TLC5923 Datasheet, PDF (10/15 Pages) Texas Instruments – LED DRIVER

TLC5923
SLVS550 – DECEMBER 2004
www.ti.com
Error Information Output
The open-drain output XERR is used to report both of the TLC5923 error flags, TEF and LOD. During normal
operating conditions, the internal transistor connected to the XERR pin is turned off. The voltage on XERR is
pulled up to V_CC through a external pullup resistor. If TEF or LOD is detected, the internal transistor is turned on,
and XERR is pulled to GND. Since XERR is an open-drain output, multiple ICs can be OR'ed together and pulled
up to V_CC with a single pullup resistor. This reduces the number of signals needed to report a system error.
To differentiate LOD and TEF signal from XERR pin, LOD can be masked out with BLANK = HIGH.
Table 3. XERR Truth Table
ERROR CONDITION
TEMPERATURE
OUNTn VOLTAGE
T_J < T_(TEF)
T_J > T_(TEF)
T_J < T_(TEF)
T_J > T_(TEF)
Don't Care
Don't Care
OUTn > V_(LOD)
OUTn < V_(LOD)
OUTn > V_(LOD)
OUTn < V_(LOD)
ERROR INFORMATION
TEF
LOD
L
X
H
X
L
L
L
H
H
L
H
H
SIGNALS
BLANK
XERR
H
H
L
L
H
L
L
L
TEF: Thermal Error Flag
The TLC5923 provides a temperature error flag (TEF) circuit to indicate an overtemperature condition of the IC. If
the junction temperature exceeds the threshold temperature T_(TEF) (160°C typical), the TEF circuit trips and pulls
XERR to ground.
LOD: LED Open Detection
The TLC5923 provides an LED open-detection circuit (LOD). This circuit reports an error if any one of the 16
LEDs is open or disconnected from the circuit. The LOD circuit trips when the following two conditions are met
simultaneously:
1. BLANK is set to LOW
2. When the voltage at OUTn is less than V_(LOD) (0.3 V typ.) (Note: the voltage at each OUTn is sampled 1 µs
after being turned on).
The LOD circuit also pulls XERR to GND when tripped.
The LOD status of each channel can also be read out from the TLC5923 SOUT pin. When MODE is low and
On/Off data is latched with rising edge of XLAT, LOD data is written to the input shift register with the falling edge
of XLAT. These LOD data is clocked out to SOUT when new On/Off data is clocked in. These allow to control the
LOD status of each OUTn channel. Figure 12 shows the LOD data format.
LSB
0
LOD
OUT0
LOD
OUT1
LOD
OUT2
LOD
OUT3
LOD
OUT4
LOD
OUT5
LOD
OUT6
LOD LOD LOD
OUT7 OUT8 OUT9
LOD Data
LOD
OUT10
LOD
OUT11
LOD
OUT12
LOD
OUT13
LOD
OUT14
MSB
15
LOD
OUT15
Figure 12. LOD Data
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