TLC59581 Datasheet, PDF (19/28 Pages) Texas Instruments – 48-Channel, 16-Bit ES-PWM LED Driver

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TLC59581, TLC59582
SLVSCZ9A – OCTOBER 2015 – REVISED NOVEMBER 2015
9.3.4.1 Example 1: Red LED Current is 20 mA, Green LED Needs 12 mA, Blue LED needs 8 mA
1. Red LED needs the largest current; choose 511d for CCR
2. 511 x 12 mA / 20 mA = 306.6; choose 307d for CCG. With same method, choose 204d for CCB.
3. According to the required red LED current, choose 7h for BC.
4. According to Equation 2, R_IREF = 1.209 V/20 mA x 157.4 = 9.5 kΩ
In this example, choose 7h for BC instead of using the default 4h. This is because the Red LED current is 20
mA, approaching the upper limit of current range. To prevent the constant output current from exceeding the
upper limit in case a larger BC code is input accidently, choose the maximum BC code here.
9.3.4.2 Example 2: Red LED Current is 5 mA, Green LED Needs 2 mA, Blue LED Needs 1 mA.
1. Red LED requires the largest current; choose 511d for CCR.
2. 511 x 2 mA / 5 mA = 204.4; choose 204d for CCG. With same method, choose 102d for CCB.
3. According to the required blue LED current, choose 0h for BC.
4. According to Equation 2, R_IREF = 1.209 V / 5 mA x 20.4 = 4.93 kΩ
In this example, choose 0h for BC, instead of using the default 4h. This is because the Blue LED current is 1 mA,
is approaching the lower limit of current range. To prevent the constant output current from exceeding the lower
limit in case a lower BC code is input accidently, choose the minimum BC code here. In general, if LED current is
in the middle of the range (i.e, 10 mA), use the default 4h as BC code.
9.3.5 LED Open Detection (LOD)
The LOD function detects faults caused by an open circuit in any LED string; or, a short from OUTXn to ground
with low impedance. It does this by comparing the OUTXn voltage to the LOD detection threshold voltage level
set by LODVLT in the FC1 register. If the OUTXn voltage is lower than the programmed voltage, the
corresponding output LOD bit is set to '1' to indicate an open LED. Otherwise, the output of that LOD bit is '0'.
LOD data output by the detection circuit are valid only during the ‘on’ period of that OUTXn output channel. The
LOD data are always ‘0’ for outputs that are turned off.
9.3.6 Internal Circuit for Caterpillar Removal
Caterpillar effect is a common issue for the LED panel. It is usually caused by LED lamp open, LED lamp
leakage or LED lamp short. The TLC59581/82 device implements an internal circuit that can eliminate the
caterpillar issue caused by LED open. The caterpillar removal function is enabled by setting LOD_MMC_EN (bit4
of FC1 register) to ‘1’. When powered on, the default value of this bit is ‘0’. When this function is enabled, the IC
automatically detects the open LED lamp, and the lamp does not turn on until IC reset.
9.3.7 Power Save Mode (PSM)
The power-save mode (PSM) is enabled by setting PSAVE_ENA (bit5 of FC2 register) to ‘1’. At power on, this bit
default is ‘0’.
When this function is enabled, if the GS data received for the next frame is all ‘0’, the IC enters power-save
mode immediately.
When the IC is in power-save mode, it resumes normal mode when it detects non-zero GS data input. In power-
save mode all analog circuits such as constant current output and the LOD circuit are not operational; the device
total current consumption, I_CC, is below 1 mA.
9.3.8 Internal Pre-Charge FET
The internal pre-charge FET can prevent ghosting of multiplexed LED modules. One cause of this phenomenon
is the charging current for parasitic capacitance of the OUTXn through the LED when the supply voltage switches
from one common line to the next common line.
To prevent this unwanted charging current, the TLC59581/82 device uses an internal FET to pull OUTXn up to
VCC –1.4 V during the common line switching period. As a result, no charging current flows through LED and
ghosting is eliminated.
Copyright © 2015, Texas Instruments Incorporated
TLC59582
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