TLC5911 Datasheet, PDF (21/30 Pages) Texas Instruments – LED DRIVER

PRINCIPLES OF OPERATION
TLC5911
LED DRIVER
SLLS402 – DECEMBER 1999
LOD function (LED open detection)
When LEDCHK is low, the LED disconnection detection function is disabled and XDOWN2 goes to a
high-impedance state. When LEDCHK is high, the LED disconnection detection function is enabled, and
XDOWN2 goes low if any LED is disconnected while monitoring the OUTn terminals to be turned on. This
function is operational for sixteen OUTn terminals individually. To determine which constant current output is
disconnected, the level of XDOWN2 is checked 16 times from OUT0 to OUT15 turning one constant current
output on. The power supply voltage should be set so the constant current output applied is above 0.4 V when
the LED is turned on normally. Also, since approximately 1000 ns is required from turning the constant current
output on to XDOWN2 output, the gray scale data to be turned on during that period should be applied.
Table 8 is an example of XDOWN2 output status using four LEDs .
Table 8. XDOWN2 Output Example
LED NUMBER
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ _{LED STATUS}
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ _OUTn
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ _{DETECTION RESULT}
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ _XDOWN2
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ _{LED NUMBER}
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ _{LED STATUS}
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ OUTn
DETECTION RESULT
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ _XDOWN2
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ _{LED NUMBER}
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ _{LED STATUS}
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ _OUTn
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ _{DETECTION RESULT}
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ _XDOWN2
1
GOOD
ON
GOOD
1
GOOD
ON
GOOD
1
GOOD
OFF
GOOD
2
3
NG
GOOD
ON
ON
NG
GOOD
LOW (by case 2, 4)
2
3
NG
GOOD
ON
OFF
NG
GOOD
LOW (by case 2)
2
3
NG
GOOD
OFF
OFF
GOOD
GOOD
HIGH-IMPEDANCE
4
NG
ON
NG
4
NG
OFF
GOOD
4
NG
OFF
GOOD
noise reduction
concurrent switching noise reduction
Concurrent switching noise has a potential to occur when multiple outputs turn on or off at the same time. To
prevent this noise, the device has delay output terminals such as XGSOUT, BOUT for GSCLK (gray scale clock),
and BLANK (blanking signal) respectively. By connecting these outputs to the GSCLK and BLANK terminals
of next stage IC, it allows differences in the switching time between ICs. When GSCLK is output to GSOUT
through the device, duty will be changed between input and output. The number of stages to be connected will
be limited depending on the frequency.
delay between constant current output
The constant current output has a delay time of approximately 20 ns between outputs. It means approximately
300 ns delay time exists between OUT0 and OUT15. This time difference by delay is effective for the reduction
of concurrent switching noise.
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