ZVN4525 ZVP4525 FMMT458 ZVN4525G ZVN4525Z ZVN4525E6 ZVP4525G ZVP4525Z ZVP4525E6

Issue 1 May 2001 Zetex High Voltage MOSFETS in Call Router Circuits A router is a device that receives data from a telephone line

Design Note 60 Issue 1 May 2001 Zetex High Voltage MOSFETS in Call Router Circuits A router is a device that receives data from a telephone line and decides which route the data should be sent. Routers are used extensively in computer networks. They are increasingly being used in devices installed on subscriber's premises to reduce the cost of calls. When used in this application the router performs the following functions: 1)Stops the dialed signals from reaching the telephone line. 2)Analyzes the dialed number and identifies the cheapest provider using stored data. 3)Regenerates and transmits the dialing signal with appropriate prefix denoting the best route. This note shows the use of Zetex high voltage MOSFETs in this application. The diagram below shows the ZVN4525 ZVN4525 in a call router circuit. With different drive circuits the complementary P-channel device ZVP4525 ZVP4525 may be used. Gyrator Z1 2 ZVN4525 ZVN4525 10M 1 BR 3 Phone Line 4 10M Z2 ZVN4525 ZVN4525 100K FMMT458 FMMT458 Gyrator 100K 100K Controller 100K FMMT458 FMMT458 Figure 1: Call router interface circuit 3 Design Note 60 Issue 1 May 2001 The FMMT458 FMMT458 devices are part of a comprehensive range of Zetex high voltage transistors that can be used to interface controllers to telephone lines. The circuit is symmetrical and will work when the polarity of the line connections is reversed. MOSFETs are used as the pass element to enable a signal path to be maintained continuously from the line to the telephone circuit through the body diode. Signals from the telephone to the line are controlled by the call router. The ZVN4525 ZVN4525 and ZVP4525 ZVP4525 250V MOSFET devices indicated in this design note are available in a variety of package outlines and full part numbers and short form details are provided in the table below. The Gyrator is a circuit that maintains a DC path between the telephone and the line while blocking any AC signals. The bridge BR ensures the correct polarity of the MOSFET gate signals. The zener diode pairs Z1 and Z2 provide gate protection for the MOSFETs. BVDSS ID PD V Device Type A VGS(th) Min Max V V W RDS(on) @2.4V Package ZVN4525G ZVN4525G 250 0.31 2.0 0.8 1.8 9.5 SOT223 ZVN4525Z ZVN4525Z 250 0.24 1.2 0.8 1.8 9.5 SOT89 ZVN4525E6 ZVN4525E6 250 0.23 1.1 0.8 1.8 9.5 SOT23-6 BVDSS ID PD RDS(on) @2.4V Package V A W Device Type VGS(th) Min Max V V ZVP4525G ZVP4525G 250 0.265 2.0 0.8 2.0 18 SOT223 ZVP4525Z ZVP4525Z 250 0.205 1.2 0.8 2.0 18 SOT89 ZVP4525E6 ZVP4525E6 250 0.197 1.1 0.8 2.0 18 SOT23-6 4