3Jtech uModem Technical Document page 12

APPENDIX_A DESIGN CONSIDERATION
How to enhance the over-current/over-voltage protection and RF noise
immunity
The use of silicon DAA makes it possible to design the analog front end of a modem without an isolation
transformer, relays and hybrid. This solution also adopts the latest silicon DAA technology which is a
software-programmable DAA, enabling the designers to have a single worldwide solution for various PTT
certifications. ZyDAS USB modem solution takes advantage of Si3034, Silicon Lab's silicon DAA, as the
default design. However, ZyDAS also provides two reference circuit designs based on Si3034 to
enhance the over-current / over-voltage protection and RF noise immunity. Please note that the inductors
L1, L2, L3 and L4 must be located beside the sidactor RV1 shown below. The rating current of L1, L2, L3
and L4 must be 200 mA. The rating voltage of C1 and C3 must be 3 KV. The rating voltage of C2 is 300
V.
P1B
B1
1
B2
2
B3
3
B4
LINE
4
B5
5
B6
6
RJ11/6P4C
P1B
B1
1
B2
2
B3
3
B4
LINE
4
B5
5
B6
6
RJ11/6P4C
2003/6 From 3JTech
L1 470uH 200mA
RV1
TVB270SC
L2 470uH 200mA
RV2
TVB270SC
L1 470uH 200mA
RV1
TVB270SC
L2 470uH 200mA
RV3
TVB270SC
Revision 1.0
L3 470uH 200mA
C2
15nF
300V
L4 470uH 200mA
Research & Development
C1
1000PF
3KV 10%
C3
1000PF
3KV 10%
C1
1000PF
3KV 10%
C3
1000PF
3KV 10%
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