Users Manual

LTE Standard Module Series
EC25 Hardware Design
EC25_Hardware_Design
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The voltage range of SD card power supply VDD_3V is 2.7V~3.6V and a sufficient current up to 0.8A
should be provided. As the maximum output current of VDD_SDIO is 50mA which can only be used
for SDIO pull-up resistors, an externally power supply is needed for SD card.

To avoid jitter of bus, resistors R7~R11 are needed to pull up the SDIO to VDD_SDIO. Value of these
resistors is among 10kΩ~100kΩ and the recommended value is 100kΩ. VDD_SDIO should be used
as the pull-up power.

In order to adjust signal quality, it is recommended to add 0Ω resistors R1~R6 in series between the
module and the SD card. The bypass capacitors C1~C6 are reserved and not mounted by default. All
resistors and bypass capacitors should be placed close to the module.

In order to offer good ESD protection, it is recommended to add a TVS diode on SD card pins near
the SD card connector with junction capacitance less than 15pF.

Keep SDIO signals far away from other sensitive circuits/signals such as RF circuits, analog signals,
etc., as well as noisy signals such as clock signals, DC-DC signals, etc.

It is important to route the SDIO signal traces with total grounding. The impedance of SDIO data
trace is 50Ω (±10%).

Make sure the adjacent trace spacing is two times of the trace width and the load capacitance of
SDIO bus should be less than 15pF.

It is recommended to keep the trace length difference between CLK and DATA/CMD less than 1mm
and the total routing length less than 50mm. The total trace length inside the module is 27mm, so the
exterior total trace length should be less than 23mm.
3.14. Wireless Connectivity Interfaces
EC25 supports a low-power SDIO 3.0 interface for WLAN and UART/PCM interfaces for BT function.
The following table shows the pin definition of wireless connectivity interfaces.
Table 16: Pin Definition of Wireless Connectivity Interfaces
Pin Name Pin No. I/O Description Comment
WLAN Part
SDC1_DATA3 129 IO WLAN SDIO data bus D3 1.8V power domain
SDC1_DATA2 130 IO WLAN SDIO data bus D2 1.8V power domain
SDC1_DATA1 131 IO WLAN SDIO data bus D1 1.8V power domain
SDC1_DATA0 132 IO WLAN SDIO data bus D0 1.8V power domain
SDC1_CLK 133 DO WLAN SDIO bus clock 1.8V power domain