N720 OpenLinux
Hardware User Guide
Copyright © Neoway Technology Co., Ltd
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2.85V, connect to VCC of the SD card. If the IO is 1.8V, connect to the VDD_1P8 pin of the
module.
The recommended supply voltage of VCC ranges 2.85V to 3.0V and current is larger than 500
mA. An LDO or DC-DC is recommended.
Connect a resistor of 15Ω to 24Ω to SDC_CLK in series.
The SD card detection function is implemented by the interrupt, which is triggered by level
change at the SDC_DET pin after an SD card is installed in the card connector. As shown in
Figure 3-21, SDC_DET is left floating before an SD card is inserted and grounded after an SD
card is inserted, and the level at SDC_DET changes from high to low.
Add an ESD protector of lower than 10 pF to each pin. ESD protection diode array is an option.
In Figure 3-21, ESD1 and ESD2 consist of four same ESD protectors.
PCB Design Guidelines
Place ESD protectors close to SD connector. The pin numbers of ESD arrays can be adjusted in
actual applications.
The trace of power supply should be wider than 0.5 mm.
Place the resistor on the CLK line close to the module.
Control the length difference of DATA, CMD, and CLK signal traces to 1 mm.
Keep the total length of DATA, CMD, and CLK signal traces to 40 mm.
Spacing between CMD, CLK, and DATA traces should be larger than 2 times trace width.
Spacing between CMD, CLK, and DATA traces and other signal traces should be larger than 2
times trace width.
Control the impedance for CMD, CLK, and DATA traces to 50Ω individually.
For the timing of the SDC interface in SDR and DDR mode, see Figure 3-22 and Figure 3-23. For
parameter values for the SD interface, see Table 3-4.
Figure 3-22 SDC SDR timing
SDC_CLK
Read
Write
t(pddwr)
t(pdcwr)
t(cdvrd)
t(dvrd)
t(csurd)
t(dsurd)
t(chrd)
t(dhrd)