glitches that commonly occur when changing logic states,

minimizing parasitic feedback and making them easier to

use. In addition, they include internal hysteresis (±3mV)

to ensure clean output switching, even with slow-moving

input signals. The inputs can be taken above and below

the supply rails up to 300mV without damage. Input

voltages beyond this range can forward bias the ESD-

protection diodes and should be avoided.

The MAX951–MAX954 comparator outputs swing rail-to-

using a 5V ±10% supply.

The MAX951–MAX954 comparators continuously output

source currents as high as 40mA and sink currents of

over 5mA, while keeping quiescent currents in the micro-

5V) for short pulses, as long as the package’s maximum

power dissipation is not exceeded. The output stage does

not generate crowbar switching currents during transi-

tions; this minimizes feedback through the supplies and

helps ensure stability without bypassing.

Reference

The internal reference in the MAX951/MAX952 has an

in the -40°C to +85°C temperature range. It is comprised

of a trimmed bandgap reference fed by a proportional-to-

absolute-temperature (PTAT) current source and buffered

by a micropower unity-gain amplifier. The REF output is

typically capable of sourcing and sinking 20μA. Do not

bypass the reference output. The reference is stable for

capacitive loads less than 100pF.

Applications Information

The micropower MAX951–MAX954 are designed to

extend battery life in portable instruments and add func-

tionality in power-limited industrial controls. Following are

some practical considerations for circuit design and layout.

Comparator Hysteresis

Hysteresis increases the comparator’s noise immunity by

increasing the upper threshold and decreasing the lower

threshold. The comparator in these devices contain a

±3mV wide internal hysteresis band to ensure clean out-

put switching, even with slow-moving signals.

When necessary, hysteresis can be increased by using

external resistors to add positive feedback, as shown in

Figure 2. This circuit increases hysteresis at the expense

of more supply current and a slower response. The

design procedure is as follows:

1) Set R2. The leakage current in COMPIN+ is less than

5nA (up to +85°C), so current through R2 can be as

little as 500nA and still maintain good accuracy. If R2

= 2.4MΩ, the current through R2 at the upper trip point

2) Choose the width of the hysteresis band. In this exam-

(

)

EHYST

IHYST

DD

IHYST

V

2V

R1 R2

V

2V

−





=

+

3) Determine R1. If the supply voltage is 5V, then R1 =

24kΩ.

4) Check the hysteresis trip points. The upper trip point is

(

) (

)

IN(H)

REF

IHYST

R1 + R2

V

V

V

R2

+

=

or 1.22V in our example. The lower trip point is 50mV

less, or 1.17V in our example.

If a resistor divider is used for R1, the calculations

should be modified using a Thevenin equivalent

model.

Figure 2. External Hysteresis

REF

RB

RA

R2

COMPOUT

REF

R1

R2

COMPOUT

MAX951–MAX954

Ultra-Low-Power, Single-Supply

Op Amp + Comparator + Reference

www.maximintegrated.com

Maxim Integrated │ 9