Service Guide

LTE Standard Module Series
EG91_Series_Hardware_Design
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3.18. USB_BOOT Interface
EG91 series module provides a USB_BOOT pin. You can pull up USB_BOOT to VDD_EXT before
VDD_EXT is powered up, and the module will enter emergency download mode when it is powered on. In
this mode, the module supports firmware upgrade over USB interface.
Table 21: Pin Definition of USB_BOOT Interface
The following figures show the reference circuit of USB_BOOT interface and timing sequence of entering
emergency download mode.
Module
USB_BOOT
VDD_EXT
4.7K
Test point
TVS
Close to test point
Figure 28: Reference Circuit of USB_BOOT Interface
Pin Name Pin No. I/O Description Comment
USB_BOOT 75 DI
Force the module to enter
emergency download mode
1.8 V power domain.
Active high.
It is recommended to
reserve test point.