TLC5944 Datasheet, PDF (25/34 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
Auto Output Off
The TLC5944 current consumption increases if any output (OUTn) is turned on and no LED is connected, the
LED is an open circuit, or the output is shorted to GND. The TLC5944 has the auto output off function to reduce
consumption current in these cases. This function turns off any OUTn where LED open has been detected to
reduce the current into the VCC pin during error conditions. Figure 35 illustrates the auto output off function.
Therefore, the LED anode voltage must be held over the LED forward voltage (V_F) plus the maximum voltage of
the LED open detection threshold (V_LOD = 0.4 V_MAX) while the LED is on, in any case. Otherwise, the LED is
forced off by the auto output off function.
VCC
Dissipation
Current
Higher
Lower
BLANK
GSCLK
1234
30 31 32 33 34 35
4094 4096
4093 4096
1 2 3 30 31 32 33 34 35
OFF
Voltage of
ON
OUTn
GND
V_OUTn
If LOD error is detected
If no LOD error is detected
SID Register Value
Old LED open detection data
(Internal)
ON Signal of OUTn
ON
(Internal) OFF
(GS data = FFFh)
New LED open detection data
ON (if no LOD error detected)
ON
OFF
OFF (if LOD error is detected)
Figure 35. Auto Output Off Function
ON (if no LOD error detected)
OFF (if LOD error is detected)
Noise Reduction
Large surge currents may flow through the IC and the printed circuit board (PCB) on which the device is mounted
if all 16 LED channels turn on simultaneously at the start of each grayscale cycle. This large current surge could
introduce detrimental noise and electromagnetic interference (EMI) into other circuits. The TLC5944 turns on the
LED channels in a series delay to provide a circuit soft-start feature. The output current sinks are grouped into
four groups of four channels each. The first group is OUT0/4/8/12; the second group is OUT1/5/9/13; the third
group is OUT2/6/10/14; and the fourth group is OUT3/7/11/15. Each group is turned on sequentially with a small
delay between groups; Figure 14 shows this delay. Both turn-on and turn-off are delayed.
Copyright © 2008, Texas Instruments Incorporated
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