Nokia RH-9 Series Ccs Technical Documentation page 30

RH-9
System Module & UI
Keyboard light
The keyboard light consists of 2 TBSF white LEDs, which are placed under the keyboard
and use the light guide to distribute the light
LED driver circuit
The LCD & Keyboard backlight LEDs are drivenfrom a sharedLED driver with a constant
current vharge-pump circuit (LM2795) as shown below in figure 3. The driver circuit is
controlled by the UEM output pin [DLIGHT] and drive current is 20mA pr. output. Sepa-
rate outputs are used for LEDs for LCD, and a shared output is used for Keyboard LEDs
(10mA). By appropriate SW the driver can be PWM controlled for dimming purpose.
Figure 3: Shared LED driver circuit for LCD and Keyboard backlight
Page 30 ãNokia Corporation
CCS Technical Documentation
Issue 1 11/02