UCC1884 Unitrode Semiconductor, UCC1884 Datasheet - Page 6

• Manufacturer Part Number: UCC1884
• Description: Frequency Foldback Current Mode PWM Controller
• Manufacturer: Unitrode Semiconductor

APPLICATION INFORMATION (cont.)
OSCILLATOR INFORMATION
The oscillator has charge and discharge currents pro-
grammed with resistors to ground from ION and IOFF re-
spectively, as seen on the Oscillator Block Diagram
(Figure 1). This generates a linear sawtooth waveform on
CT. Frequency foldback is accomplished by the level
shifted output voltage controlling the VOUT voltage which
decreases the discharge current and the frequency.
Figure 2. Oscillator Synchonization
Connection Diagram
Figure 1. UCC3884 Oscillator
UDG-96027
6
Synchronization is accomplished by coupling the fastest
oscillator CLKSYNC signal as shown on the Oscillator
Synchronization Diagram (Figure 2). The fastest (master)
CLKSYNC pin will couple a negative pulse into the
slower (slave) CLKSYNC pins forcing the slaves’ CT pins
to quickly discharge as shown on the Oscillator Wave-
form diagram (Figure 3).
Figure 3. Oscillator Waveforms
UCC1884
UCC2884
UCC3884
UDG-96029-1
UDG-96028-1