NCP1000, NCP1001, NCP1002

http://onsemi.com

11

Applications

Do not attempt to construct a converter circuit on a

wire−wrap or plug−in prototype board. In order to ensure

proper device operation and stability, it is important to

minimize the lead length and the associated inductance of

the ground pin. This pin must connect as directly as possible

to the printed circuit ground plane and should not be bent or

offset by the board layout. The Power Switch Circuit pin can

be offset if additional layout creepage distance is required.

Due to the potentially high rate of change in switch current,

a capacitor (if used), at pin 2, should have traces as short as

possible, from pin 2 and ground. This will significantly

reduce the level of switching noise that can be imposed upon

the feedback control signal.

Thermal

Shutdown

Figure 17. Representative Block Diagram

Snubber

Feedback

Input

Power Switch

Circuit

+

+

+

+

−

Converter

DC Output

2

4

AC Line

Input

1

Internal

Bias

State Control

Power up−reset

Ck

R

Divide

by 8

S

R

Q

PWM Latch

Leading Edge

Blanking

Undervoltage

Lockout

Driver

10 V

Oscillator

Duty Cycle

Ramp

Clock

PWM

Comparator

7.0 kHz

Filter

Loop Compensation

Ground

3

Startup

+

Auxiliary Output

5

Auto Restart Timing

+

2.7 k

+

+

Q

Startup

Current Limit

Comparator

10 V

10 mA

Opto Fail−safe

8.5 V/

7.5 V

Bypass