STMicroelectronics

Description

The UC3842 oscillator is programmed as shown in figure 7a. Oscillator timing capacitor CT is charged from VREF (5 V) through RT, and discharged by an internal current source. Charge and discharge times are given by : tc 0.55 RT CT. 0.0063 RT 2.7 td RT CT ln (. ) 0.0063 RT 4.0. 1 frequency, then, is : f = tc + td . This series of controller is similar to XX3842 series in general use but with improved features and characteristics. REFERENCE including Buck, Boost, Flyback, and Forward converters. Improvement over the original 3842 . t(off) t( on). Rt. TC = 0.55RtCt. TD = RtCtLn[(0.0063Rt-2.7)/(0.0063Rt-4)]. Frequency = ( TC+ TD )-1 UC3842A /3843A. LINEAR INTEGRATED CIRCUIT. UNISONIC TECHNOLOGIES CO., LTD. 2 of 9 www.unisonic.com.tw. QW-R103-002.I. . that capacitor C, forms a filter with R2 to suppress the leading edge switch spikes. OSCILLATOR SECTION. Dead time vs. CT(RT>5k ). Timing Resistance vs. Frequency td ( s). for SG3842 ; ISTART is the maximum start-up cur- rent of SG384x (in the . maximum tON is restricted when the sense input . 1V (IP RS 1V). Furthermore, the maximum output power is also affected by 384xs response time tD -. From the moment caused by the input voltage and the delay time tD . The resistance of controller ICs, such as UCC3842 , UCC3843, or UCC3844. Due to a regenerative action from the motor, Use of controllers like the UCC3842 device presents other challenges, for example, limiting the power .. TD is the current-sense delay including MOSFET turn-off delay. Add 50 ns to the MOSFET delay. NPA is the