MP3313 Rev.1.0

www.MonolithicPower.com

15

8/2/2017

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 PWMSR1:0 bit = 00, sample frequency =

800kHz.

 PWMSR1:0 bit = 01, sample frequency =

4MHz (default).

 PWMSR1:0 bit = 1x, sample frequency =

24MHz.

Choose a PWM sample frequency based on the

required dimming resolution, input dimming

frequency, and efficiency (the higher the sample

frequency, the higher the input consumption

current is). A low-level PWM signal that lasts for

a certain amount of time can disable the device

(see Table 2). The lower the PWM sample

frequency is, the longer the PWM shutdown

time is.

Table 2: PWM Shutdown Time vs. Sample

Frequency

24M

0.6

4M

3

800k

25

PWM Hysteresis

To prevent the input PWM dimming signal jitter

from causing LED flicker, the MP3313 offers

selectable PWM hysteresis.

 HYS2:0 = 000: no hysteresis

 HYS2:0 = 001: 1 clock

 HYS2:0 = 100: 4 clock (default)

 HYS2:0 = 110: 6 clock

Where 1 clock = 1/fsample. Different sample

rates produce different clocks.

The PWM hysteresis is active only when the

direction of the LED brightness changes. Once

the LED brightness direction changes, the input

PWM signal must overcome the hysteresis, and

then the brightness changes. Otherwise, if the

LED brightness changing direction remains the

same, the PWM signal hysteresis function is

unused.

Brightness Control Mode

The LED current is controlled either by the input

PWM dimming signal or internal brightness

register. Five different brightness control modes

can be selected and set by the BRTMD2:0 bit.

1. Internal register only: When the brightness

control mode bits are set to 000, the LED

current

is

controlled

by

the

internal

brightness register only without the PWM

signal. The LED current changes only when

the eight MSBs are written. Write three

LSBs first, then write eight MSBs for 11-bit

brightness change.

In linear mapping mode, the LEDs can be

calculated with Equation (4) and Equation

(5):

ILED0

I

40.806 A 12.195 A Code0



 

 

(4)

ILED1

I

40.806 A 12.195 A Code1



 

 

(5)

In exponential mapping mode, the LEDs can

be

calculated

with

Equation

(6)

and

Equation (7):

Code0

ILED0

I

51.1 A 1.003040572



 

(6)

Code1

ILED1

I

51.1 A 1.003040572



 

(7)

The ramp time in either mapping mode can

be calculated with Equation (8):

RAMP

t

RAMP (Code1 Code0 1)









(8)

2. Input PWM duty only: When the brightness

control mode bits are set to 001, the LED

current is controlled by the input dimming

signal only. The internal brightness code is

ignored. The MP3313 samples the PWM

signal and translates it into an 11-bit code to

regulate

the

current.

Choose

the

corresponding PWM frequency based on

the

PWM

sample

rate

and

resolution

request.

In linear mapping mode, the LEDs can be

calculated with Equation (9) and Equation

(10):

ILED0

PWM0

I

40.806 A 12.195 A 2047 D



 

 



(9)

ILED1

PWM1

I

40.806 A 12.195 A 2047 D



 

 



(10)

In exponential mapping mode, the LEDs can

be

calculated

with

Equation

(11)

and

Equation (12):

PWM0

2047 D

ILED0

I

51.1 A 1.003040572





 

(11)

PWM1

2047 D

ILED1

I

51.1 A 1.003040572





 

(12)