TLC5903

LED DRIVER

SLLS383 – DECEMBER 1999

15

POST OFFICE BOX 655303

PRINCIPLES OF OPERATION

Figure 1. WDT Operational Time

3000

300

33

3

0103

104

105

C1 – External Capacitor – pF

WDT Operational Time

T (ms)

≅ 3+0.03 × C1 (pF)

Figure 2. WDT Usage Example

TLC5903

WDT

WD_CAP

Scan Signal

C1

TSD (thermal shutdown)

When the junction temperature exceeds the limit, TSD functions and turns the constant current output off. When

TSD is used, TS_ENA is pulled high. When TSD is not used, TS_ENA is pulled low. To recover to normal

operation, the power supply is turned off or TS_ENA is pulled low.

noise reduction

concurrent switching noise reduction

The 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 delay output terminals such as GSOUT, BOUT for GSCLK, and BLANK

respectively. Connecting these outputs to the GSCLK and BLANK terminals of the next stage IC allows

differences in the switching time between ICs to be made. When GSCLK is output to GSOUT through the device,

duty is changed, so that the number of stages to be connected will be limited to a maximum of 10 at

GSCLK = 4 MHz.

output slope

The on and off time of the constant current output at an output current of 80 mA is approximately 150 ns and

250 ns respectively. It is effective in reducing the concurrent switching noise that occurs when multiple outputs

turn on or off at the same time.

delay between constant current output

The constant current output has a delay time of approximately 5 ns by two outputs. This means approximately

35 ns delay time exists between OUT0 and OUT15. This time difference by delay is effective for reduction of

concurrent switching noise as well as output slope. This delay time has the same value at 8-bits or 16-bits

operation mode.