TLC5946_16 Datasheet, PDF (16/41 Pages) Texas Instruments – 16-Channel, 12-Bit PWM LED Driver with 6-Bit Dot Correction

TLC5946
SLVS824B – MARCH 2008 – REVISED JUNE 2008 .......................................................................................................................................................... www.ti.com
When the IC powers on, the data in the shift register and latch are not set to any default value. Therefore, GS
data must be written to the GS latch before turning the constant current output on. Additionally, BLANK should
be high when the device is powered on, to prevent the outputs from turning on before the proper grayscale and
dot correction values are written. All constant current outputs are always off when BLANK is high.
Each output (OUTn) on-time (t_OUTON) is calculated by Equation 3:
t_OUTON (ns) = t_GSCLK (ns) ´ GSn
(3)
Where:
• t_GSCLK = the period of GSCLK
• GSn = the programmed grayscale value of output n (GSn = 0 to 4095d)
If XLAT goes high during a grayscale cycle, then new GS data are immediately latched into the GS latch. This
action can cause the outputs to turn on or off unexpectedly. For proper operation, GS data should only be
latched into the IC at the end of a GS period when BLANK is high.
When MODE is low, the input shift register works as a GS shift register. The shift registers and data latches are
each 192 bits in length, and are used to set the PWM timing for each constant current driver. Figure 25 shows
the GS serial data configuration. Refer to Figure 12 for a timing diagram for writing data into the shift register and
latch. The driver on-time is set by the data in the GS data latch. GS data present on the SIN pin are clocked into
the shift register with each rising edge of the SCLK pin. Data are shifted in MSB first. Data are latched from the
shift register into the GS data latch with a rising edge on the XLAT pin.
When the IC powers on, the data in the shift register and data latch are not set to any default value. Therefore,
grayscale data must be written to the GS latch before turning on the constant current output. Also, BLANK
should be high when powered on because the constant current may also turn on. All constant current outputs are
off when BLANK is high. The status information data (SID) byte overwrites on the most significant 17 bits of the
input shift register at the rising edge of the first SCLK after XLAT goes low.
MSB
191
180
179
LSB
12
11
0
GS 15.11
GS 15.0 GS 14.11
GS 1.0 GS 0.11
GS 0.0
GS OUT15
GS OUT14 to GS OUT1
GS OUT0
Figure 25. Grayscale Serial Data Configuration
16
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