Smart LTE Module Series
SC66 Hardware Design
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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.
3.23. Emergency Download Interface
USB_BOOT is an emergency download interface. Pulling up LDO13A_1P8 during power-up will force the
module into emergency download mode. This is an emergency option when there are failures such as
abnormal startup or operation. For convenient future firmware upgrade and debugging in the future,
please reserve the reference circuit design shown below.
LDO13A_1P8
S1
Module
USB_BOOT
R1
10K
Figure 35: Reference Circuit Design for Emergency Download Interface
