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SD_CMD
40
SD_DATA0
41
SD_DATA1
42
SD_DATA2
43
SD_DATA3
44
SD_DET
45
A reference circuit for SD card interface is shown as below.
SD_DATA2
SD_DATA3
SD_CMD
SD_CLK
SD_DATA0
SD_DATA1
SD_DET
Module
SD_LDO11 is a peripheral driver power supply for SD card. The maximum drive current is approx. 600mA.
Because of the high drive current, it is recommended that the trace width is 0.5mm or more. In order to
ensure the stability of drive power, a 2.2uF capacitor should be added in parallel near the SD card
connector.
CMD, CLK, DATA0, DATA1, DATA2 and DATA3 are all high-speed signal lines. In PCB design, please
control the characteristic impedance of them as 50Ω, and do not cross with other traces. It is
recommended to route the trace on the inner layer of PCB, and keep the same trace length for CLK, CMD,
DATA0, DATA1, DATA2 and DATA3. CLK additionally needs ground shielding.
Layout guidelines:
required.
SC20-WL_Hardware_Design
I/O
Command signal of SD card
I/O
High speed bidirectional
I/O
digital signal lines of SD
I/O
card
I/O
DI
SD card insertion detection
LDO5_1V8
R1
R2
R3
120K
NM_51K
NM_51K NM_10K NM_51K NM_51K
R7
33R
R8
33R
R9
33R
R10
33R
R11
33R
R12
33R
R13
1K
D1
D2
D3
Figure 17: Reference Circuit for SD Card Interface
Control impedance as 50Ω± 10%, and ground shielding is
The total trace length difference between CLK and other
Active low
SD_LDO11
SD_LDO12
R6
R4
R5
C1
D4
D5
D7
D6
2.2uF
Smart Wi-Fi Module Series
SC20-WL Hardware Design
1
P1-DAT2
2
P2-CD/DAT3
3
P3-CMD
4
P4-VDD
5
P5-CLK
6
P6-VSS
7
P7-DAT0
8
P8-DAT1
9
DETECTIVE
10
GND
D8
11
GND
12
GND
13
GND
SD card
connector
41 / 81
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