DLPS039F December 2015 – April 2019 TPS99000-Q1
The power supply architecture depends on the amount of power required for the illumination source. For HUD applications which require precise color and white point control, it is highly recommended to pre-regulate the illumination power supply, as voltage variations can cause variations in the LED output. For non-color critical applications, the designer may choose to completely isolate the illumination driver. In addition, if 2 or more LEDs are driven in series, then the pre-regulated voltage must be higher than the voltage of the LEDs. The different architectures are shown below.
Note that the architectures make use of the LM25118 as a pre-regulator. This part uses a buck-boost architecture which allows it to supply the required 6.5 V with a battery voltage input of 6 V to 18 V. If the battery input can be assured to be above the 6.5 V output voltage, then a buck architecture can be used instead, resulting in BOM savings.
In this application, the same pre-regulator is used to power the 6.5 V rail as well as the LM3409. Since the LM3409 input voltage must be kept above 6 V, the pre-regulator is set to 6.5 V.
In this application, the pre-regulator must be designed to operate at a higher output voltage in order to drive 2 LEDs in series. Because the TPS99000-Q1 requires a VIN from 5.5 V to 7 V, a small buck regulator is used to generate a 6 V power rail.
In this application, the power used to drive the illumination is separate from the TPS99000-Q1. This is possible in applications where the illumination driver can be very simple. Although the LM25118 is shown here, a different regulator would likely be selected in this application because the maximum current requirements are much less with the illumination power path removed.