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Function-Control Description
V
LED
Current from parasitic capacitor
SW 0
V
LED
Parasitic
Capacitor
SW 1
V
LED
Parasitic
Capacitor
SW 2
V
Z
Parasitic
Capacitor
TLC6946
TLC6948
The TLC694x device implements an internal circuit that can eliminate the caterpillar issue caused by an
open LED. The caterpillar removal function is configured by register LODRM_EN in FC1
When enabled, LODRM_EN = 1 (default), and the caterpillar removal function is enabled. By enabling the
caterpillar removal function, the corresponding channel OUTn is turned off when the line with the open
LED is selected, and thus the caterpillar issue is eliminated until device reset or LODRM_EN is set to 0.
The internal caterpillar elimination circuit can handle a maximum of three lines that have an open-LED
fault condition. If there is an open LED located in three or fewer lines, the TLC69x device is able to handle
the open LEDs all in these lines. If there are open LEDs in more than three lines, the caterpillar issue is
solved for the lines where the first three open LEDs were detected, but the open LEDs in the fourth and
subsequent lines still cause the caterpillar issue.
2.3.3 Precharge Function
The precharge function is implemented to remove the ghosting issue in multiplexed LED display modules.
One cause of this ghosting phenomenon is the charging current from the parasitic capacitance of OUTn
through the LED when the supply voltage switches from one common line to next common line. To
prevent this unwanted charging current, the TLC694x device uses an internal precharge FET to pull OUTn
up during the scan-line switching period. Thus, no charging current flows through the LED and the
ghosting issue is eliminated.
2.3.4 Power-Save Mode (PSM)
To minimize the power-supply current consumption, the TLC694x device features a power-save operating
mode. In the power-save mode (PSM), all analog circuits such as constant current output, LOD circuit,
and so forth are not operational. The device total power supply current, I
mode.
24
Function Control
TI Information — Selective Disclosure
LED 0-0
LED 0-1
LED 0-2
LED 1-0
LED 1-1
LED 1-2
LED Open
LED 2-0
LED 2-1
LED 2-2
OUT0
OUT1
OUT2
OUT0
OUT1
OUT2
ON
ON
ON
Figure 2-18. Caterpillar Issue
Copyright © 2018–2019, Texas Instruments Incorporated
ON
SW 0
Line 0
OFF
V
LED
Line 0
V
Z
Voltage
< V
F
ON
SW 1
Line 1
OFF
V
LED
Line 1
V
Z
Voltage
High
GCLK
Line 2
Low
ON
OUT1
Status
OFF
V
PCHG
OUT1
V
± V
LED
F
Voltage
GND
I
SET
LED 0-1
Current
0mA
Constant
Current
I
SET
Control
LED 1-1
(open)
Current
0mA
SLVUBF4A – February 2018 – Revised June 2019
www.ti.com
(Table
2-2).
, is typical 1 mA in power-save
CC
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