TLC5955 Datasheet, PDF (29/53 Pages) Texas Instruments – TLC5955 48-Channel, 16-Bit, PWM LED Driver with DC, BC, LED Open-Short Detection, and Internal Current Setting

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TLC5955
SBVS237 – MARCH 2014
8.4.3 Global Brightness Control (BC) Function
The TLC5955 has the ability to adjust the output current of all constant-current outputs of each color group
(OUTR0 to OUTR15, OUTG0 to OUTG15, and OUTB0 to OUTB15) simultaneously to the same current ratio.
This function is called global brightness control (BC). The BC function allows the global brightness of LEDs
connected to the output to be adjusted. All outputs of each color group can be adjusted in 128 steps from 10% to
100% of the maximum output current, I_OLCMax. BC data are programmed into the TLC5955 with the serial
interface. When the BC data change, the output current also changes immediately. When the device is powered
on, the BC data contain random data. Table 10 summarizes the BC data versus the set current value.
BINARY
000 0000
000 0001
000 0010
—
111 1101
111 1110
111 1111
Table 10. BC Data versus Constant-Current Ratio and Set Current Value
BCX⁽¹⁾ DATA
DECIMAL
0
HEX
00
DCXn⁽²⁾ DATA
(Hex)
7F
RATIO OF
OUTPUT
CURRENT TO
I_OLCMax(%)
10.0
I_OUT (mA)
(MC = 7, typical)
3.19
1
01
7F
10.7
3.42
2
02
7F
11.4
3.64
—
—
—
—
—
125
7D
7F
98.6
31.5
126
7E
7F
99.3
31.7
127
7F
7F
100.0
31.9
I_OUT (mA)
(MC = 0, typical)
0.32
0.34
0.37
—
3.15
3.18
3.20
(1) X = R, G, or B.
(2) X = R, G, or B. n = 0 to 15.
8.4.4 Grayscale (GS) Function (PWM Control)
The TLC5955 can adjust the brightness of each output channel using a pulse width modulation (PWM) control
scheme. The architecture of 16 bits per channel results in 65,536 brightness steps, from 0% up to 100%
brightness.
The PWM operation for OUTn is controlled by a 16-bit grayscale (GS) counter. The GS counter increments on
each GS reference clock (GSCLK) rising edge. The GS counter resets to 0000h when the LAT rising signal for a
GS data write is input with the display timing reset mode enabled.
The TLC5955 has two types of PWM control: conventional PWM control and enhanced spectrum (ES) PWM
control. The conventional PWM control can be selected when the ESPWM bit in the control data latch is 0. The
ES PWM control is selected when the ESPWM bit is 1. The conventional PWM control should be selected for
multiplexing a drive. The ES-PWM control should be selected for a static drive.
The on-time (t_{OUT_ON}) of each output (OUTn) can be calculated by Equation 2.
t_{OUT_ON} (ns) = t_GSCLK (ns) × GSXn
where:
• TGSCLK = one GS clock period,
• GSXn = the programmed GS value for OUTXn (GSXn = 0d to 65535d),
• X = R, G, or B for the red, green, or blue color group, and
• n = 0 to 15.
(2)
Copyright © 2014, Texas Instruments Incorporated
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