TLC5954 Datasheet, PDF (20/45 Pages) Texas Instruments – TLC5954 48-Channel, Constant-Current LED Driver with Global Brightness Control, LED Open-Short Detection, and Power-Save Mode

TLC5954
SBVS241 – APRIL 2014
www.ti.com
Feature Description (continued)
8.3.3 LED Open Detection (LOD)
LOD detects a fault caused by an open circuit in the nth LED string, or a short from OUTXn to ground with low
impedance, by comparing the OUTXn voltage to the LOD detection threshold voltage level set by LODVLT in the
function control data latch (see Table 6 and Table 8). If the OUTXn voltage is lower than the programmed
voltage, the corresponding output LOD bit is set to 1 to indicate a shorted LED. Otherwise, the LOD bit is set to
0. LOD data are only valid for outputs that are set to 1 in the output on-off data latch. LOD data are always 0 for
outputs that are set to 0 in the output on-off data latch.
LOD data are stored in a 48-bit register called the SID holder (see the Functional Block Diagram) at the BLANK
rising edge when the SIDLD bits are set to 01b (see Table 7). The loaded LOD data can be read out through the
common shift register as SID data at the SOUT pin. LOD data are not valid for 1 μs after the output is turned on.
If the OUTXn controlled by the BLANK pin is less than 1 µs, the LOD data must be ignored.
When the device resumes operation from power-save mode, all OUTXn can be controlled by the internal on-off
control data and the BLANK level after the setup time (t_SU2) elapses. LOD data are valid after the propagation
delay. Figure 29 illustrates an LOD and LSD circuit, Table 1 shows the SID bit settings for LOD and LSD, and
Figure 30 illustrates the LED open-detection operating timing diagram.
VLED
LED Lamp
LSD Data
1 = Error
LOD Data
1 = Error
V_LSD
On or Off
Control
OUTXn
2.9 mA to 34.9 mA (for OUTRn, OUTGn)
2.0 mA to 24.4 mA (for OUTBn)
with Maximum BC Data
V_LOD
GND
Figure 29. LOD, LSD Circuit
Table 1. LOD, LSD Truth Table
LOD
LED is not open (V_OUTXn > V_LOD)
LED is open or shorted to GND (V_OUTXn ≤ V_LOD)
LSD
LED is not shorted (V_OUTXn ≤ V_LSD)
LED is shorted between anode and cathode, or
shorted to higher voltage side (V_OUTXn > V_LSD)
CORRESPONDING BIT
IN SID
0
1
20
Submit Documentation Feedback
Product Folder Links: TLC5954
Copyright © 2014, Texas Instruments Incorporated