HUAWEI MU509-65 HSDPA LGA Module
Hardware Guide
Description of the Application Interfaces
Issue 01 (2016-04-08)
Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
31
Figure 3-13
Driving circuit
R
LED_STATUS
LED_MODE
R
VBAT
V
F
I
F
V
F
I
F
Module
(DCE)
For resistance of R placed on user board, choose the value such that it satisfies the
following equation:
I
F
*R+V
F
= VBAT
V
F
: Forward voltage
I
F
: Forward current
Take an LED as an example, Figure 3-14 shows its I
F
- V
F
curves. If VBAT is 3.8 V and
the desired current through the LED I
F
is 3 mA, then the voltage of the LED V
F
is 1.5 V
according to I
F
- V
F
curves, and the corresponding value for resistance of R is
(3.8-1.5)/0.003 = 767
Ω.
The brightness of the LED depends on the current value, and for most of the indicator
lights the current from 2 mA to 5 mA is already enough.