TC1174

DS21363B-page 4

© 2002 Microchip Technology Inc.

3.0

DETAILED DESCRIPTION

The TC1174 is an adjustable low drop-out regulator.

Unlike bipolar regulators, the TC1174’s supply current

remains stable and within regulation over the entire

important consideration in RTC and CMOS RAM

battery back-up 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

The output capacitor should have an effective series

resistance greater than 0.1

Ω and less than 5.0Ω.A 1µF

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 approximately -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.

3.3

Adjust Input

The output voltage setting is determined by the values

of R1 and R2 (Figure 3-1). The ohmic values of these

resistors should be between 470K and 3M to minimize

bleeder current.

The output voltage setting is calculated using the

following equation.

EQUATION 3-1:

The voltage adjustment range of the TC1174 is from

TC1174

1

2

3

4

5

6

7

8

470pF

(Optional)

Shutdown

Control

(from Power

Control Logic)

C1

1

µF

GND

NC

ADJ

NC

Bypass

SHDN

R1

470K

470K

R2

C2

1

µF

Battery

+

+

+

–

[

+1

]

R1

R2