Ultra Low-Power,

Single/Dual-Supply Comparators

8

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_______________Detailed Description

The MAX921–MAX924 comprise various combinations

of a micropower 1.182V reference and a micropower

comparator. The Typical Operating Circuit shows the

MAX921 configuration, and Figures 1a-1c show the

MAX922–MAX924 configurations.

Each comparator continuously sources up to 40mA,

and the unique output stage eliminates crowbar

glitches during output transitions. This makes them

immune to parasitic feedback (which can cause

instability) and provides excellent performance, even

when circuit-board layout is not optimal.

Internal hysteresis in the MAX921 and MAX923 provides

the easiest method for implementing hysteresis. It also

produces faster hysteresis action and consumes much

less current than circuits using external positive feedback.

Power-Supply and Input Signal Ranges

This family of devices operates from a single +2.5V to

+11V power supply. The MAX921 and MAX924 have a

separate ground for the output driver, allowing

operation with dual supplies ranging from ±1.25V to

±5.5V. Connect V- to GND when operating the

MAX921 and the MAX924 from a single supply. The

maximum supply voltage in this case is still 11V.

For proper comparator operation, the input signal can

swing from the negative supply (V-) to within one volt of

the positive supply (V+ – 1V). The guaranteed

common-mode input voltage range extends from V- to

(V+ - 1.3V). The inputs can be taken above and below

the supply rails by up to 300mV without damage.

Operating the MAX921 and MAX924 at ±5V provides

TTL/CMOS compatibility when monitoring bipolar input

signals. TTL compatibility for the MAX922 and MAX923

is achieved by operation from a single +5V supply.

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

The guaranteed minimum operating voltage is 2.5V (or

±1.25V). As the total supply voltage is reduced below

2.5V, the performance degrades and the supply

current falls. The reference will not function below

OUTA

V-

INA+

INA-

OUTB

V+

INB+

INB-

MAX922

1

2

3

4

8

7

6

5

Figure 1a. MAX922 Functional Diagram

OUTA

V-

INA+

INB-

OUTB

V+

REF

HYST

MAX923

1

2

3

4

8

7

6

5

V-

Figure 1b. MAX923 Functional Diagram

OUTA

V+

INA-

INA+

OUTD

GND

IND+

IND-

MAX924

2

3

4

5

15

14

13

12

16

11

10

9

1

6

7

8

OUTB

INB-

INB+

REF

OUTC

INC+

INC-

V-

Figure 1c. MAX924 Functional Diagram