Product Info

LTE Module Series
EC25 Hardware Design
EC25_Hardware_Design 59 / 112
The following figure shows a reference design of SD card.
Figure 25: Reference Circuit 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.
card supported level,
please refer to SD 3.0
protocol for more details.
If unused, keep it open.
VDD_SDIO 34 PO SD card SDIO bus pull up power
1.8V/2.85V configurable.
Cannot be used for SD
card power. If unused,
keep it open.
SD_INS_DET 23 DI SD card insertion detection
1.8V power domain.
If unused, keep it open.