_______________Detailed Description

Timing

Noise or undesired parasitic AC feedback cause most

high-speed comparators to oscillate in the linear region

(i.e., when the voltage on one input is at or near the

voltage on the other input). The MAX907/MAX908/

MAX909 eliminate this problem by incorporating inter-

nal hysteresis. When the two comparator input volt-

ages are equal, hysteresis effectively causes one com-

parator input voltage to move quickly past the other,

thus taking the input out of the region where oscillation

occurs. Standard comparators require that hysteresis

be added through the use of external resistors. The

MAX907/MAX908/MAX909’s fixed internal hysteresis

eliminates these resistors (and the equations required

to determine appropriate values).

Adding hysteresis to a comparator creates two trip

points: one for the input voltage rising and one for the

input voltage falling (Figure 1). The difference between

these two input-referred trip points is the hysteresis.

Figure 1 illustrates the case where IN- is fixed and IN+

is varied. If the inputs were reversed, the figure would

look the same, except the output would be inverted.

The MAX909 includes an internal latch, allowing the

result of a comparison to be stored. If LE is low, the

latch is transparent (i.e., the comparator operates as

though the latch is not present). The state of the com-

parator output is stored when LE is high. See Figure 2.

Note that the MAX909 can be operated with V- con-

nected to ground or to a negative supply voltage. The

MAX909’s input range extends from (V- - 0.2V) to

(V+ - 1.5V).

Single/Dual/Quad High-Speed, Ultra Low-Power,

Single-Supply TTL Comparators

8

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______________________________________________________________Pin Description

PIN

NAME

FUNCTION

MAX907

MAX908

MAX909

1

1

OUTA

Comparator A Output

2

2

INA-

Comparator A Inverting Input

3

3

INA+

Comparator A Noninverting Input

8

4

1

V+

Positive Supply

5

5

INB+

Comparator B Noninverting Input

6

6

INB-

Comparator B Inverting Input

7

7

OUTB

Comparator B Output

8

OUTC

Comparator C Output

9

INC-

Comparator C Inverting Input

10

INC+

Comparator C Noninverting Input

4

11

6

GND

Ground

12

IND+

Comparator D Noninverting Input

13

IND-

Comparator D Inverting Input

14

OUTD

Comparator D Output

2

IN+

Noninverting Input

3

IN-

Inverting Input

4

V-

Negative Supply or Ground

5

LE

7

QOUT

Comparator Output

8

QOUT

Inverted Comparator Output

The latch is transparent when LE is low. The comparator output is

stored when LE is high.