TC1037CECT datasheet(5/18 Pages) MICROCHIP

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DS21344B-page 5

TC1037/TC1038/TC1039

3.0

DETAILED DESCRIPTION

The TC1037/TC1038/TC1039 are a series of very low

power, linear building block products targeted at low

voltage, single supply applications. The TC1037/

TC1038/TC1039 minimum operating voltage is 1.8V

and typical supply current is only 4

µA for the TC1037

and TC1038 (fully enabled) and 6

µA for the TC1039.

3.1

Comparator

The

TC1037/8/9

contain

one

comparator.

The

comparator’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 comparator exhibits a propagation delay and

supply current which is largely independent of supply

voltage. The low input bias current and offset voltage

makes it suitable for high impedance precision

applications.

The TC1038 comparator is disabled during shutdown

and has a high impedance output.

3.2

Voltage Reference

A 2.0% tolerance, internally biased, 1.20V bandgap

voltage reference is included in the TC1039. It has a

push-pull output capable of sourcing and sinking at

least 50

µA.

3.3

Shutdown Input (TC1038 Only)

SHDN at VIL disables the comparator and reduces the

supply current to less than 0.3

µA. The SHDN input

cannot be allowed to float. When not used, connect it to

VDD. The comparator’s output is in a high impedance

state when the TC1038 is disabled. The comparator’s

inputs can be driven from rail-to-rail by an external

voltage when the TC1038 is disabled. No latchup will

occur when the device is driven to its enabled state

when SHDN is set to VIH.

4.0

TYPICAL APPLICATIONS

The TC1037/TC1038/TC1039 family 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 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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