© 2002 Microchip Technology Inc.

DS21379B-page 5

TC1268

3.2

Bypass Input

A 10nF 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 this results in a longer time period to achieve

the rated output voltage, once power is initially applied.

3.3

Output Capacitor

A1

The output capacitor should have an effective series

resistance greater than 0.1

Ω and less than 5Ω, and a

resonant frequency above 1MHz. A 1

µF capacitor

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.

3.4

ERROR Output

regulation by more than -5% (typical). This condition

may be caused by low input voltage, output current

limiting, or thermal limiting.

regardless of the programmed output voltage value

regulator). ERROR output operation is shown in

As shown in Figure 3-1, ERROR canbeusedas a

battery low flag, or as a processor RESET signal (with

the addition of timing capacitor C1). R1 x C1 should be

RESET input for at least 200msec to allow time for the

system to stabilize. Pull-up resistor R1 can be tied to

FIGURE 3-3:

ERROR OUTPUT

OPERATION

ERROR