Micropower, Low-Voltage, UCSP/SC70,

Rail-to-Rail I/O Comparators

8

_______________________________________________________________________________________

5) Calculate R2 as follows. For this example, choose an

8.2kΩ standard value:

6) Verify trip voltages and hysteresis as follows:

MAX986/MAX990/MAX994

The MAX986/MAX990/MAX994 have ±3mV internal

hysteresis. They have open-drain outputs and require

an external pullup resistor (Figure 2). Additional hys-

teresis can be generated using positive feedback, but

the formulas differ slightly from those of the

MAX985/MAX989/MAX993.

Use the following procedure to calculate resistor

values:

smaller of the two resulting resistor values.

example, choose 50mV.

3) Calculate R1 according to the following equation:

voltage at which the comparator switches its output

5) Calculate R2 as follows:

6) Verify trip voltages and hysteresis as follows:

Board Layout and Bypassing

Power-supply bypass capacitors are not typically need-

ed, but use 100nF bypass capacitors when supply

impedance is high, when supply leads are long,

or when excessive noise is expected on the supply

lines. Minimize signal trace lengths to reduce stray

capacitance.

V

rising: V

= V

x R1 x

1

R1

V

falling

IN

THR

REF

IN

:

++

+

⎛

⎝

⎜

⎞

⎠

⎟

=

−

+

⎛

⎝

⎜

⎞

⎠

⎟

=

−

1

2

1

34

1

34

RR

R

VV

Rx V

RR

Hysteresis

V

V

THF

THR

CC

THR

THF

R2 =

1

V

V

THR

R

R

R

1

1

1

1

34

⎛

⎝

⎜

⎞

⎠

⎟ −−

+

V

rising: V

= V

x R1 x

1

R1

V

falling

IN

THR

REF

IN

:

++

⎛

⎝

⎜

⎞

⎠

⎟

=

−

⎛

⎝

⎜

⎞

⎠

⎟

=

−

1

2

1

3

1

3

RR

VV

Rx V

R

Hysteresis

V

V

THF

THR

CC

THR

THF

R2 =

1

V

V

R2 =

1

3.0V

1.2 x 12k

THR

REF

.

.

xR

R

R

kM

k

1

1

1

1

3

1

12

1

22

803

⎛

⎝

⎜

⎞

⎠

⎟ −−

⎛

⎝

⎜

⎞

⎠

⎟ −−

=

ΩΩ

Ω

Ω

OUT

R3

R2

R1

R4

MAX986

MAX990

MAX994

Figure 2. Additional Hysteresis (MAX986/MAX990/MAX994)