Tool/software:
Hi Sir :
1、 Description of problem phenomenon
1. TL7660 noise issue
1.1 Scheme 1
When loaded, there is a buzzing sound, but there is no such phenomenon when unloaded. After power-off, the noise lasts for 3-4 seconds (it disappears immediately after removing the load, and the measured output ripple is 230mVpp).
After adding LC filtering, the measured output ripple is around 30mVpp, but there is still a buzzing sound.
[Attachment 1]: Schematic screenshot
[Attachment 2]: Ripple waveform screenshot
1.2 Scheme 2
After replacing TL7660 with a plug-in, the ripple is significantly reduced and the buzzing sound is also reduced, and only when it is close can the sound be heard. And the sound of the same batch of boards is different, some can still be heard when approaching, while others have extremely weak sound when approaching.
2. Differential voltage problem of diode
As shown in [Attachment 2], if capacitors C4, C5, C6 are not installed, the overall output is -8V, but the diode voltage difference is as high as 2V, which means the voltage of TL7660 PIN5 is -6V.
2、 Key points for seeking help
1. Noise sources and how to optimize them?
2. The problem of diode voltage difference?
3. As shown in [Attachment 1] and [Attachment 3], since three TL7660 chips need to be connected in parallel, may I ask how to place the diodes more appropriately?
