LT1247CS8#PBF

Frequency - Switching:	1MHz
Base Part Number:	LT1247
Supplier Device Package:	8-SOIC
Package / Case:	8-SOIC (0.154", 3.90mm Width)
Operating Temperature:	0°C ~ 100°C (TJ)
Control Features:	Frequency Control
Serial Interfaces:	--
Clock Sync:	No
Synchronous Rectifier:	No
Duty Cycle (Max):	100%
Series:	--
Voltage - Supply (Vcc/Vdd):	8.4 V ~ 25 V
Output Phases:	1
Number of Outputs:	1
Topology:	Buck
Output Configuration:	Positive
Function:	Step-Down
Output Type:	Transistor Driver
Part Status:	Active
Packaging:	Tube

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LT1247CS8#PBF Application Field and Working Principle

LT1247CS8#PBF can be categorized as PMIC – Voltage Regulators – DC DC Switching Controllers. This product, designed by Linear Technology, is a current mode, single-ended primary-side regulator (PSR) for off-line, constant voltage or constant current regulated power supplies.

What Is PSR?

PSR, or primary-side regulation, is a technique for controlling the output voltage or current in a power supply using only the primary-side power elements and signals. PSR eliminates the need for a secondary-side regulating circuit, reducing components count and costs. This is especially beneficial for AC/DC power supplies in isolated output applications.

Application Fields and Operation Mode

LT1247CS8#PBF is used to design off-line flyback transformers. This device can also provide offline continuous conduction mode (CCM) and discontinuous conduction mode (DCM). It is suitable for a wide range of power levels, from 10W to 100W, with a supply voltage range of 90-265 VAC. The power density of the designed flyback converter may be up to 1.2KW/in3 by utilizing the device’s internal startup circuit, powergood output and a soft-start function.

Operating Frequency

With the help of the onboard frequency jittering mechanism, the working frequency can be set to 50 kHz to 400 kHz, thus protecting the entire system from component ringing.

Protection Features

LT1247CS8#PBF features a variety of integrated protection features, such as:

• Peak Current Limit (PCL): The PCL adjusts the maximum output current of the flyback converter.
• Overvoltage Protection (OVP): OVP protects the output against an excessive output voltage.
• Undervoltage Lockout (UVLO): UVLO prevents damaging high voltage switching during start-up.
• Thermal Shutdown (TSD): TSD protects the IC from any kind of thermal flash.
• Soft-start (Ramp-up): Soft-start prevents circuit instability and potential damage during the power-up phase.
• Fault monitoring (PowerGood): PowerGood indicates the failure of the circuit if the output voltage is not correct.

Working Principle

LT1247CS8#PBF contains a wide-range start-up circuit connected to the main power input. This circuit provides a high start-up voltage for the switching regulator.The frequency is set by the onboard frequency jittering circuit. This circuit also protects the system from component ringing and acts as a noise filter for the entire system.The device\'s controller contains an on-chip peak current limit comparator that adjusts the maximum output current of the flyback converter, and the OVP, UVLO and TSD circuits to prevent the system from damage caused by excess current or voltage.In addition, the soft-start circuit provides a gradual ramp-up of the V OUT , preventing instability in the system and reducing inrush current. Finally, the PowerGood circuit monitors the power supply output voltage and provides a warning signal in case of failure.

Conclusion

LT1247CS8#PBF is an ideal DC/DC controller for high-density, low-power switching supplies, providing high efficiency, accurate regulation and easy programming. The onboard protection features ensure a reliable and safe operation.

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