UC1842A-EP, UC1843A-EP, UC1844A-EP, UC1845A-EP

CURRENT-MODE PWM CONTROLLER

SGLS134B – SEPTEMBER 2002 – REVISED APRIL 2003

8

POST OFFICE BOX 655303

APPLICATION INFORMATION

High peak currents associated with capacitive loads necessitate careful grounding techniques. Timing and bypass capacitors should be

connected close to pin 5 in a single point ground. The transistor and 5k potentiometer are used to sample the oscillator waveform and apply an

adjustable ramp to pin 3.

Figure 7. Open-Loop Laboratory Text Fixture

A fraction of the oscillator ramp can be resistively summed

with the current sense signal to provide slope compensation

for converters requiring duty cycles over 50%.

Note that capacitor, C, forms a filter with R2 to suppress the

leading edge switch spikes.

Figure 8. Slope Complression