User Guide

CCS Technical Documentation System Module LG4 and Grip Module LS4

Issue 2 11/02 ¤Nokia Corporation Page 61

Backlight

NHL-2NA grip keyboard uses six white backlight LEDs. These LEDs are “smart LEDs”

(0.6mm height). The LED type is LWL88S, NMP code 4860331. NHL-2NA grip uses bright-

ness groups M1-M2, N1-N2 and P1. There is only one brightness group in one grip-mod-

ule.

Electrical interface

The idea is to connect these six LEDs parallel. LEDs are using current that is taken from

battery voltage. The voltage is controlled by charge pump (NMP code 4341137) and the

current by serial resistor. The idea of the charge pump is to keep the supply voltage of the

LEDs constant although Vbat changes. Serial resistors limit the current that goes to LEDs.

Current for one LED is ~4mA. The circuit and LEDs consume ~52mA current.

LEDs need one line of flex (Called1). Called1 controls the charge pump SD pin. Called1

signal rises close to Vbat voltage (required for the SD signal in specification of the cur-

rent pump). The output of the current pump is 4.1V (@Vbat 3.0V to 4.2V).

Figure 38: Electrical implementation of the grip keyboard backlight

Called1

10u

330n 330n

4u7

37R4 // 49R9

6 x LED

Vbat Vbat

100k

BatGND

Vout Vin

C1-

C1+

C2-

C2+

CFilt