Quectel EG12 Series Hardware Design page 63

The following figure shows an SDIO interface reference design.
Module
SD_VDD
R7
100K
R1 0R
SD_DATA3
R2 0R
SD_DATA2
R3 0R
SD_DATA1
R4 0R
SD_DATA0
R5 0R
SD_CLK
R6 0R
SD_CMD
SD_DET
Please follow the principles below in the SD card circuit design:

The voltage range of SD power supply is 2.7V~3.6V and a sufficient current up to 0.8A should be
provided. As the maximum output current of SD_VDD is 50mA which can only be used for SDIO
pull-up resistors, an external power supply is needed for SD card.

To avoid jitter of bus, resistors R7~R11 are needed to pull up the SDIO to SD_VDD. Value of these
resistors is among 10kΩ~100kΩ and the recommended value is 100kΩ.
 In order to improve 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.

The load capacitance of SDIO bus needs to be less than 40pF.

It is important to route the SDIO signal traces with total grounding. The impedance of SDIO data
trace is 50Ω (± 10%).

Keep SDIO signals far away from other sensitive circuits/signals such as RF circuits, and analog
signals, as well as noisy signals such as clock signals, and DCDC signals.

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 36mm, so the
exterior total trace length should be less than 14mm.

Make sure the adjacent trace spacing is two times of the trace width and the load capacitance of
SDIO bus should be less than 40pF.
EG12_Hardware_Design
R8 R9 R10
100K 100K 100K
C1 D1 C2 D2 C3 D3 C4
NM NM NM NM
Figure 31: Reference Circuit of SD Card Application
VDD_EXT
+
C10
R12
R11
100uF
100K 470K
D4 C5 D5 C6 D6
D7
NM NM
LTE-A Module Series
EG12 Hardware Design
SD Card Connector
VDD_2V85
VDD
C9 C8 C7
100nF 33pF 10pF
CD/DAT3
DAT2
DAT1
DAT0
CLK
CMD
DETECTIVE
VSS
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