Datasheet LT8705 (Analog Devices) - 15
| 制造商 | Analog Devices |
| 描述 | 80V VIN and VOUT Synchronous 4-Switch Buck-Boost DC/DC Controller |
| 页数 / 页 | 44 / 15 — operaTion. Figure 2. Start-Up and Fault Sequence. Fault Conditions |
| 文件格式/大小 | PDF / 508 Kb |
| 文件语言 | 英语 |
operaTion. Figure 2. Start-Up and Fault Sequence. Fault Conditions
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LT8705
operaTion
TJUNCTION < 160°C AND SHDN > 1.234V AND V SHDN < 1.184V OR IN > 2.5V TYPICAL VALUES AND V TYPICAL VALUES IN < 2.5V OR (SWEN* < 1.184V OR (INTV T CC AND GATEVCC < 4.65V) JUNCTION > 165°C OR LDO33 < 3.04V) CHIP OFF SWITCHER OFF • SWITCHER OFF • SWITCHER DISABLED • LDOs OFF • INTVCC AND LDO33 OUTPUTS ENABLED SHDN > 1.234V AND VIN > 2.5V AND SWEN* > 1.206V AND TYPICAL VALUES (INTVCC AND GATEVCC > 4.81V) AND LDO33 > 3.075V INITIALIZE • SS PULLED LOW FAULT • FORCE DISCONTINOUS MODE UNLESS Burst Mode OPERATION SELECTED SS < 50mV FAULT DETECTED SOFT-START FAULT • SS CHARGES UP • SS CHARGES UP • SWITCHER DISABLED • SWITCHER ENABLED • CLKOUT DISABLED SS > 1.6V AND NO FAULT CONDITIONS NORMAL MODE STILL DETECTED • NORMAL OPERATION POST FAULT DELAY • WHEN SS > 1.6V ... FAULT FAULT • CLKOUT ENABLED • SS SLOWLY DISCHARGES • ENABLE FORCED CONTINUOUS MODE IF SELECTED SS < 50mV *SWEN IS CONNECTED TO INTVCC IN THE TSSOP PACKAGE FAULT = OVERVOLTAGE (IMON_IN OR IMON_OUT > 1.61V TYP) 8705 F02
Figure 2. Start-Up and Fault Sequence
from being drawn out of the output and forced into the allowed to enter forced continuous mode (if MODE is low) input. After SS has been discharged to less than 50mV, and an internal regulator pulls SS up quickly to ≅2.5V. a soft-start of the switching regulator begins (soft-start Typical values for the external soft-start capacitor range state). The soft-start circuitry provides for a gradual from 100nF to 1μF. A minimum of 100nF is recommended. ramp-up of the inductor current by gradually allowing the VC voltage to rise (refer to VC vs SS Voltage in the Typical
Fault Conditions
Performance Characteristics). This prevents abrupt surges The LT8705 activates a fault sequence under certain op- of current from being drawn out of the input power supply. erating conditions. If any of these conditions occur (see An integrated 100k resistor pulls the SS pin to ≅2.5V. The Figure 2) the CLKOUT pin and internal switching activity ramp rate of the SS pin voltage is set by this 100k resis- are disabled. At the same time, a timeout sequence com- tor and the external capacitor connected to this pin. Once mences where the SS pin is charged up to a minimum SS gets to 1.6V, the CLKOUT pin is enabled, the part is of 1.6V (fault detected state). The SS pin will continue 8705ff For more information www.linear.com/LT8705 15 Document Outline Features Description Applications Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Typical Applications Package Description Revision History Typical Application Related Parts
operaTion
TJUNCTION < 160°C AND SHDN > 1.234V AND V SHDN < 1.184V OR IN > 2.5V TYPICAL VALUES AND V TYPICAL VALUES IN < 2.5V OR (SWEN* < 1.184V OR (INTV T CC AND GATEVCC < 4.65V) JUNCTION > 165°C OR LDO33 < 3.04V) CHIP OFF SWITCHER OFF • SWITCHER OFF • SWITCHER DISABLED • LDOs OFF • INTVCC AND LDO33 OUTPUTS ENABLED SHDN > 1.234V AND VIN > 2.5V AND SWEN* > 1.206V AND TYPICAL VALUES (INTVCC AND GATEVCC > 4.81V) AND LDO33 > 3.075V INITIALIZE • SS PULLED LOW FAULT • FORCE DISCONTINOUS MODE UNLESS Burst Mode OPERATION SELECTED SS < 50mV FAULT DETECTED SOFT-START FAULT • SS CHARGES UP • SS CHARGES UP • SWITCHER DISABLED • SWITCHER ENABLED • CLKOUT DISABLED SS > 1.6V AND NO FAULT CONDITIONS NORMAL MODE STILL DETECTED • NORMAL OPERATION POST FAULT DELAY • WHEN SS > 1.6V ... FAULT FAULT • CLKOUT ENABLED • SS SLOWLY DISCHARGES • ENABLE FORCED CONTINUOUS MODE IF SELECTED SS < 50mV *SWEN IS CONNECTED TO INTVCC IN THE TSSOP PACKAGE FAULT = OVERVOLTAGE (IMON_IN OR IMON_OUT > 1.61V TYP) 8705 F02
Figure 2. Start-Up and Fault Sequence
from being drawn out of the output and forced into the allowed to enter forced continuous mode (if MODE is low) input. After SS has been discharged to less than 50mV, and an internal regulator pulls SS up quickly to ≅2.5V. a soft-start of the switching regulator begins (soft-start Typical values for the external soft-start capacitor range state). The soft-start circuitry provides for a gradual from 100nF to 1μF. A minimum of 100nF is recommended. ramp-up of the inductor current by gradually allowing the VC voltage to rise (refer to VC vs SS Voltage in the Typical
Fault Conditions
Performance Characteristics). This prevents abrupt surges The LT8705 activates a fault sequence under certain op- of current from being drawn out of the input power supply. erating conditions. If any of these conditions occur (see An integrated 100k resistor pulls the SS pin to ≅2.5V. The Figure 2) the CLKOUT pin and internal switching activity ramp rate of the SS pin voltage is set by this 100k resis- are disabled. At the same time, a timeout sequence com- tor and the external capacitor connected to this pin. Once mences where the SS pin is charged up to a minimum SS gets to 1.6V, the CLKOUT pin is enabled, the part is of 1.6V (fault detected state). The SS pin will continue 8705ff For more information www.linear.com/LT8705 15 Document Outline Features Description Applications Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Typical Applications Package Description Revision History Typical Application Related Parts