From cb938405186b29b06fb793974818a5fe45bc78ce Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Leopoldo=20Rodr=C3=ADguez?= Date: Sat, 5 Sep 2026 01:11:02 +0000 Subject: [PATCH] v6 Copper Plan: U18 V_BCKP (pin 36) decoupling fix - pin 36 is V_BCKP on /3V3 (always-on), deliberately not /3V3_GNSS: RTC + ephemeris survive when U21's switched rail is off - no /3V3 cap existed within 19 mm of the pin; spare Cu4 (100nF, already /3V3-GND) reassigned to sit at pin 36 - C123 clarified: U18 has only two VCC pins; C123 is the U21-output third 100nF, not a VCC-pin cap Co-Authored-By: Claude Fable 5 Claude-Session: https://claude.ai/code/session_01YJ4eAB6zjQT49RVwpgfKdt --- ..._Drogheda_v6-Copper-Plan_Placement-EMC-Guide.html | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) diff --git a/03-Architecture-Hardware/2026-09-02_Drogheda_v6-Copper-Plan_Placement-EMC-Guide.html b/03-Architecture-Hardware/2026-09-02_Drogheda_v6-Copper-Plan_Placement-EMC-Guide.html index 08840da..1204ece 100644 --- a/03-Architecture-Hardware/2026-09-02_Drogheda_v6-Copper-Plan_Placement-EMC-Guide.html +++ b/03-Architecture-Hardware/2026-09-02_Drogheda_v6-Copper-Plan_Placement-EMC-Guide.html @@ -162,7 +162,9 @@ a{color:var(--plane)} RefValueBelongs toPlacement C11910 µFU21 input (SW_5V)at the LDO input pin C120 C12410 µF ×2U21 out → U18 VCCone at U21 output, one at U18's main VCC entry -C121 C122 C123100 nF ×3U18 VCC pinsone per supply pin, at the pin +C121 C122100 nF ×2U18 VCC pins 33/34one per supply pin, at the pin +C123100 nFU21 VOUT, beside C120U18 has only two VCC pins — C123 is the rail-entry third +Cu4100 nFU18 pin 36 V_BCKP (/3V3!)V_BCKP rides the always-on 3V3, not 3V3_GNSS — that is deliberate (RTC + ephemeris survive when U21 is switched off). It needs its own /3V3 cap at the pin; C120–C124 are all on /3V3_GNSS and cannot serve it. Repurpose the spare Cu4. C144 C145100 nF · 100 pFU18 VCC_RF · L21 bias teeat L21's feed side — the antenna supply injection C143100 nF RFJ12 RF line (DC block)inline in the 50 Ω run between L21 tap and J12 D27ESD9L (≤0.5 pF)J12at the connector, stub-less tap on the RF line @@ -286,7 +288,9 @@ a{color:var(--plane)} Q6 R2 C101MMBT3904 · 10k · 22 µFK1 coil side🟠relay driver + coil supply cap U18 — ZED-F9P GNSS (+U21 LDO · J12) -C121 C122 C123100 nF ×3U18 VCC pins, one each🔴per-pin decouplers +C121 C122100 nF ×2U18 VCC pins 33/34, one each🔴per-pin decouplers +C123100 nFU21 VOUT beside C120🟠third 100 nF — rail entry, not a third VCC pin +Cu4100 nFU18 pin 36 V_BCKP — on /3V3🔴only /3V3 cap in the corner; backup rail stays alive when U21 is off C120 C12410 µF ×2U21 output · U18 VCC entry🔴LDO stability + local bulk C11910 µFU21 input pin🔴LDO input C3 C4047 µF · 22 µFSW_5V feed near U21🟠upstream bulk @@ -360,7 +364,7 @@ a{color:var(--plane)} Panel · sensors · leftovers Cu3100 nFU3 SHT40 VDD pin🔴sensor supply -Cu4100 nF— spare (ex-TMP102)🔵reassign to any bare VDD pin or delete +Cu4100 nFreassigned → U18 pin 36 V_BCKP🔴see the GNSS group — it is already on /3V3–GND, so a board move is all it takes C992.2 nFU17/U12 area rail bypass🔵verify its role in the sch before final spot R4110kU3/U16 I2C area🔵pull-up strap R3 D1120R · LEDP9 pins🔵R3 at the jack @@ -390,5 +394,5 @@ a{color:var(--plane)}
  • Bench items carried forward: measure U21's 3V3_GNSS rise (F9P ramp window), verify U25's EP against the TI DDA drawing, and the DzG1 jumper check on the fabbed v5.5 boards.
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    EinarBoard HBOX v6 · Helgen · updated 04-Sep-2026: master proximity table (§8) from the live netlist; sch↔pcb designators verified in sync (P1–P12, 0 mismatches).

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    EinarBoard HBOX v6 · Helgen · updated 05-Sep-2026: U18 V_BCKP (pin 36, /3V3) gets Cu4; C123 clarified as U21-output cap; §8 rows corrected.