TLC5944 Datasheet, PDF (17/34 Pages) Texas Instruments – 16-Channel, 12-Bit PWM LED Driver with 6-Bit Dot Correction and Pre-Charge FET

TLC5944
www.ti.com ...................................................................................................................................................................................................... SBVS112 – JUNE 2008
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 (GSCLK). The counter is reset to zero when BLANK is high. The
counter value is held at zero while BLANK is high, even if the GSCLK input is toggled high and low. After the
falling edge of BLANK, the counter increments with each rising edge of GSCLK. Any constant current sink output
(OUT0 through OUT15) with a nonzero value in the corresponding grayscale latch starts to sink current after the
first rising edge of GSCLK following a high-to-low transition of BLANK. The internal counter keeps track of the
number of GSCLK pulses. Each output channel stays on as long as the internal counter is equal to or less than
the respective output GSCLK. Each channel turns off at the rising edge of GSCLK 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 GSCLK after
BLANK goes low. It turns off at the second rising edge of GSCLK. Figure 27 shows the PWM timing diagram.
BLANK
GSCLK
1234
¼
2048
2049
2050
4094
4095
4096
¼
OUTn
(GSDATA = 000h)
OFF ^(VOUTn^{H) GSCLK counter starts to count GSCLK after BLANK goes low.}
ON
No driver turns on when Gray Scale data is zero
OUTn
(GSDATA = 001h)
OFF
ON
(V_OUTnH)
(V_OUTnL)
OUTn
(GSDATA = 002h)
OFF
ON
(V_OUTnH)
(V_OUTnL)
OUTn
(GSDATA = 003h)
OFF
ON
(V_OUTnH)
(V_OUTnL)
T = GSCLK 1
´
T = GSCLK 2
´
T = GSCLK 3
´
OUTn
(GSDATA = 7FFh)
OFF
ON
(V_OUTnH)
(V_OUTnL)
OUTn
(GSDATA = 800h)
OFF
ON
(V_OUTnH)
(V_OUTnL)
OUTn
(GSDATA = 801h)
OFF
ON
(V_OUTnH)
(V_OUTnL)
T = GSCLK 2047
´
T = GSCLK 2048
´
T = GSCLK 2049
´
OUTn
(GSDATA = FFDh)
OFF
ON
(V_OUTnH)
(V_OUTnL)
OUTn
(GSDATA = FFEh)
OFF
ON
(V_OUTnH)
(V_OUTnL)
T = GSCLK 4093
´
T = GSCLK 4094
´
OUTn
(GSDATA = FFFh)
OFF
ON
(V_OUTnH)
(V_OUTnL)
T = GSCLK 4095
´
OUTn turns on at first rising edge of GSCLK
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 27. PWM Operation Timing
Copyright © 2008, Texas Instruments Incorporated
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