Datasheet LT8708-1 (Analog Devices) - 14
| Manufacturer | Analog Devices |
| Description | 80V Synchronous 4-Switch Buck-Boost DC/DC Slave Controller for LT8708 Multiphase System |
| Pages / Page | 36 / 14 — OPERATION. Table 1. LT8708 Data Sheet Sections that Apply to the … |
| Revision | A |
| File Format / Size | PDF / 2.0 Mb |
| Document Language | English |
OPERATION. Table 1. LT8708 Data Sheet Sections that Apply to the LT8708-1. ADDITIONAL INFORMATION. LT8708 DATA SHEET SECTION
Model Line for this Datasheet
Text Version of Document
link to page 14 link to page 14 link to page 15 link to page 15 link to page 19 LT8708-1
OPERATION
The LT8708-1 is a high performance 4-switch buck-boost
Table 1. LT8708 Data Sheet Sections that Apply to the LT8708-1
slave controller that is paralleled with the master LT8708
ADDITIONAL INFORMATION
to increase power capability. Using LT8708-1(s) with the
LT8708 DATA SHEET SECTION IN THIS DATA SHEET
LT8708, an application can command power to be deliv-
Operation
ered from VIN to VOUT or from VOUT to VIN as needed. Start-Up: SHDN Pin Power Switch Control
COMMON LT8708-1 AND LT8708 FEATURES
Unidirectional and Bidirectional Conduction Yes INTV The LT8708-1 and LT8708 share many common func- CC/EXTVCC/GATEVCC/LDO33 Power tions and features that are already documented in the CLKOUT and Temperature Sensing LT8708 data sheet. Table 1 lists the LT8708 data sheet
Applications Information
sections that also apply to the LT8708-1. For some of Internal Oscillator these features, additional LT8708-1 specific information SYNC Pin and Clock Synchronization is provided in this data sheet, as indicated in Table 1. CLKOUT Pin and Clock Synchronization Inductor Current Sensing and Slope The focus of this data sheet is on how to use the Compensation LT8708-1 to increase the number of switching phases RSENSE Selection and Maximum Current in an LT8708-based application. As such, functionality RSENSE Filtering that is identical in both the LT8708 and LT8708-1 will not Inductor (L) Selection necessarily be repeated here. It is assumed that readers Power MOSFET Selection of this data sheet are already familiar with the LT8708. Schottky Diode (D1, D2, D3, D4) Selection Topside MOSFET Driver Supply
ADDING PHASES TO AN LT8708 APPLICATION
(CB1, DB1, CB2, DB2) VINHIMON, VOUTLOMON and RVSOFF Yes In a multiphase LT8708 application, a single LT8708 is the INTVCC Regulators and EXTVCC Connection master of the system. One or more LT8708-1s are slaves LDO33 Regulator that provide additional current as needed. As the master Voltage Lockouts Yes of the multiphase system, the LT8708 and its respec- Junction Temperature Measurement tive error amplifiers, determine the current necessary to Thermal Shutdown regulate the VIN voltage, VOUT voltage, VIN current and Efficiency Considerations VOUT current. The slave LT8708-1 operates by sensing Circuit Board Layout Checklist Yes the IOUT(MASTER) (see Figure 2) and delivering a propor- tional amount of IOUT(SLAVE). Again, since IOUT(SLAVE) is proportional to IOUT(MASTER), the master LT8708 is in LT8708-1s. It illustrates the basic connections needed to control of setting regulation voltages and current limits add LT8708-1s to a multiphase system. to the system.
Adding Phases: The Master LT8708
Each LT8708 and LT8708-1, connected in parallel, is hereon referred to as a phase, the master and slave The master controls the overall current delivered by the V multiphase system. For example, the LT8708 controls the IN current is referred to as IIN(MASTER) and IIN(SLAVE), respectively. For multiphase operation, the LT8708 VIN and VOUT regulation voltages through its FBIN and should be configured according to the LT8708 data sheet. FBOUT pins. Since the slaves primarily duplicate the mas- Configuration of LT8708-1s should follow instructions ter’s IOUT(MASTER) current, the slave’s FBIN and FBOUT in this data sheet. Figure 2 shows a simplified drawing pins and related circuitry are typically not used. See the of a multiphase system with one LT8708 and multiple Error Amplifiers section on how they can affect VC and how to disable them. Rev 0 14 For more information www.analog.com Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Package Description Typical Application Related Parts Features Applications Typical Application Description Absolute Maximum Ratings Order Information Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Common LT8708-1 and LT8708 Features Adding Phases to an LT8708 Application Adding Phases: The Master LT8708 Adding Phases: The Slave LT8708-1 Start-Up Start-Up: SWEN Pin Start-Up: Soft-Start of Switching Regulator Control Overview Power Switch Control Unidirectional and Bidirectional Conduction Error Amplifiers Transfer Function: IOUT(SLAVE) Vs IOUT(MASTER) Transfer Function: CCM Transfer Function: DCM, HCM and Burst Mode Operation Current Monitoring and Limiting Monitoring: IOUT(SLAVE) Monitoring and Limiting: IIN(SLAVE) Multiphase Clocking Applications Information Quick-Start Multiphase Setup Quick Setup: Design the Master Phase Quick Setup: Design the Slave Phase(s) Quick Setup: Evaluation Choosing the Total Number of Phases Operating Frequency Selection CIN and COUT Selection CIN and COUT Selection: VIN Capacitance CIN and COUT Selection: VOUT Capacitance VINHIMON, VOUTLOMON and RVSOFF Configuring the IIN(SLAVE) Current Limits Regulating IOUT(SLAVE) IOUT(SLAVE): Circuit Description IOUT(SLAVE): Configuration Loop Compensation Voltage Lockouts Circuit Board Layout Checklist Design Example Typical Applications Package Description Typical Application Related Parts
OPERATION
The LT8708-1 is a high performance 4-switch buck-boost
Table 1. LT8708 Data Sheet Sections that Apply to the LT8708-1
slave controller that is paralleled with the master LT8708
ADDITIONAL INFORMATION
to increase power capability. Using LT8708-1(s) with the
LT8708 DATA SHEET SECTION IN THIS DATA SHEET
LT8708, an application can command power to be deliv-
Operation
ered from VIN to VOUT or from VOUT to VIN as needed. Start-Up: SHDN Pin Power Switch Control
COMMON LT8708-1 AND LT8708 FEATURES
Unidirectional and Bidirectional Conduction Yes INTV The LT8708-1 and LT8708 share many common func- CC/EXTVCC/GATEVCC/LDO33 Power tions and features that are already documented in the CLKOUT and Temperature Sensing LT8708 data sheet. Table 1 lists the LT8708 data sheet
Applications Information
sections that also apply to the LT8708-1. For some of Internal Oscillator these features, additional LT8708-1 specific information SYNC Pin and Clock Synchronization is provided in this data sheet, as indicated in Table 1. CLKOUT Pin and Clock Synchronization Inductor Current Sensing and Slope The focus of this data sheet is on how to use the Compensation LT8708-1 to increase the number of switching phases RSENSE Selection and Maximum Current in an LT8708-based application. As such, functionality RSENSE Filtering that is identical in both the LT8708 and LT8708-1 will not Inductor (L) Selection necessarily be repeated here. It is assumed that readers Power MOSFET Selection of this data sheet are already familiar with the LT8708. Schottky Diode (D1, D2, D3, D4) Selection Topside MOSFET Driver Supply
ADDING PHASES TO AN LT8708 APPLICATION
(CB1, DB1, CB2, DB2) VINHIMON, VOUTLOMON and RVSOFF Yes In a multiphase LT8708 application, a single LT8708 is the INTVCC Regulators and EXTVCC Connection master of the system. One or more LT8708-1s are slaves LDO33 Regulator that provide additional current as needed. As the master Voltage Lockouts Yes of the multiphase system, the LT8708 and its respec- Junction Temperature Measurement tive error amplifiers, determine the current necessary to Thermal Shutdown regulate the VIN voltage, VOUT voltage, VIN current and Efficiency Considerations VOUT current. The slave LT8708-1 operates by sensing Circuit Board Layout Checklist Yes the IOUT(MASTER) (see Figure 2) and delivering a propor- tional amount of IOUT(SLAVE). Again, since IOUT(SLAVE) is proportional to IOUT(MASTER), the master LT8708 is in LT8708-1s. It illustrates the basic connections needed to control of setting regulation voltages and current limits add LT8708-1s to a multiphase system. to the system.
Adding Phases: The Master LT8708
Each LT8708 and LT8708-1, connected in parallel, is hereon referred to as a phase, the master and slave The master controls the overall current delivered by the V multiphase system. For example, the LT8708 controls the IN current is referred to as IIN(MASTER) and IIN(SLAVE), respectively. For multiphase operation, the LT8708 VIN and VOUT regulation voltages through its FBIN and should be configured according to the LT8708 data sheet. FBOUT pins. Since the slaves primarily duplicate the mas- Configuration of LT8708-1s should follow instructions ter’s IOUT(MASTER) current, the slave’s FBIN and FBOUT in this data sheet. Figure 2 shows a simplified drawing pins and related circuitry are typically not used. See the of a multiphase system with one LT8708 and multiple Error Amplifiers section on how they can affect VC and how to disable them. Rev 0 14 For more information www.analog.com Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Package Description Typical Application Related Parts Features Applications Typical Application Description Absolute Maximum Ratings Order Information Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Common LT8708-1 and LT8708 Features Adding Phases to an LT8708 Application Adding Phases: The Master LT8708 Adding Phases: The Slave LT8708-1 Start-Up Start-Up: SWEN Pin Start-Up: Soft-Start of Switching Regulator Control Overview Power Switch Control Unidirectional and Bidirectional Conduction Error Amplifiers Transfer Function: IOUT(SLAVE) Vs IOUT(MASTER) Transfer Function: CCM Transfer Function: DCM, HCM and Burst Mode Operation Current Monitoring and Limiting Monitoring: IOUT(SLAVE) Monitoring and Limiting: IIN(SLAVE) Multiphase Clocking Applications Information Quick-Start Multiphase Setup Quick Setup: Design the Master Phase Quick Setup: Design the Slave Phase(s) Quick Setup: Evaluation Choosing the Total Number of Phases Operating Frequency Selection CIN and COUT Selection CIN and COUT Selection: VIN Capacitance CIN and COUT Selection: VOUT Capacitance VINHIMON, VOUTLOMON and RVSOFF Configuring the IIN(SLAVE) Current Limits Regulating IOUT(SLAVE) IOUT(SLAVE): Circuit Description IOUT(SLAVE): Configuration Loop Compensation Voltage Lockouts Circuit Board Layout Checklist Design Example Typical Applications Package Description Typical Application Related Parts
