© 2002 Microchip Technology Inc.

DS21725B-page 5

TC1026

3.0

DETAILED DESCRIPTION

The TC1026 is one of a series of very low power, linear

building block products targeted at low voltage, single

supply applications. The TC1026 minimum operating

voltage is 1.8V, and typical supply current is only 12

µA.

It combines a comparator, an op amp and a voltage

reference in a single package.

3.1

Comparator

The TC1026 contains one comparator. 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 inverting input is internally connected

to the output of the reference.

The comparator exhibits propagation delay and supply

current which are largely independent of supply

voltage. The low input bias current and offset voltage

make

it

suitable

for

high

impedance

precision

applications.

3.2

Operational Amplifier

The TC1026 contains one rail-to-rail op amp. The

amplifier’s input range extends beyond both supplies

by 200mV and the outputs will swing to within several

millivolts of the supplies depending on the load current

being driven.

The amplifier design is such that large signal gain, slew

rate and bandwidth are largely independent of supply

voltage. The low input bias current and offset voltage of

the TC1026 make it suitable for precision applications.

3.3

Voltage Reference

A 2.0% tolerance, internally biased, 1.20V bandgap

voltage reference is included in the TC1026. It has a

push-pull output capable of sourcing and sinking at

least 50

µA.

4.0

TYPICAL APPLICATIONS

The TC1026 lends itself to a wide variety of

applications, particularly in battery powered systems. It

typically finds application in power management,

processor supervisory and interface circuitry.

4.1

External Hysteresis (Comparator)

Hysteresis can be set externally with three resistors

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

The design procedure for setting external comparator

hysteresis is as follows:

1.

input bias current of the comparator is at most

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

and retain excellent accuracy. The current

2.

the upper and lower thresholds.

3.

EQUATION 4-1:

4.

5.

EQUATION 4-2:

6.

Verify

the

threshold

voltages

with

these

formulas:

EQUATION 4-3:

EQUATION 4-4:

R

A

R

C

V

HY

V

DD

-----------





=

R

B

1

V

THR

V

R

R

A

×

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







 1

R

A

-------

–

1

R

C

-------

–

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

=

V

TH R

V

R

() R

A

()

1

R

A

-------





1

R

B

-------





1

R

C

-------





++

=

V

THF

V

THR

R

A

V

DD

×

R

C

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





–

=