Single/Dual/Quad, Micropower,

Ultra-Low-Voltage, Rail-to-Rail I/O Comparators

function below about 1.5V, although the comparators

typically continue to operate with a supply voltage as

low as 1V. At low supply voltages (<1.6V), the input

common-mode range remains rail-to-rail, but the com-

parator’s output sink capability is reduced and propa-

gation delay increases (see Typical Operating

Characteristics).

Figure 1 shows a typical comparator application that

1.6V and approaches 1V, the reference voltage typical-

ly falls below the divider voltage (V+). This causes the

comparator output to change state. If OUT’s state must

be maintained under these conditions, a latching circuit

is required.

Comparator Output

The MAX965–MAX970 contain a unique slew-rate-

controlled output stage capable of rail-to-rail operation

with an external pull-up resistor. Typical comparators

consume orders of magnitude more current during

switching than during steady-state operation. With the

MAX965 family of comparators, during an output transi-

tion from high to low, the output slew rate is limited to

minimize switching current.

Voltage Reference

nal 1.235V bandgap reference is ±1.5% accurate over

the commercial temperature range and ±2.5% accu-

rate over the extended temperature range. The REF

output is typically capable of sourcing 50µA. To reduce

reference noise or to provide noise immunity, bypass

REF with a capacitor (0.1nF to 0.1µF).

Noise Considerations

The comparator has an effective wideband peak-to-

peak noise of around 10µV. The voltage reference has

peak-to-peak noise approaching 1.0mV with a 0.1µF

bypass capacitor. Thus, when a comparator is used

with the reference, the combined peak-to-peak noise is

about 1.0mV. This, of course, is much higher than the

individual components’ RMS noise. Avoid capacitive

coupling from any output to the reference pin. Crosstalk

can significantly increase the references’ actual noise.

__________Applications Information

Hysteresis

Many comparators oscillate in the linear region of oper-

ation because of noise or undesired parasitic feed-

back. This tends to occur when the voltage on one

input is equal or very close to the voltage on the other

input. The MAX965–MAX970 have internal hysteresis to

counter parasitic effects and noise. In addition, with the

use of external resistor, the MAX965/MAX967/

MAX968/MAX969’s hysteresis can be programmed to

as much as ±50mV (see the section Adding Hysteresis

to the MAX965/MAX967/MAX968/MAX969).

The hysteresis in a comparator creates two trip points:

one for the rising input voltage and one for the falling

input voltage (Figure 2). The difference between the trip

points is the hysteresis. When the comparator’s input

voltages 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.

THRESHOLDS

OUT

IN-

IN+

HYSTERESIS

BAND

Figure 2. Threshold Hysteresis Band

REF

GND

+ 1

OUT

R1

47k

R2

150k

V+

V+

t

1.6V

1.0V

100k

MAX965

R1

R2

R1 =

x R2

- 1

1.22

Figure 1. Operation below 1.6V

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