Usb Interface - SimCom SIM808 Hardware Design

Note: The recommend Transistors' part numbers are 2SC4617TLR and PBHV8115Z. when update firmware via the TXD/RXD
circuit as figure 25 and figure 26 shows, customer should make sure the VDD_EXT has voltage output, or a external LDO should
be added to power VDD_EXT.
4.6.3

USB Interface

USB interface supports software debug function. When power on the module, connect VBUS, USB_DP,
USB_DM and GND to PC, then install the driver successfully, a UART port could be recognized by the PC,
customer could achieve the software Debug purpose with this UART port.
The following diagram is recommended:
The maximum allowable cap load of TVS on USB data line should be less than 5pF (e.g. ESD9L5.0ST5G and
ESD9M5.0ST5G). The USB_DP and USB_DM should be routed in differential traces.
Note: please reserve the USB interface or test point for debug.
Table 12: Serial port characteristics
Pin
VBUS
SIM808_Hardware Design_V1.00
VDD_EXT
Module
VDD_EXT
RXD
Figure 26: RX level converting by transistor
Figure 27: USB reference circuit
Min Typ
4.3 5
Customer
MCUVDD
47K
MCUTXD
Max
7
34
Smart Machine Smart Decision
Unit
V
2014.03.27