16

INC-

INC+

IND-

IND+

GND

OUTD

OUTC

Noninverting input of comparator C

Inverting input of comparator D

Noninverting input of comparator D

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

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

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

_______________________________________________________________________________________

7

Ultra Low-Power,

Single/Dual-Supply Comparators

separate ground for the output driver, allowing

_______________Detailed Description

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.

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.

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.

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.

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.

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.

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

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

OUTA

OUTB 8

1

2 V-

V+ 7

INB+ 6

INB- 5

MAX924

1

2

OUTC 16

OUTD 15

OUTB

OUTA

INA+

3

4 INA-

3 V+

GND 14

IND+ 13

IND- 12

INA-

4

Figure 1a. MAX922 Functional Diagram

5 INA+

INB-

6

INC+ 11

INC- 10

V- 9

MAX923

OUTA

OUTB 8

1

7 INB+

2 V-

V+ 7

REF 6

8

REF

INA+

3

4 INB-

HYST 5

V-

Figure 1c. MAX924 Functional Diagram

Figure 1b. MAX923 Functional Diagram

8

_______________________________________________________________________________________

Ultra Low-Power,

Single/Dual-Supply Comparators

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.

THRESHOLDS

IN+

HYSTERESIS

BAND

IN-

VREF - VHYST

V

HB

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 1ꢀ 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

Noise Considerations

Although the comparators have a very high gain, useful

gain is limited by noise. This is shown in the Transfer

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 sig-

nificantly below 2.5V.

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 V_IN= V_OS. (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

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.

2.5V TO 11V

7

I

6

5

REF

V+

REF

Comparator Output

With 100mV of overdrive, propagation delay is typically

3µs. The Typical Operating Characteristics show the

propagation delay for various overdrive levels.

R1

R2

MAX921

MAX923

HYST

V-

2

The MAX921 and MAX924 output swings from V+ to

GND, so TTL compatibility is assured by using a +5V

10ꢀ supply. The negative supply does not affect the

output swing, and can range from 0V to -5V 10ꢀ.

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.

Figure 3. Programming the HYST Pin

_______________________________________________________________________________________

9

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.

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.

__________Applications Information

2. Choose the hysteresis voltage (V_HB), the voltage

between the upper and lower thresholds. In this

example, choose V_HB= 50mV.

Hysteresis

Hysteresis increases the comparators’ noise margin by

increasing the upper threshold and decreasing the

lower threshold (see Figure 2).

3. Calculate R1.

V

V +

HB

R1 = R3 ×

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, V_HB) 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:

0.05

5

= 10M ×

=

100k

Ω

4. Choose the threshold voltage for V_INrising (V_THR).

In this example, choose V_THR= 3V.

5. Calculate R2.

1

R2 =

⎡

⎢

⎤

⎥

⎛

⎞

V

1

THR

−

⎜

⎟

(V

R1 R3

⎢

⎝

⎣

⎥

⎦

REF × R1)

⎠

1

=

⎡

⎢

⎤

⎥

⎛

⎞

3

1

−

V

⎜

⎟

HB

R1 =

(1.182 × 100k)

100k 10M

⎝

⎢

⎣

⎠

⎥

⎦

2 × I

(

)

REF

= 65.44kΩ

V

⎛

⎞

⎟

HB

2 ⎠

A 1ꢀ preferred value is 64.9kΩ.

1.182 –

⎜

⎝

R2 =

I

REF

V+

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_REFvalues between 0.1µA and 4µA are

R3

R1

V

IN

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

=

0.5µA), the equation for R1 and V_HBcan be

approximated as:

V+ OUT

V-

R2

MAX924

GND

R1 (kΩ) = V (mV)

HB

When hysteresis is obtained in this manner for the

MAX923, the same hysteresis applies to both comparators.

V

REF

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

Figure 4. External Hysteresis

10 ______________________________________________________________________________________

Ultra Low-Power,

Single/Dual-Supply Comparators

_______________Typical Applications

MOMENTARY

SWITCH

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 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.

4.5V TO 6.0V

7

V+

MAX921

IN+ 3

6

REF

47k

R

C

5

HYST

1.1M

100k

OUT 8

VBATT -0.15V

10mA

4 IN-

The RC time constant determines the maximum power-

on time of the OUT pin before power-down occurs.

This period can be approximated by:

V-

GND

1

2

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.

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

current.

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 active-

high, power-good signal.

6. Verify the threshold voltages with these formulas:

V

rising:

IN

1

R1

1

R2

1

R3

⎛

⎞

V

= V

× R1 ×

+

⎜

⎝

⎟

⎠

THR

REF

V

falling:

IN

R1 × V +

(

−

THR

)

V

= V

THF

R3

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= V_HB/2). This means that the

hysteresis apparent at V_INwill be larger because of

the input resistor divider.

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.

______________________________________________________________________________________ 11

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

V

= 5.5V

= 4.5V

V

OTH

UTH

IN

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.

+5V

V+

R3

INA+

3. Calculate R2 + R3. The overvoltage threshold

should be 5.5V when V_INis rising. The design

equation is as follows:

OUTA

UNDERVOLTAGE

POWER GOOD

HYST

REF

⎛

⎞

V

OTH

+ V

H

R2 + R3 = R1 ×

− 1

⎟

10k

R5

⎜

V

⎝

⎠

R2

REF

⎛

⎞

5.5

(1.182 + 0.005)

= 294k ×

− 1

R4

2.4M

⎜

⎟

⎝

⎠

OUTB

OVERVOLTAGE

= 1.068MΩ

INB-

V-

4. Calculate R2. The undervoltage threshold should

be 4.5V when V_INis falling. The design equation is

as follows:

MAX923

R1

(V

− V )

REF

V

H

R2 = (R1 + R2 + R3) ×

− R1

UTH

(1.182 − 0.005)

= (294k + 1.068M) ×

= 62.2kΩ

− 294k

Figure 6. Window Detector

4.5

Choose R2 = 61.9kΩ (1ꢀ standard value).

Bar-Graph Level Gauge

5. Calculate R3.

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.

R3 = (R2 + R3) − R2

= 1.068M − 61.9k

The full-scale threshold (all LEDs on) is given by V_IN

=

(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.

= 1.006MΩ

Choose R3 = 1MΩ (1ꢀ standard value)

6. Verify the resistor values. The equations are as

follows, evaluated for the above example.

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 :

(R1 + R2 + R3)

V

= (V

+ V ) ×

OTH

REF H

R1

= 5.474V.

Undervoltage threshold :

(R1 + R2 + R3)

V

= (V

− V ) ×

UTH

REF H

(R1 + R2)

= 4.484V,

R5

R4

where the hysteresis voltage V = V

×

REF

.

H

12 ______________________________________________________________________________________

Ultra Low-Power,

Single/Dual-Supply Comparators

R2

R1

V

IN

+5V

V+

+5V

3

V+

MAX924

10k

MAX924

INA+

1.182V

8

5

REF

V

INA

OUTA

0 FOR V < 0V

INA

V-

9

2

1 FOR V > 0V

INB

INA-

INB+

INB-

INA+

182k

250k

OUTA

OUTB

OUTC

OUTD

330Ω

1V

4

INA-

INB+

INB-

V

INB

INC

IND

OUTB

OUTC

7

1

10k

INC+

INC-

IND+

IND-

750mV

6

V

INC+

11

16

15

500mV 10 INC-

OUTD

REF

13

IND+

250k

N.C.

250mV 12 IND-

V-

GND

14

-5V

Figure 7. Bar-Graph Level Gauge

Figure 8. Level Shifter: 5V Input to CMOS Output

______________________________________________________________________________________ 13

Ultra Low-Power,

Single/Dual-Supply Comparators

_________________Pin Configurations

_Ordering Information (continued)

PART

TEMP RANGE

-55°C to +125°C

0°C to +70°C

PIN-PACKAGE

TOP VIEW

MAX921MSA/PR

MAX921MSA/PR-T

MAX922CPA

MAX922CSA

MAX922CUA

MAX922C/D

8 SO**

1

2

3

4

8

7

6

5

8 SO**

GND

V-

OUT

V+

8 Plastic DIP

8 SO

MAX921

0°C to +70°C

REF

IN+

IN-

0°C to +70°C

8 µMAX

HYST

0°C to +70°C

Dice*

DIP/SO/μMAX

MAX922EPA

-40°C to +85°C

-55°C to +125°C

0°C to +70°C

8 Plastic DIP

8 SO

MAX922ESA

MAX922MJA

MAX922MSA/PR

MAX922MSA/PR-T

MAX923CPA

MAX923CSA

MAX923CUA

MAX923C/D

8 CERDIP**

8 SO**

1

2

3

4

8

7

6

5

OUTA

V-

OUTB

V+

8 SO**

MAX922

INB+

INB-

INA+

INA-

8 Plastic DIP

8 SO

0°C to +70°C

8 µMAX

DIP/SO/μMAX

0°C to +70°C

Dice*

MAX923EPA

-40°C to +85°C

-55°C to +125°C

0°C to +70°C

8 Plastic DIP

8 SO

MAX923ESA

1

2

3

4

8

7

6

5

OUTA

V-

OUTB

V+

MAX923MJA

MAX923MSA/PR

MAX923MSA/PR-T

MAX924CPE

MAX924CSE

8 CERDIP**

8 SO**

MAX923

REF

INA+

INB-

8 SO**

HYST

16 Plastic DIP

16 Narrow SO

Dice*

0°C to +70°C

DIP/SO/μMAX

MAX924C/D

0°C to +70°C

MAX924EPE

-40°C to +85°C

-55°C to +125°C

16 Plastic DIP

16 Narrow SO

16 CERDIP**

16 Narrow SO**

OUTB

OUTA

V+

OUTC

OUTD

GND

IND+

IND-

INC+

INC-

V-

MAX924ESE

1

16

15

14

13

12

11

10

9

MAX924MJE

2

3

4

5

6

7

8

MAX924MSE/PR

MAX924MSE/PR-T

INA-

MAX924

*Dice are tested at T = +25°C, DC parameters only.

A

**Contact factory for availability.

INA+

INB-

INB+

REF

DIP/Narrow SO

14 ______________________________________________________________________________________

Ultra Low-Power,

Single/Dual-Supply Comparators

__________________________________________________________Chip Topographies

MAX921/MAX922/MAX923

MAX924

OUTB OUTC

OUTA

OUTD

10

V+

1

9

8

2

3

GND

0.075"

(1.91mm)

4

5

7

6

0.108"

(2.74mm)

IND+

INA-

INA+

IND-

INC+

0.059"

INB-

(1.50mm)

INB+ REF

V- INC-

DIE PAD

MAX921

GND

V-

MAX922

OUTA

V-

MAX923

OUTA

V-

0.069"

(1.75mm)

1

2

3

V-

4

IN+

IN-

INA+

INA-

INB-

INB+

V+

INA+

INB-

HYST

REF

TRANSISTOR COUNT: 267

SUBSTRATE CONNECTED TO V+

5

6

HYST

REF

V+

7

8

V+

9

V+

10

OUT

OUTB

TRANSISTOR COUNT: 164

SUBSTRATE CONNECTED TO V+

______________________________________________________________________________________ 15

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.

PACKAGE TYPE

8 Plastic DIP

16 Plastic DIP

8 SO

PACKAGE CODE

DOCUMENT NO.

21-0043

P8-1

P16-1

S8-2

21-0043

21-0041

16 SO

S16-3

U8-1

J8-1

21-0041

8 µMAX

21-0036

8 CERDIP

16 CERDIP

21-0045

J16-3

21-0045

16 ______________________________________________________________________________________

Ultra Low-Power,

Single/Dual-Supply Comparators

Revision History

REVISION

NUMꢁER

REVISION

DATE

PAGES

DESCRIPTION

CHANGED

4

5

6

8/08

4/09

Updated TOCs 5 and 10

5

Adding information for rugged plastic product

1, 14

Updated Ordering Information

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

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


型号：	MAX923CUA-T
厂家：	Rochester Electronics
描述：	DUAL COMPARATOR, 10000uV OFFSET-MAX, 14000ns RESPONSE TIME, PDSO8, UMAX-8 放大器光电二极管
文件：	总18页 (文件大小：893K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

MAX923CUA-T [ROCHESTER]

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