Datasheet LT8570, LT8570-1 (Analog Devices) - 9
| Manufacturer | Analog Devices |
| Description | Boost/SEPIC/Inverting DC/DC Converter with 65V Switch, Soft-Start and Synchronization |
| Pages / Page | 34 / 9 — OPERATION Start-Up Operation. Current Limit and Thermal Shutdown Operation |
| File Format / Size | PDF / 906 Kb |
| Document Language | English |
OPERATION Start-Up Operation. Current Limit and Thermal Shutdown Operation
Model Line for this Datasheet
- LT8570EDD#PBF LT8570EDD#PBF LT8570EDD#TRPBF LT8570EDD#TRPBF LT8570EDD-1#PBF LT8570EDD-1#TRPBF LT8570EMS8E#PBF LT8570EMS8E#PBF LT8570EMS8E#TRPBF LT8570EMS8E#TRPBF LT8570EMS8E-1#PBF LT8570EMS8E-1#TRPBF LT8570HDD#PBF LT8570HDD-1#PBF LT8570HMS8E#PBF LT8570HMS8E-1#PBF LT8570IDD#PBF LT8570IDD#PBF LT8570IDD#TRPBF LT8570IDD#TRPBF LT8570IDD-1#PBF LT8570IDD-1#TRPBF LT8570IMS8E#PBF LT8570IMS8E#PBF LT8570IMS8E#TRPBF LT8570IMS8E#TRPBF LT8570IMS8E-1#PBF LT8570IMS8E-1#TRPBF
Text Version of Document
LT8570/LT8570-1
OPERATION Start-Up Operation
duty cycle that the part can achieve thus allowing better Several functions are provided to enable a very clean control of the switch current during start-up. When the start-up for the LT8570/LT8570-1. FBX voltage is pulled outside of this range, the switching frequency returns to normal. • First, the SHDN pin voltage is monitored by an internal voltage reference to give a precise turn-on voltage level.
Current Limit and Thermal Shutdown Operation
An external resistor (or resistor divider) can be connected The LT8570/LT8570-1 have a current limit circuit not from the input power supply to the SHDN pin to provide shown in the Block Diagram. The switch current is con- a user-programmable undervoltage lockout function. stantly monitored and not allowed to exceed the maximum • Second, the soft-start circuitry provides for a gradual switch current at a given duty cycle (see the Electrical ramp-up of the switch current. When the part is brought Characteristics table). If the switch current reaches this out of shutdown, the external SS capacitor is first value, the SR latch (SR1) is reset regardless of the state discharged (providing protection against SHDN pin of the comparator (A1/A2). Also, not shown in the Block glitches and slow ramping), then an integrated 280k Diagram is the thermal shutdown circuit. If the temperature resistor pulls the SS pin up to ~2.1V. By connecting an of the part exceeds approximately 165°C, the SR2 latch is external capacitor to the SS pin, the voltage ramp rate set regardless of the state of the amplifier (A1/A2). When on the pin can be set. Typical values for the soft-start the part temperature falls below approximately 160°C, a capacitor range from 100nF to 1µF. full soft-start cycle will then be initiated. The current limit and thermal shutdown circuits protect the power switch • Finally, the frequency foldback circuit reduces the switch- as well as the external components connected to the ing frequency when the FBX pin is in a nominal range LT8570/LT8570-1. of 300mV to 920mV. This feature reduces the minimum 85701fa For more information www.linear.com/LT8570 9 Document Outline Features Applications Typical Application Description 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 Start-Up Operation
duty cycle that the part can achieve thus allowing better Several functions are provided to enable a very clean control of the switch current during start-up. When the start-up for the LT8570/LT8570-1. FBX voltage is pulled outside of this range, the switching frequency returns to normal. • First, the SHDN pin voltage is monitored by an internal voltage reference to give a precise turn-on voltage level.
Current Limit and Thermal Shutdown Operation
An external resistor (or resistor divider) can be connected The LT8570/LT8570-1 have a current limit circuit not from the input power supply to the SHDN pin to provide shown in the Block Diagram. The switch current is con- a user-programmable undervoltage lockout function. stantly monitored and not allowed to exceed the maximum • Second, the soft-start circuitry provides for a gradual switch current at a given duty cycle (see the Electrical ramp-up of the switch current. When the part is brought Characteristics table). If the switch current reaches this out of shutdown, the external SS capacitor is first value, the SR latch (SR1) is reset regardless of the state discharged (providing protection against SHDN pin of the comparator (A1/A2). Also, not shown in the Block glitches and slow ramping), then an integrated 280k Diagram is the thermal shutdown circuit. If the temperature resistor pulls the SS pin up to ~2.1V. By connecting an of the part exceeds approximately 165°C, the SR2 latch is external capacitor to the SS pin, the voltage ramp rate set regardless of the state of the amplifier (A1/A2). When on the pin can be set. Typical values for the soft-start the part temperature falls below approximately 160°C, a capacitor range from 100nF to 1µF. full soft-start cycle will then be initiated. The current limit and thermal shutdown circuits protect the power switch • Finally, the frequency foldback circuit reduces the switch- as well as the external components connected to the ing frequency when the FBX pin is in a nominal range LT8570/LT8570-1. of 300mV to 920mV. This feature reduces the minimum 85701fa For more information www.linear.com/LT8570 9 Document Outline Features Applications Typical Application Description 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
