Hi Charles, Thank you for reply. Here is the new update: 1. We have taken all of the chips(6 chips: LM96551 , LM96530 , LM96570 , 74AC08MTC, LMV321 , FXL4TD245BQX ) off the board, and we checked that there are no short between all the powers and GND on the board. 2. We take 6 new chips onto the board, and follow the powering squence, but when we turn on -50V, the 3.3V are overloaded. 3. We take all the 6 chps off, and take a new LM96570 onto the board, with the other 5 chips not mounted, as shown in the following picture. According to the schematic of TX_SDK board, the LM96570 only take 1.8V and 3.3V. We take the following powering sequence: step0. We checked that, all the powers on the board are not short to each other or to the GND. step1. Turn 3.3V on. 3.3V takes neally 0mA. step2. Turn 1.8V on. 1.8V takes about 22mA. step3. Turn VSUB on. Nothing happens, that is normal. step4. Turn -50V on. The 1.8V and 3.3V are both overloaded. And when we take LM96570 off, we find the 1.8V and 3.3V of LM96570are both short to GND. So this is really strange, the LM96570 only takes 3.3V and 1.8V. And there is only LM96570 on the board. And we measure the impedence between 3.3V and -50V is several MOhm, impedence between 1.8V and -50V is also several MOhm. And when we did the test, we use the power supply's button to turn on/off the power, without our switch board. 4. We changed another LM96570 and follow the steps in 3. The same thing happens. So the problem is narrowed to the LM96570 . Till now, 4 pieces of LM96570 are damaged. That is strange, the powering of -50V damaged the LM96570 , we can't believe that. Any possibilities for that? Thank you. Frank
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