SLUSDU3 May   2021 BQ25720

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  Power-Up Sequence
      2. 9.3.2  Vmin Active Protection (VAP) with Battery only
      3. 9.3.3  Two-Level Battery Discharge Current Limit
      4. 9.3.4  Fast Role Swap Feature
      5. 9.3.5  CHRG_OK Indicator
      6. 9.3.6  Input and Charge Current Sensing
      7. 9.3.7  Input Voltage and Current Limit Setup
      8. 9.3.8  Battery Cell Configuration
      9. 9.3.9  Device HIZ State
      10. 9.3.10 USB On-The-Go (OTG)
      11. 9.3.11 Converter Operation
      12. 9.3.12 Inductance Detection Through IADPT Pin
      13. 9.3.13 Converter Compensation
      14. 9.3.14 Continuous Conduction Mode (CCM)
      15. 9.3.15 Pulse Frequency Modulation (PFM)
      16. 9.3.16 Switching Frequency and Dithering Feature
      17. 9.3.17 Current and Power Monitor
        1. 9.3.17.1 High-Accuracy Current Sense Amplifier (IADPT and IBAT)
        2. 9.3.17.2 High-Accuracy Power Sense Amplifier (PSYS)
      18. 9.3.18 Input Source Dynamic Power Management
      19. 9.3.19 Input Current Optimizer (ICO)
      20. 9.3.20 Two-Level Adapter Current Limit (Peak Power Mode)
      21. 9.3.21 Processor Hot Indication
        1. 9.3.21.1 PROCHOT During Low Power Mode
        2. 9.3.21.2 PROCHOT Status
      22. 9.3.22 Device Protection
        1. 9.3.22.1 Watchdog Timer
        2. 9.3.22.2 Input Overvoltage Protection (ACOV)
        3. 9.3.22.3 Input Overcurrent Protection (ACOC)
        4. 9.3.22.4 System Overvoltage Protection (SYSOVP)
        5. 9.3.22.5 Battery Overvoltage Protection (BATOVP)
        6. 9.3.22.6 Battery Discharge Overcurrent Protection (BATOC)
        7. 9.3.22.7 Battery Short Protection (BATSP)
        8. 9.3.22.8 System Undervoltage Lockout (VSYS_UVP) and Hiccup Mode
        9. 9.3.22.9 Thermal Shutdown (TSHUT)
    4. 9.4 Device Functional Modes
      1. 9.4.1 Forward Mode
        1. 9.4.1.1 System Voltage Regulation with Narrow VDC Architecture
        2. 9.4.1.2 Battery Charging
      2. 9.4.2 USB On-The-Go
      3. 9.4.3 Pass Through Mode (PTM)-Patented Technology
    5. 9.5 Programming
      1. 9.5.1 SMBus Interface
        1. 9.5.1.1 SMBus Write-Word and Read-Word Protocols
        2. 9.5.1.2 Timing Diagrams
    6. 9.6 Register Map
      1. 9.6.1  ChargeOption0 Register (SMBus address = 12h) [reset = E70Eh]
      2. 9.6.2  ChargeCurrent Register (SMBus address = 14h) [reset = 0000h]
        1. 9.6.2.1 Battery Pre-Charge Current Clamp
      3. 9.6.3  ChargeVoltage Register (SMBus address = 15h) [reset value based on CELL_BATPRESZ pin setting]
      4. 9.6.4  ChargerStatus Register (SMBus address = 20h) [reset = 0000h]
      5. 9.6.5  ProchotStatus Register (SMBus address = 21h) [reset = B800h]
      6. 9.6.6  IIN_DPM Register With 10-mΩ Sense Resistor (SMBus address = 22h) [reset = 4100h]
      7. 9.6.7  ADCVBUS/PSYS Register (SMBus address = 23h)
      8. 9.6.8  ADCIBAT Register (SMBus address = 24h)
      9. 9.6.9  ADCIINCMPIN Register (SMBus address = 25h)
      10. 9.6.10 ADCVSYSVBAT Register (SMBus address = 26h)
      11. 9.6.11 ChargeOption1 Register (SMBus address = 30h) [reset = 3300h]
      12. 9.6.12 ChargeOption2 Register (SMBus address = 31h) [reset = 00B7]
      13. 9.6.13 ChargeOption3 Register (SMBus address = 32h) [reset = 0434h]
      14. 9.6.14 ProchotOption0 Register (SMBus address = 33h) [reset = 4A81h(2S~) 4A09(1S)]
      15. 9.6.15 ProchotOption1 Register (SMBus address = 34h) [reset = 41A0h]
      16. 9.6.16 ADCOption Register (SMBus address = 35h) [reset = 2000h]
      17. 9.6.17 ChargeOption4 Register (SMBus address = 36h) [reset = 0048h]
      18. 9.6.18 Vmin Active Protection Register (SMBus address = 37h) [reset = 006Ch(2s~4s)/0004h(1s)]
      19. 9.6.19 OTGVoltage Register (SMBus address = 3Bh) [reset = 09C4h]
      20. 9.6.20 OTGCurrent Register (SMBus address = 3Ch) [reset = 3C00h]
      21. 9.6.21 InputVoltage (VINDPM) Register (SMBus address = 3Dh) [reset = VBUS-1.28V]
      22. 9.6.22 VSYS_MIN Register (SMBus address = 3Eh) [reset value based on CELL_BATPRESZ pin setting]
      23. 9.6.23 IIN_HOST Register (SMBus address = 3Fh) [reset = 4100h]
      24. 9.6.24 ID Registers
        1. 9.6.24.1 ManufactureID Register (SMBus address = FEh) [reset = 0040h]
        2. 9.6.24.2 Device ID (DeviceAddress) Register (SMBus address = FFh) [reset = 00E1h]
  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 ACP-ACN Input Filter
        2. 10.2.2.2 Inductor Selection
        3. 10.2.2.3 Input Capacitor
        4. 10.2.2.4 Output Capacitor
        5. 10.2.2.5 Power MOSFETs Selection
      3. 10.2.3 Application Curves
  11. 11Power Supply Recommendations
  12. 12Layout
    1. 12.1 Layout Guidelines
    2. 12.2 Layout Example
      1. 12.2.1 Layout Example Reference Top View
      2. 12.2.2 Inner Layer Layout and Routing Example
  13. 13Device and Documentation Support
    1. 13.1 Device Support
      1. 13.1.1 Third-Party Products Disclaimer
    2. 13.2 Documentation Support
      1. 13.2.1 Related Documentation
    3. 13.3 Receiving Notification of Documentation Updates
    4. 13.4 Support Resources
    5. 13.5 Trademarks
    6. 13.6 Electrostatic Discharge Caution
    7. 13.7 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

Package Options

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

10.2.2.5 Power MOSFETs Selection

Four external N-channel MOSFETs are used for a synchronous switching battery charger. The gate drivers are integrated into the IC with 6 V of gate drive voltage. 30 V or higher voltage rating MOSFETs are preferred for 19-V to 20-V input voltage.

Figure-of-merit (FOM) is usually used for selecting proper MOSFET based on a tradeoff between the conduction loss and switching loss. For the top side MOSFET, FOM is defined as the product of a MOSFET's on-resistance, RDS(ON), and the gate-to-drain charge, QGD. For the bottom side MOSFET, FOM is defined as the product of the MOSFET's on-resistance, RDS(ON), and the total gate charge, QG.

Equation 5. FOMtop = RDS(on) · QGD; FOMbottom = RDS(on) · QG

The lower the FOM value, the lower the total power loss. Usually lower RDS(ON) has higher cost with the same package size.

The top-side MOSFET loss includes conduction loss and switching loss. Taking buck mode operation as an example the power loss is a function of duty cycle (D=VOUT/VIN), charging current (ICHG), MOSFET's on-resistance (RDS(ON)_top), input voltage (VIN), switching frequency (fS), turn-on time (ton) and turn-off time (toff):

Equation 6. Ptop =Pcon_top+Psw_top
Equation 7. Pcon_top =D · IL_RMS2 · RDS(on)_top;
Equation 8. IL_RMS2=IL_DC2+Iripple2/12
  • IL_DC is the average inductor DC current under buck mode;
  • Iripple is the inductor current ripple peak-to-peak value;
Equation 9. Psw_top =PIV_top+PQoss_top+PGate_top;

The first item Pcon_top represents the conduction loss which is straight forward. The second term Psw_top represents the multiple switching loss items in top MOSFET including voltage and current overlap losses (PIV_top), MOSFET parasitic output capacitance loss (PQoss_top) and gate drive loss (PGate_top). To calculate voltage and current overlap losses (PIV_top):

Equation 10. PIV_top =0.5x VIN · Ivalley · ton· fS+0.5x VIN · Ipeak · toff · fS
Equation 11. Ivalley =IL_DC- 0.5 · Iripple (inductor current valley value);
Equation 12. Ipeak =IL_DC+ 0.5 · Iripple (inductor current peak value);
  • ton is the MOSFET turn-on time that VDS falling time from VIN to almost zero (MOSFET turn on conduction voltage);
  • toff is the MOSFET turn-off time that IDS falling time from Ipeak to zero;

The MOSFET turn-on and turn-off times are given by:

Equation 13. GUID-66D54DC8-331A-4159-84C7-3FAB15FEA334-low.gif

where Qsw is the switching charge, Ion is the turn-on gate driving current, and Ioff is the turn-off gate driving current. If the switching charge is not given in MOSFET datasheet, it can be estimated by gate-to-drain charge (QGD) and gate-to-source charge (QGS):

Equation 14. Qsw =QGD+QGS

Gate driving current can be estimated by REGN voltage (VREGN), MOSFET plateau voltage (Vplt), total turn-on gate resistance (Ron), and turn-off gate resistance (Roff) of the gate driver:

Equation 15. GUID-2A574F33-73D8-4CE8-BFE8-F907B6945821-low.gif

To calculate top MOSFET parasitic output capacitance loss (PQoss_top):

Equation 16. PQoss_top =0.5 · VIN· Qoss · fS
  • Qoss is the MOSFET parasitic output charge which can be found in MOSFET datasheet;

To calculate top MOSFET gate drive loss (PGate_top):

Equation 17. PGate_top =VIN· QGate_top · fS
  • QGate_top is the top MOSFET gate charge which can be found in MOSFET datasheet;
  • Note here VIN is used instead of real gate drive voltage 6 V because, the gate drive 6 V is generated based on LDO from VIN under buck mode, the total gate drive related loss are all considered when VIN is used for gate drive loss calculation .

The bottom-side MOSFET loss also includes conduction loss and switching loss:

Equation 18. Pbottom =Pcon_bottom+Psw_bottom
Equation 19. Pcon_bottom =(1 - D) · IL_RMS2 · RDS(on)_bottom;
Equation 20. Psw_bottom =PRR_bottom+PDead_bottom+PGate_bottom;

The first item Pcon_bottom represents the conduction loss which is straight forward. The second term Psw_bottom represents the multiple switching loss items in bottom MOSFET including reverse recovery losses (PRR_bottom), Dead time body diode conduction loss (PDead_bottom) and gate drive loss (PGate_bottom). The detail calculation can be found below:

Equation 21. PRR_bottom=VIN · Qrr · fS
  • Qrr is the bottom MOSFET reverse recovery charge which can be found in MOSFET data sheet;
Equation 22. PDead_bottom=VF · Ivalley · fS · tdead_rise+VF · Ipeak · fS · tdead_fall
  • VF is the body diode forward conduction voltage drop;
  • tdead_rise is the SW rising edge deadtime between top and bottom MOSFETs which is around 40 ns;
  • tdead_fall is the SW falling edge deadtime between top and bottom MOSFETs which is around 30 ns;

PGate_bottom can follow the same method as top MOSFET gate drive loss calculation approach refer to Equation 17.

P-channel MOSFETs is used for battery charging BATFET. The gate drivers are internally integrated into the IC with 10 V of gate drive voltage. 20 V or higher voltage rating MOSFETs are preferred for 1- to 4-cell battery application, the Ciss of P-channel MOSFET should be chosen less than 5 nF.