TLC5910

LED DRIVER

SLLS392 – NOVEMBER 1999

21

POST OFFICE BOX 655303

PRINCIPLES OF OPERATION

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 monitoring OUTn terminals to be turned on. This function is

operational for sixteen OUTn terminals individually. To know which constant current output is disconnected, the

level of XDOWN2 is repeatedly 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 is applied to above 0.4 V when the LED

is lighting normally. Also, since the time of 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 for XDOWN2 output status using four LEDs .

Table 8. XDOWN2 Output Example

LED NUMBER

1

2

3

4

LED STATUS

GOOD

NG

GOOD

NG

OUTn

ON

ON

ON

ON

XDOWN2

LOW (by case 2, 4)

LED NUMBER

1

2

3

4

LED STATUS

GOOD

NG

GOOD

NG

OUTn

ON

ON

OFF

OFF

DETECTION RESULT

GOOD

NG

GOOD

GOOD

XDOWN2

LOW (by case 2)

LED NUMBER

1

2

3

4

LED STATUS

GOOD

NG

GOOD

NG

OUTn

OFF

OFF

OFF

OFF

DETECTION RESULT

GOOD

GOOD

GOOD

GOOD

XDOWN2

HIGH–IMPEDANCE

noise reduction

concurrent switching noise reduction

Concurrent switching noise has the potential to occur when multiple outputs turn on or off at the same time. To

prevent this noise, the device has a delay output terminal such as XGSOUT and BOUT for GSCLK (gray scale

clock) and BLANK (blanking signal) respectively. Connecting these outputs to the GSCLK and BLANK terminals

of next stage IC allows differences of 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 frequency.

delay between constant current output

The constant current output has a delay time of approximately 20 ns between outputs. This means

approximately 300 ns delay time exists between OUT0 and OUT15. This time differences by delay reduces the

concurrent switching noise.