Bq40370: Work

1. Overview: What is the bq40370?

The bq40370 is a Li-Ion / Li-Polymer battery pack manager with a CEDV (Compensated End of Discharge Voltage) gas gauge. It integrates:

• Analog front-end (AFE) for cell protection
• A 16-bit microcontroller with gas gauge algorithms
• I²C communication interface
• Internal temperature sensor (plus support for external thermistors)

It is designed for 2-series (2S) to 4-series (4S) battery packs, commonly used in: bq40370

• Power tools
• E-bikes / e-scooters
• UPS / backup systems
• Medical devices
• Portable electronics

Note: The bq40370 is a ROM-based device (firmware is fixed in ROM, not flash-programmable). Configuration is done via data flash parameters over I²C. Analog front-end (AFE) for cell protection A 16-bit

11. Example: Single-Cell Protection Circuit (Description)

• Battery positive connects to PACK+; PACK- goes to system ground through device.
• R_sense placed in the negative leg of the battery; the sense amplifier measures drop across it.
• Two external N-channel MOSFETs (back-to-back) placed between PACK- and system ground, driven by charge and discharge gates.
• TS pin connected to a 10 kΩ NTC mounted on the cell.
• Decoupling: 1 µF ceramic at VCC, 10 µF bulk on PACK+ to GND.
• FAULT pin to MCU interrupt; device configured to auto-retry once every 1 s after trip (example behavior — actual timer varies by variant).

4.3. Protection Logic

• Programmable thresholds and delays for:
  • Overvoltage (OV)
  • Undervoltage (UV)
  • Overcurrent in charge (OCC) / discharge (OCD)
  • Short circuit (SCD)
  • Overtemperature (OT)

4. Functional Blocks