Smart Module Series
SC206E_Series_Hardware_Design 50 / 115
A reference circuit for the SD card interface is shown below.
SD_CMD
120K
NM_51K
SD_DATA3
SD_DATA2
SD_CLK
SD_DATA0
SD_DET
SD_DATA1
P1-DAT2
P2-CD/DAT3
P3-CMD
P4-VDD
P5-CLK
P8-DAT1
GND
P6-VSS
P7-DAT0
DETECTIVE
GND
GND
GND
1
2
3
4
5
6
7
8
9
10
11
12
13
SD_LDO21
33R
33R
33R
33R
33R
33R
1K
33 pF
4.7
μF
SD_LDO4
Module
R1
R2
R3
R4
R5
R6
NM_51K NM_10K NM_51K NM_51K
R7
R8
R9
R10
R11
R12
R13
D1
D2
D3
D4
D5
D6
D7
D8
C1
C2
SD Card Connector
LDO15A_1V8
GND
R14
0R
Figure 17: Reference Circuit for the SD Card Interface
SD_LDO21 is the power supply for the SD card and can provide up to 841 mA output current. Due to the
high output current, it is recommended that the trace width should be at least 0.8 mm. To ensure output
current stability
, add a 4.7 μF and a 33 pF capacitor 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 to 50
Ω, and do not cross them with other
traces. It is recommended to route the traces on the inner layer of the PCB and keep them of the same
length. Additionally, SD_CLK needs ground shielding separately.
Trace length requirements:
⚫
Control the impedance to 50 Ω ±10 % and add ground shielding.
⚫
Keep the trace length difference among SD_CLK, SD_CMD and SD_DATA less than 2 mm.
Table 15: SD Card Trace Length Inside the Module
Pin No.
Signal
Length (mm)
39
SD_CLK
35.01
40
SD_CMD
35.12
41
SD_DATA0
34.98
42
SD_DATA1
35.04
43
SD_DATA2
34.98
