SLUSB48 July   2014

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Simplified Schematic
  5. 5 Revision History
  6. 6 Description (continued)
  7. 7 Pin Configuration and Functions
  8. 8 Specifications
    1. 8.1  Absolute Maximum Ratings
    2. 8.2  Handling Ratings
    3. 8.3  Recommended Operating Conditions
    4. 8.4  Thermal Information
    5. 8.5  Electrical Characteristics: Supply Current
    6. 8.6  Electrical Characteristics: I/O
    7. 8.7  Electrical Characteristics: ADC
    8. 8.8  Electrical Characteristics: Power-On Reset
    9. 8.9  Electrical Characteristics: Oscillator
    10. 8.10 Electrical Characteristics: Data Flash Memory
    11. 8.11 Electrical Characteristics: Register Backup
    12. 8.12 SMBus Timing Specifications
    13. 8.13 Typical Characteristics
  9. 9 Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1 Primary (1st Level) Safety Features
      2. 9.3.2 Secondary (2nd Level) Safety Features
      3. 9.3.3 Charge Control Features
      4. 9.3.4 Fuel Gauging
      5. 9.3.5 Lifetime Data Logging
      6. 9.3.6 Authentication
      7. 9.3.7 Battery Parameter Measurements
        1. 9.3.7.1 Current and Coulomb Counting
        2. 9.3.7.2 Voltage
        3. 9.3.7.3 Temperature
    4. 9.4 Device Functional Modes
    5. 9.5 Programming
      1. 9.5.1 Physical Interface
      2. 9.5.2 SMBus Address
      3. 9.5.3 SMBus On and Off State
  10. 10Application and Implementation
    1. 10.1 Application Information
    2. 10.2 Typical Applications
      1. 10.2.1 Schematic
      2. 10.2.2 Design Requirements
      3. 10.2.3 Detailed Design Procedure
        1. 10.2.3.1 Measurement System
          1. 10.2.3.1.1 Cell Voltages
          2. 10.2.3.1.2 External Average Cell Voltage
          3. 10.2.3.1.3 Current
          4. 10.2.3.1.4 Temperature
        2. 10.2.3.2 Gas Gauging
        3. 10.2.3.3 Charging
          1. 10.2.3.3.1 Fast Charging Voltage
          2. 10.2.3.3.2 Fast Charging Current
          3. 10.2.3.3.3 Other Charging Modes
        4. 10.2.3.4 Protection
        5. 10.2.3.5 Peripheral Features
          1. 10.2.3.5.1 LED Display
          2. 10.2.3.5.2 SMBus Address
      4. 10.2.4 Application Performance Plots
  11. 11Power Supply Recommendations
  12. 12Layout
    1. 12.1 Layout Guidelines
      1. 12.1.1 Power Supply Decoupling Capacitor
      2. 12.1.2 MRST Connection
      3. 12.1.3 Communication Line Protection Components
      4. 12.1.4 ESD Spark Gap
    2. 12.2 Layout Example
  13. 13Device and Documentation Support
    1. 13.1 Related Documentation
    2. 13.2 Trademarks
    3. 13.3 Electrostatic Discharge Caution
    4. 13.4 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

9 Detailed Description

9.1 Overview

The bq78350 Li-Ion and LiFePO4 Battery Management Controller is the companion to the bq769x0 family of Analog Front End (AFE) protection devices. This chipset supports from 3-series to 15-series cell applications with capacities up to 320 Ahr, and is suitable for a wide range of portable or stationary battery applications. The bq78350 provides an accurate fuel gauge and state-of-health (SoH) monitor, as well as the cell balancing algorithm and a full range of voltage-, current-, and temperature-based protection features.

The battery data that the bq78350 gathers can be accessed via an SMBus 1.1 interface and state-of-charge (SoC) data can be displayed through optional LED or LCD display configurations. Battery history and diagnostic data is also kept within the device in non-volatile memory and is available over the same SMBus interface.

9.2 Functional Block Diagram

Func_Block_Diagram.gifFigure 7. Functional Block Diagram

9.3 Feature Description

The following section provides an overview of the device features. For full details on the bq78350 features, refer to the bq78350 Technical Reference Manual (SLUUAN7).

9.3.1 Primary (1st Level) Safety Features

The bq78350 supports a wide range of battery and system protection features that can be configured. The primary safety features include:

  • Cell over/undervoltage protection
  • Charge and discharge overcurrent
  • Short circuit protection
  • Charge and discharge overtemperature with independent alarms and thresholds for each thermistor

9.3.2 Secondary (2nd Level) Safety Features

The secondary safety features of the bq78350 can be used to indicate more serious faults via the SAFE pin. This pin can be used to blow an in-line fuse to permanently disable the battery pack from charging or discharging. The secondary safety protection features include:

  • Safety overvoltage
  • Safety undervoltage
  • Safety overcurrent in charge and discharge
  • Safety overtemperature in charge and discharge
  • Charge FET and Precharge FET fault
  • Discharge FET fault
  • Cell imbalance detection
  • Open thermistor detection
  • AFE communication fault

9.3.3 Charge Control Features

The bq78350 charge control features include:

  • Provides a range of options to configure the charging algorithm and its actions based on the application requirements
  • Reports the appropriate charging current needed for constant current charging, and the appropriate charging voltage needed for constant voltage charging
  • Supports pre-charging/0-volt charging
  • Supports charge inhibit and charge suspend if battery pack temperature is out of temperature range

9.3.4 Fuel Gauging

The bq78350 uses Compensated End-of-Discharge Voltage (CEDV) technology to measure and calculate the available charge in battery cells. The bq78350 accumulates a measure of charge and discharge currents and compensates the charge current measurement for the temperature and state-of-charge of the battery. The bq78350 estimates self-discharge of the battery and also adjusts the self-discharge estimation based on temperature.

9.3.5 Lifetime Data Logging

The bq78350 offers lifetime data logging, where important measurements are stored for warranty and analysis purposes. The data monitored includes:

  • Lifetime maximum temperature
  • Lifetime minimum temperature
  • Lifetime maximum battery cell voltage per cell
  • Lifetime minimum battery cell voltage per cell
  • Cycle count
  • Maximum charge current
  • Maximum discharge current
  • Safety events that trigger SafetyStatus() updates. (The 12 most common are tracked.)

9.3.6 Authentication

The bq78350 supports authentication by the host using SHA-1.

9.3.7 Battery Parameter Measurements

The bq78350 digitally reads bq769x0 registers containing recent values from the integrating analog-to-digital converter (CC) for current measurement and a second delta-sigma ADC for individual cell and temperature measurements.

9.3.7.1 Current and Coulomb Counting

The integrating delta-sigma ADC (CC) in the companion bq769x0 AFE measures the charge/discharge flow of the battery by measuring the voltage drop across a small-value sense resistor between the SRP and SRN pins. The 15-bit integrating ADC measures bipolar signals from –0.20 V to 0.20 V with 15-µV resolution. The AFE reports charge activity when VSR = V(SRP) – V(SRN) is positive, and discharge activity when VSR = V(SRP) – V(SRN) is negative. The bq78350 continuously monitors the measured current and integrates the digital signal from the AFE over time, using an internal counter.

To support large battery configurations, the current data can be scaled to ensure accurate reporting through the SMBus. The data reported is scaled based on the setting of the SpecificationInfo() command.

9.3.7.2 Voltage

The bq78350 updates the individual series cell voltages through the bq769x0 at 1-s intervals. The bq78350 configures the bq769x0 to connect to the selected cells in sequence and uses this information for cell balancing and individual cell fault functions. The internal 14-bit ADC of the bq769x0 measures each cell voltage value, which is then communicated digitally to the bq78350 where they are scaled and translated into unit mV. The maximum supported input range of the ADC is 6.075 V.

The bq78350 also separately measures the average cell voltage through an external translation circuit at the BAT pin. This value is specifically used for the fuel gauge algorithm. The external translation circuit is controlled via the VEN pin so that the translation circuit is only enabled when required to reduce overall power consumption. For correct operation, VEN requires an external pull-up to VCC, typically 100 k.

In addition to the voltage measurements used by the bq78350 algorithms, there is an optional auxiliary voltage measurement capability via the VAUX pin. This feature measures the input on a 1-s update rate and provides the programmable scaled value through an SMBus command.

To support large battery configurations, the voltage data can be scaled to ensure accurate reporting through the SMBus. The data reported is scaled based on the setting of the SpecificationInfo() command.

9.3.7.3 Temperature

The bq78350 receives temperature information from external or internal temperature sensors in the bq769x0 AFE. Depending on the number of series cells supported, the AFE will provide one, two, or three external thermistor measurements.

9.4 Device Functional Modes

The bq78350 supports three power modes to optimize the power consumption:

  • In NORMAL mode, the bq78350 performs measurements, calculations, protection decisions, and data updates in 1-s intervals. Between these intervals, the bq78350 is in a reduced power mode.
  • In SLEEP mode, the bq78350 performs measurements, calculations, protection decisions, and data updates in adjustable time intervals. Between these intervals, the bq78350 is in a reduced power mode.
  • In SHUTDOWN mode, the bq78350 is completely powered down.

The bq78350 indicates through the PWRM pin which power mode it is in. This enables other circuits to change based on the power mode detection criteria of the bq78350.

9.5 Programming

9.5.1 Physical Interface

The bq78350 uses SMBus 1.1 with packet error checking (PEC) as an option and is used as a slave only.

9.5.2 SMBus Address

The bq78350 determines its SMBus 1.1 slave address through a voltage on SMBA, Pin 30. The voltage is set with a pair of high value resistors if an alternate address is required and is measured either upon exit of POR or when system present is detected. ADREN, Pin 29, may be used to disable the voltage divider after use to reduce power consumption.

9.5.3 SMBus On and Off State

The bq78350 detects an SMBus off state when SMBC and SMBD are logic-low for ≥ 2 seconds. Clearing this state requires either SMBC or SMBD to transition high. Within 1 ms, the communication bus is available.