Datasheet for BYD BM3451 series ICs that protect 3‑, 4‑ and 5‑cell rechargeable battery packs.
The BM3451 series from BYD Microelectronics provides high‑integration protection for 3‑, 4‑ and 5‑cell rechargeable battery packs used in power tools, e‑bikes and UPS systems. It monitors cell voltage, charge/discharge current and temperature to prevent over‑charge, over‑discharge, over‑current, short‑circuit, and temperature hazards, and includes a capacity‑balancing function.
The device is offered in TSSOP20 and TSSOP28 packages, supports cascade operation for packs of six cells or more, and features external‑capacitor‑adjustable delay times. Detailed electrical characteristics, pin assignments, absolute maximum ratings, and application notes are provided in the following sections.
| Operating current (with temperature protection) | 25 µA typical |
|---|---|
| Operating current (without temperature protection) | 15 µA typical |
| Sleep current | 6 µA typical |
| Over‑charge detection voltage range | 3.6 V ~ 4.6 V |
| Charging over‑current detection voltage | -0.03 V / -0.05 V / -0.1 V / -0.15 V / -0.2 V |
The typical operating current is 25 µA when temperature protection is enabled, and 15 µA without temperature protection.
If any cell voltage exceeds the over‑charge detection threshold VDET1 for the programmed delay TOV, the chip pulls the CO control pin low to disable charging.
Yes, the series supports cascade operation, allowing protection of six‑cell or larger packs by linking the DOIN/COIN pins between chips.
The balance pins (BAL1‑BAL5 and BALUP/BALDN) enable cell‑to‑cell capacity balancing to reduce voltage differences and extend pack life.