SLUSDA7A April   2018  – January 2021 BQ25121A

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Description (continued)
  6. 6 Device Comparison Table
  7. 7 Pin Configuration and Functions
  8. 8 Specifications
    1. 8.1 Absolute Maximum Ratings
    2. 8.2 ESD Ratings
    3. 8.3 Recommended Operating Conditions
    4. 8.4 Thermal Information
    5. 8.5 Electrical Characteristics
    6. 8.6 Timing Requirements
    7. 8.7 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  Ship Mode
        1. 9.3.1.1 Ship Mode Entry and Exit
      2. 9.3.2  High Impedance Mode
      3. 9.3.3  Active Battery Only Connected
      4. 9.3.4  Voltage Based Battery Monitor
      5. 9.3.5  Sleep Mode
      6. 9.3.6  Input Voltage Based Dynamic Power Management (VIN(DPM))
      7. 9.3.7  Input Overvoltage Protection and Undervoltage Status Indication
      8. 9.3.8  Battery Charging Process and Charge Profile
      9. 9.3.9  Dynamic Power Path Management Mode
      10. 9.3.10 Battery Supplement Mode
      11. 9.3.11 Default Mode
      12. 9.3.12 Termination and Pre-Charge Current Programming by External Components (IPRETERM)
      13. 9.3.13 Input Current Limit Programming by External Components (ILIM)
      14. 9.3.14 Charge Current Programming by External Components (ISET)
      15. 9.3.15 Safety Timer
      16. 9.3.16 External NTC Monitoring (TS)
      17. 9.3.17 Thermal Protection
      18. 9.3.18 Typical Application Power Dissipation
      19. 9.3.19 Status Indicators ( PG and INT)
      20. 9.3.20 Chip Disable ( CD)
      21. 9.3.21 Buck (PWM) Output
      22. 9.3.22 Load Switch / LDO Output and Control
      23. 9.3.23 Manual Reset Timer and Reset Output ( MR and RESET)
    4. 9.4 Device Functional Modes
    5. 9.5 Programming
      1. 9.5.1 Serial Interface Description
      2. 9.5.2 F/S Mode Protocol
    6. 9.6 Register Maps
      1. 9.6.1  Status and Ship Mode Control Register
      2. 9.6.2  Faults and Faults Mask Register
      3. 9.6.3  TS Control and Faults Masks Register
      4. 9.6.4  Fast Charge Control Register
      5. 9.6.5  Termination/Pre-Charge Register
      6. 9.6.6  Battery Voltage Control Register
      7. 9.6.7  SYS VOUT Control Register
      8. 9.6.8  Load Switch and LDO Control Register
      9. 9.6.9  Push-button Control Register
      10. 9.6.10 ILIM and Battery UVLO Control Register
      11. 9.6.11 Voltage Based Battery Monitor Register
      12. 9.6.12 VIN_DPM and Timers Register
  10. 10Application and Implementation
    1. 10.1 Application Information
    2. 10.2 Typical Application
      1. 10.2.1 Design Requirements
      2. 10.2.2 Detailed Design Procedure
        1. 10.2.2.1 Default Settings
        2. 10.2.2.2 Choose the Correct Inductance and Capacitance
        3. 10.2.2.3 Calculations
          1. 10.2.2.3.1 Program the Fast Charge Current (ISET)
          2. 10.2.2.3.2 Program the Input Current Limit (ILIM)
          3. 10.2.2.3.3 Program the Pre-charge/termination Threshold (IPRETERM)
          4. 10.2.2.3.4 TS Resistors (TS)
      3. 10.2.3 Application Performance Curves
        1. 10.2.3.1 Charger Curves
        2. 10.2.3.2 SYS Output Curves
        3. 10.2.3.3 Load Switch and LDO Curves
        4. 10.2.3.4 LS/LDO Output Curves
        5. 10.2.3.5 Timing Waveforms Curves
  11. 11Power Supply Recommendations
  12. 12Layout
    1. 12.1 Layout Guidelines
    2. 12.2 Layout Example
  13. 13Device and Documentation Support
    1. 13.1 Device Support
      1. 13.1.1 Third-Party Products Disclaimer
    2. 13.2 Receiving Notification of Documentation Updates
    3. 13.3 Trademarks
    4. 13.4 Support Resources
    5. 13.5 Electrostatic Discharge Caution
    6. 13.6 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

Package Options

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

9.3.21 Buck (PWM) Output

The device integrates a low quiescent current switching regulator with DCS control allowing high efficiency down to 10-µA load currents. DCS control combines the advantages of hysteretic and voltage mode control. The internally compensated regulation network achieves fast and stable operation with small external components and low ESR capacitors. During PWM mode, it operates in continuous conduction mode, with a frequency up to 2 MHz. If the load current decreases, the converter enters a power save mode to maintain high efficiency down to light loads. In this mode, the device generates a single switching pulse to ramp up the inductor current and recharge the output capacitor, followed by a sleep period where most of the internal circuits are shut down to achieve a low quiescent current. The duration of the sleep period depends on the load current and the inductor peak current. For optimal operation and maximum power delivery allow VPMID > VSYS + 0.7V.

The output voltage is programmable using the SYS_SEL and SYS_VOUT bits in the SYS VOUT control register.

The SW output is enabled using the EN_SYS_OUT bit in the register. This bit is for testing and debug only and not intended to be used in the final system. When the device is enabled, the internal reference is powered up and the device enters softstart, starts switching, and ramps up the output voltage. When SW is disabled, the output is in shutdown mode in a low quiescent state. The device provides automatic output voltage discharge so the output voltage will ramp up from zero once the device in enabled again. Once SYS has been disabled, either VIN needs to be connected or the MR button must be held low for the tRESET duration to re-enable SYS.

The output is optimized for operation with a 2.2-µH inductor and 10-µF output capacitor. Table 9-6 shows the recommended LC output filter combinations.

Table 9-6 Recommended Output Filter
INDUCTOR VALUE (µH) OUTPUT CAPACITOR VALUE (µF)
2.2 4.7 10 22
Recommended Possible Recommended Possible

The inductor value affects the peak-to-peak ripple current, the PWM-to-PFM transition point where the part enters and exits Pulse Frequency Modulation to lower the power consumed at low loads, the output voltage ripple and the efficiency. The selected inductor must be selected for its DC resistance and saturation current. The inductor ripple current (ΔIL) can be estimated according to Equation 7.

Equation 7. ΔIL = VSYS x (1-(VSYS/VPMID))/(L x f)

Use Equation 8 to calculate the maximum inductor current under static load conditions. The saturation current of the inductor should be rated higher than the maximum inductor current. As the size of the inductor decreases, the saturation “knee” must be carefully considered to ensure that the inductance does not decrease during higher load condition or transient. This is recommended because during a heavy load transient the inductor current rises above the calculated value. A more conservative way is to select the inductor saturation current above the high-side MOSFET switch current.

Equation 8. IL(max) = ISYS(max) + ΔIL / 2

Where

  • F = Switching Frequency
  • L = Inductor Value
  • ΔIL = Peak to Peak inductor ripple current
  • IL(max) = Maximum Inductor current

In DC/DC converter applications, the efficiency is affected by the inductor AC resistance and by the inductor DCR value.

Table 9-7 shows recommended inductor series from different suppliers.

Table 9-7 Inductor Series
INDUCTANCE (µH) DCR (Ω) DIMENSIONS (mm3) INDUCTOR TYPE SUPPLIER (1) COMMENT
2.2 0.300 1.6 x 0.8 x 0.8 MDT1608CH2R2N TOKO Smallest size, 75mA max
2.2 0.170 1 .6 x 0.8 x 0.8 GLFR1608T2R2M TDK Smallest size, 150mA max
2.2 0.245 2.0 x 1.2 x 1.0 MDT2012CH2R2N TOKO Small size, high efficiency
2.2 0.23 2.0 x 1.2 x 1.0 MIPSZ2012 2R2 TDK
2.2 0.225 2.0 x 1.6 x 1.0 74438343022 Wurth
2.2 0.12 2.5 x 2.0 x 1.2 MIPSA2520 2R2 TDK
2.2 0.145 3.3 x 3.3 x 1.4 LPS3314 Coicraft

The PWM allows the use of small ceramic capacitors. Ceramic capacitors with low ESR values have the lowest output voltage ripple and are recommended. The output capacitor requires either an X7R or X5R dielectric. At light load currents, the converter operates in Power Save Mode and the output voltage ripple is dependent on the output capacitor value and the PFM peak inductor current. Because the PWM converter has a pulsating input current, a low ESR input capacitor is required on PMID for the best voltage filtering to ensure proper function of the device and to minimize input voltage spikes. For most applications a 10-µF capacitor value is sufficient. The PMID capacitor can be increased to 22 µF for better input voltage filtering.

Table 9-8 shows the recommended input/output capacitors.

Table 9-8 Capacitors
CAPACITANCE (µF) SIZE CAPACITOR TYPE SUPPLIER(1) COMMENT
10 0603 GRM188R60J106ME84 Murata Recommended
10 0402 CL05A106MP5NUNC Samsung EMA Smallest size