MAP3202 Просмотр технического описания (PDF) - MagnaChip Semiconductor

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MAP3202

High Efficiency Switch Mode LED Driver

MagnaChip Semiconductor 

Confidential

Datasheet Version 1.1

SCP Circuit uses very fast comparator in order to turn off

MOSFET when the abnormal condition of SCP Level is

detected. Because high current can be driven into channel of

MOSFET when LED string is shorted.

5. Auto-Restart Protection

The MAP3202 offers Auto Restart protection function which is

recovered into normal operation mode when protection

condition is cleared. The auto restart time (TAR) is fixed at 1mS,

Fosc = 100KHz. it is recovered to normal operating mode if

SCP or OVP condition is cleared.

Dimming Control

1. LED Current

The MAP3202 decides LED Current setting by the value of

RLED resistance and voltage on FBP pin as below

LED _ Current = V _ FBP

RLED

The MAP3202 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) ]

Where,

R0(max) = Maximum output impedance

TS(min) = Minimum Switching Period

Closed Loop Network Selection

The MAP3202 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

Figure 7 LED Current Setting

2. PWM Dimming

The MAP3202 makes same phase PWMO output from logic

PWM signal of PWMI using internal 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, inductor 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.

March 2012

(Optional)

Vc

-

++

Rc

Vref

Cc

Figure 8 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.

Ro * (1 − D)2

f RHP = 2π * L

2. Select fPO

f PO = fC * GO

A

( GO = DC Gain of plant =

)

B

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