Planar LC640.480.33-AC manual Backlight Dimming Modes, Dimming Control Interfacing

Backlight Dimming Modes

The backlight may be operated in one of four modes without the use of jumpers or switches. The mode is selected based on the state of the /ABCOFF input and on whether the dimming input is left open or connected to a voltage source.

Table 16. Backlight Dimming Modes.

Mode	VRLUM	/ABCOFF	Comments
Extended	open	GND	Display operates at approximately half
backlight life			luminance.
Manual dimming	Rpot or	GND	Minimum-to-maximum luminance as defined
	Vin		by pot or voltage at VRLUM (J2-2):
			0 Vdc = min, +5 Vdc = max luminance
Automatic	open	open	Default mode. Minimum-to-maximum
brightness			luminance as defined by ambient light sensor:
control (ABC)			0 lx = min, 3000 lx = max luminance.
Biased ABC	Rpot or	open	Combination of dimming control and
	Vin		ambient light sensor sets display luminance.
			In this mode, VRLUM has twice the influence
			compared to the ambient light sensor, hence
			VRLUM can drive luminance to either extreme
			regardless of ambient light conditions.
			Ambient light influence max is capped at
			3000 lux.

Dimming Control Interfacing

An analog dimming control is available on J2. Some common methods to use this input are shown in Figure 12. In this figure, the schematic shown is an approximation of the circuitry actually present in the LC640.480.33-AC and is meant to give an indication of the dimming interface DC characteristics. The VRLUM input expects a 0 to +5 Vdc voltage which may be supplied either directly or generated from a potentiometer.

In Figure 12 below, A, B, and C are analog dimming methods. D, E, and F are methods to drive the two mode set inputs.

Figure 12. Dimming Control Methods.

20 LC640.480.33-AC Operations Manual (OM600-01)