SGLS121D December 2002 – June 2020 UCC2800-Q1 , UCC2801-Q1 , UCC2802-Q1 , UCC2803-Q1 , UCC2804-Q1 , UCC2805-Q1
PRODUCTION DATA.
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Synchronization of these PWM controllers is best obtained by the universal technique shown in Figure 19. The ICs oscillator is programmed to free run at a frequency about 20% lower than that of the synchronizing frequency. A brief positive pulse is applied across the 50-Ω resistor to force synchronization. Typically, a 1-V amplitude pulse of 100-ns width is sufficient for most applications.
The ICs can also be synchronized to a pulse train input directly to the oscillator RC pin. Note that the IC internally pulls low at this node once the upper oscillator threshold is crossed. This 130-Ω impedance to ground remains active until the pin is lowered to approximately 0.2 V. External synchronization circuits must accommodate these conditions.