LM5039 datasheet(19/33 Pages) TI

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LM5039

AGND

Current

Sense

Power

Transformer

VIN

VPWR

LM5039

AGND

Power

Transformer

VPWR

VIN

Current

Sense

LM5039

VPWR

8.3V - 15V

(from aux winding)

VIN

VCC

LM5039

www.ti.com

SNVS621D – FEBRUARY 2010 – REVISED MARCH 2013

Current Sense

The CS pin needs to receive an input signal representative of the transformer’s primary current, either from a

current sense transformer or from a resistor in series with the source of the LO switch, as shown in Figure 20

and Figure 21. In both cases, the sensed current creates a ramping voltage across R1, and the RF/CF filter

suppresses noise and transients. R1, RF and CF should be located as close to the LM5039 as possible, and the

ground connection from the current sense transformer, or R1, should be a dedicated track to the AGND pin. The

current sense components must provide greater than 0.6V (typ) at the CS pin when an over-current condition

exists.

Figure 19. Start-up Regulator for VPWR >100V

Figure 20. Current Sense Using Current Sense Transformer

Figure 21. Current Sense Using Current Sense Resistor (R1)

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LM5039 Datasheet(PDF) 19 Page - Texas Instruments