Figure 28: Reference Circuit of SD Card Application
Please follow the principles below in the SD card circuit design:
The voltage range of SD power supply VDD_2V85 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 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, analog signals,
etc., as well as noisy signals such as clock signals, DCDC signals, etc.
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.
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