Design Log DEC 047 or ing mosfet corrected to csd17578q5a - thepinkmile/Enigma-NG GitHub Wiki

DEC-047 - OR-ing MOSFET Corrected to CSD17578Q5A

  • Status: Decided
  • Date: 2025-07-05
  • Category: Component Selection / Part Number Correction
  • Area: Power Module (Q1, Q2, Q3)
  • Author: Izzyonstage & GitHub Copilot

Summary

The OR-ing MOSFET for the Power Module ideal-diode circuit was incorrectly specified as CSD17483F4T. This has been corrected to CSD17578Q5A.

Problem

Q1, Q2, and Q3 (LM74700-Q1 ideal-diode OR-ing MOSFETs) were listed as CSD17483F4T with a description of "30V 10A SON-8". The local datasheet (csd17483f4-datasheet.md) confirmed this part is actually a 1.5A / 260mΩ / PICOSTAR YJC 3-pin FemtoFET - completely unsuitable for an OR-ing application handling multi-ampere input currents.

Decision

Replace CSD17483F4T with CSD17578Q5A (TI NexFET N-channel MOSFET):

  • V_DSS: 30V
  • I_D: 25A continuous (package limited), 59A (silicon limited)
  • R_DS(on): 5.9mΩ @ V_GS = 10V; 7.9mΩ @ V_GS = 4.5V
  • Package: SON 5x6mm
  • DigiKey: 296-48512-1-ND | Mouser: 595-CSD17578Q5A | JLCPCB: C2871447

Rationale

CSD17578Q5A is designed specifically for point-of-load and OR-ing converter applications. Its 5.9mΩ R_DS(on) provides extremely low conduction losses, and 25A package rating gives adequate headroom above the expected OR-ing path current. The LM74700-Q1 gate-drive requirements (charge-pump +7V above source) are fully compatible with this device's ±20V V_GS limit.

Alternatives Considered

Alternative Reason rejected
Retain CSD17483F4T Incorrect part - 1.5A FemtoFET cannot handle OR-ing path currents
Other SON-8 OR-ing MOSFETs CSD17578Q5A already approved and datasheet verified; no need to evaluate alternatives

Impact

  • design/Electronics/Power_Module/Design_Spec.md: Q1/Q2/Q3 MPN, PNs, and specs updated.
  • design/Electronics/Consolidated_BOM.md: CSD17578Q5A row replaces CSD17483F4T.
  • design/Electronics/all_boards_bom.json: Updated accordingly.

Cross-ref

design/Electronics/Power_Module/Design_Spec.md §5 (Q1, Q2, Q3 BOM row), design/Datasheets/TI-csd17578q5a-datasheet.pdf.