SLUSCB6B May   2015  – June 2017

UNLESS OTHERWISE NOTED, this document contains PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 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 Timing Requirements
    7. 6.7 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1  Battery Preconditioning
      2. 7.3.2  Battery Fast-Charge Constant Current
      3. 7.3.3  Charge-Current Monitor
      4. 7.3.4  Battery Fast-Charge Voltage Regulation
      5. 7.3.5  Charge Termination Detection and Recharge
      6. 7.3.6  Charge Status Outputs
      7. 7.3.7  PG Output (bq24080-Q1)
      8. 7.3.8  Charge-Enabled (CE) Input (bq24080-Q1)
      9. 7.3.9  Timer Enabled (TE) Input (bq24081-Q1)
      10. 7.3.10 Temperature Qualification (bq24081-Q1)
      11. 7.3.11 Timer Fault and Recovery
        1. 7.3.11.1 Condition Number 1
        2. 7.3.11.2 Condition Number 2
    4. 7.4 Device Functional Modes
      1. 7.4.1 Sleep Mode
  8. 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. 8.2.2.1 Calculations
        2. 8.2.2.2 Battery Temperature Sense (bq24081-Q1):
        3. 8.2.2.3 STAT Pins (All Devices) and PG Pin (bq24080-Q1):
        4. 8.2.2.4 Selecting Input and Output Capacitors
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
    3. 10.3 Thermal Considerations
  11. 11Device and Documentation Support
    1. 11.1 Device Support
    2. 11.2 Documentation Support
    3. 11.3 Related Links
    4. 11.4 Receiving Notification of Documentation Updates
    5. 11.5 Community Resources
    6. 11.6 Trademarks
    7. 11.7 Electrostatic Discharge Caution
    8. 11.8 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

7 Detailed Description

7.1 Overview

The device supports a precision Li-Ion, Li-Pol charging system suitable for single cells. Figure 6 shows a typical charge profile, and Figure 7 shows an operational flow chart.

bq24080-Q1 bq24081-Q1 m0066-01_lus698.gif Figure 6. Typical Charging Profile
bq24080-Q1 bq24081-Q1 f0018-01_lus698.gif Figure 7. Operational Flow Chart

7.2 Functional Block Diagram

bq24080-Q1 bq24081-Q1 fbd_sluscb6.gif
1. bq24080-Q1 only
2. bq24081-Q1 only
3. Signal deglitched

7.3 Feature Description

7.3.1 Battery Preconditioning

During a charge cycle, if the battery voltage is below the V(LOWV) threshold, the device applies a precharge current, IO(PRECHG), to the battery. This feature revives deeply discharged cells. Resistor RSET, connected between the ISET and VSS, determines the precharge rate. The V(PRECHG) and K(SET) parameters are specified in the Electrical Characteristics table.

Equation 1. bq24080-Q1 bq24081-Q1 q_io_prechg_lvs563.gif

The device activates a safety timer, t(PRECHG), during the conditioning phase. If the V(LOWV) threshold is not reached within the timer period, the device turns off the charger and enunciates FAULT on the STATx pins. See the Timer Fault and Recovery section for additional details.

7.3.2 Battery Fast-Charge Constant Current

The device offers on-chip current regulation with programmable set point. Resistor RSET, connected between the ISET and VSS, determines the charge rate. The V(SET) and K(SET) parameters are specified in the specifications table.

Equation 2. bq24080-Q1 bq24081-Q1 q_io_out_lvs563.gif

7.3.3 Charge-Current Monitor

When the charge function is enabled internal circuits generate a current proportional to the charge current at the ISET pin. This current, when applied to the external charge current programming resistor RISET generates an analog voltage that can be monitored by an external host to calculate the current sourced from the OUT pin.

Equation 3. bq24080-Q1 bq24081-Q1 eq_Viset_sluscb6.gif

7.3.4 Battery Fast-Charge Voltage Regulation

The voltage regulation feedback is through the OUT pin. This input is tied directly to the positive side of the battery pack. The device monitors the battery-pack voltage between the OUT and VSS pins. When the battery voltage rises to the VO(REG) threshold, the voltage regulation phase begins and the charging current begins to taper down.

As a safety backup, the device also monitors the charge time in the charge mode. If charge is not terminated within this time period, t(CHG), the charger is turned off and FAULT is set on the STATx pins. See the Timer Fault and Recovery section for additional details.

7.3.5 Charge Termination Detection and Recharge

The device monitors the charging current during the voltage regulation phase. Once the termination threshold, I(TERM), is detected, charge is terminated. The V(TERM) and K(SET) parameters are specified in the Electrical Characteristics table.

Equation 4. bq24080-Q1 bq24081-Q1 q_io_taper_lus698.gif

After charge termination, the device restarts the charge once the voltage on the OUT pin falls below the V(RCH) threshold. This feature keeps the battery at full capacity at all times.

The device monitors the charging current during the voltage regulation phase. Once the termination threshold, I(TERM), is detected, the charge is terminated immediately.

Resistor RSET, connected between the ISET and VSS, determines the current level at the termination threshold.

7.3.6 Charge Status Outputs

The open-drain STAT1 and STAT2 outputs indicate various charger operations as shown in Table 1. These status pins can be used to drive LEDs or communicate to the host processor. Note that OFF indicates the open-drain transistor is turned off.

Table 1. Status Pin Summary

CHANGE STATE STAT1 STAT2
Precharge in progress ON ON
Fast charge in progress ON OFF
Charge done OFF ON
Charge suspend (temperature) OFF OFF
Timer fault
Sleep mode

7.3.7 PG Output (bq24080-Q1)

The open-drain power-good (PG) output pulls low when a valid input voltage is present. This output is turned off (high-impedance) in sleep mode. The PG pin can be used to drive an LED or communicate to the host processor.

7.3.8 Charge-Enabled (CE) Input (bq24080-Q1)

The CE digital input is used to disable or enable the charge process. A low-level signal on this pin enables the charge and a high-level signal disables the charge and places the device in a low-power mode. A high-to-low transition on this pin also resets all timers and timer fault conditions.

7.3.9 Timer Enabled (TE) Input (bq24081-Q1)

The TE digital input is used to disable or enable the fast-charge timer. A low-level signal on this pin enables the fast-charge timer, and a high-level signal disables this feature.

7.3.10 Temperature Qualification (bq24081-Q1)

The bq24081-Q1 continuously monitors battery temperature by measuring the voltage between the TS and VSS pins. An internal current source provides the bias for common 10-kΩ negative-temperature-coefficient thermistors (NTC) (see the functional block diagram). The device compares the voltage on the TS pin with the internal V(TS1) and V(TS2) thresholds to determine if charging is allowed. If a temperature outside the V(TS1) and V(TS2) thresholds is detected, the device immediately suspends the charge by turning off the power FET and holding the timer value (i.e., timers are not reset). Charge is resumed when the temperature returns within the normal range.

The allowed temperature range with a 103AT-type thermistor is 0°C to 45°C. However, the user may modify these thresholds by adding external resistors (see Figure 8 and Figure 9).

bq24080-Q1 bq24081-Q1 Default_Temp_Thresholds_sluscb6.gif Figure 8. Default Temperature Thresholds
bq24080-Q1 bq24081-Q1 Temp_Thresholds_Modified_sluscb6.gif Figure 9. Temperature Thresholds Modified by External Resistors

7.3.11 Timer Fault and Recovery

As shown in Figure 7, the device provides a recovery method to deal with timer fault conditions. The following summarizes this method:

7.3.11.1 Condition Number 1

OUT pin voltage is above the recharge threshold (V(RCH)), and a timeout fault occurs.

Recovery method: the device waits for the OUT pin voltage to fall below the recharge threshold. This could happen as a result of a load on the battery, self-discharge, or battery removal. Once the OUT pin voltage falls below the recharge threshold, the device clears the fault and starts a new charge cycle. A POR, TE, or CE toggle also clears the fault.

7.3.11.2 Condition Number 2

OUT pin voltage is below the recharge threshold (V(RCH)), and a timeout fault occurs

Recovery method: Under this scenario, the device applies the I(FAULT) current. This small current is used to detect a battery removal condition and remains on as long as the battery voltage stays below the recharge threshold. If the OUT pin voltage goes above the recharge threshold, then the device disables the I(FAULT) current and executes the recovery method described for condition number 1. Once the OUT pin voltage falls below the recharge threshold, the bq24080-Q1 clears the fault and starts a new charge cycle. A POR, TE, or CE toggle also clears the fault.

7.4 Device Functional Modes

7.4.1 Sleep Mode

The device enters the low-power sleep mode if the input power (IN) is removed from the circuit. This feature prevents draining the battery during the absence of input supply.