Backlight And Illumination; Display And Menu Key Illumination; Menu Keys - Nokia n81 Service Manual

RM-179; RM-223
System Module and User Interface
Figure 68 RM-179 key matrix

Backlight and illumination

Display and menu key illumination

Display
The display has 2x2 LEDs in series included for backlight illumination. They are connected to have 4 LEDs in
series and driven with a constant current source SMPS (N2301). Driving current is 15mA and its PWM dimmed
(EN). In addition a "load-disconnect" circuit (N2302) is implemented. This avoids ringing of the output
capacity C2314. Basic filtering on VLEDOUT is done with L2302, C2305 and C2316.

Menu keys

Three LED chains for S60 Keys, Music Keys and Gaming Keys are derived from VLEDOUT and driven by a constant
current source at 5 mA. Each chain has separate ENABLE signal and dimmed with VLEDOUT. Gaming Key LEDs
have additional ESD protection.
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