TC1269

DS21380B-page 4

© 2002 Microchip Technology Inc.

3.0

DETAILED DESCRIPTION

The TC1269 is a precision regulator available in fixed

voltages. Unlike the bipolar regulators, the TC1269

supply current does not increase with load current. In

range, (an important consideration in RTC and CMOS

RAM battery backup applications).

Figure 3-1 shows a typical application circuit. The

regulator is enabled any time the shutdown input

controlled by a CMOS logic gate, or I/O port of a

microcontroller. If the SHDN input is not required, it

should be connected directly to the input supply. While

in shutdown, supply current decreases to 0.05

µA

FIGURE 3-1:

TYPICAL APPLICATION

CIRCUIT

3.1

Bypass Input

A 470pF capacitor connected from the Bypass input to

ground

reduces

noise

present

on

the

internal

reference, which in turn significantly reduces output

noise. If output noise is not a concern, this input may be

left unconnected. Larger capacitor values may be

used, but results in a longer time period to rated output

voltage when power is initially applied.

3.2

Output Capacitor

A1

recommended. The output capacitor should have an

effective series resistance greater than 0.1

Ω and less

than 5.0

Ω, and a resonant frequency above 1MHz. A

1

there is more than 10 inches of wire between the

regulator and the AC filter capacitor, or if a battery is

used as the power source. Aluminum electrolytic or

tantalum capacitor types can be used. (Since many

aluminum electrolytic capacitors freeze at approxi-

mately -30°C, solid tantalums are recommended for

applications operating below -25°C.) When operating

from sources

other

than

batteries,

supply-noise

rejection and transient response can be improved by

increasing the value of the input and output capacitors

and employing passive filtering techniques.

TC1269

1

2

3

4

6

7

8

NC

NC

GND

Bypass

NC

SHDN

Battery

470pF

(Optional)

Shutdown Control

(from Power

Control Logic)

C1

1

µF

+

C1

1

µF

+

+

–