APPLICATIONS DATA (cont.)
Oscillator Section
Oscillator Frequency vs Timing Resistance
UC1842A/3A/4A/5A
UC2842A/3A/4A/5A
Maximum Duty Cycle vs Timing Resistor
Open-Loop Laboratory Test Fixture
High peak currents associated with capacitive loads necessi-
tate careful grounding techniques. Timing and bypass capaci-
tors should be connected close to pin 5 in a single point
ground. The transistor and 5k potentiometer are used to sam-
ple the oscillator waveform and apply an adjustable ramp to
pin 3.
Slope Compensation
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.
6
TI [ TEXAS INSTRUMENTS ]
