Figure 17: Reference Circuit for SD Card Interface
SD_LDO9C is a peripheral driver power supply for SD card. The maximum drive current is 600 mA.
Because of the high drive current, it is recommended that the trace width is 0.6 mm or above. To ensure
the stability of drive power, add a 4.7 μF and a 33 pF capacitor in parallel near the SD card connector.
SD_CMD, SD_CLK and SD_DATA[0:3] are all high speed signal traces. In PCB design, control the
characteristic impedance of them as 45 Ω, and do not cross them with other traces. It is recommended to
route these traces on the inner layer of PCB, and keep them of the same length. Additionally, SD_CLK
needs separate ground shielding.
Layout guidelines:
⚫ Control impedance to 45 Ω ±10 %, and add ground shielding.
⚫ The trace length difference between SD_CLK and SD_CMD/SD_DATA[0:3] should be less than
2 mm.
⚫ Trace length requirements: less than 150 mm for traces of 50 Mbps, less than 50 mm for traces of
140 Mbps.
⚫ The spacing between signal lines should be 1.5 times the line width.
⚫ The capacitive reactance of SD_DATA[0:3] traces should be less than 8 pF.
Table 17: SD Card Signal Trace Length Inside the Module
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