MAP3204 查看數據表（PDF） - Unspecified

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MAP3204

4-channelLED Driverfor High Brightness LEDs

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Confidential

Preliminary Datasheet Version 0.0

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.

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 1.25V, a comparator turns off

the external power MOSFET. This switch is re-enabled

after the OVP pin voltage drops 100mV(typical) hysteresis

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.

The OVP level can be calculated with the following

equation.

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.

LED OPEN PROTECTION

In case the voltage on LED current sink pins (FB1~4)

are below 0.2V due to LED open, the MAP3204 turns off

the corresponding string and the remaining string(s) will

continue operation. Once the LED open status is

removed, the corresponding string is automatically

recovered.

LED SHORT PROTECTION

If the voltage at any of the FB1-4 pins exceeds a

threshold of approximately 5.5V due to LED short

during normal operation, the MAP3204 turns off the

corresponding string and the remaining string(s) will

continue operation. If all the strings are shorted, the

MAP3204A will be shutdown and latched. The operation

is resumed by a toggling of the EN pin.

VOUT _ OVP = 1.25 × ROVPH + ROVPL

ROVPL

Jan. 28th 2011

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