Confidential

Datasheet Version 1.1

Jun 28

Application Information

CURRENT MODE BOOST SWITCHING CONVERER OPERATION

The MAP3702 employs current mode control boost architecture that has a fast current sense loop and a slow

voltage feedback loop. Internal slope compensation feature ensures stable CCM operation.

Such architecture achieves a fast transient response that is essential for the LED backlight application.

SOFT-START

The MAP3702 has following two soft-start circuitry internally to smooth start-up and reduce the start-up current.

(1) After the device is enabled, the FB pin voltage ramps to the reference voltage(200mV) in 32 steps, each step

takes 213μs.

(2) After the COMP voltage ramps, for the first 5msec, the current limit of the internal boost MOSFET is set to typ.

0.4A.

LED CURRENT SETTING

The FB pin voltage can be regulated up to 200mV. Max. LED current value is programmed by external current

sense resistor in series with the LED string and calculated by following equation.

To reduce LED current tolerance, 1% resistor should be used.

ISET

FB

LED

R

V

I

=

DIMMING MODE SELECTION

The MAP3702 offers two dimming modes, filtered-PWM and the SWIRE digital dimming. The CTRL pin is used for

the control input for both dimming modes. The MAP3702 checks the dimming mode each time the device is enabled.

The default mode is filtered-PWM dimming. To enter SWIRE mode, the following digital pattern must be applied to

the CTRL pin every time the MAP3702 starts from the shutdown mode.

(1) Pull CTRL pin high to enable the MAP3702 and to start the SWIRE detection window.

min. 1msec) ends. The SWIRE detection window starts from the first CTRL pin low to high transition.

Once the above 3 conditions are met, the MAP3702 enters the SWIRE mode immediately. The SWIRE

communication can start before the detection window ends. Once the dimming mode is selected, it cannot be

changed without another start up. This means the IC needs to be shutdown by pulling the CTRL low for more than

2.0ms and restarts to change dimming mode. When the IC enters shutdown mode, the MAP3702 memorizes the

latest FB voltage(the latest programming code) before shutdown and when re-enters the SWIRE mode, the

MAP3702 outputs the memorized FB voltage otherwise new programming code is applied.

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