# Prius 4S BM3451 BMS uUHq ## Description Custom 4S CATL NCM module BMS/CMU sampling and passive balancing board for a Toyota Prius hybrid battery retrofit using BM3451SMDC-T28A with isolated CO/DO fault outputs and M4 sense studs. ## Project Details - **Owner:** zmltyta543 - **Created:** 6/8/2026 - **Last Updated:** 6/8/2026 - **Visibility:** Public - **Forks:** 1 ## Key Components ### B- — [Generic Testpoint](https://www.flux.ai/jharwinbarrozo/generic-testpoint~esx.md) - Role Details: M4-sized voltage sense stud/pad for Toyota harness ring terminal at B-. - Testpoint Size: 0.5 - Role: Sensing (Shunt) **Pins:** - P1 ### B1 P1 - U1 P3.5/TA0.1 — [Generic Testpoint](https://www.flux.ai/jharwinbarrozo/generic-testpoint~esx.md) - Role Details: M4-sized voltage sense stud/pad for Toyota harness ring terminal at B1. - Role: Sensing (Shunt) - Testpoint Size: 0.5 **Pins:** - P1 ### B2 P1 - U1 P3.7/TA1CLK — [Generic Testpoint](https://www.flux.ai/jharwinbarrozo/generic-testpoint~esx.md) - Role: Sensing (Shunt) - Testpoint Size: 0.5 - Role Details: M4-sized voltage sense stud/pad for Toyota harness ring terminal at B2. **Pins:** - P1 ### B3 P1 - U1 TDO/TDI/UCB0SIMO/UCB0SDA/A7/P1.7 — [Generic Testpoint](https://www.flux.ai/jharwinbarrozo/generic-testpoint~esx.md) - Role Details: M4-sized voltage sense stud/pad for Toyota harness ring terminal at B3. - Testpoint Size: 0.5 - Role: Sensing (Shunt) **Pins:** - P1 ### B4 P1 - RVCC P1 — [Generic Testpoint](https://www.flux.ai/jharwinbarrozo/generic-testpoint~esx.md) - Role Details: M4-sized voltage sense stud/pad for Toyota harness ring terminal at B4 / pack positive. - Role: Sensing (Shunt) - Testpoint Size: 0.5 **Pins:** - P1 ### COC1 — [Generic Capacitor](https://www.flux.ai/jharwinbarrozo/generic-capacitor~1d.md) - Part Type: Non-Polarized Capacitor - Voltage Rating: 50V - Role: Timing - Role Details: BM3451 TOC1 discharge overcurrent delay capacitor; datasheet typical 0.1uF. - Capacitance: 1e-7F - Package: SMD_0603_1608Metric **Pins:** - P1 [pin 1] - P2 [pin 2] ### COC2 — [Generic Capacitor](https://www.flux.ai/jharwinbarrozo/generic-capacitor~1d.md) - Voltage Rating: 50V - Part Type: Non-Polarized Capacitor - Role Details: BM3451 TOC2 discharge overcurrent delay capacitor; datasheet typical 0.1uF. - Package: SMD_0603_1608Metric - Capacitance: 1e-7F - Role: Timing **Pins:** - P1 [pin 1] - P2 [pin 2] ### COV — [Generic Capacitor](https://www.flux.ai/jharwinbarrozo/generic-capacitor~1d.md) - Capacitance: 1e-7F - Package: SMD_0603_1608Metric - Voltage Rating: 50V - Part Type: Non-Polarized Capacitor - Role Details: BM3451 TOV overcharge protection delay capacitor; datasheet typical 0.1uF. - Role: Timing **Pins:** - P1 [pin 1] - P2 [pin 2] ### COVD — [Generic Capacitor](https://www.flux.ai/jharwinbarrozo/generic-capacitor~1d.md) - Role Details: BM3451 TOVD over-discharge protection delay capacitor; datasheet typical 0.1uF. - Capacitance: 1e-7F - Package: SMD_0603_1608Metric - Role: Timing - Voltage Rating: 50V - Part Type: Non-Polarized Capacitor **Pins:** - P1 [pin 1] - P2 [pin 2] ### CVC1 — [Generic Capacitor](https://www.flux.ai/jharwinbarrozo/generic-capacitor~1d.md) - Voltage Rating: 50V - Role: Filtering - Part Type: Non-Polarized Capacitor - Capacitance: 0.000001F - Package: SMD_0603_1608Metric - Role Details: BM3451 cell 1 sense filter capacitor; datasheet C1-C5 typical 1uF, >50V endurance. **Pins:** - P1 [pin 1] - P2 [pin 2] ### CVC2 — [Generic Capacitor](https://www.flux.ai/jharwinbarrozo/generic-capacitor~1d.md) - Capacitance: 0.000001F - Package: SMD_0603_1608Metric - Role Details: BM3451 cell 2 sense filter capacitor; datasheet C1-C5 typical 1uF, >50V endurance. - Role: Filtering - Voltage Rating: 50V - Part Type: Non-Polarized Capacitor **Pins:** - P1 [pin 1] - P2 [pin 2] ### CVC3 — [Generic Capacitor](https://www.flux.ai/jharwinbarrozo/generic-capacitor~1d.md) - Role: Filtering - Voltage Rating: 50V - Part Type: Non-Polarized Capacitor - Role Details: BM3451 cell 3 sense filter capacitor; datasheet C1-C5 typical 1uF, >50V endurance. - Capacitance: 0.000001F - Package: SMD_0603_1608Metric **Pins:** - P1 [pin 1] - P2 [pin 2] ### CVC4 — [Generic Capacitor](https://www.flux.ai/jharwinbarrozo/generic-capacitor~1d.md) - Voltage Rating: 50V - Part Type: Non-Polarized Capacitor - Package: SMD_0603_1608Metric - Capacitance: 0.000001F - Role Details: BM3451 cell 4 sense filter capacitor; datasheet C1-C5 typical 1uF, >50V endurance. - Role: Filtering **Pins:** - P1 [pin 1] - P2 [pin 2] ### CVCC — [Generic Capacitor](https://www.flux.ai/jharwinbarrozo/generic-capacitor~1d.md) - Voltage Rating: 50V - Part Type: Non-Polarized Capacitor - Role Details: BM3451 VCC supply decoupling; datasheet CVCC typical 10uF from VCC to GND. - Role: Decoupling - Capacitance: 0.00001F - Package: SMD_0603_1608Metric **Pins:** - P1 [pin 1] - P2 [pin 2] ### FLT_A — [Generic Testpoint](https://www.flux.ai/jharwinbarrozo/generic-testpoint~esx.md) - Testpoint Size: 0.5 - Role Details: One side of isolated floating, non-grounded fault loop; not connected to BMS ground. - Role: Isolation **Pins:** - P1 ### FLT_B — [Generic Testpoint](https://www.flux.ai/jharwinbarrozo/generic-testpoint~esx.md) - Role Details: Other side of isolated floating, non-grounded fault loop; not connected to BMS ground. - Role: Isolation - Testpoint Size: 0.5 **Pins:** - P1 ### ISO_CO — [LTV-817S](https://www.flux.ai/lcsc/ltv-817s~nmy4.md) - JLCPCB Part Class: Extended Part - Product Info Url: https://lcsc.com/product-detail/SMD-Optocouplers_LTV-817S_C189217.html - Part Type: Optocouplers - Phototransistor Output - Role: Isolation - Manufacturer Part Number: LTV-817S - Manufacturer Name: LITEON(光宝) - Datasheet URL: https://storage.googleapis.com/graviton-electric-symbols/document_assets/lcsc/1810161120_Lite-On-LTV-817S_C189217.pdf - LCSC Part Number: C189217 - Role Details: Phototransistor output forms a floating, non-grounded isolated charge-fault loop contact for vehicle ECU interface. - Package or Case Code: OPTO-SMD-4_L4.6-W6.5-P2.54-LS10.3-TL **Pins:** - AN [pin 1] - CA [pin 2] - COL [pin 4] - EM [pin 3] ### ISO_DO — [LTV-817S](https://www.flux.ai/lcsc/ltv-817s~nmy4.md) - Datasheet URL: https://storage.googleapis.com/graviton-electric-symbols/document_assets/lcsc/1810161120_Lite-On-LTV-817S_C189217.pdf - LCSC Part Number: C189217 - Package or Case Code: OPTO-SMD-4_L4.6-W6.5-P2.54-LS10.3-TL - Role: Isolation - Role Details: Phototransistor output forms a floating, non-grounded isolated discharge-fault loop contact for vehicle ECU interface. - Manufacturer Part Number: LTV-817S - Manufacturer Name: LITEON(光宝) - Part Type: Optocouplers - Phototransistor Output - Product Info Url: https://lcsc.com/product-detail/SMD-Optocouplers_LTV-817S_C189217.html - JLCPCB Part Class: Extended Part **Pins:** - AN [pin 1] - CA [pin 2] - COL [pin 4] - EM [pin 3] ### Q1 — [BSS138](https://www.flux.ai/kicad-part-library/bss138~ed2.md) - Role: Switching - Role Details: N-channel MOSFET used as low-side switch for local passive cell balancing resistor. - Package or Case Code: SOT-23 - Datasheet URL: https://www.onsemi.com/pub/Collateral/BSS138-D.PDF - Manufacturer Part Number: BSS138 **Pins:** - D [pin 3] - G [pin 1] - S [pin 2] ### Q2 — [BSS138](https://www.flux.ai/kicad-part-library/bss138~ed2.md) - Package or Case Code: SOT-23 - Role Details: N-channel MOSFET used as low-side switch for local passive cell balancing resistor. - Role: Switching - Datasheet URL: https://www.onsemi.com/pub/Collateral/BSS138-D.PDF - Manufacturer Part Number: BSS138 **Pins:** - D [pin 3] - G [pin 1] - S [pin 2] ### Q3 — [BSS138](https://www.flux.ai/kicad-part-library/bss138~ed2.md) - Role: Switching - Package or Case Code: SOT-23 - Datasheet URL: https://www.onsemi.com/pub/Collateral/BSS138-D.PDF - Manufacturer Part Number: BSS138 - Role Details: N-channel MOSFET used as low-side switch for local passive cell balancing resistor. **Pins:** - D [pin 3] - G [pin 1] - S [pin 2] ### Q4 — [BSS138](https://www.flux.ai/kicad-part-library/bss138~ed2.md) - Package or Case Code: SOT-23 - Role: Switching - Role Details: N-channel MOSFET used as low-side switch for local passive cell balancing resistor. - Manufacturer Part Number: BSS138 - Datasheet URL: https://www.onsemi.com/pub/Collateral/BSS138-D.PDF **Pins:** - D [pin 3] - G [pin 1] - S [pin 2] ### RBAL1 — [Generic Resistor](https://www.flux.ai/jharwinbarrozo/generic-resistor~3e.md) - Role Details: Cell 1 passive balancing resistor; 75Ω gives about 55mA near 4.1V and dissipates about 0.23W, with 2W minimum rating requested. - Role: Current Limiting - Resistance: 75Ω - Package: SMD_0603_1608Metric - Power Rating: 2W - Part Type: Resistor **Pins:** - P1 [pin 1] - P2 [pin 2] ### RBAL2 — [Generic Resistor](https://www.flux.ai/jharwinbarrozo/generic-resistor~3e.md) - Part Type: Resistor - Resistance: 75Ω - Package: SMD_0603_1608Metric - Role: Current Limiting - Role Details: Cell 2 passive balancing resistor; 75Ω gives about 55mA near 4.1V and dissipates about 0.23W, with 2W minimum rating requested. - Power Rating: 2W **Pins:** - P1 [pin 1] - P2 [pin 2] ### RBAL3 — [Generic Resistor](https://www.flux.ai/jharwinbarrozo/generic-resistor~3e.md) - Part Type: Resistor - Package: SMD_0603_1608Metric - Resistance: 75Ω - Role Details: Cell 3 passive balancing resistor; 75Ω gives about 55mA near 4.1V and dissipates about 0.23W, with 2W minimum rating requested. - Power Rating: 2W - Role: Current Limiting **Pins:** - P1 [pin 1] - P2 [pin 2] ### RBAL4 — [Generic Resistor](https://www.flux.ai/jharwinbarrozo/generic-resistor~3e.md) - Role Details: Cell 4 passive balancing resistor; 75Ω gives about 55mA near 4.1V and dissipates about 0.23W, with 2W minimum rating requested. - Package: SMD_0603_1608Metric - Resistance: 75Ω - Part Type: Resistor - Role: Current Limiting - Power Rating: 2W **Pins:** - P1 [pin 1] - P2 [pin 2] ### RCO — [Generic Resistor](https://www.flux.ai/jharwinbarrozo/generic-resistor~3e.md) - Part Type: Resistor - Role: Pull Up / Down - Resistance: 10000000Ω - Package: SMD_0603_1608Metric - Role Details: Pulls BM3451 CO low when the open-drain output is high impedance during charge fault. **Pins:** - P1 [pin 1] - P2 [pin 2] ### RDO — [Generic Resistor](https://www.flux.ai/jharwinbarrozo/generic-resistor~3e.md) - Package: SMD_0603_1608Metric - Role: Current Limiting - Resistance: 2000Ω - Role Details: Limits current from BM3451 DO output into optocoupler LED input. - Part Type: Resistor **Pins:** - P1 [pin 1] - P2 [pin 2] ### RISO_CO — [Generic Resistor](https://www.flux.ai/jharwinbarrozo/generic-resistor~3e.md) - Package: SMD_0603_1608Metric - Power Rating: 0.25W - Role: Current Limiting - Resistance: 10000Ω - Part Type: Resistor - Role Details: Limits current into CO optocoupler LED from B4/VCC; about 1.5mA at 16.8V stack voltage. **Pins:** - P1 [pin 1] - P2 [pin 2] ### RISO_DO — [Generic Resistor](https://www.flux.ai/jharwinbarrozo/generic-resistor~3e.md) - Role: Current Limiting - Role Details: Limits current into DO optocoupler LED from B4/VCC; about 1.5mA at 16.8V stack voltage. - Power Rating: 0.25W - Part Type: Resistor - Package: SMD_0603_1608Metric - Resistance: 10000Ω **Pins:** - P1 [pin 1] - P2 [pin 2] ### RT1 — [TX08F103F3435ER](https://www.flux.ai/adrian95/tx08f103f3435er~b0z.md) - License: https://creativecommons.org/licenses/by/4.0/ - Datasheet URL: https://www.ohmite.com/assets/images/res-tx.pdf - Part Type: Thermistor - Manufacturer Part Number: TX08F103F3435ER - Role: Sensing (Shunt) - Manufacturer Name: Ohmite - Role Details: 10k NTC temperature sensor for BM3451 hardware over-temperature comparator. **Pins:** - 1 [pin 1] - 2 [pin 2] ### RTRH — [Generic Resistor](https://www.flux.ai/jharwinbarrozo/generic-resistor~3e.md) - Role: Voltage Reference - Part Type: Resistor - Resistance: 7000Ω - Package: SMD_0603_1608Metric - Role Details: BM3451 TRH temperature protection reference; datasheet example uses RTRH=7kΩ with 103AT-class 10k NTC. **Pins:** - P1 [pin 1] - P2 [pin 2] ### RVC1 — [Generic Resistor](https://www.flux.ai/jharwinbarrozo/generic-resistor~3e.md) - Resistance: 1000Ω - Tolerance: 1% - Package: SMD_0603_1608Metric - Part Type: Resistor - Role Details: Series sense resistor from raw B1 tap to filtered BM3451 VC2 node; with CVC1=1µF gives τ=1ms. - Role: Filtering **Pins:** - P1 [pin 1] - P2 [pin 2] ### RVC2 — [Generic Resistor](https://www.flux.ai/jharwinbarrozo/generic-resistor~3e.md) - Resistance: 1000Ω - Tolerance: 1% - Role: Filtering - Package: SMD_0603_1608Metric - Part Type: Resistor - Role Details: Series sense resistor from raw B2 tap to filtered BM3451 VC3 node; with CVC2/CVC3 network gives τ=1ms. **Pins:** - P1 [pin 1] - P2 [pin 2] ### RVC3 — [Generic Resistor](https://www.flux.ai/jharwinbarrozo/generic-resistor~3e.md) - Part Type: Resistor - Package: SMD_0603_1608Metric - Tolerance: 1% - Resistance: 1000Ω - Role: Filtering - Role Details: Series sense resistor from raw B3 tap to filtered BM3451 VC4 node; with CVC3/CVC4 network gives τ=1ms. **Pins:** - P1 [pin 1] - P2 [pin 2] ### RVC4 — [Generic Resistor](https://www.flux.ai/jharwinbarrozo/generic-resistor~3e.md) - Role: Filtering - Role Details: Series sense resistor from raw B4 tap to filtered BM3451 VC5 node; with CVC4=1µF gives τ=1ms while RVCC/CVCC retain VCC filtering. - Package: SMD_0603_1608Metric - Resistance: 1000Ω - Tolerance: 1% - Part Type: Resistor **Pins:** - P1 [pin 1] - P2 [pin 2] ### RVCC — [Generic Resistor](https://www.flux.ai/jharwinbarrozo/generic-resistor~3e.md) - Role Details: BM3451 VCC input filter resistor from pack positive/B4, per datasheet RVCC typical 1kΩ. - Role: Filtering - Resistance: 1000Ω - Package: SMD_0603_1608Metric - Part Type: Resistor **Pins:** - P1 [pin 1] - P2 [pin 2] ### RVM — [Generic Resistor](https://www.flux.ai/jharwinbarrozo/generic-resistor~3e.md) - Resistance: 220000Ω - Package: SMD_0603_1608Metric - Role Details: BM3451 VM terminal bias/load-detection resistor per datasheet typical value. - Part Type: Resistor - Role: Sensing (Shunt) **Pins:** - P1 [pin 1] - P2 [pin 2] ### U1 — [MSP430G2233IPW28](https://www.flux.ai/kicad-part-library/msp430g2233ipw28~jzs.md) - Role: Protection - Datasheet URL: https://cdn.flux.ai/project/chat/attachments/BM3451-0329c543-c764-42dc-9506-1a52b37dc2b0.PDF - Integrated Circuit Type: 3/4/5-cell lithium battery protector with external balancing - Package or Case Code: TSSOP-28 - Manufacturer Name: BYD Microelectronics - Manufacturer Part Number: BM3451SMDC-T28A - Role Details: BM3451SMDC-T28A mapped onto TSSOP-28 template by physical pad number: 1 BALUP NC, 2 DOIN NC, 3 COIN NC, 4 TOV, 5 TOVD, 6 TOC1, 7 TOC2, 8 NTC, 9 TRH, 10 VM, 11 CO, 12 DO, 13 BALDN NC, 14 VIN NC, 15 OCCT NC, 16 SET=VCC, 17 GND, 18 BAL1 NC in 4S, 19 VC1=GND, 20 BAL2, 21 VC2=B1, 22 BAL3, 23 VC3=B2, 24 BAL4, 25 VC4=B3, 26 BAL5, 27 VC5=B4, 28 VCC. **Pins:** - ~{RST}/NMI/SBWTDIO [pin 24] - ADC10CLK/VREF-/VeREF-/A3/P1.3 [pin 5] - DVCC [pin 1] - DVSS [pin 28] - P3.0/TA0.2 [pin 9] - P3.1/TA1.0 [pin 8] - P3.2/TA1.1 [pin 13] - P3.3/TA1.2 [pin 14] - P3.4/TA0.0 [pin 15] - P3.5/TA0.1 [pin 19] - P3.6/TA0.2 [pin 20] - P3.7/TA1CLK [pin 21] - TA0.0/UCA0RXD/UCA0SOMI/A1/P1.1 [pin 3] - TA0.1/UCA0TXD/UCA0SIMO/A2/P1.2 [pin 4] - TA0.1/XIN/P2.6 [pin 27] - TA0CLK/ACLK/CA0/A0/P1.0 [pin 2] - TA1.0/P2.0 [pin 10] - TA1.0/P2.3 [pin 16] - TA1.1/P2.1 [pin 11] - TA1.1/P2.2 [pin 12] - TA1.2/P2.4 [pin 17] - TA1.2/P2.5 [pin 18] - TCK/SMCLK/UCB0STE/UCA0CLK/VREF+/VeREF+/A4/P1.4 [pin 6] - TDI/TCLK/TA0.1/UCB0SOMI/UCB0SCL/A6/P1.6 [pin 22] - TDO/TDI/UCB0SIMO/UCB0SDA/A7/P1.7 [pin 23] - TEST/SBWTCK [pin 25] - TMS/TA0.0/UCB0CLK/UCA0STE/A5/P1.5 [pin 7] - XOUT/P2.7 [pin 26] *The full schematic, PCB layout, bill of materials, and interactive design are available at [https://www.flux.ai/zmltyta543/prius-4s-bm3451-bms-uuhq~pf](https://www.flux.ai/zmltyta543/prius-4s-bm3451-bms-uuhq~pf).* --- *Generated from [https://www.flux.ai/zmltyta543/prius-4s-bm3451-bms-uuhq~pf](https://www.flux.ai/zmltyta543/prius-4s-bm3451-bms-uuhq~pf)*