The design work for a 5-inch or larger automotive LCD display may be very complicated. The display source driver requires a power rail with a voltage range of 10V to 15V called the analog voltage device drain (AVDD) and two power supply rails (VGH and VGL) for the gate driver.
In many cases, you can use an LCD bias power supply, such as the TPS65150-Q1 (an automotive LCD/display biasing solution for infotainment or cluster displays that greatly simplifies your LCD power design). But there is another way to design automotive LCD displays that can be further reduced in size and BOM cost by using fewer source drivers.
Figure 1: Traditional LCD bias power method using the TPS65150-Q1
In order to follow the trend emerging in the field of design of smartphones and tablet displays (see the single-inductor-based split-rail converter TPS65132 for these applications) about three years ago, a new driving method has emerged in the automotive world – the source The pole driver now requires a positive AVDD (6.xV) supply rail and a negative AVDD (-6.xV) supply rail.
Figure 2: New method using a single inductor (based on a split-rail converter such as the TPS65132)
Both panel makers and source driver manufacturers favor this technique of reducing display power consumption through the use of charge sharing methods. In addition, this new method can also save money and reduce the size, because the source driver can control more channels, which can reduce the number of source drivers required for each display.
When designing for display power management functions that require +/-AVDD drive, you can further simplify your design by using the TPS65131-Q1, an efficient split-rail converter that meets the requirements of automotive applications. This flexible device includes a separate EN pin for fully adjustable sequencing and a resistor divider to set the output voltage value, providing the source driver with the +AVDD and -AVDD supply rails.
For designs where the source drivers do not have integrated VGH and VGL rails, installing a charge pump and inverting charge pump to support those rails will complement the power rail provided by the TPS65131-Q1. To learn how to install and enable these power rails and how you can adapt them to your next design, see this TI Designs Reference Design (PMP9780).