ELI43-CR
User’s Manual
04/23/2018
Copyright ©2018, Future
Designs, Inc.
Page
9
of
16
PWM Control of Backlight
Figure 4. PWM Backlight Control
J5 mating connector housing information:
•
Manufacturer: Hirose
•
Part Number: DF12-3S-1.25C
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https://www.digikey.com/products/en?keywords=H2180-ND
•
Pre-terminated wires
https://www.digikey.com/products/en?PPV=1811-9-566967
ELI provides an input so an external processor can control the display backlight to vary the display
brightness or to reduce power consumption (the display backlight is typically one of the larger
sources of power consumption in the system). PWM dimming is an input with a 0 to 3.3 VDC range
and the user should drive this with a push-pull type output or a suitable open collector output.
To control the display backlight the user should connect an externally generated Pulse Width
Modulated (PWM) signal to J5 pin 2 with a common ground to J5 pin 3. The frequency range for this
signal is from 5KHz to 100KHz. Each ELI unit’s unique sized display backlight properties will vary,
so the user should test their version for an acceptable range of brightness control. For example, the
actual display 0 to 100% brightness range may be 40% to 90% of the PWM range. In certain
installations, a series resistor may be required to ensure a clean PWM signal is provided to the ELI.
The suggested value for the resistor is 100ohms. See
below, for example of connectivity.
Actual testing in your installation may require this resistor to be changed, or possibly not required at
all.
On the ELI unit, the PWM dimming signal is pulled up to LCD_VDD providing 100% backlight
power when no PWM signal is applied at pin 2 of J5. If nothing is connected to J5 the ELI will drive
the display at 100% brightness (default).
