TC1027CEPR datasheet(4/18 Pages) MICROCHIP

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TC1027

DS21284B-page 4

3.0

DETAILED DESCRIPTION

The TC1027 is one of a series of very low-power, linear

building block products targeted at low-voltage, single-

supply applications. The TC1027 minimum operating

voltage is 1.8V, and typical supply current is only 18

µA.

It combines four comparators and a voltage reference

inasinglepackage.

3.1

Comparators

The TC1027 contains four comparators. The compara-

tor's input range extends beyond both supply voltages

by 200mV and the outputs will swing to within several

millivolts of the supplies depending on the load current

being driven.

The comparators exhibit propagation delay and supply

current which are largely independent of supply

voltage. The low input bias current and offset voltage

make them suitable for high impedance precision

applications.

3.2

Voltage Reference

A 2.0% tolerance, internally biased, 1.20V bandgap

voltage reference is included in the TC1027. It has a

push pull output capable of sourcing and sinking at

least 50

µA.

GND (Pin 9) is connected to VSS (Pin 14) through the

substrate of the integrated circuit. Large currents can

flow between GND and VSS if the pins are not at the

same voltage.

4.0

TYPICAL APPLICATIONS

The TC1027 lends itself to a wide variety of

applications, particularly in battery-powered systems. It

Typically it finds application in power management,

processor supervisory and interface circuitry.

4.1

External Hysteresis (Comparator)

Hysteresis can be set externally with two resistors

using positive feedback techniques (see Figure 4-1).

The design procedure for setting external comparator

hysteresis is as follows:

Choose the feedback resistor RC.Since the

input bias current of the comparator is at most

100pA, the current through RC canbeset to

100nA (i.e., 1000 times the input bias current)

and retain excellent accuracy. The current

through RC at the comparator’s trip point is VR/

RC where VR is a stable reference voltage.

Determine the hysteresis voltage (VHY) between

the upper and lower thresholds.

Calculate RA as follows:

EQUATION 4-1:

Choose the rising threshold voltage for VSRC

(VTHR).

Calculate RB as follows:

EQUATION 4-2:

Verify

the

threshold

voltages

with

these

formulas:

VSRC rising:

EQUATION 4-3:

VSRC falling:

EQUATION 4-4:

-----------





THR

---------------------







 1

-------

–

-------

–

-----------------------------------------------------------

TH R

() R

()

-------





-------





-------





THF

THR

-------------------------





–

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