Part Number: LM3880
Hello,
We made about 80 boards, using the LM3880 to control the power-on sequence. The circuit of the LM3880 is as follows. The input power of the board is VCC_5V.
One board out of these boards cannot be powered up in the chassis. We find that FLAG1 of the LM3880 on this board hold low, FLAG2 and FLAG3 hold high. So the power controlled by FLAG1 cannot be powered up.
We find that when there are less than five boards in the chassis, this board can be powered up. When there are five boards in the chassis, this board cannot be powered up.
When there are five boards in the chassis, we tested the voltage of the power supply. The voltage of the power supply is about 5V. The voltage is normal.
We tested the power-on startup waveform of the power supply. When there is one board in the chassis, startup waveform of the power supply is as follows.
When there are five boards in the chassis, startup waveform of the power supply is as follows.
We can find that when there are five boards in the chassis, temporary voltage drop during power on.
is the voltage drop during power on the reason why LM3880 works abnormally?
Best Regards,
Lin