DC2418A-2

DC2418-LVC — 2S LiPo/LiHV Low-Voltage Cutoff & Protection Board

An inline protection board for replacing 2S NiMH/NiCd packs with 2S LiPo/LiHV, built around the Analog Devices LTC4368-1. NiMH tolerates being run flat; LiPo/LiHV does not. This board adds the low-voltage cutoff those older packs never needed, plus reverse-battery and bidirectional overcurrent protection, between the battery and the existing load.

Pack-total sensing on the two main leads only — cell balancing is handled by the charger via the balance lead. Adapted from the ADI DC2418A demo board, rescaled from 24 V / 10 A to a 2S (6.0–8.7 V) pack.

Status: built and bench-tested (smoke-stopper current-limited first power-up) on the current revision.

Front (F.Cu)	Back (B.Cu)

Board outline 60.0 × 33.5 mm, 2 layers, XT30PW-M (VIN) and XT30PW-F (VOUT) horizontal connectors, 4× M5.5 mounting holes.

Features

• Under-voltage cutoff (LVC), over-voltage backstop
• Bidirectional overcurrent circuit breaker (fast, resettable)
• Reverse-battery protection (back-to-back N-FETs)
• ~4–10 µA quiescent; enable pin can be switched for µA-level off
• Auto-retry or latch-off, selectable by the RETRY cap

Specifications (as configured)

Thresholds are ratios against the LTC4368's 0.5 V references, so only ratios matter:

V_UV   = 0.5 x (R7+R1+R2+R3) / (R2+R3)   -> 6.36 V
V_OV   = 0.5 x (R7+R1+R2+R3) / R3        -> 9.9 V
I_trip = 0.050 / R4                       -> ~42 A at 1.2 mohm

For 3.0 V/cell set V_UV = 6.0 V; for a different breaker point R4 = 0.050 / I_trip.

Repository contents

DC2418-LVC-end/             KiCad project + Gerbers; XT30 connectors at the board ends
  DC2418A-2.kicad_sch / .kicad_pcb / .kicad_pro
  DC2418A-2-*.gbr / *.drl / *-job.gbrjob    Fabrication outputs (Gerber X2 + Excellon)
DC2418-LVC-side/            Electrically identical; XT30 connectors to the side
  LVC.kicad_sch / .kicad_pcb / .kicad_pro
  LVC-*.gbr / *.drl / *-job.gbrjob          Fabrication outputs
BOM.csv                     LCSC-referenced bill of materials
front.png / back.png        Layout views of DC2418-LVC-end

Bill of materials

Divider values are E96 1%. Cap voltage ratings are inherited 100 V parts; 25 V is sufficient for a 2S pack.

Not in the BOM: the XT30 connectors are not listed — both boards place an AMASS_XT30PW-M (VIN) and an AMASS_XT30PW-F (VOUT), source them separately. The bidirectional TVS recommended under Usage is also not listed.

Do not populate: R5 (2512) — the DC2418A's version-option pair with R4. On the -A build, R4 is the live sense position (1.2 mΩ); R5 is the -B's 0.02 Ω slot. Verified: R4 and R5 bridge the same two nodes (VOUT ↔ Net-(U1-SENSE)), i.e. parallel alternates, not in series — so leaving R5 empty is harmless. Also C9 and C10, both marked OPT.

Build notes

• 2-layer board. Keep VIN → Q2 → Q3 → R4 → VOUT short and wide; 2 oz copper on that path.
• Kelvin-sense R4: route SENSE and VOUT to the resistor's own pads, not the current trace.
• Q2/Q3 PDFN have a bottom thermal pad. The footprints on both boards include it as pad 5 (drain: VIN on Q2, SENSE on Q3) with a paste opening. Without it, solder wicks under the large exposed pad and pulls the FET off its small pins. Needs hot-air/reflow with paste, not an iron. Swap to DPAK (IRLR7843) for iron/heat-gun assembly (footprint changes; keep sources common, drains out).
• Before power-up, net-highlight two nets: the FET common-source node (both sources, not a drain) and the UV/OV tap order (UV taps above OV).

Usage

• Wire battery → VIN/GND and VOUT/GND → the existing load input (not across a motor directly).
• Fit a bidirectional TVS across VOUT–GND to clamp the inductive kick when the breaker opens.
• Charge externally on a balance charger set to the right chemistry (LiHV vs LiPo). Never charge through this board — it does not charge or balance.

⚠️ Safety

Discharge-side protection only. LiPo/LiHV is hazardous if abused — charge on a proper balance charger in a fireproof location, never unattended. Provided as-is, without warranty; verify in your own application.

Provenance & license

Topology adapted from Analog Devices' DC2418A demo board for the LTC4368; independently re-drawn schematic and layout, not affiliated with or endorsed by ADI.

Hardware (schematics, layout, Gerbers): CERN-OHL-S-2.0 — strongly reciprocal. Documentation (this README, BOM, images): CC-BY-4.0.