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MAX9108
(Rev.:2001)

25ns, Dual/Quad/Single, Low-Power, TTL Comparators

Maxim Integrated 

25ns, Dual/Quad/Single, Low-Power,

TTL Comparators

______________________________________________________________Pin Description

MAX9107

1

2

3

7

6

5

—

—

—

—

—

—

—

—

—

8

4

—

—

PIN

MAX9108

MAX9109

SC70/SOT23

SO

1

—

—

2

—

—

3

—

—

7

—

—

6

—

—

5

—

—

8

—

—

9

—

—

10

—

—

14

—

—

13

—

—

12

—

—

—

1

7

—

3

2

—

4

3

4

6

1

11

2

6

—

5

5

—

—

4, 8

NAME

FUNCTION

OUTA

INA-

INA+

OUTB

INB-

INB+

OUTC

INC-

INC+

OUTD

IND-

IND+

OUT

IN+

IN-

VCC

GND

LE

N.C.

Channel A Output

Channel A Inverting Input

Channel A Noninverting Input

Channel B Output

Channel B Inverting Input

Channel B Noninverting Input

Channel C Output

Channel C Inverting Input

Channel C Noninverting Input

Channel D Output

Channel D Inverting Input

Channel D Noninverting Input

Output

Noninverting Input

Inverting Input

Positive Supply

Ground

Latch Enable. The latch is transparent when LE is low.

No Connection. Not internally connected.

_______________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 MAX9107/MAX9108/

MAX9109 eliminate this problem by incorporating an

internal hysteresis of 2mV. When the two comparator

input voltages are equal, hysteresis effectively causes

one comparator 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 resis-

tors. The MAX9107/MAX9108/MAX9109’s fixed internal

hysteresis eliminates these resistors. To increase hys-

teresis and noise margin even more, add positive feed-

back with two resistors as a voltage divider from the

output to the noninverting input.

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.

The average of the trip points is the offset voltage.

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 MAX9109 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 latched when LE is high (Figure 2).

Applications Information

Circuit Layout

Because of the MAX9107/MAX9108/MAX9109’s high

gain bandwidth, special precautions must be taken to

realize the full high-speed capability. A printed circuit

board with a good, low-inductance ground plane is

mandatory. Place the decoupling capacitor (a 0.1µF

ceramic capacitor is a good choice) as close to VCC as

6 _______________________________________________________________________________________

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