Detailed Description

The MAX9140/MAX9141/MAX9142/MAX9144 single-

supply comparators feature internal hysteresis, high

speed, and low power. Their outputs are pulled to with-

in 300mV of either supply rail without external pullup or

pulldown circuitry. Rail-to-rail input voltage range and

low-voltage single-supply operation make these

devices

ideal

for

portable

equipment.

The

MAX9140/MAX9141/MAX9142/MAX9144 interface

directly to CMOS and TTL logic.

Most high-speed comparators oscillate in the linear

region because of noise or undesired parasitic feed-

back. This tends to occur when the voltage on one

input is at or equal to the voltage on the other input. To

counter the parasitic effects and noise, the MAX9140/

MAX9141/MAX9142/MAX9144 have an internal hystere-

sis of 1.5mV.

The hysteresis in a comparator creates two trip points:

one for the rising input voltage and one for the falling

input voltage (Figure 1). The difference between the trip

points is the hysteresis. The average of the trip points is

the offset voltage. When the comparator’s input volt-

ages are equal, the 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 hys-

teresis to be added with external resistors. The

MAX9140/MAX9141/MAX9142/MAX9144’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.

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 MAX9141 includes an internal latch that allows

storage of comparison results. The L

—

E pin has a high

input impedance. If L

—

E is high, the latch is transparent

(i.e., the comparator operates as though the latch is not

present). The comparator's output state is latched

when L

—

E is pulled low (Figure 2).

Shutdown Mode (MAX9141 Only)

The MAX9141 shuts down when the

–

S

—

H

—

D

—

N

–

pin is low.

When shut down, the supply current drops to less than

12µA, and the three-state output becomes high imped-

ance. The

–

S

—

H

—

D

—

N

–

pin has a high-input impedance.

—

H

—

D

—

N

–

—

E

high (transparent state); otherwise, the

output will be indeterminate.

Input Stage Circuitry

The MAX9140/MAX9141/MAX9142/MAX9144 include

internal protection circuitry that prevents damage to the

precision input stage from large differential input volt-

ages. This protection circuitry consists of two back-to-

back diodes between IN+ and IN- as well as two series

4.1k

Ω resistors (Figure 3). The diodes limit the differen-

tial voltage applied to the internal circuitry of the com-

ward voltage drop of the diode (about 0.7V at +25°C).

this protection circuitry increases the input bias current

at IN+ (source) and IN- (sink).

Input Current =

2 x 4.1k

Ω

Input current with large differential input voltages

rect logic state if one or both inputs are within the com-

mon-mode range.

40ns, Low-Power, 3V/5V, Rail-to-Rail

Single-Supply Comparators

_______________________________________________________________________________________

7

COMPARATOR

OUTPUT

2

Figure 1. Input and Output Waveform, Noninverting Input

Varied