ZHCSIA7 May 2018 DLPA4000
PRODUCTION DATA.
To connect the 0.65 WXGA DMD (DLP650LE) or 0.65 1080p DMD (DLP650NE), DLPC4422 controller and DLPA4000, see the reference design schematic. When a circuit board layout is created from this schematic a very small circuit board is possible. An example small board layout is included in the reference design data base. Comply with the layout guidelines to achieve reliable projector operation. The optical engine that has the LED packages and the DMD mounted to it is typically supplied by an optical OEM who specializes in designing optics for DLP projectors.
The component selection of the buck converter is mainly determined by the output voltage. Table 9 shows the recommended value for inductor LOUT and capacitor COUT for a given output voltage.
VOUT (V) | LOUT (µH) | COUT (µF) | |||
---|---|---|---|---|---|
MIN | TYP | MAX | MIN | MAX | |
1 - 1.5 | 1.5 | 2.2 | 4.7 | 22 | 68 |
1.5 - 3.3 | 2.2 | 3.3 | 4.7 | 22 | 68 |
3.3 - 5 | 3.3 | 4.7 | 22 | 68 |
Use Equation 11 to calculate the inductor peak-to-peak ripple current. Use Equation 12 the peak current. Use Equation 13to calculate teh RMS current. The inductor saturation current rating must be greater than the calculated peak current. The RMS or heating current rating of the inductor must be greater than the calculated RMS current.
where
The capacitor value and ESR determines the level of output voltage ripple. Use ceramic or other low ESR capacitors. Recommended values range from 22 to 68 μF. Use Equation 14 to determine the required RMS current rating for the output capacitor.
One other component for the buck converter configuration is needed. Use a charge pump capacitor between PWRx_SWITCH and PWRx_BOOST to drive the high-side MOSFET. The recommended value for the charge pump capacitor is 100 nF.
Because the switching edges of the buck converter are relatively fast, voltage overshoot and ringing can become a problem. To overcome this problem a snubber network is used. The snubber circuit consists of a resistor and capacitor that are connected in series from the switch node to ground. The snubber circuit is used to damp the parasitic inductances and capacitances during the switching transitions. This circuit reduces the ringing voltage and also reduces the number of ringing cycles. The snubber network is formed by RSNx and CSNx. More information on controlling switch-node ringing in synchronous buck converters and configuring the snubber can be found in Analog Applications Journal.