The DLPA3000 contains circuitry to sequentially control the three color-LEDs (red, green and blue). This circuitry consists of three NMOS switches, the actual strobe decoder, and the LED current control (Figure 8-7). The NMOS switches are connected to the cathode terminals of the external LED package and turn on and off the currents through the LEDs.

Figure 8-7 Switch Connection for a Common-Anode LED assembly

The NMOS FETs P, Q, and R are controlled by the CH_SEL_0 and CH_SEL_1 pins. CH_SEL[1:0] typically receive a rotating code switching from RED to GREEN to BLUE and then back to RED. The relation between CH_SEL[0:1] and which switch is closed is indicated in Table 8-1.

Besides enabling one of the switches, CH_SEL[1:0] also selects a 10-bit current setting for the control IDAC that is used as the set current for the LED. This set current together with the measured current through R_LIM is used to control the illumination driver to the appropriate V_LED. The current through the 3 LEDs can be set independently by registers SW1_IDAC to SW3_IDAC, 0x03 to 0x08 (Table 8-1).

Each current level can be set from off to 150mV/R_LIM in 1023 steps:

Equation 5.

The maximum current for R_LIM= 25 mΩ is thus 6 A.