Typically the forward voltages of the GREEN and BLUE diodes are close to each other (about 3 V to 5 V) however the forward voltage of the red diode is significantly lower (2 V to 4 V). This can lead to a current spike in the RED diode when the strobe controller switches from green or blue to red. This happens because V_LED is initially at a higher voltage than required to drive the red diode. DLPA3000 provides transient current limiting for each switch to limit the current in the LEDs during the transition. The transient current limit value is controlled through register ILLUM_ILIM (0x02, bit [6:3]). In a typical application it is required only for the RED diode. The value for ILLUM_ILIM (0x02, bit [6:3]) should be set at least 20% higher than the DC regulation current. Register ILLUM_SW_ILIM_EN(0x02, bit [2:0]) contains three bits to select which switch employs the transient current limiting feature. The effect of the transient current limit on the LED current is shown in Figure 8-9.

Figure 8-9 LED Current Without (Left) and With (Right) Transient Current Limit