LTE Standard Module Series
EG915U-EU_Hardware_Design 42 / 81
⚫ The following principles should be complied with when designing the USB interface, to meet USB
specifications.
⚫ It is important to route the USB signal traces as differential pairs with total grounding. The impedance
of USB differential trace is 90 Ω.
⚫ Do not route signal traces under crystals, oscillators, magnetic devices and RF signal traces. It is
important to route the USB differential traces in inner-layer of the PCB, and surround the traces with
ground on that layer and ground planes above and below.
⚫ Please pay attention to the selection of the ESD component on the USB data line. Its parasitic
capacitance should not exceed 2 pF and should be placed as close as possible to the USB interface.
For more details about the USB specifications, please visit http://www.usb.org/home.
4.3. USB_BOOT Interface
The module provides a USB_BOOT pin. You can pull up USB_BOOT to VDD_EXT before powering up,
and the module will enter download mode when it is powered on. In this mode, the module supports
firmware upgrade over USB interface.
Please make sure that VBAT is stable before pulling down PWRKEY pin. It is recommended that the time
between powering up VBAT and pulling down PWRKEY pin is no less than 30 ms.
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