Smart LTE Module Series
SC650T Hardware Design
SC650T_Hardware_Design 79 / 131
that the resonant frequency point of a capacitor largely depends on the material and production technique.
Therefore, customers would have to discuss with their capacitor vendors to choose the most suitable
capacitor for filtering out high-frequency noises.
The severity degree of the RF interference in the voice channel during GSM transmitting largely depends
on the application design. In some cases, EGSM900 TDD noise is more severe; while in other cases,
DCS1800 TDD noise is more obvious. Therefore, a suitable capacitor can be selected based on the test
results. Sometimes, even no RF filtering capacitor is required.
In order to decrease radio or other signal interference, RF antennas should be placed away from audio
interfaces and audio traces. Power traces cannot be parallel with and also should be far away from the
audio traces.
The differential audio traces must be routed according to the differential signal layout rule.
3.24. Emergency Download Interface
USB_BOOT is an emergency download interface. Pull up to LDO5_1P8 during power-up will force the
module enter into emergency download mode. This is an emergency option when there are failures such
as abnormal startup or operation. For convenient firmware upgrade and debugging in the future, please
reverse the reference circuit design shown as below.
LDO5_1P8
S1
Module
USB_BOOT
R1
10K
Figure 31: Reference Circuit Design for Emergency Download Interface
3.25. LED Driver Interfaces
The following is the pin definition of LED driver interfaces.
