Single/Dual/Quad, SOT23, Single-Supply,

High-Speed, Low-Power Comparators

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7

example, choose 100mV.

values for this example,

R1 = 1.2M

Ω x (100mV / 5.0V) = 24kΩ

threshold voltage at which the comparator switches

this example, choose 3.0V.

5) Calculate R2 as follows:

Choose a standard value for R2 of 16k

Ω.

6) Verify the trip voltage and hysteresis as follows:

IR Receiver

The

Typical Operating Circuit shows an application using

the MAX998 as an infrared receiver. The infrared photo-

diode creates a current relative to the amount of infrared

When this voltage level crosses the voltage applied by the

voltage divider to the inverting input, the output transitions.

Window Comparator

The MAX976 is ideal for making a window detector

(undervoltage/overvoltage detector). The schematic

shown in Figure 3 uses a MAX6120 reference and com-

ponent values selected for a 2.0V undervoltage thresh-

old and a 2.5V overvoltage threshold. Choose different

thresholds by changing the values of R1, R2, and R3.

OUTA provides an active-low undervoltage indication,

and OUTB gives an active-low overvoltage indication.

ANDing the two outputs provides an active-high,

power-good signal. The design procedure is as follows:

1) Select R1. The leakage current into INB- is normally

75nA, so the current through R1 should exceed

1.0µA for the thresholds to be accurate. R1 values in

the 50k

Ω to 100kΩ range are typical.

is rising, and calculate R2 and R3 with the following

formula:

is falling, and calculate R2 with the following formula:

4) Calculate R3 with the following formula:

5) Verify the resistor values. The equations are as follows:

V

rising: V

= V

x R1 x

1

R1

V

falling

IN

THR

REF

IN

:

+

+









=

−









=

−

1

2

1

3

1

3

R

R

V

V

R x V

R

Hysteresis

V

V

THF

THR

CC

THR

THF

R2 =

1

V

V

x R1

1

R1

1

R3

R2 =

1

3.0V

1.2 x 24k

1

24k

1

1.2M

16.2k

THR

REF









−

−









−

−

=

Ω

Ω

Ω

MAX976

MAX978

MAX998

OUT

0.1

µF

R3

R1

R2

GND

Figure 2. Additional Hysteresis

3

1

3

4

R3

82.1k, 1%

R2

24.9k,

1%

R1

100k,

1%

2

6

OVERVOLTAGE

UNDERVOLTAGE

POWER GOOD

1/2

MAX976

MAX6120

1

2

8

7

5

0.1

µF

1/2

MAX976

Figure 3. Window Comparator