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ADCMP341ARJ

Dual Comparators with 400mV Reference and programmable Hysteresis

Analog Devices 

Preliminary Technical Data

APPLICATIONS INFORMATION

The ADCMP341/3 is a dual low power comparators with a built

in 400mV reference that operates from 1.7V to 5.5V. The

comparators are approx 0.8% accurate with fully programmable

accurate hysteresis implementing a new technique of a three

resistor string on the input. The outputs are open drain capable

of sinking up to 40mA.

COMPARATORS AND INTERNAL REFERENCE

Each of the comparators has one input available externally, the

other comparator inputs are connected internally to the 400mV

reference. The ADCMP341 has two noninverting comparators

and the ADCMP343 has two inverting comparators.

There are two input pins available to each comparator.

However, these two input pins(INx_U, INx_U) connect to the

same input leg of the comparator via a muxing system. This is

to provide fully programmable rising and falling trip points.

The output of the said comparator determines which pin is

connected to the input of the same comparator. Taking Figure

30. as an example, when OUTA is high INA_U is connected to

the comparator input. When the input voltage drops and passes

below the 400mV reference the output goes low. This in turn

disconnects INA_U from the comparator and connects INA_L.

This leg of the string will be at a lower voltage and thus

instantaneously the effect of hysteresis is applied. Therefore,

using a resistor string on the input as shown in Figure 30., the

voltages for the rising and falling trip points can be

programmed by selecting the appropriate resistors in the string.

PROGRAMMING HYSTERESIS

The resistor values can be calculated as follows. The total

resistance of the string is first determined based on the power

budget available. Using the maximum voltage expected on the

pin and the maximum acceptable current available to flow

through the string1, the total resistance of the string is

calculated as follows:

RTOT

= VINMAX

I MAX

1 Assuming the leakage current into the comparator to be negligible

ADCMP341/ADCMP343

Now calculate the three resistor values as follows:

R1

=

RTOT

× (VFALLING

VFALLING

− 0.4)

R3

=

RTOT × 0.4

VRISING

;

R2 = RTOT − R1 − R3 ;

Where:

R1, R2 and R3 are the three resistors as shown in Figure 30.

RTOT is the sum of R1, R2 and R3.

VFALLING is the desired falling trip voltage and lower of the two.

VRISING is the desired rising trip voltage and higher of the two.

VHYST is therefore = V -V RISING FALLING

VINA

R1

INA_U

R2

INA_L

R3

VCC

ADCMP341

OUTA

400mV

Figure 30.

Rev. PrD | Page 11 of 13

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