Skip to content

fix(hw): PHY 88E1512 primary, KSZ9031RNX substitute (closes #36) #37

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
marcos-mendez merged 1 commit into from
May 6, 2026
Merged

fix(hw): PHY 88E1512 primary, KSZ9031RNX substitute (closes #36) #37

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
26 changes: 21 additions & 5 deletions docs/PCB_DESIGN.md
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -56,11 +56,25 @@ host link to a Mini-ITX (or other) carrier board.

```
LiteEth ── ECP5 SerDes pair ── SGMII PHY chip ── magnetics ── RJ45 ── 1000BASE-T
(fabric) (1.25 GBaud) (Microchip
KSZ9031RNX
or equivalent)
(fabric) (1.25 GBaud) (Marvell Alaska
88E1512
or KSZ9031RNX
substitute)
```

**Primary PHY: Marvell Alaska 88E1512** (32-pin QFN, 5×5 mm).
Selected for broad LATAM distributor stocking (Mouser, Digi-Key,
Arrow), smaller package than the alternative (32-pin vs 48-pin
QFN), and an NDA-free public datasheet (`88E151x_PB.pdf`).

**Documented substitute: Microchip KSZ9031RNX** (48-pin QFN). The
2.5 V analog and 1.0 V digital-core rails are fungible between the
two parts at this voltage class, so no power-tree change is needed
if a builder swaps. See
[`hw/schematic-page-breakdown.md`](hw/schematic-page-breakdown.md)
§P4 (Stays PR #35) for the full criteria-based selection rationale
and the swap procedure that placement PR P4 will codify.

The SGMII PHY chip needs **2.5 V** (analog) and **1.0 V** (digital
core) rails, both added to the rev-A power tree below.

Expand Down Expand Up @@ -111,7 +125,8 @@ chosen part is `LFE5UM5G-85F-8BG756I` per
- **2.5 V step-down — FPGA `VCCAUX` *and* `VCCAUXA`** (datasheet
range 2.375–2.625 V, nominal 2.5 V; one rail can feed both per
Table 3.2 footnote 2 since they share voltage); also feeds the
SGMII PHY analog supply (KSZ9031RNX VDDA_2V5).
SGMII PHY analog supply (88E1512 AVDD25, or KSZ9031RNX VDDA_2V5
substitute).
- 1.8 V step-down — DDR3L controller-side logic auxiliary
(general-purpose 1.8 V rail; **not** the FPGA aux bank — VCCAUX
is 2.5 V per datasheet Table 3.2).
Expand All @@ -135,7 +150,8 @@ chosen part is `LFE5UM5G-85F-8BG756I` per
separately per the *ECP5 and ECP5-5G SerDes/PCS Usage Guide*
(FPGA-TN-02206); routing decision deferred to schematic
capture.
- 1.0 V step-down — SGMII PHY digital core (KSZ9031RNX VDDC_1V0)
- 1.0 V step-down — SGMII PHY digital core (88E1512 DVDD, or
KSZ9031RNX VDDC_1V0 substitute)
- 0.675 V LDO — DDR3L VTT termination (= VDD/2 of the 1.35 V
module rail; was 0.75 V in the standard-DDR3 draft).

Expand Down
Loading