SC5010 datasheet(19/36 Pages) SEMTECH

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SC5010

Applications Information (continued)

PWM output dimming frequency independent of the

PWMI input.

If the PWMI signal has jitter, then SC5010 provides an

option to filter it out. Hysteresis is also provided by select-

ing the WND[1:0] bits in the DCR register (address 0x01).

WND[1:0] bits set the window comparator such that if a

change in the duty cycle is detected which is smaller than

the set window, then it is ignored.

Mode 3 — I2C Control

In this mode (see Figure 1), both the output LED duty cycle

and the dimming frequency are set via the internal regis-

ters. PWMI pin should be connected to ground in this

mode. In this mode, the LED dimming duty cycle is set via

the duty cycle registers (address 0x03, 0x04); and the

dimming frequency is set via the FREQ register (address

0x05) and the FAST_FREQ bit.

Phase-Shifted PWM Dimming

The SC5010 provides an option for the phase shifted LED

PWM dimming. This option is available in both PWMI indi-

rect control and I2C control. Phase-shift option is set by the

PH_SHIFT bit in the DCR register. This option delays the

turn-on of the LED strings based on the number of the

strings in operation. It is shown by the following equation.

frequency

dimming

PWM

LED

operation

strings

number

PWM

phase

Phase-shift mode is disabled during soft-start, this allows

the output to ramp up to the correct voltage in a con-

trolled fashion.

Phase-shifting reduces the peak input current, decreases

EMI and improves the dimming linearity. The figures in the

Typical Characteristic Section shows the reduction in the

input current with phase shift feature enabled compared

to the non-phase shifted mode of operation.

Backlight Fade-in and Fade-out Options

The SC5010 features an option for fade-in and fade-out

brightness control, which allows smooth transition from

one brightness level to another.

Registers associated with this fading functions are shown

in this section.

Fade Option (register address 0x09) — sets fade

enable options, fade time, fade type.

Fade Rate (register address 0x0A) — sets fade step

size option.

Fade option register allows user to select fading, choose

between linear or logarithmic fading, and to set up the

fading time. The default setting is fading enabled with

logarithmic mode. The fading time is determined by the

LED PWM dimming frequency.

An example for calculating the fading time is shown in

this section

Assuming LED PWM dimming frequency is 10kHz, then

the PWM dimming period is 100 μs. Fade setting is shown

in the following table.

Duty Cycle Range

Step Increment

Step Interval

0 to 511

512 to 767

768 to 1024

10 bits are assigned for 1024 duty cycle settings.

Time required to go from 10% (102/1024) to 90%

(922/1024) duty cycle can be calculated using the follow-

ing equation.

115.1

1151

Time

Total

1151

)

768

922

(

256

)

102

511

(

Cycle

Total

Period)

Dimming

(PWM

100

PWM

Optional Synchronization to SYNC Input

The SC5010 provides an option to synchronize the LED

dimming to an external clock source connected to the

SYNC pin. In certain applications, it may be beneficial to

synchronize the LED drive signal to the LCD screen refresh

signals such as VSYNC or HSYNC. This helps reduce or

eliminate some of the problems associated with using LED

backlights, such as flickering, shimmering, etc.

The phase lock loop available on the SC5010 can be pro-

grammed via I2C to synchronize the internal 10MHz oscil-

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