User Guide

RH-30/RH-31 Company Confidential

System Module Nokia Customer Care

Figure 27: White LED driver

Driver is controlled by UEM via CallLED1 output. This signal is connected to driver EN-pin

(on/off). PWM control for LEDs facilitates the ‘fading’ effect when LEDs are turned on/

off. PWM control can also be used to limit the average current through LEDs for example

in high temperature.

Flashlight

Flashlight is controlled via CallLED2 output to external BJTswitch/driver. CAllLED2 output

is open drain driver and needs voltage matching for higher voltage/current. Two flash-

light LEDs are supplied from VLED voltage supply. Flashlight is enabled/disabled by hold-

ing down the ‘*’ key.

• Flashlight uses two hyperbright LEDs, luminous intensity ~780mcd(typ.)/

each@20mA

• current consumption ~20mA total

• LEDs are connected in series

Driver will increase or decrease the output voltage for LEDs to keep the current stable.

This means that constant current flow through LEDs. Serial resistance 33R is used to

limit the current through the LEDs.