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ucc2897A輸出異常

Other Parts Discussed in Thread: PMP21103, TPS2373

Hello,

目前按照PMP21103_RevB設計,輸入=40~57Vdc, 輸出=12V/7.5A, 變壓器=150uH(1:0.5:0.5)並將輸出的SR MOSFET改為一般的schottky,

Vdd是由DC  source提供15V,但目前輸出異常。電路圖如附件。

UB012D_1V1_F_20200616-01.pdf問題如下

1. 輸入40V時,空載輸出只有3V

2. 有輸出後Vfb電壓從5V降到2.5V

3. VREF, SS pin都為一個5V的直流準位

4. 輔助繞組的L2與TPS2373已經斷開

在請幫忙抽空回答,謝謝