--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/pirelli/chg-circuit	Wed Mar 23 20:06:08 2022 +0000
@@ -0,0 +1,62 @@
+VBUS from USB connector on L1: microvia at (5679,1177).  On L2 a transition is
+made to two directly adjacent inner vias at (5689,1157) and (5709,1186).  On L5
+another transition is made to a new pair of inner vias at (5565,1089) and
+(5569,1125).  On L7 yet another transition to what appears to be a pair of
+microvias to L8, guessing center coordinates at (5546,1077) and (5546,1108).
+On L8 this VBUS supply passes through a series component marked "H" before going
+to the rest of the circuit.  After passing through this "H" series component,
+the fat power trace goes to a polygon on L8 whose bottom y coord is 1041, top y
+coord 834.  This polygon contains pads for 3 caps (other sides remain to be
+traced) and a microvia at (5592,1034).  The left x coord boundary of the polygon
+is at 5515 where the cap is, or 5474 to the left and up from the cap.  The right
+x coord boundary is at 5627.
+
+The big polygon identified in the previous paragraph feeds VBUS power to a 6-pin
+component that might be the power P-MOSFET for charging.  The 4 pins that could
+constitute the drain output of this big MOSFET land on another polygon which in
+turns feeds to a 2-pin component: it might be the Schottky diode.
+
+Out of the 3 caps connected to what seems to be VCHG (VBUS passed through the
+"H" component), the lower little seems to go to GND, but where does the upper
+little go?  Apparent microvia from L8 to L7 at (5709,940), on L7 there seems to
+be a trace going back to L8 at (5663,858) and an inner via at (5675,965).  It
+looks like ICTL net!
+
+Now let's trace the other side of the left bigger cap from MOSFET VCHG input.
+L8 pad center is at (5469,950), on L7 that spot is solid GND fill - consistent
+with the natural expectation that this cap goes to GND.
+
+Let's trace the presumed ICTL net and see if it really is what it seems to be.
+Inner via at (5675,965) - found it on L2.  Microvia to L1 at (2923,1163), on L1
+it goes to Iota ball D6 - it is indeed ICTL!
+
+Now let's trace the branch from VCHG (VBUS after "H") polygon that starts with
+L8-L7 microvia at (5592,1034).  On L7 it goes to an inner via at (5618,1019) -
+but no connections are seen on any other layer!
+
+Let's try tracing VBUS connection to CP2102.  There appears to be an L8-L7
+microvia at (5349,1392).  On L7 this spot falls on a fat power trace made out
+of a polygon.  This polygon has two visible via holes at (5390,1271) and
+(5631,1250).  It also has spots that may contain hidden microvias back to L8:
+candidate spots (5459,1177), (5460,1059), (5635,1226).  Looking on L8, we see
+that the L7 via hole at (5631,1250) is likely a microvia back to L8, connecting
+to the VBUS-after-"H" fat trace, whereas (5390,1271) is probably an inner via.
+The other 3 spots found from L7 are either false leads or contain microvias to
+the same power trace on L8, as that's where the coordinates fall.
+
+Looking for (5390,1271) inner via on other layers: found it on L2, connects to
+L2-L1 microvia at (5371,1298).  Also on L4: a thick power trace to another inner
+via at (4031,1549).  Let's go back to L2-L1 microvia at (5371,1298): on L1 it
+is a test point and nothing more.  Now let's look for the inner via at
+(4031,1549): on L2 it connects to L2-L1 microvia at (4000,1563).  On L1 this
+microvia falls into the pad of some 2-pad component to GND, and also goes to
+another microvia at (4011,1435).  On the populated pic, the 2-pad component
+appears to be a diode, with the cathode connected to the power net (VCHG?) and
+with the anode to GND.
+
+Continuing the trace from L1-L2 microvia at (4011,1435): on L2 there is a power
+trace to another microvia at (3003,1363).  On L1 it goes to Iota ball A5 - it
+is VCHG.
+
+The via hole on L7 at (5631,1250) appears to be an inner via after all: let's
+look for it on other layers.  Couldn't find any connections.