TC1040

DS21345B-page 4

© 2002 Microchip Technology Inc.

3.0

DETAILED DESCRIPTION

The TC1040 is one of a series of very low power, linear

building block products targeted at low voltage, single

supply applications. The TC1040 minimum operating

voltage is 1.8V and typical supply current is only 10

µA

(fully enabled). It combines two comparators and a

voltage reference in a single package. A shutdown

mode is incorporated for easy adaptation to system

power management schemes. During shutdown, one

comparator is disabled (i.e., powered down with output

at a high impedance). The “still awake” comparator and

voltage reference can be used as a wake-up timer,

power

supply

monitor,

LDO

controller

or

other

continuous duty circuit function.

3.1

Comparators

The TC1040 contains two 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 inverting input of Comparator A and

the non-inverting input of Comparator B are internally

connected to the output of the voltage reference.

The comparators exhibit a 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.

Comparator B is disabled during shutdown and has a

high impedance output. Comparator COMPA remains

active.

3.2

Voltage Reference

A 2.0 percent tolerance, internally biased, 1.20V

bandgap voltage reference is included in the TC1040.

It has a push-pull output capable of sourcing and

sinking 50

µA. The voltage reference remains fully

enabled during shutdown.

3.3

Shutdown Input

cannot be allowed to float; when not used, connect it to

impedance state when shutdown is active. The

disabled comparator’s inputs and outputs can be driven

from rail-to-rail by an external voltage when the

TC1040 is in shutdown. No latchup will occur when the

device is driven to its enabled state when SHDN is set

4.0

TYPICAL APPLICATIONS

The TC1040 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

Wake-Up Timer

Many microcontrollers have a low-power “sleep” mode

that significantly reduces their supply current. Typically,

the microcontroller is placed in this mode via a software

instruction, and returns to a fully-enabled state upon

reception of an external signal (“wake-up”). The wake-

up signal is usually supplied by a hardware timer. Most

system applications demand that this timer have a long

duration (typically seconds or minutes), and consume

as little supply current as possible.

The circuit shown in Figure 4-1 is a wake-up timer

made from Comparator A. (Comparator A is used

because the wake-up timer must operate when SHDN

is active.) Capacitor C1 charges through R1 until a

“wake-up”

is driven active. Upon

wake-up, the

microcontroller resets the timer by forcing a logic low

on a dedicated, open drain I/O port pin. This discharges

C1 through R4 (the value of R4 is chosen to limit

maximum current sunk by the I/O port pin). With a 3V

supply, the circuit as shown consumes typically 8

µA

and furnishes a nominal timer duration of 25 seconds.

FIGURE 4-1:

WAKE-UP TIMER

Wake-Up

R1

5M

R4

10

µF

–

+

I/O*

*Open Drain Port Pin

Microcontroller

COMPA

1/2

TC1040