LV5026MC

No.A2042-6/16

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

LED current and inductance setting

It is available to use both no-isolation and isolation applications.

(For non-isolation application)

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 IL_PK so that (average of current value at one cycle)

is equal to (LED current value).

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)

RESET

REF_IN

CLK

Q

CS

VREF

(0.605V typ)

Rcs

a blockdiagram in outline

+

-

-

OUT

Vac

L

LED

R1

R2

Vzd

Inductor current

Inductor

current

FET

Vac

T

ON

OFF

Ipk

Ipk = (Vac-Vf)/L

× T_c

= Vf/L

× T_d

IL = Vac/L

× T

T_c

T_d

FET_on

FET_off

T (1cycle)

IL = Vf/L

× T

REF_IN

VREF (0.605V typ)/built-in reference

ILED slope is proportion to

Vac voltage (REF pin voltage)