Hello,
I had a design with A20 allwinner. I did not use and connect battery pins. On my PCB I had many problems with AXP209 power manager. for example,
- IPS output stays at ~3V, not 5V (I noticed when I touch some pins, around APS or BIAS, suddenly it jumps and luck to 5V.)
- power-ok is not activated (then other components are not reset properly)
I made the A20 work, after doing surgery on the PCB. But for next revision, finally I decided to change the design without using AXP209, instead using multiple small and cheap LDOs. I don't want to spend more time on the power manager as it delayed me a lot. I want to know is using AXP209 mandatory or it is just recommended? I see there is a I2C bus between them, but I already cut it.
Best regards,
While it is possible to skip it, it will cause you many troubles in the long run. It is not recommended to skip the PMU of Allwinner chips. You will face lot of compatibility issues with the Linux software, a lot of things you would have to manually control, probably overheating and more.
Thank you for your comment. I don't know why the IPS is ~3V, not 5V, in my PCB. Compared to reference designs, like Olimex-lime2, I have same circuits for A20's power manager, except not having battery pins connected (all float). All LDO outputs are all correct, except the IPS and power-ok. I have APS feedback line properly connected,..... I accidentally noticed that sometimes when I touch a part of circuit around Bias or APS pins, IPS suddenly locks as 5V. Do you have any idea?
It's hard to speculate what you have done wrong based on above information.
My guess is that you didn't route the PCB correctly so your DCDC part do not operate correctly. These DCDC operate at very high frequency, PCB routing is very critical for their correct operation.
Thank you,
I have a question about schematic design of A20-OlinuxXino-Lime2. Why the input power of external regulators (specifically U16/17) are from AXP209 5V output (IPSOUT line)?
Why they are not fed directly from 5VEXT?
thank you very much.