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ADCMP361

Single 0.275% Comparator and Reference with Dual Polarity Outputs

Analog Devices 

Data Sheet

APPLICATION INFORMATION

The ADCMP361 is a low power comparator and reference

circuit featuring a 400 mV reference that operates from 1.7 V

to 5.5 V. The comparator is 0.275% accurate with a built-in

hysteresis of 9.3 mV. There are two outputs, one the inverse

of the other. This enables the ADCMP361 to be used as an

inverting or a noninverting comparator circuit. These open-

drain outputs are capable of sinking 40 mA.

COMPARATORS AND INTERNAL REFERENCE

The comparator has one input available externally; the other

comparator input is connected internally to the 400 mV reference.

The rising input threshold voltage of the comparators is designed

to be equal to that of the reference.

POWER SUPPLY

The ADCMP361 is designed to operate from 1.7 V to 5.5 V. A 100 nF

decoupling capacitor is recommended between VDD and GND.

INPUTS

The comparator input is limited to the maximum VDD voltage

range. The voltage on these inputs can be above VDD but never

above the maximum allowed VDD voltage. When adding a resistor

string to the input, take care when choosing resistor values. This

is due to the fact that the input bias current will be in parallel

with the bottom resistor, R2, of the input resistor divider string.

This bottom resistor must therefore be chosen carefully in order

to reduce the error introduced by this bias current (see Figure 30).

VIN

R1

VDD

ADCMP361

IN

R2

IBIAS

OUT

400mV

OUT

GND

Figure 30. Input Bias Current Effect on Input Resistor String

OUTPUTS

The open-drain comparator outputs are limited to the

maximum specified VDD voltage range, regardless of the

VDD voltage. These outputs are capable of sinking up 40 mA.

ADDING HYSTERESIS

To prevent oscillations at the output caused by noise or slowly

moving signals passing the switching threshold, each compara-

tor has built-in hysteresis of approximately 9.3 mV. Positive

feedback can be used to increase hysteresis.

For the configuration shown in Figure 31, two resistors are used

to create different switching thresholds, depending on whether

the input signal is increasing or decreasing in magnitude. When

ADCMP361

the input voltage is increasing, the threshold is above VREF, and

when it is decreasing, the threshold is below VREF. VIN_HI is the

high input threshold used to trigger the output low to high

transmission. VIN_LO is the low input threshold used to trigger

the output high to low transmission.

The upper input threshold level is given by

VIN_HI

=

VREF (R1 +

R2

R2)

assuming RLOAD >> R2, RPULLUP where VREF = 0.4 V.

The lower input threshold level is given by

( ) VIN_LO = VREF

R1 + R2 + RPULLUP

R2 + RPULLUP

− VCC R1

The hysteresis is the difference between these voltage levels and

is given by

∆VIN

=

VCC R1

R2 + RPULLUP

VDD

VIN

R1

VREF = 0.4V

ADCMP361

RPULLUP

OUT

OUT

RLOAD

R2

Figure 31. Comparator Configuration with Added Hysteresis

VCC = 5V

ADCMP361

IN–

VREF

OUT

IN+

VIN

R1 = 200kΩ

VOUT

R2 = 1MΩ

VIN_LO VIN_HI

VIN

Figure 32. Noninverting Comparator Configuration with Hysteresis

Rev. B | Page 11 of 12

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