APPLICATION NOTE 3614

Staggering the Burst Dimmer on CCFL Displays


Abstract: To reduce the instantaneous current demand on the DC inverter power supply, the DS3984/DS3988 cold-cathode fluorescent lamp controllers stagger the start of the burst dimming cycle for each of the channels of a backlit LCD display.

Figure 1 shows the delay of channels 1 through 4 staggered by the DS3984/DS3988 cold-cathode fluorescent lamp controllers. The other channels are staggered in a similar fashion by using the DS3988 for up to 8 channels, or by cascading multiple DS3984/DS3988 controllers for applications requiring additional channels.

Figure 1. DS3984/DS3988 staggered burst dimming delay on channels 1 to 4.
Figure 1. DS3984/DS3988 staggered burst dimming delay on channels 1 to 4.

Figure 2 shows the effect the staggered delay has on the current demand of the DC-inverter power supply. In this example, the burst dimming is set to approximately 50%. The power supply slowly ramps up to just over 3A, and then slowly returns to 0A.

Figure 2. DC inverter supply current ramp at 50% burst dimming.
Figure 2. DC inverter supply current ramp at 50% burst dimming.