LV5028TT

No.A1999-6/16

LED current and inductande setting

• Relation ship beween REF_IN and CS pin voltage(Power Factor Crrection(PFC))

The output current value is the average of the current value that flows during one cycle. The current value that flows into

coil is a triangular wave shown in the figure below. Make sure to set Ipk so that (average of current value at one cycle)

is equal to (LED current value).Ipk is set by the relationship between REF_IN voltage and Rcs voltage.

This relationship make Power Factor Correction (PFC).Therefore, it is available to make LED current a sine curve.

• Setting Zener voltage

Vzd depend on LED voltage (VF). Choose Zener diode around Vf (LED voltage).When VAC voltage is lower than Vf,

LED operation is not normal. Using Zener diode prevents incorrect operating during VAC voltage lower than Vf. In

detail, refer to [LED current and inductance setting]

In case of REF_IN pin open, this error amplifier negative input(-) is under control of internal VREF voltage

(0.605Vtyp).

Ipk =

(Vac-Vzd)

×

R2

R1+R2

Rcs

Ipk: peak inductor current

Vf: LED forward voltage drop

Vac: effective value, R.M.S value

VREF: Built-in reference voltage (0.605V)

VREF_IN: REF_IN voltage (6 pin)

Rs: External sense resistor

Vzd: Zener diode voltage (REF_IN pin)

RESET

REF_IN

CLK

Q

CS

VREF

(0.605V typ)

Rcs

a blockdiagram in outline

+

-

-

OUT

L

R1

R2

Vzd

FET current

FET

Vac

REF_IN

FET current

T

ON

OFF

Toff

Ton

VREF (0.605V typ)