TLC5942 Datasheet, PDF (17/33 Pages) Texas Instruments – 16-Channel, 12-Bit PWM LED Driver with 7-Bit Dot Correction

TLC5942
www.ti.com
SBVS096B – OCTOBER 2007 – REVISED OCTOBER 2007
Grayscale (GS) Function (PWM Operation)
The pulse width modulation (PWM) operation is controlled by a 12-bit grayscale counter that is clocked on each
rising edge of the grayscale reference clock, GSSCLK. The counter is reset to zero when the BLANK signal is
set high. The counter value is held at zero while BLANK is high, even if the GSSCLK input toggles high and low.
After the falling edge of BLANK, the counter increments with each rising edge of GSSCLK. Any constant current
sink output (OUT0 through OUT15) with a nonzero value in its corresponding grayscale latch starts to sink
current after the first rising edge of GSSCLK following a high-to-low transition of BLANK. The internal counter
keeps track of the number of GSSCLK pulses. Each output channel stays on as long as the internal counter is
equal to or less than the respective output GSSCLK. Each channel turns off at the rising edge of GSSCLK when
the grayscale counter value is larger than the grayscale latch value.
For example, an output that has a grayscale latch value of '1' turns on at the first rising edge of GSSCLK after
BLANK goes low. It turns off at the second rising edge of GSSCLK. Figure 21 shows the PWM timing diagram.
BLANK
1234
GSSCLK
¼
OFF
OUTn
ON
(GSDATA = 0d)
OFF
OUTn
ON
(GSDATA = 1d)
OFF
OUTn
ON
(GSDATA = 2d)
OFF
OUTn
ON
(GSDATA = 3d)
(V_OUTnH)
(V_OUTnH)
(V_OUTnL)
(V_OUTnH)
(V_OUTnL)
(V_OUTnH)
(V_OUTnL)
GSSCLK counter starts to count GSSCLK
after BLANK goes low.
Drivers do not turn on when grayscale data are zero.
T = GSSCLK ´ 1
T = GSSCLK ´ 2
T = GSSCLK ´ 3
2049
2048 2050
4095
4094 4096
¼
OFF
OUTn
ON
(GSDATA = 2047d)
OFF
OUTn
ON
(GSDATA = 2048d)
OFF
OUTn
ON
(GSDATA = 2049d)
(V_OUTnH)
(V_OUTnL)
(V_OUTnH)
(V_OUTnL)
(V_OUTnH)
(V_OUTnL)
T = GSSCLK ´ 2047
T = GSSCLK ´ 2048
T = GSSCLK ´ 2049
OFF
OUTn
ON
(GSDATA = 4093d)
OFF
OUTn
ON
(GSDATA = 4094d)
OFF
OUTn
ON
(GSDATA = 4095d)
(V_OUTnH)
(V_OUTnL)
(V_OUTnH)
(V_OUTnL)
(V_OUTnH)
(V_OUTnL)
T = GSSCLK ´ 4093
T = GSSCLK ´ 4094
T = GSSCLK ´ 4095
OUTn turns on at first rising edge of GSSCLK
after BLANK goes low except when grayscale data are zero.
OUTn does not turn on again until
BLANK goes high to reset the grayscale clock
and then goes low to enable all OUTn.
Figure 21. PWM Operation Timing
Copyright © 2007, Texas Instruments Incorporated
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