Quectel EC25-AUX Hardware Design page 58

SDC2_CMD 33
VDD_SDIO 34
SD_INS_DET 23
The following figure shows a reference design of SD card.
In SD card interface design, in order to ensure good communication performance with SD card, the
following design principles should be complied with:
 SD_INS_DET must be connected.
 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, DCDC signals, etc.
EC25_Hardware_Design
IO SD card SDIO bus command
PO SD card SDIO bus pull up power
DI SD card insertion detection
Figure 25: Reference Circuit of SD Card Interface
LTE Standard Module Series
EC25 Hardware Design
1.8V/2.85V configurable.
Cannot be used for SD
card power.
If unused, keep it open.
1.8V power domain.
If unused, keep it open.
57 / 130