Status Information Data (SID)

StatusInformationData(SID)Configuration

GrayscaleShiftRegister(12Bits

16Channels)

´

¼

¼

¼

¼

¼

MSB

17

OUT15

LODData

OUT14

LODData

OUT0

LODData

TEFData

PTWData

16

2

1

LSB

0

LODDataofOUT15toOUT0(16Bits)

The16LODbitsforeachchannelandtheTEFandPTWbits

overwrite themostsignificant18bitsofthegrayscaleshiftregister

attherisingedgeofthefirstSCLKafterXLATgoeslow.

SOUT

(DCSEL=L)

MSB

191

LSB

0

180

179

12

11

OUT15-Bit11

(LOD-OUT15)

OUT0-Bit0

OUT15-Bit0

(LOD-OUT4)

OUT14-Bit11

(LOD-OUT3)

OUT1-Bit0

OUT0-Bit11

SIN

SCLK

(DCSEL=L)

GSDataforOUT15

GSDataforOUT14

GSDataforOUT1

¼

GSDataforOUT0

¼

¼

175

174

OUT14-Bit7

(TEF)

OUT14-Bit6

(PTW)

TLC5944

Status information data (SID) are 18-bit, read-only data. The 16-bit LED open detection (LOD) error, the thermal

error flag (TEF), and the pre-thermal warning (PTW) are shifted out onto the SOUT pin with each rising edge of

the serial data shift clock, SCLK. The 16 LOD bits for each channel and the two TEF bits are written into the 18

most significant bits of the grayscale shift register at the rising edge of the first SCLK after XLAT goes low. As a

result, the previous data in the 18 most significant bits of the grayscale information are lost at the same time. No

data are loaded into the other 174 bits. Figure 30 shows the bit assignments. Figure 16 illustrates the read timing

for the status information data.

Figure 30. Status Information Data Configuration

The LOD data update at the rising edge of the next 33rd GSCLK of the subsequent PWM cycle; the LOD data

are retained until the next 33rd GSCLK. LOD data are only checked for outputs that are turned on during the

rising edge of the 33rd GSCLK 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).

The PTW and TEF bits indicate that the IC temperature is high and too high, respectively. The TEF flag also

indicates that the IC has turned off all drivers to avoid damage by overheating the device. A '1' in the TEF bit

is forced off. A '0' in the TEF bit indicates the driver has not exceeded the high temperature. The PTW flag

indicates that the IC temperature has exceeded the detect temperature threshold, but does not force the driver

off. A '1' in the PTW bit indicates that the IC temperature has exceeded the pre-thermal warning threshold

temperature conditions. When the PTW is set, the IC temperature should be reduced by lowering the power

dissipated in the driver to avoid a forced shutdown by the thermal shutdown circuit. This reduction can be

accomplished by lowering the values of the GS or DC data.

When the IC powers on, LOD data do not show correct values. Therefore, LOD data must be read from the 33rd

GSCLK pulse input after BLANK goes low. Table 4 shows a truth table for both LOD and TEF.

Table 4. LOD and TEF Truth Table

CONDITION

SID DATA

LED OPEN DETECTION (LODn)

THERMAL ERROR FLAG (TEF)

PRE-THERMAL WARNING (PTW)

Device temperature is lower than the

Device temperature is lower than the

LED is connected

0

high-side detect temperature

low-side detect temperature

(temp

Device temperature is higher than the

Device temperature is higher than the

LED is open or shorted to GND

high-side detect temperature and the

1

low-side detect temperature

driver is forced off

(temp

Copyright © 2008, Texas Instruments Incorporated

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