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SI8281 Scheda tecnica(PDF) 10 Page - Silicon Laboratories |
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SI8281 Scheda tecnica(HTML) 10 Page - Silicon Laboratories |
10 / 43 page The high supply voltage configuration is used when a higher voltage power supply rail (up to 24 V) is available. All product options of the Si8282 and Si8284 are intended for this configuration. The dc-dc converter uses the isolated flyback topology. With this topology, the switch and sense resistor are external, allowing higher switching voltages. The output voltage is sensed on the secondary side without requiring additional optocouplers and support circuitry to bias those opto- couplers. This allows the dc-dc to operate with superior line and load regulation. The figure below shows the block diagram of an Si828x with external components. The Si8284 product option has externally controlled switching frequency and soft start. The dc-dc requires input capacitor C28, transformer T1, switch Q4, sense resistor Rsense, rectifying diodes D1 and D2, and output capacitors C26 and C27. To supply VDDA, Q3 transistor is biased by R23, 5.6 V Zener diode D5 and filtered by C30 and C11. External frequency and soft start behavior is set by CSS and RFSW. Resistors R1 and R2 divide the output voltage to match the internal reference of the error amplifier. The ratio of the two secondary windings splits the output voltage into two portions. The positive VDDB and the negative VSSB with common reference to VMID (IGBT Emitter). VDDB = VOUT × ( S1 S1 + S2 ) VSSB = − VOUT × ( S2 S1 + S2 ) Type 1 loop compensation made by RCOMP and CCOMP are required at the COMP pin. The combination of RCOMP = 49.9 kΩ and CCOMP = 1.5 nF satisfies most Si8282 and Si8284 dc-dc applications. Though it is not necessary for normal operation, we recommend to use RC snubbers (not shown) on both primary and secondary windings to minimize high-frequency emissions. RDY /FLT VH VL Si8282/Si8284 Error Amp and Compensation Encoder UVLO VDDB VSNS COMP VSSB R1 VSSB Vin T1 D1 C26 HF RX HF TX R2 C28 RCOMP CCOMP DSAT Detection HF RX Driver Miller Clamp CLMP DSAT VMID HF TX Decoder Encoder Decoder /RST +IN -IN Input Control & Reset D2 C27 Freq. Control and Shutdown Soft Start DC-DC Controller Current Sensing UVLO FET Driver ESW VDDA RSN GNDP Rsense R23 Q4 Q3 FC_SH SS CSS RFSW 5.6V C11 C30 D5 Figure 2.6. Si8282/84 Block Diagram: >5.5 V Input to Split Voltage Output Si8281/82/83/84 Data Sheet System Overview silabs.com | Smart. Connected. Energy-friendly. Preliminary Rev. 0.5 | 9 |
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Descrizione simile - SI8281 |
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