MP3313 Rev1.0

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14

8/2/2017

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output voltage of the error amplifier, the LS-FET

is turned off. Then the inductor current flows

through the free-wheeling diode, which forces

the inductor current to decrease. The output

voltage of the internal error amplifier is an

amplified signal of the difference between the

reference voltage and the feedback voltage

from the LED load cathode. The converter

chooses the lowest active LEDx pin voltage

automatically to provide a high enough bus

voltage to power all of the LED arrays. If the

feedback voltage drops below the reference, the

output of the error amplifier increases. This

results in more current flowing through the

LS-FET and delivers more power to the output.

This forms a closed control loop that regulates

the output voltage.

LED String Selection

There are three LED strings for the MP3313,

and each string has an independent EN bit. This

allows

for

1-string,

2-string,

or

3-string

application. By default, all three strings are

enabled.

Flash Mode

The MP3313 can also work in flash mode by

setting the FL_EN bit to 1. The flash time

depends on the FL_T bit and ranges from 50 -

800ms. The flash current is set by I_FL bit.

When flash mode is enabled, the inductor

peak-current limit value jumps to the flash

current limit automatically, which is set by the

FL_CL bit (2.5A/3A selectable), and the LED

current jumps to the flash current. When the

flash is timed out, the LED current and inductor

peak current limit returns to backlight mode, and

the FL_EN bit is reset to 0. When protection is

triggered during the flash, flash mode ends, and

the FL_EN bit is reset.

Dimming Control

The MP3313 supports ultra-high resolution

analog dimming by converting the PWM input

signal or internal register code to the 11-bit

brightness code. Two kinds of LED current

dimming

curve

are

available:

linear

and

exponential mapping.

The MP3313 converts the external PWM signal

into an internal reference via the duty detection

circuit

to

regulate

the

current

linearly

or

exponentially.

Calculate

the

linear

analog

dimming

with

Equation (1):

ILED

I

40.806 A 12.195 A Code



 

 

(1)

Where Code ranges from 1 to 2047. Code 0

sets the LED current to 0.

Calculate the exponential analog dimming with

Equation (2):

Code

ILED

I

51.1 A 1.003040572



 

(2)

Where Code ranges from 1 to 2047. Code 0

sets the LED current to 0.

Figure 2 shows the linear and exponential

dimming curve for the LED current.

Figure 2: LED Current for Each Channel with

Brightness Code

LED Current Ramp Up/Down

The

LED

current

ramps

up

and

down

step-by-step from one brightness code to the

next when the LED current slope function is

enabled by setting the SLPEN bit to 1. The ramp

time can be calculated with Equation (3):

RAMP

t

RAMP (Code1 Code0 1)









(3)

Where RAMP is the slope rate set by the TSLP

bit, Code 0 is the original brightness point, and

Code 1 is the target brightness point.

PWM Sample Frequency

Three different sample frequencies can be

chosen for the input PWM dimming signal for

the MP3313.