TLC5905 Datasheet, PDF (18/27 Pages) Texas Instruments – LED DRIVER

TLC5905
LED DRIVER
SLLS401 – NOVEMBER 1999
PRINCIPLES OF OPERATION
protection (continued)
WDT (watchdog timer)
The constant current output is forced to turn off and XDOWN1 goes low when the fixed period elapsed after the
signal applied to WDTRG has not been changed. Therefore, by a connecting scan signal (signal to control line
displayed) to WDTRG, the stop of the scan signal can be detected and the constant current output is turned
off preventing the LED from burning and damage by continuous LED turnon at the dynamic scanning operation.
The detection time can be set using an external capacitor, Cext. The typical value is approximately 10 ms without
a capacitor, 160 ms with a1000 pF capacitor and 1500 ms with a 0.01 µF capacitor. During static operation,
the WDT function is disabled connecting WDCAP to GND (high or low level should be applied to WDTRG). Note
that normal operation will be resumed changing the WDTRG level when WDT functions.
WDT operational time T (ms) ≅ 10 + 0.15 x Cext (pF)
1500
160
Scan Signal
Cext
TLC5905
WDTRG
WDCAP
10
0
0.001
0.01
Cext – External Capacitor – µF
Figure 6. WDT Operational Time and Usage Example
TSD (thermal shutdown)
When the junction temperature exceeds the limit, TSD functions and turns the constant current output off, and
XDOWN1 goes low. When TSD is used, TSENA is pulled high. When TSD is not used, TSENA is pulled low.
To recover from constant current output off-state to normal operation, the power supply should be turned off or
TSENA should be pulled low once.
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