SC5010 datasheet(18/36 Pages) SEMTECH

18 / 36 page

SC5010

Applications Information (continued)

a micro-controller sets a register or counter that varies the

pulse width on a GPIO pin. The SC5010 allows dimming

over a wide frequency range (100Hz-30kHz) in order to

allow compatibility with a wide range of devices. This

includes the newest dimming strategies that avoid the

audio band by using high frequency PWM dimming. In

this manner, a wide range of illumination can be gener-

ated while keeping the instantaneous LED current at its

peak value for high efficiency and color temperature. The

SC5010 provides 1000:1 dimming range at 1kHz PWM fre-

quency. The LED current sinks turn on /off very rapidly

(<25ns, typical). This allows wide dimming ratio. An addi-

tional advantage of PWM dimming comes to customers

who prefer to avoid in-rush currents when filling the boost

output capacitor. Apply the PWMI signal to the device at

10% duty for a millisecond or two, and in-rush current is

reduced. This dimming time will vary based on the number

of LEDs and the size of the output capacitor. This can be

easily determined during testing and programmed into

the micro-controller firmware.

Mode 2 — Indirect Control

This is the default mode for LED PWM dimming in SC5010.

In this mode, the input signal applied on PWMI pin is passed

through a duty cycle extractor block. The extractor mea-

sures the duty cycle of the PWMI input and converts it to a

10-bit value. This value is then passed to the PWM genera-

tor block as shown in the Figure 1 below.

The LED PWM output frequency is set via the FREQ regis-

ter (address 0x05) and the FAST_FREQ bit.

With FAST_FREQ = 0, low dimming frequency option is

selected and the PWM dimming frequency will be accord-

ing to the following equation.

10kHz(max)

]

[

FREQ

[

1024

MHz

Frequency

Dimming

PWM

With FAST_FREQ = 1, high dimming frequency option is

selected and the PWM dimming frequency is shown by

the following equation.

20kHz(max)

]

[

FREQ

[

512

MHz

Frequency

Dimming

PWM

The default option is FAST_FREQ = 1. This gives 9-bit duty

cycle resolution and up to 20kHz dimming frequency

range. The PWMI input is usually generated by the system

graphics processor. This mode allows the user to set the

Softstart

I2C Interface

IN T_DUTY B it

D [9:0] B its

PW M

G enerator

FR E Q B its

P hase S hifting

(45º)

FastFreq B it

PH _S H IFT Bit

PW M I

IN T_PW M Bit

E xtracted duty

cycle from

P W M I Input

LE D Frequency and P haseS hifter B lock

PW M _ps[8:1]

A ll bits identical

w hen phase

shifting disabled

P W M [8:1]

Duty Cycle

E xtractor

PW M I

Input

Figure 1— LED PWM Dimming Control

SC5010 Datasheet(PDF) 18 Page - Semtech Corporation

SC5010 Datasheet(HTML) 18 Page - Semtech Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

Datasheet Download

Link URL