TLC5944 Datasheet, PDF (22/34 Pages) Texas Instruments – 16-Channel, 12-Bit PWM LED Driver with 6-Bit Dot Correction and Pre-Charge FET

TLC5944
SBVS112 – JUNE 2008 ...................................................................................................................................................................................................... www.ti.com
Continuous Base LED Open Detection
At the rising edge of the 33rd GSCLK after the falling edge of BLANK, the LED open detection (LOD) circuit
checks the voltage of each constant current output (OUT0 through OUT15 = OUTn) that is turned on to detect
open LEDs and short LEDs to GND. The channels corresponding to the LOD bit in the status information data
(SID) register are set to '1' if the voltage of the OUTn pin (V_OUTn) is less than the LED open detection threshold
(V_LOD = 0.3 V_TYP). This status information can be read from the SOUT pin when DCSEL is low. No special test
sequence is required for LED open detection.
The LOD function automatically checks for open LEDs and short LEDs to GND during each grayscale PWM
cycle. The SID information of LOD is latched into the LED open detection data latch and does not change until
the rising edge of the 33rd GSCLK pulse following the next falling edge of BLANK. To eliminate false detection of
open LEDs, the LED driver design must ensure that the TLC5944 output voltage is greater than V_LOD when the
outputs are on. The GS data must be 21h (33d) or more to get the LOD result. Figure 31 shows the LED open
detection timing.
BLANK
GSCLK
1234
30 31 32 33 34 35
4094 4096
4093 4095
1 2 3 30 31 32 33 34 35
1st GSCLK Period
OFF
OUTn
(Data = FFFh)
ON
GND
V_OUTn
SID Value
Old LED open detection data
(Internal)
If LOD error is detected
If no LOD error is detected
If the OUTn voltage (V_OUTn) is less than VLOD (0.3 V, typ) at the rising edge of the 33rd
GSCLK after the falling edge of BLANK, the LOD sets the SID bit corresponding
to the output channel in which LED is open or shorted to GND equal to ‘1’.
OUTn is turned off at the 33rd falling edge of GSCLK if the LOD error flag is set.
New LED open detection data
Hi-Z
XERR
If no LOD error is detected
Low
Depends on LOD data
('L')
If LOD error is detected
Depends on previous
LOD data
If XERR goes low because of an LOD error,
XERR is forced high when BLANK goes high.
Figure 31. LED Open Detection (LOD) Timing
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