Smart Module Series
SC20_Series_Hardware_Design 49 / 133
A reference circuit for SD card interface is shown below.
Figure 19: Reference Circuit for SD Card Interface
SD_LDO11 is the power supply for the external SD card. The maximum drive current is about 600 mA.
Because of the high drive current, it is recommended that the trace width is 0.6 mm or more. In order to
ensure the stability of drive power, a 2.2 μF capacitor should be added in parallel near the SD card
connector.
SD_CMD, SD_CLK, SD_DATA0, SD_DATA1, SD_DATA2 and SD_DATA3 are all high-speed signal lines.
In PCB design, control the characteristic impedance of them as 50 Ω, and do not cross them with other
traces. It is recommended to route the traces on the inner layer of PCB, and keep the same trace length
for them. Additionally, SD_CLK needs ground shielding.
Layout guidelines:
Control impedance as 50 Ω ±10 %, and ground shielding is required.
The total trace length difference between SD_CLK and other signal traces should not exceed 1 mm.
Table 16: SD Card Trace Length Inside the Module
Pin No. Signal Length (mm)
39 SD_CLK 14.60
40 SD_CMD 14.55
41 SD_DATA0 14.53
42 SD_DATA1 14.56
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