7

UCC283-3/-5/-ADJ

UCC383-3/-5/-ADJ

UNITRODE CORPORATION

7 CONTINENTAL BLVD. • MERRIMACK, NH 03054

TEL. (603) 424-2410

_FAX (603) 424-3460

When the UCC383 regulator is in pulsed mode due to an

overload or short circuit in the application, the maximum

average power dissipation is calculated as follows:

()

PV

V

I

T

T

Watts

PULSE AVE

IN

OUT

CL

ON

ON

_

–

=·

·

·

33

(6)

As seen in equation 6, the average power during a fault

is reduced dramatically by the duty cycle, allowing the

heat sink to be sized for normal operation. Although the

significant, the thermal mass of the package will gener-

ally keep the junction temperature from rising unless the

Ripple Rejection

Even though the UCC383 family of linear regulators are

not optimized for fast transient applications (Refer to

UC182 Fast LDO Linear Regulator), they do offer

significant power supply rejection at lower frequencies.

Figure 6 depicts ripple rejection performance in a typical

application. The performance can be improved with

additional filtering.

Figure 7. Ripple rejection vs. frequency.

UDG-94093

Figure 6. Typical supply current vs. load current.