The **BQ20Z95** is a highly integrated gas gauge IC designed for battery pack systems, specifically for Li-Ion and Li-Polymer chemistries. It utilizes TI’s proprietary **Impedance Track™** technology to provide accurate state-of-charge (SoC) data. --- ### 1. Key Technical Specifications The device acts as a complete solution for monitoring, protecting, and balancing battery cells. | Feature | Specification | | :--- | :--- | | **Cell Count** | 2, 3, or 4 cells in series | | **Communication** | SMBus v1.1 | | **Gauging Technology** | Impedance Track™ (No discharge cycle required) | | **Package** | 30-pin TSSOP | | **ADC Resolution** | 16-bit Delta-Sigma (Current/Voltage/Temp) | --- ### 2. Functional Electronic Blocks The BQ20Z95 architecture is divided into several specialized electronic subsystems: #### A. The Impedance Track™ Gas Gauge Unlike traditional Coulomb counters that drift over time, this part measures the internal resistance (impedance) of the cells in real-time. This allows the IC to account for: * Cell aging. * Temperature fluctuations. * Self-discharge. #### B. Analog Front End (AFE) The IC includes integrated high-accuracy ADCs: * **Voltage Measurement:** Monitors individual cell voltages to ensure balance. * **Current Measurement:** Uses a low-side sense resistor to measure charging and discharging currents. * **Temperature Sensing:** Supports multiple NTC thermistor inputs to monitor the pack and FET temperatures. #### C. Protection Circuitry The BQ20Z95 provides hardware-level safety features to prevent catastrophic failure: * **Overvoltage (OV) / Undervoltage (UV):** Individual cell monitoring. * **Overcurrent (OCD/OCC):** Protection during charge and discharge. * **Short Circuit (SCD):** Immediate shutdown of power FETs. * **Thermal Protection:** Over-temperature (OT) and Under-temperature (UT) safety. #### D. Cell Balancing It contains internal bypass FETs. When one cell's voltage is higher than others during charging, the IC bypasses a small amount of current around that cell to ensure all cells reach full charge simultaneously, extending the overall lifespan of the battery pack. --- ### 3. Peripheral Components To implement a BQ20Z95 circuit, the following external electronic parts are required: 1. **Sense Resistor:** A high-precision, low-value resistor (typically 5mΩ to 20mΩ) for current sensing. 2. **Power FETs:** N-Channel MOSFETs for Charge (CHG) and Discharge (DSG) control. 3. **Chemical Fuse:** A three-terminal fuse that the IC can blow as a final safety measure if FETs fail. 4. **Thermistors:** 10kΩ NTC resistors for temperature monitoring. 5. **Decoupling Capacitors:** Essential for stabilizing the internal LDO and ADC references. --- ### 4. Implementation Example (Basic Logic) ```c // Example logic of how a host communicates with BQ20Z95 via SMBus #define BQ20Z95_ADDR 0x16 #define CMD_VOLTAGE 0x09 // Read total pack voltage uint16_t readBatteryVoltage() { return smbus_read_word(BQ20Z95_ADDR, CMD_VOLTAGE); } ```