<![CDATA[āš ļø M5Stack Core2 v1.3 - Ouroboros-like power loop -]]>Hi all, Iā€™m investigating a power management issue on the M5Stack Core2 (AXP192 + external SY7088 boost) and Iā€™m looking for confirmation or a proper solution.

šŸ”§ System Architecture (as implemented)
From schematic analysis and testing:

AXP192 IPSOUT powers the system and the boost converter

// VBUS ALWAYS INPUT ENABLED  
 writeAxpReg(0x30, 0x80);

SY7088 generates 5V (when EXTEN = 1)
SY7088 output is directly connected to VBUS
VBUS is also connected back into the AXP192 as an input
ACIN is the real USB 5V input

So effectively:
BAT ā†’ IPSOUT ā†’ SY7088 ā†’ VBUS ā†’ AXP192 ā†’ IPSOUT

ā— Observed Problem
When running on battery:

-Enable 5V output (EXTEN = 1)
-Disconnect USB cable
-Immediately, battery current jumps to ~450 mA
-System enters a self-sustained power loop

šŸ” Key Observations
EXTEN is correctly set (verified via register dumps, Reg 0x12 bit 6)
VBUS input is permanently enabled (Reg 0x30 = 0x80)
Boost converter behaves normally
Loop appears only when USB is disconnected

šŸ’” Root Cause
SY7088 output is physically tied to VBUS
AXP192 does not fully isolate VBUS internally
The supposed N_VBUSEN mechanism does NOT break the electrical path

šŸ”„ As a result:
BAT ā†’ boost ā†’ VBUS ā†’ AXP internal path ā†’ IPSOUT ā†’ boost...

This leads to:
continuous energy circulation
high battery drain (~400 mA)
no stable operating point

ā“ Question to the community
Has anyone:

  • Observed this behavior on Core2 or similar AXP192 designs?
  • Found a way to safely use 5V boost to power external accssories from battery without loop?

Thank you,
Cheers,
Adrian YO3HJV

]]>https://community.m5stack.com/topic/8254/m5stack-core2-v1.3-ouroboros-like-power-loopRSS for NodeThu, 11 Jun 2026 17:30:22 GMTMon, 08 Jun 2026 20:09:28 GMT60<![CDATA[Reply to āš ļø M5Stack Core2 v1.3 - Ouroboros-like power loop - on Thu, 11 Jun 2026 07:24:05 GMT]]>Hello @YO3HJV

yes, I measured the current from the battery with this mA-meter and also used the AXP192 registers.

Thanks
Felix

]]>https://community.m5stack.com/post/31063https://community.m5stack.com/post/31063Thu, 11 Jun 2026 07:24:05 GMT<![CDATA[Reply to āš ļø M5Stack Core2 v1.3 - Ouroboros-like power loop - on Thu, 11 Jun 2026 05:55:56 GMT]]>Did you actually measured the current from the battery with a mA-meter?
I am working directly with the AXP192 registers, I tried something simple with UIFlow but was not to my taste...

Here is the project:
Video: https://www.youtube.com/watch?v=Goauv9xGJqY

Adrian

]]>https://community.m5stack.com/post/31062https://community.m5stack.com/post/31062Thu, 11 Jun 2026 05:55:56 GMT<![CDATA[Reply to āš ļø M5Stack Core2 v1.3 - Ouroboros-like power loop - on Wed, 10 Jun 2026 16:26:01 GMT]]>Hello @YO3HJV

glad to hear you figured it out.

I was just setting up a test to see if I get this 400 mA power loop too with my M5Core2; but I do not.

When I set input mode I see about 82 mA drawn from the battery. When I set output mode I see about 99 mA drawn from the battery. (Note: an LED is connected to the Grove port.)

In case your still interested in my UIFlow2 test program. It's in UIFlow2 Project Zone called: M5Core2_Input_Output_Test_UIFlow2.4.6

Thanks
Felix

]]>https://community.m5stack.com/post/31060https://community.m5stack.com/post/31060Wed, 10 Jun 2026 16:26:01 GMT<![CDATA[Reply to āš ļø M5Stack Core2 v1.3 - Ouroboros-like power loop - on Tue, 09 Jun 2026 20:27:05 GMT]]>Finally, I solved it...
No need for 5V output on 5V_BUS because it came from magnetic base charger.
Therefore an interlock code was added:
--When 5V from battery is needed for external acc., VBUS== OFF & EXTEN==1;
--When magnetic base charger (or external 5V is applied to Socket Power (J3) on Bottom2, VBUS == INPUT & EXTEN==0.

This way, the Bottom2 LED's and othe devices are powered with 5V in any situation.

Cheers,
Adrian

]]>https://community.m5stack.com/post/31057https://community.m5stack.com/post/31057Tue, 09 Jun 2026 20:27:05 GMT