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SG6841/2 應用研討

SG6841/2 應用研討. 林乾元 /Lawrence Lin System General Corp. Outline. SG6841/2 應用注意事項 Layout 與 EMC 常見問題 Q & A. SG6841/2 參考電路. Sense pin 加 RC filter. 100~200 . 100~470pF. 1. 把 sense pin 的負壓壓制在 -0.3V 以內 2.C 儘可能靠近 IC 的 sense-GND 3.R 太大會造成斜率補償過重 , 影響正常操作 4. 太大的 RC 常數值會造成高壓過載點太高.

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SG6841/2 應用研討

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  1. SG6841/2應用研討 林乾元/Lawrence Lin System General Corp.

  2. Outline • SG6841/2應用注意事項 • Layout與EMC常見問題 • Q & A

  3. SG6841/2參考電路

  4. Sense pin加RC filter 100~200 100~470pF 1.把sense pin的負壓壓制在-0.3V以內 2.C儘可能靠近IC的sense-GND 3.R太大會造成斜率補償過重,影響正常操作 4.太大的RC常數值會造成高壓過載點太高

  5. FB pin的RC filter Opto- coupler FB pin 1.適當的RC值基本上不影響電路操作 2.太大的RC常數將使迴路反應變慢 3.加RC在降頻時會看到較穩定的頻率

  6. RT pin的濾波電容 • RT pin若因干擾出現雜訊,建議加電容濾除(47pF~1000pF) • 電容若加太大將造成無法開機 • 若不使用RT pin,直接open即可,但是如果出現上述現象,請並聯電容.

  7. 其他注意事項 • 除Vin,VDD,Gate pin之外,其餘耐壓僅7V • RI pin勿做其他應用 • Vin pin不使用open即可,或接C對地.

  8. Layout與EMC

  9. Layout的注意事項 • 小訊號與大電流迴路必須分開 • Sense pin的訊號線勿經過變壓器下方,或與Drain平行且太接近. • 地線的分配必須考慮到EMC • 零件的配置需考量到耦合問題

  10. 零件的配置(錯誤) EMI filter 小訊號迴路 Secondary & Inverter Power Stage INLET MOSFET 雜訊將跳過濾波電路偶合到線端

  11. 零件的配置(錯誤) EMI filter Power Stage Secondary INLET 小訊號迴路 shielding Inverter

  12. 零件的配置 EMI filter Power Stage MOSFET Secondary & Inverter INLET 小訊號迴路

  13. Surge放電路徑(L/N-F.G) 跨在初次級的Y電容,在初級應直接且獨立連接到整 流後的濾波電容;次極端應接近輸出地線或螺絲孔

  14. Lightening Surge:VDD注意事項 • VDD迴路應注意零件順序,如下圖. • 若VDD電容無法靠近IC,請在VDD前再加RC filter.

  15. ESD放電路徑

  16. 地線的配置

  17. Q & A

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