PROJECT
TITLE
Radom.XIANG
CHECKED BY
Mountain.ZHOU
DRAWN BY
OF
A
6
5
4
32
1
SHEET
A
B
C
D
123456
D
C
B
Quectel Wireless Solutions
SIZE
VER
84
1.0
DATE
2015/3/30
EC20 Reference Design
A2
1. R401~R403 are applied to suppress the EMI spurious transmission
Notes:
2. R404 can improve anti-jamming capability of the USIM circuit, and
USIM and UART Design
and enhance the ESD protection.
it should be placed close to the USIM connector.
UART Translation IC Solution
UART Transistor Solution (Recommend)
3. VCCA should not exceed VCCB. For more information about TXS0108E,
please refer to the datasheet from TI.
4. If you need to enable high baud rate, it is highly recommended to install
a 1nF capacitor (C407/C408) on transistor circiut.
USIM and UART Design
5. The DTR transistor circuit is similar with RTS interface, and the RI and DCD
transistor circuit is similar with CTS interface.
C401
100nF
1
2
3
4
5
6
U401
ESDA6V8AV6
C403
33pF
C404
33pF
C402
33pF
R401
22R
R402
22R
R403
22R
R404
15K
GND
VPP
I/OCLK
RST
VCC
J401
C405
100nF
R406
120K
R405
10K
C406
100nF
Q401
2SC4617TLQ
Q402 2SC4617TLQ
R408
4.7K
R407
4.7K
C407
1nF
R409
4.7K
R410
4.7K
C408
1nF
Q403
2SC4617TLQ
R412
4.7K
R411
4.7K
Q404
2SC4617TLQ
R413
4.7K
R414
4.7K
6
A5
7
A6
8
A7
9
A8
10
OE
5
A4
4
A3
19
VCCB
20
B1
18
B2
14
B6
13
B7
12
B8
11
GND
3
A2
2
VCCA
1
A1
17
B3
16
B4
15
B5
U402
TXS0108E
USIM_VDD
[1]
USIM_RST
[1]
USIM_CLK
[1]
USIM_DATA
USIM_VDD
[1]
USIM_GND
VDD_EXT
VDD_EXT
VDD_MCU
[1,4]
TXD_EC20
[1,4]
RXD_EC20
[1]
RI_EC20
[1]
DTR_EC20
[2,4]
RXD_MCU
[2,4]
TXD_MCU
[2]
DTR_MCU
[2]
RI_MCU
[2,4]
TXD_MCU
[1,4]
RXD_EC20
VDD_EXTVDD_EXT
[2,4]
RXD_MCU
[1,4]
TXD_EC20
VDD_EXTVDD_MCU
VDD_EXT
[1,4]
RTS_EC20
[2,4]
RTS_MCU
VDD_EXT
VDD_MCU
[2,4]
CTS_MCU
[1,4]
CTS_EC20
VDD_EXT
[2,4]
CTS_MCU
[2,4]
RTS_MCU
[1,4]
CTS_EC20
[1,4]
RTS_EC20
[1]
DCD_EC20
[2]
DCD_MCU
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