TLC5942_16 Datasheet, PDF (21/29 Pages) Texas Instruments – 16-Channel, 12-Bit PWM LED Driver with 7-Bit Dot Correction

Not Recommended for New Designs
TLC5942
www.ti.com
SBVS096B – OCTOBER 2007 – REVISED OCTOBER 2007
The LOD data are updated at the rising edge of the 33rd GSSCLK pulse after BLANK goes low; the LOD data
are retained until the next 33rd GSSCLK. LOD data are only checked for outputs that are turned on during the
rising edge of the 33rd GSSCLK pulse. A '1' in an LOD bit indicates an open LED condition for the corresponding
channel. A '0' indicates normal operation. It is possible for LOD data to show a '0' even if the LED is open when
the grayscale data are less than 20h (32d). Therefore, the GS data must be set to 21h (33d) or higher to get
updated LOD data beyond 20h (32d).
The TEF bit indicates that the IC temperature is too high. The flag also indicates that the IC has turned off all
drivers to avoid damage by overheating the device. A '1' in the TEF bit means that the IC temperature has
exceeded the detect temperature threshold (T_TEF) and the driver is turned off. A '0' in the TEF bit indicates
normal operating temperature conditions. The IC automatically turns the drivers back on when the IC
temperature decreases to less than T_TEF-THYS. When the IC is powered on, LOD data do not show correct values.
Therefore, LOD data must be read from the 33rd GSSCLK pulse input after BLANK goes low. Table 4 shows a
truth table for both LOD and TEF.
SID DATA
0
1
Table 4. LOD and TEF Truth Table
CONDITION
LED OPEN DETECTION (LODn)
THERMAL ERROR FLAG (TEF)
LED is connected (V_OUTn > V_IOD)
LED is open or shorted to GND (V_OUTn ≤ V_IOD)
Device temperature is low (temp ≤ T_{TEF–THYS})
Device temperature is high (temp > T_TEF)
Continuous Base LED Open Detection
The LED Open Detection (LOD) circuit checks the voltage of each active (that is, on) constant current sink output
(OUT0 through OUT15) at the rising edge of the 33rd GSSCLK after the falling edge of BLANK to detect open
and short LEDs to GND. The channels corresponding to the LOD bit in the Status Information Data register (SID)
are set to a '1' if the voltage of the OUTn pin is less than the LED open detection threshold (V_LOD = 0.3 V_TYP).
This status information can be read from the GSSOUT pin. No special test sequence is required for LED open
detection.
The LOD function automatically checks for open and short LEDs to GND during each grayscale PWM cycle. The
SID information of the LOD is latched into the LED Open Detection data latch and does not change until the
rising edge of the 33rd GSSCLK pulse following the next falling edge of BLANK. To eliminate false detection of
open LEDs, the LED driver design must ensure that the TLC5942 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.
BLANK
GSSCLK
4086 4088 4090 4093 4094 4096
¼ ¼ _{1 2} 3 ₄
28 29 30 31 32 33 34 35 36 37 38 39
4085 4087 4089 4091 4093 4095
OUTn
OUTn ON
GND
OUTn OFF
V_OUTn
Internal SID
Register Value
Old LED Open Detection Data
If the OUTn voltage (V_OUT) is less than VLOD (0.3 V, typ) at the rising edge of the 33rd
GSSCLK 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’.
New LED Open Detection Data
This LED Open Detection (LOD) data are
kept until the next 33rd rising edge of
GSSCLK after BLANK goes low.
Figure 25. LED Open Detection (LOD) Timing
Copyright © 2007, Texas Instruments Incorporated
Product Folder Link(s): TLC5942
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