VIN

FB

COMP

VCC

OUT

RT

UVLO

GND

CS

SS

L1

D1

Q1

C1

C2

R1

LM5022

www.ti.com

SNVS480E – JANUARY 2007 – REVISED OCTOBER 2011

Example Circuit

Figure 2. Design Example Schematic

Applications Information

OVERVIEW

The LM5022 is a low-side N-channel MOSFET controller that contains all of the features needed to implement

single ended power converter topologies. The LM5022 includes a high-voltage startup regulator that operates

over a wide input range of 6V to 60V. The PWM controller is designed for high speed capability including an

oscillator frequency range up to 2 MHz and total propagation delays less than 100 ns. Additional features include

an error amplifier, precision reference, input under-voltage lockout, cycle-by-cycle current limit, slope

compensation, soft-start, oscillator sync capability and thermal shutdown.

The LM5022 is designed for current-mode control power converters that require a single drive output, such as

boost and SEPIC topologies. The LM5022 provides all of the advantages of current-mode control including input

voltage feed-forward, cycle-by-cycle current limiting and simplified loop compensation.

HIGH VOLTAGE START-UP REGULATOR

The LM5022 contains an internal high-voltage startup regulator that allows the VIN pin to be connected directly to

line voltages as high as 60V. The regulator output is internally current limited to 35 mA (typical). When power is

rising threshold of 5V, the controller output is enabled. The controller will remain enabled until VCC falls below

4.7V. In applications using a transformer, an auxiliary winding can be connected through a diode to the VCC pin.

This winding should raise the VCC pin voltage to above 7.5V to shut off the internal startup regulator. Powering

VCC from an auxiliary winding improves conversion efficiency while reducing the power dissipated in the

UVLO falling threshold (4.7V) during the initial start-up. During a fault condition when the converter auxiliary

winding is inactive, external current draw on the VCC line should be limited such that the power dissipated in the

start-up regulator does not exceed the maximum power dissipation capability of the controller.

An external start-up or other bias rail can be used instead of the internal start-up regulator by connecting the

VCC and the VIN pins together and feeding the external bias voltage (7.5V to 14V) to the two pins.

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