On , Lyubcho Haralanov wrote:
> VR1 is not assembled (NA). It is not placed. Only pads are provided in
> case you don't want to power the camera from the AXP209 but
> externally, in which case you should place VR1 and disconnect the SMT
> jumper LDO3_2.8V_E.
> By original design the camera is powered only by the AXP209.
> Best regards,
Thanks for the explanation of the EVB :)
Can you also elaborate on the 10 uF for all designs however?
Some extra information, I ran some current tests on the LDO3
power-up/shutdown and while 200 mA max sourcing current is never
reached, the chip does shut down before the max voltage has been
reached. For example setting ldo3 to max ( i2c mw 0x34 0x29 0x7f ) we
get screenshot 3v6.png where we can see the max voltage is only 2.32.
Repeating the same test however with 2.3 V ( i2c mw 0x34 0x29 0x40 )
yields 2V3.png, which also causes an AXP209 failure. This supprised me a
little, as I expected the 2.3V to actually work, as that is the voltage
we failed before. Also failure happens sooner and max current is lower.
After some trial and error, we find that 1.95 V, in this case, still
works, but that I suppose really depends on the capacitance, but by no
Due to the small timebase (50 uS) we cannot clearly see the power rail
dropping, but be assured, for the 2V3 and 3V6, power slowly drops as
While this can and should be solved in hardware (smaller capacitor)
there's hundreds of thousands of boards in the wild with this
configuration and thus a software solution is needed.
The AXP209 does have slew rate control, however this does not apply when
toggling the LDO3 output switch. What I thus propose, is a quirk-flag,
for buggy boards, where we set the minimal voltage, enable power and
than set the desired voltage, letting the internal slew rate control
slowly ramp up voltage.
What I still would love to hear from you guys, is why this could be
happening. The spec-sheet does say 200 mA of sourcing capability. But it
seems this is not exactly true? At least not when toggling LDO3 via
reg12 for sure.