SELC2010M Просмотр технического описания (PDF) - MagnaChip Semiconductor

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SELC2010M

High current switch mode PWM LED Driver

MagnaChip Semiconductor 

In figure 10

VFBP

=

VREF * R2

R1+ R2

VFBN = I LED * RLED

∴ I LED

=

5* R2

(R1 + R2) * RLED

Preliminary – Subject to change without notice

Closed Loop Network Selection

The MAP3201 controls in peak current mode. Current mode easily

achieves compensation by consisting simple single Pole from

Double Pole that LC filer makes at Voltage mode

Vout

Vc ~~ iL

Co Ro

2. PWM Dimming

The MAP3201 makes same phase PWMO output from logic PWM

signal of PWMI using intenral Level shift. PWMO of operating

voltage level is between GND and VCC.

Inductor Selection

Inductor value should be decided before system design.

Because the selection of the inductor affects the operating

mode of CCM (Continuous current mode) or DCM (Discontinuous

current mode).

In CCM operation, indutor size should be bigger, even though the

ripple current and peak current of inductor can be small.

In DCM operation, even ripple current and peak current of inductor

should be large while the inductor size can be smaller so that it is

more effective in BLU of TV and Notebook application.

The MAP3201 was designed for DCM operation.

In CCM operation, sub-harmonic oscillation may occur if duty cycle

exceeds over 50%. Because there is no slope compensation

functions.

The following is the equation to calculate Max.Value of Inductor in

DCM operation.

L(max)

=

[(1 −

D)2

*

D * RO(max)

2

*Ts(min) ]

* RO(max) = Maximum _ Output _ Im pedance

*TS(min ) = Minimum _ Switching _ period

(Optional)

Vc

-

++

Rc

Vref

Cc

Figure 11 Current mode Loop Compensation

1. Select fC (Crossover frequency)

In general, crossover frequency is selected from 1/3 ~ 1/6 range of

the switching frequency. If fc is large, there is possibility of oscillation

to occur, although time response gets better.

On the other hand, if fc is small, time response will be bad, while it

has improved stability, which may cause over shoot or under shoot

in abnormal condition.

It should be noted that fc should be set at smaller location than RHP

Zero.

f RHP

=

Ro * (1 − D)2

2π * L

(Boost)

2. Select fPO

f PO = f C * GO

( GO

= DC Gain of plant =

A

)

B

A=

1

2 (m − 0.5) * (1 − D)3

+

R

L*F

Selecting approximately m = 1.4

B = RS * (1 − D)

RS = Sensing Resistor

OCT.15 2009. Version 0.3

MagnaChip Semiconductor Ltd.

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