MP3313 Rev1.0

www.MonolithicPower.com

16

8/2/2017

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The ramp time in either mapping mode can

be calculated with Equation (13):

RAMP

PWM1

PWM0

t

RAMP | 2047 D

2047 D

1|













(13)

3. Internal register multiplies PWM duty before

ramping: LED slope step controlled by

internal register and PWM duty. When the

brightness control mode bits are set to 010,

the LED current is controlled by the input

PWM dimming duty multiplied by the internal

brightness register. The slope step is also

controlled

by

the

PWM dimming

duty

multiplied by the brightness register.

In linear mode, the LEDs can be calculated

with Equation (14) and Equation (15):

ILED0

PWM0

I

40.806 A 12.195 A Code0 D



 

 



(14)

ILED1

PWM1

I

40.806 A 12.195 A Code1 D



 

 



(15)

In exponential mode, the LEDs can be

calculated with Equation (16) and Equation

(17):

PWM0

Code0 D

ILED0

I

51.1 A 1.003040572





 

(16)

PWM1

Code1 D

ILED1

I

51.1 A 1.003040572





 

(17)

The ramp time in either mapping mode can

be calculated with Equation (18):

RAMP

PWM1

PWM0

t

RAMP | Code1 D

Code0 D

1|













(18)

4. Ramp before internal register multiplies

input PWM dimming duty, LED slope step

controlled by internal register only: When the

brightness control mode bits are set to 011,

the LED current is controlled by the input

PWM dimming duty multiplied by the internal

brightness register.

The

slope

step

is

controlled by the internal brightness register

only.

In this mode, the LED current jumps

immediately

when

the

external

PWM

dimming duty changes. Then the LED

current changes step-by-step to the new

brightness register.

In linear mapping mode, the original current

can be calculated with Equation (19):

ILED0-

PWM0

I

40.806 A 12.195 A Code0 D



 

 



(19)

The LED current jumps immediately when

the duty changes, as shown in Equation

(20):

ILED0+

PWM1

I

40.806 A 12.195 A Code0 D



 

 



(20)

The LED current follows the code changes

shown in Equation (21):

ILED1

PWM1

I

40.806 A 12.195 A Code1 D



 

 



(21)

In exponential mapping mode, the original

current can be calculated with Equation (22):

PWM0

Code0 D

ILED0-

I

51.1 A 1.003040572





 

(22)

The LED current jumps immediately when

the duty changes, as shown in Equation

(23):

PWM1

Code0 D

ILED0+

I

51.1 A 1.003040572





 

(23)

Then, the LED current follows the code

changes shown in Equation (24):

PWM1

Code1 D

ILED1

I

51.1 A 1.003040572





 

(24)

The ramp time in either mode can be

calculated with Equation (25):

RAMP

t

RAMP | Code1 Code0 1|









(25)

For example, the PWM duty changes from

50% to 100%, and the brightness register

changes from 1024 to 2047, the slope is

1ms/step in linear analog dimming.

The original LED current can be calculated

with Equation (26):

ILED0-

I

40.806 A

12.195 A (1024 0.5)

6.28mA



 

 





(26)

Then the LED current jumps immediately, as

shown in Equation (27):

ILED0+

I

40.806 A 12.195 A (1024 1)

12.52mA



 

 

 

(27)

The LED current rise up step-by-step,

shown in Equation (28):

ILED1

I

40.806 A 12.195 A (2047 1)

25mA



 

 

 

(28)

The ramp-up time can be calculated with

Equation (29):

RAMP

t

1ms / step | 2047 1024 1| 1022ms







 

(29)