Design Log DEC 002 poe option a2 selected coilcraft poe600f 12ld - thepinkmile/Enigma-NG GitHub Wiki
DEC-002 - PoE Option A2 Selected: Coilcraft POE600F-12LD
- Status: Decided
- Date: 2025
- Category: Electrical
- Area: Power Module PoE subsystem, T2 transformer, TPS23730 feedback network
Decision
The PoE transformer T2 uses a Coilcraft POE600F-12LD off-the-shelf ACF transformer (12V output, 60W, 200kHz, ≥1500Vrms isolation, SMT package). The remainder of the PoE chain uses TPS2372-4 (802.3bt Type 4 PD interface) and TPS23730 (ACF controller), with TPS23730 feedback resistors adjusted for the 12V output.
Rationale
- Replaces a custom-wound transformer design (Option A: 15V, 8-16 week lead time, ~£35-46 BOM) with a catalogue part available from Coilcraft Direct.
- Off-the-shelf: £3.54 qty-1, ~£1.86 volume, in stock. Lead time: days not weeks.
- Same ACF topology as the custom design - only feedback resistors change. No PCB layout changes to high-current paths.
- 12V output falls within the TPS25980 eFuse UVLO/OVLO window (11V - 16.9V) with no additional buck stage needed.
Alternatives Considered
-
Option A (Custom T2, 15V): Higher voltage headroom. Rejected: custom winding, long lead time, cost.
-
Option C (Silvertel Ag59812-LPB integrated module): Higher integration, 95% efficiency, ~£19-27. Rejected: higher cost, fixed form factor, less flexibility for thermal management, vendor
lock-in.
-
Kinetic Technologies KPM5912: 85W, 93% efficiency. Rejected: not stocked by any UK/EU distributor.
Key Parameters
| Parameter | Value |
|---|---|
| Part | Coilcraft POE600F-12LD |
| Output | 12V nominal |
| Power | 60W (Type 4 PD, 72W class) |
| Isolation | ≥1500Vrms |
| Topology | Active Clamp Flyback (ACF) |
| Package | SMT |
| Price (qty-1) | ~£3.54 |