SimCom SIM8905A User Manual page 29


External components should be located near the USB connector.

Should be routed away from sensitive circuits and signals.

If there are test points, place them on the trace to keep branches as short as possible

If USB connector is used as the charger input, USB_VBUS node must be routed to the module using
extremely wide traces or sub planes.
Refer to the following table for the length of USB traces inside the module.
Table 17: Length of USB traces inside the module
Pin#
13 USB_DM
14 USB_DP
SDC Signal

Protect other sensitive signals/circuits from SDC corruption.

Protect SDC signals from noisy signals (clocks, SMPS, etc.).

Up to 200 MHz clock rate
50 Ω nominal, ±10% trace impedance


CLK to DATA/CMD length matching < 1 mm
30–35 Ω termination resistor on clock lines near the module


Total routing length < 50 mm recommended

Spacing to all other signals = 2x line width

Bus capacitance < 15 pF
Refer to the following table for the length of SD traces inside the module.
Table 18: Length of SD traces inside the module
Pin#
39 SD_CLK
40 SD_CMD
41 SD_DATA0
42 SD_DATA1
43 SD_DATA2
44 SD_DATA3
Audio
Analog input

4 to 5 mil trace widths; 4 to 5 mil spacing between traces

Differential route for MIC1P with GND_MIC and MIC2P with GND_MIC;

Isolate from noise sources, such as antenna, RF signals, SMPS, clocks, and other digital signals with fast
Net Name
Net Name
29
Smart Machine Smart Decision
Length(mm)
30.58
30.22
Length(mm)
14.24
15.19
14.87
13.63
12.90
13.05