SC5010 View Datasheet(PDF) - Semtech Corporation
Part Name
Description
MFG CO.
SC5010
Semtech Corporation
'SC5010' PDF : 36 Pages View PDF
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.
TIphase
1
fPWM ,
N
N number of strings in operation
fPWM LED PWM dimming frequency
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.
1. Fade Option (register address 0x09) — sets fade
enable options, fade time, fade type.
2. 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
0 to 511
512 to 767
768 to 1024
Step Increment
1
1
2
Step Interval
2
1
1
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.
TPWM 100 ȝs (PWM Dimming Period)
Total Cycle 2 u (511 102) 256 1 u (922 768)
2
Total Time 1151u TPWM 115.1ms
1151
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-
19
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