4

UCC1581

UCC2581

UCC3581

The UCC3581’s oscillator allows the user the flexibility to

program the frequency and the duty cycle by adjusting

two resistors and a capacitor. Application Diagram Fig. 1

grams the timing capacitor charging current which results

plished though RT2 which results in a standard RC dis-

calculated by the formula

tRT

C

ON

T

=•

•

0 082

1

.

.

tRT

C

OFF

T

=•

•

095

1

.

.

Resistor RT1 programs the charging current. The current

is

2.0V

RT1

.

CT charging current is 9.2 times the current in RT1. RT1

can range from 220k

Ω to 1MΩ. Minimum capacitor size

is 100pF, and minimum RT2 size is 10k.

A Block Diagram of the Oscillator is shown in Fig. 2. The

oscillator also has an external synchronization pin.

When a low to high level is detected, and if the oscilla-

tor

output

immediately

goes

low

and

starts

discharging. The sync input is rising edge sensitive and

is ignored when the oscillator output is low.

APPLICATION INFORMATION

1

3

2

14

C

T

RT2

V

IN

1

µF

D2

4

Q1

5

6

1

µF

7

T1

R

L

REF &

E/A

U1

CT

GT

VDD

OUT

GND

REF

ISEN

V

IN

8

VC

9

DCMIN

10

SS

11

EN

U1

REF

REF

C

SS

12

RT1

13

SYNC

RT2

RT1

REF

UCC3581

D1

BSS129 OR

EQUIV.

Figure 1. Application diagram.

UDG-99043

Figure 2. Oscillator.

UDG-96105