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A reference circuit for SD card interface is shown below.
SD_DATA2
SD_DATA3
SD_CMD
SD_CLK
SD_DATA0
SD_DATA1
SD_DET
Module
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
Pin No.
188
SG560D_Series_Hardware_Design
LDO18B_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
Signal
SD_CLK
SD_LDO9C
SD_LDO6C
R4
R5
R6
C1
D4
D5
D6
D7
4.7 μF
Length (mm)
49.18
Smart Module Series
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
C2
11
GND
12
33 pF
GND
13
GND
SD Card Connector
64 / 134
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