MAP3204 查看數據表（PDF） - MagnaChip Semiconductor

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MAP3204

4-channelLED Driverfor High Brightness LEDs

MagnaChip Semiconductor 

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Datasheet Version 1.5

Application Information

CURRENT MODE BOOST SWITCHING

CONTROLLER OPERATION

The MAP3204 employs current mode control boost

architecture that has a fast current sense loop and a

slow voltage feedback loop. Such architecture

achieves a fast transient response that is essential for

the LED backlight application.

DYNAMIC HEADROOM CONTROL

The MAP3204 features a proprietary Dynamic

Headroom Control circuit that detects the lowest

voltage from any of the FB1-FB4 pins. This lowest

channel voltage is used as the feedback signal for the

boost controller. Since all LED stacks are connected in

parallel to the same output voltage, the other FB pins

will have a higher voltage, but the regulated current

source circuit on each channel will ensure that each

channel has the same current.

INTERNAL 5V/10V REGULATOR

The MAP3204 has built-in 5V LDO regulator to supply

internal analog and logic blocks. The LDO is powered up

when the EN pin is Logic High.

A 10V LDO is used to drive external MOSFET connected

to the GATE pin. A 2.2uF bypass capacitor is required for

stable operation of the LDO.

DIMMING SCHEME

When PWMI signal stays at low level (<0.8V) for a

long time, the MAP3204 turns off the boost circuitry,

but internal circuit is enabled so the MAP3204

increases the output voltage promptly.

The minimum dimming on duty is 1% at 1kHz = 10us.

PARALLEL OPERATION

Even the MAP3204 has 4Ch and 150mA LED current

capability per channel, 2Ch and 300mA application

can be supported by tying 2FBs into 1ch, so the LED

current capability can be increased to 300mA.

BOOST SWITCHING FREQUENCY

ADJUSTMENT

The switching frequency of the MAP3204 should be

programmed between 100kHz and 500kHz by an

external resistor connected between the FSW pin and

ground. Do not leave this pin open. The approximate

operating boost switching frequency can be calculated

by following equation.

f sw[MHz]

=

50

RFSW [kΩ]

LED CURRENT ADJUSTMENT

The full scale LED drive current of the MAP3204

should be programmed up to 150mA by an external

resistor connected between the ISET pin and ground.

Do not leave this pin open. The LED current can be

set by following table.

ILED

[mA]

50

60

70

80

90

100

110

120

130

140

150

Used

4-CH

216

184

159

139

123

111

100

92

85

79

73

RISET [kΩ]

Used Used

3-CH 2-CH

RISET RISET

(4-CH) (4-CH)

ⅹ1.025 ⅹ1.05

Used

1-CH

RISET

(4-CH)

ⅹ1.08

Due to internal GND impedance, the LED current

increases with increase of the number of open channel. If

there are open channels, specific weight should be

multiplied to 4-channel RISET with the number of open

channel. For example, the RISET value is 111kΩ for

100mA LED current for 4-channel application, but in case

of 3-channel application, the RISET should be chosen by

113.8kΩ(=111ⅹ1.025).

It is needed fine tuning for these RISET values

considering deviation of resistors and etc.

OVER VOLTAGE PROTECTION

To protect the boost converter when the load is open,

or the output voltage becomes excessive for any

reason, the MAP3204 features a dedicated

overvoltage feedback input. The OVP pin is connected

to the center tap of a resistive voltage-divider from the

high voltage output (see the typical application). When

the OVP pin voltage exceeds typical 1.28V, a comparator

turns off the external power MOSFET. This switch is re-

enabled after the OVP pin voltage drops hysteresis(∆OVP)

below the protection threshold. This over voltage

protection feature ensures the boost converter fail-safe

operation when the LED channels are disconnected from

the output.

It is recommended that the OVP voltage be set to 1.2

times of output voltage. The OVP level can be calculated

with the following equation.

VOUT _ OVP = 1.28 × ROVPH + ROVPL

ROVPL

Feb 28th 2012.

6

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