TC43

LINEAR BUILDING BLOCK –

VOLTAGE REFERENCE, DUAL OP AMP,

DUAL COMPARATOR WITH SHUTDOWN MODE

4

PRELIMINARY INFORMATION

Voltage Reference

A 4% tolerance, internally biased, 1.20V bandgap volt-

age reference is included in the TC43. It has a push-pull

output capable of sourcing 5mA or sinking 200

µA. The

voltage reference remains fully enabled during shutdown.

Shutdown Input

tor. The SHDN input cannot be allowed to float; when not

TYPICAL APPLICATIONS

The TC43 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.

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 instruc-

tion, and returns to a fully enabled state upon reception of

an external signal (“wake-up”). The wake-up signal is usu-

ally 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 1 is a wake-up timer made

from comparator CMPTR2. (CMPTR2 is used because the

wake-up timer must operate when SHDN is active.) Capaci-

tor C1 charges through R1 until a voltage equal to

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.

Precision Battery Monitor

Figure 2 is a precision battery low/battery dead monitor-

ing circuit. Typically, the battery low output warns the user

that a battery dead condition is eminent. Battery dead

typically initiates a forced shutdown to prevent operation at

low internal supply voltages (which can cause unstable

system operation).

The circuit of Figure 2 uses a single TC43 (one Op Amp

unused) and only 7 external resistors. AMP 1 is a simple

buffer while CMPTR1 and CMPTR2 provide precision volt-

age detection using Vr as a reference. Resistors R2 and R4

set the detection threshold for BATT LOW while resistors

R1 and R7 set the detection threshold for BATT FAIL. The

component values shown assert BATT LOW at 2.2V (typi-

cal) and BATT FAIL at 2.0V (typical). Total current con-

sumed by this circuit is typically 22

µA at 3V.

DUAL LDO with Shutdown

Figure 3 shows a portion of a TC43 configured as a dual

low drop regulator with shutdown. AMP1 and AMP2 are

independent error amplifiers that use Vr as a reference.

Resistors RA and RB set the feedback around the amplifier

and therefore determine the output voltage setting (please

see equation in the figure). RA and RB can have large ohmic

values (i.e. 100’s of K

Ω) to minimize supply current.

Using the 2N2222 output transistors as shown, these

regulators exhibit low dropout operation. For example, with

output current of 50mA. The unused comparators can be

used in conjunction with this circuit as power-on reset or low

voltage detectors for a complete LDO solution at a very low

installed cost.

EVALUATION KIT

The TC43EV consists of a four inch by six inch pre-wired

application circuit board. Pre-configured circuits include a

pulse width modulator, wake-up timer, function generator,

and others. On-board current meter terminals, voltage regu-

lator and a user-prototyping area speed circuit develop-

ment. Please contact your local TelCom Semiconductor

representative for more information.

Figure 1. Wake-Up Timer

WAKE-UP

R1

5M

R4

R2, 1M

R3, 1M

C1

10

µF

+

–

I/O*

*OPEN DRAIN PORT PIN

MICROCONTROLLER

CMPTR2