TLC5973D Datasheet, PDF (14/27 Pages) Texas Instruments – 3-Channel, 12-Bit, PWM Constant-Current LED Driver

TLC5973
SBVS225A – MARCH 2013 – REVISED MAY 2013
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RESISTOR AND CAPACITOR VALUE SETTING FOR SHUNT REGULATOR
The TLC5973 internally integrates a shunt regulator to regulate V_CC voltage. Refer to Figure 15 for an application
circuit that uses the internal shunt regulator through a resistor, R_VCC. The recommended R_VCC value can be
calculated by Equation 2.
V_LED (V) - 5.9 V
13 mA
< R_VCC <
V_LED (V) - 5.9 V
11 mA
(2)
V_LED
Power
Supply
GND
R_VCC
C_VCC
(0.1 mF)
R_VCC
C_VCC
(0.1 mF)
+5 V
Controller
R_IREF
GND
VCC
IREF
OUT0
OUT1
1st Device
OUT2
SDI
SDO
R_IREF
GND
VCC
IREF
OUT0
OUT1
2nd Device
OUT2
SDI
SDO
Optional
Figure 15. Internal Shunt Regulator Mode Application Circuit
Table 2 shows the typical resistor value for several V_LED voltages. Note that the C_VCC value should be 0.1 μF.
Table 2. Resistor Example for Shunt Resistor versus LED Voltage⁽¹⁾
V_LED (V)
9
12
18
24
R_VCC (Ω)
390
820
1500
2200
RESISTOR WATTAGE (W)
0.03
0.07
0.15
0.21
(1) R_IREF is at 1.5 kΩ.
GRAYSCALE (GS) FUNCTION (PWM CONTROL)
The TLC5973 can adjust the brightness of each output channel using a pulse width modulation (PWM) control
scheme. The PWM data bit length for each output is 12 bits. The architecture of 12 bits per channel results in
4096 brightness steps, from 0% to 99.98% on-time duty cycle.
The PWM operation for OUTn is controlled by an 12-bit grayscale (GS) counter. The GS counter increments on
each internal GS clock (GSCLK) rising edge. All OUTn are turned on when the GS counter is ‘1’, except when
OUTn are programed to GS data '0' in the 36-bit GS data latch. After turning on, each output is turns off when
the GS counter value exceeds the programmed GS data for the output. The GS counter resets to 00h and all
outputs are forced off when the GS data are written to the 36-bit GS data latch. Afterwards, the GS counter
begins incrementing and PWM control is started from the next internal GS clock.
14
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