SLUSAN9A August   2011  – August 2015


  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Pin Configuration and Functions
  6. Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Power-on Reset
    7. 6.7 Data Flash Characteristics Over Recommended Operating Temperature and Supply Voltage
    8. 6.8 SMBus Timing Requirements
    9. 6.9 Typical Characteristics
  7. Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Feature Set
        1. Primary (1st Level) Safety Features
        2. Secondary (2nd Level) Safety Features
        3. Charge Control Features
        4. Gas Gauging
        5. Lifetime Data Logging Features
        6. Authentication
      2. 7.3.2 Battery Parameter Measurements
        1. Charge and Discharge Counting
        2. Voltage
        3. Current
        4. Wake Function
        5. Auto Calibration
        6. Temperature
    4. 7.4 Device Functional Modes
      1. 7.4.1 Power Modes
    5. 7.5 Programming
      1. 7.5.1 Configuration
        1. Oscillator Function
        2. System Present Operation
      2. 7.5.2 Communications
        1. SMBus On and Off State
      3. 7.5.3 SBS Commands
  8. Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. Choosing the Correct Chemistry
        2. High-Current Path
        3. Protection FETs
        4. Lithium-Ion Cell Connections
        5. Sense Resistor
        6. ESD Mitigation
        7. System Present
        8. SMBus Communication
      3. 8.2.3 Application Curves
  9. Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 Protector FET Bypass and Pack Terminal Bypass Capacitors
      2. 10.1.2 ESD Spark Gap
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Documentation Support
      1. 11.1.1 Related Documentation
    2. 11.2 Community Resources
    3. 11.3 Trademarks
    4. 11.4 Electrostatic Discharge Caution
    5. 11.5 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

Detailed Description


The bq20z655-R1 incorporating patented Impedance Track™ technology is a single IC solution designed for battery-pack or in-system installation. This SBS-compliant gas gauge and protection IC implemented with Impedance Track™ gas gauging technology continuously analyzes the battery impedance, resulting in superior gas-gauging accuracy.

Functional Block Diagram

bq20z655-R1 fb_circuit_slusan9.gif

Feature Description

Feature Set

Primary (1st Level) Safety Features

The bq20z655-R1 supports a wide range of battery and system protection features that can easily 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
  • AFE Watchdog

Secondary (2nd Level) Safety Features

The secondary safety features of the bq20z655-R1 can be used to indicate more serious faults through 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
  • 2nd level protection IC input
  • Safety overcurrent in charge and discharge
  • Safety over-temperature in charge and discharge with independent alarms and thresholds for each thermistor
  • Charge FET and zero-volt charge FET fault
  • Discharge FET fault
  • Cell imbalance detection (active and at rest)
  • Open thermistor detection
  • Fuse blow detection
  • AFE communication fault

Charge Control Features

The bq20z655-R1 charge control features include:

  • Supports JEITA temperature ranges. Reports charging voltage and charging current according to the active temperature range.
  • Handles more complex charging profiles. Allows for splitting the standard temperature range into two sub-ranges and allows for varying the charging current according to the cell voltage.
  • Reports the appropriate charging current needed for constant current charging and the appropriate charging voltage needed for constant voltage charging to a smart charger using SMBus broadcasts.
  • Determines the chemical state of charge of each battery cell using Impedance Track™ and can reduce the charge difference of the battery cells in fully charged state of the battery pack gradually using cell balancing algorithm during charging. This prevents fully charged cells from overcharging and causing excessive degradation and also increases the usable pack energy by preventing premature charge termination
  • Supports pre-charging and zero-volt charging
  • Supports charge inhibit and charge suspend if battery pack temperature is out of temperature range
  • Reports charging fault and also indicate charge status through charge and discharge alarms.

Gas Gauging

The bq20z655-R1 uses the Impedance Track™ Technology to measure and calculate the available charge in battery cells. The achievable accuracy is better than 1% error over the lifetime of the battery and there is no full charge discharge learning cycle required.

See the Theory and Implementation of Impedance Track Battery Fuel-Gauging Algorithm application note (SLUA364) for further details.

Lifetime Data Logging Features

The bq20z655-R1 offers lifetime data logging, where important measurements are stored for warranty and analysis purposes. The data monitored include:

  • Lifetime maximum temperature
  • Lifetime maximum temperature count
  • Lifetime maximum temperature duration
  • Lifetime minimum temperature
  • Lifetime maximum battery cell voltage
  • Lifetime maximum battery cell voltage count
  • Lifetime maximum battery cell voltage duration
  • Lifetime minimum battery cell voltage
  • Lifetime maximum battery pack voltage
  • Lifetime minimum battery pack voltage
  • Lifetime maximum charge current
  • Lifetime maximum discharge current
  • Lifetime maximum charge power
  • Lifetime maximum discharge power
  • Lifetime maximum average discharge current
  • Lifetime maximum average discharge power
  • Lifetime average temperature


The bq20z655-R1 supports authentication by the host using SHA-1.

Battery Parameter Measurements

The bq20z655-R1 uses an integrating delta-sigma analog-to-digital converter (ADC) for current measurement, and a second delta-sigma ADC for individual cell and battery voltage, and temperature measurement.

Charge and Discharge Counting

The integrating delta-sigma ADC measures the charge/discharge flow of the battery by measuring the voltage drop across a small-value sense resistor between the SR1 and SR2 pins. The integrating ADC measures bipolar signals from –0.25 V to 0.25 V. The bq20z655-R1 detects charge activity when VSR = V(SRP)-V(SRN)is positive and discharge activity when VSR = V(SRP) - V(SRN) is negative. The bq20z655-R1 continuously integrates the signal over time, using an internal counter. The fundamental rate of the counter is 0.65 nVh.


The bq20z655-R1 updates the individual series cell voltages at one second intervals. The internal ADC of the bq20z655-R1 measures the voltage, scales and calibrates it appropriately. This data is also used to calculate the impedance of the cell for the Impedance Track™ gas-gauging.


The bq20z655-R1 uses the SRP and SRN inputs to measure and calculate the battery charge and discharge current using a 5-mΩ to 20-mΩ typical sense resistor.

Wake Function

The bq20z655-R1 can exit sleep mode, if enabled, by the presence of a programmable level of current signal across SRP and SRN.

Auto Calibration

The bq20z655-R1 provides an auto-calibration feature to cancel the voltage offset error across SRN and SRP for maximum charge measurement accuracy. The bq20z655-R1 performs auto-calibration when the SMBus lines stay low continuously for a minimum of a programmable amount of time.


The bq20z655-R1 has an internal temperature sensor and 2 external temperature sensor inputs, TS1 and TS2, used in conjunction with two identical NTC thermistors (default are Semitec 103AT) to sense the battery environmental temperature. The bq20z655-R1 can be configured to use the internal temperature sensor or up to 2 external temperature sensors.

Device Functional Modes

Power Modes

The bq20z655-R1 supports three different power modes to reduce power consumption:

  • In Normal Mode, the bq20z655-R1 performs measurements, calculations, protection decisions and data updates in 1 second intervals. Between these intervals, the bq20z655-R1 is in a reduced power stage.
  • In Sleep Mode, the bq20z655-R1 performs measurements, calculations, protection decisions and data update in adjustable time intervals. Between these intervals, the bq20z655-R1 is in a reduced power stage. The bq20z655-R1 has a wake function that enables exit from Sleep mode, when current flow or failure is detected.
  • In Shutdown Mode, the bq20z655-R1 is completely disabled.



Oscillator Function

The bq20z655-R1 fully integrates the system oscillators therefore, no external components are required for this feature.

System Present Operation

The bq20z655-R1 periodically verifies the PRES pin and detects that the battery is present in the system through a low state on a PRES input. When this occurs, the bq20z655-R1 enters normal operating mode. When the pack is removed from the system and the PRES input is high, the bq20z655-R1 enters the battery-removed state, disabling the charge, discharge, and ZVCHG FETs. The PRES input is ignored and can be left floating when non-removal mode is set in the data flash.


The bq20z655-R1 uses SMBus v1.1 with Master Mode and package error checking (PEC) options per the SBS specification.

SMBus On and Off State

The bq20z655-R1 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.

SBS Commands

Table 1. SBS Commands

0x00 R/W ManufacturerAccess Hex 2 0x0000 0xffff
0x01 R/W RemainingCapacityAlarm Integer 2 0 700 or 1000 300 or 432 mAh or 10 mWh
0x02 R/W RemainingTimeAlarm Unsigned integer 2 0 30 10 min
0x03 R/W BatteryMode Hex 2 0x0000 0xffff
0x04 R/W AtRate Integer 2 –32,768 32,767 mA or 10 mW
0x05 R AtRateTimeToFull Unsigned integer 2 0 65,535 min
0x06 R AtRateTimeToEmpty Unsigned integer 2 0 65,535 min
0x07 R AtRateOK Unsigned integer 2 0 65,535
0x08 R Temperature Unsigned integer 2 0 65,535 0.1°K
0x09 R Voltage Unsigned integer 2 0 20,000 mV
0x0a R Current Integer 2 –32,768 32767 mA
0x0b R AverageCurrent Integer 2 –32,768 32,767 mA
0x0c R MaxError Unsigned integer 1 0 100 %
0x0d R RelativeStateOfCharge Unsigned integer 1 0 100 %
0x0e R AbsoluteStateOfCharge Unsigned integer 1 0 100+ %
0x0f R/W RemainingCapacity Unsigned integer 2 0 65,535 mAh or 10 mWh
0x10 R FullChargeCapacity Unsigned integer 2 0 65,535 mAh or 10 mWh
0x11 R RunTimeToEmpty Unsigned integer 2 0 65,534 min
0x12 R AverageTimeToEmpty Unsigned integer 2 0 65,534 min
0x13 R AverageTimeToFull Unsigned integer 2 0 65,534 min
0x14 R ChargingCurrent Unsigned integer 2 0 65,534 mA
0x15 R ChargingVoltage Unsigned integer 2 0 65,534 mV
0x16 R BatteryStatus Hex 2 0x0000 0xdbff
0x17 R/W CycleCount Unsigned integer 2 0 65,535 0
0x18 R/W DesignCapacity Integer 2 0 32,767 4400 or 6336 mAh or 10 mWh
0x19 R/W DesignVoltage Integer 2 7000 18,000 14,400 mV
0x1a R/W SpecificationInfo Hex 2 0x0000 0xffff 0x0031
0x1b R/W ManufactureDate Unsigned integer 2 0 65,535 0
0x1c R/W SerialNumber Hex 2 0x0000 0xffff 0x0000
0x20 R/W ManufacturerName String 20+1 Texas Instruments
0x21 R/W DeviceName String 20+1 bq20z655-R1
0x22 R/W DeviceChemistry String 4+1 LION
0x23 R ManufacturerData String 14+1
0x2f R/W Authenticate String 20+1
0x3c R CellVoltage4 Unsigned integer 2 0 65,535 mV
0x3d R CellVoltage3 Unsigned integer 2 0 65,535 mV
0x3e R CellVoltage2 Unsigned integer 2 0 65,535 mV
0x3f R CellVoltage1 Unsigned integer 2 0 65,535 mV

Table 2. Extended SBS Commands

0x45 R AFEData String 11+1
0x46 R/W FETControl Hex 2 0x00 0xff
0x4f R StateOfHealth Hex 2 0x0000 0xffff %
0x51 R SafetyStatus Hex 2 0x0000 0xffff
0x52 R PFAlert Hex 2 0x0000 0xffff
0x53 R PFStatus Hex 2 0x0000 0xffff
0x54 R OperationStatus Hex 2 0x0000 0xffff
0x55 R ChargingStatus Hex 2 0x0000 0xffff
0x57 R ResetData Hex 2 0x0000 0xffff
0x58 R WDResetData Unsigned integer 2 0 65,535
0x5a R PackVoltage Unsigned integer 2 0 65,535 mV
0x5d R AverageVoltage Unsigned integer 2 0 65,535 mV
0x5e R TS1Temperature Integer 2 -400 1200 0.1°C
0x5f R TS2Temperature Integer 2 -400 1200 0.1°C
0x60 R/W UnSealKey Hex 4 0x00000000 0xffffffff
0x61 R/W FullAccessKey Hex 4 0x00000000 0xffffffff
0x62 R/W PFKey Hex 4 0x00000000 0xffffffff
0x63 R/W AuthenKey3 Hex 4 0x00000000 0xffffffff
0x64 R/W AuthenKey2 Hex 4 0x00000000 0xffffffff
0x65 R/W AuthenKey1 Hex 4 0x00000000 0xffffffff
0x66 R/W AuthenKey0 Hex 4 0x00000000 0xffffffff
0x68 R SafetyAlert2 Hex 2 0x0000 0x000f
0x69 R SafetyStatus2 Hex 2 0x0000 0x000f
0x6a R PFAlert2 Hex 2 0x0000 0x000f
0x6b R PFStatus2 Hex 2 0x0000 0x000f
0x6c R ManufBlock1 String 20
0x6d R ManufBlock2 String 20
0x6e R ManufBlock3 String 20
0x6f R ManufBlock4 String 20
0x70 R/W ManufacturerInfo String 31+1
0x71 R/W SenseResistor Unsigned integer 2 0 65,535 μΩ
0x72 R TempRange Hex 2
0x73 R LifetimeData1 String 32+1
0x74 R LifetimeData2 String 8+1
0x77 R/W DataFlashSubClassID Hex 2 0x0000 0xffff
0x78 R/W DataFlashSubClassPage1 Hex 32
0x79 R/W DataFlashSubClassPage2 Hex 32
0x7a R/W DataFlashSubClassPage3 Hex 32
0x7b R/W DataFlashSubClassPage4 Hex 32
0x7c R/W DataFlashSubClassPage5 Hex 32
0x7d R/W DataFlashSubClassPage6 Hex 32
0x7e R/W DataFlashSubClassPage7 Hex 32
0x7f R/W DataFlashSubClassPage8 Hex 32