Application Note: AN-149 Increased LITELINK™ II Transmit Power AN-149-R03 www.ixysic.com 1 Application Note: AN-149 1. Introduction Some applications, such as voice computer telephony, require higher power transmission from the host equipment to the telephone network. This application note describes changes to the standard LITELINK II application circuits to provide the transmit gain needed for a particular application. Note: The recommended maximum drive level into the line from LITELINK II is 6 mA peak, which is equivalent to about +10 dBm into a 600 Ω load. Datasheet specifications for maximum current (IDDL) do not apply with higher than specified output power. LITELINK II will draw more current with higher output power. 3. Examples 3.1 PBX Example To meet +3.18 dBm into 900 Ω, use the following calculations: +3.18 dBm into 900 Ω = 1.935 VP. 1.935 V/1.1 V = 1.76. The calculations work out as follows: RZTX = 226 / 1.76 = 128.4 RZNT = 453 / 1.76 = 257 RNTF = 1M / 2.53 = 396683 2. Transmit Gain Design Procedure 1. Determine the peak transmit level needed for the application. 2. If necessary, convert the required peak transmit power into a voltage level. For example, 0 dBm into 600 Ω = 1.1 VP. 3. Calculate the required linear voltage gain AV by dividing the peak transmit voltage level from step 2 by 1.1. 4. Modify the following application circuit component vales: The closest standard resistor values are 127 Ω for RZTX, 255 Ω for RZNT, and 392 kΩ for RNTF. 3.2 +3 dBm into 600 Ohm Transmit Power Example The following application circuit uses component values determined by the design procedure above for +3 dBm transmit power into 600 Ω. Peak transmit power of +3 dBm into 600 Ω = 1.55 VP. 1.55/1.1 = 1.41. The calculations work out as follows: RZTX = 150 / 1.41 = 106.4 ZZTX ← ZZTX / AV RZNT = 301 / 1.41 = 213.5 ZZNT ← ZZNT / AV RNTF ← RNTF ((AV - 1)(RNTF / RNTS) + AV) RNTF = 1M / 1.82 = 549000 These calculations result in a transmit (4-wire to 2wire) gain of AV, and a receive gain (2-wire to 4-wire) of 1/AV. If necessary, the receive loss can be compensated with either the programmable input gain of a CODEC or with a discrete op-amp gain stage between the LITELINK RX output and the host system. AN-149-R03 Standard resistor values have been substituted in the circuit in Figure 1. www.ixysic.com 2 Application Note: AN-149 Figure 1. +3 dBm Application Circuit 3.3 or 5 V R23 10* C1 1 FB1 600 Ω 200 mA C16 10 C9 0.1 A U1 LITELINK II A 1 R1 (RTX) 80.6K 1% 2 C13 0.1 3 TX- C2 0.1 TX+ 4 5 6 7 8 OH REFL VDD TXSM TXF TX- ZTX TX+ ZNT TX TXSL REFB BR1- GND NTS OH GAT 9 RING 10 CID RING CID C14 0.1 11 RX12 RX+ C4 0.1 13 SNP+ 14 SNP- RXRX+ 15 RXF 16 RX A REFB DCS1 DCS2 ZDC BR2RPB RXS VDDL 32 31 C10 0.01 500V -BR R5 (RTXF) 49.9K 1% C15 0.01 500V 30 28 27 -BR Q1 CPC5602C R13 (RNTS) 1M 1% 29 R22 (RDCS1A) 6.8 M 1% R21 (RDCS1B) 6.2 M 1% 26 25 R14 (RGAT) 47 24 23 R12 (RNTF) 549 K 1% C12 (CDCS) 0.027 -BR 22 21 R15 (RDCS2) 1.69 M 1% R16 (RZDC) 8.2 1% 20 19 R20 (RVDDL) 2 -BR 18 + DB1 SIZB60 600V_60A 17 R2 (RRXF) 127K 1% R4 (RPB) 68.1 1% -BR Gain Setting R8 (RHTX) 200K 1% R9 (RHNT) 200K 1% R18 (RZTX) 107 1% -BR R10 (RZNT) 215 1% -BR - -BR TIP SP1 P3100SB 1 2 RING AC Termination Setting NOTE: Unless otherwise noted, all resistors are in Ohms, 5%. All capacitors are in microFarads. C7 (CSNP-) 220pF 2000V R3 (RSNPD) 1.5M 1% AN-149-R03 R6 (RSNP-2) 1.8M 1/10W 1% R44 (RSNP-1) 1.8M 1/10W 1% R7 (RSNP+2) C8 (CSNP+) 1.8M 1/10W 1% 220pF 2000V R45 (RSNP+1) 1.8M 1/10W 1% www.ixysic.com 3 Application Note: AN-149 4. LITELINK Design Resources 4.1 IXYS IC Division Design Resources 4.2 Third Party Design Resources The IXYS ICD web site has a wealth of information useful for designing with LITELINK, including application notes and reference designs that already meet all applicable regulatory requirements. LITELINK data sheets also contains additional application and design information. See the following links: The following also contain information useful for DAA designs. All of the books are available on www.amazon.com LITELINK datasheets and reference designs Newton’s Telecom Dictionary, Harry Newton, CMP Books; ISBN: 1578200695 Application note AN-107 LOCxx Series - Isolated Amplifier Design Principles Application note AN-112, Ground-start Supervision Circuit Using IAA110 Application note AN-114 ITC117P Application note AN-117 Customize Caller-ID Gain and Ring Detect Voltage Threshold for CPC5610/11 Understanding Telephone Electronics, Stephen J. Bigelow, et. al., Butterworth-Heinemann; ISBN: 0750671750 Photodiode Amplifiers: Op Amp Solutions, Jerald Graeme, McGraw-Hill Professional Publishing; ISBN: 007024247X Teccor, Inc. Surge Protection Products United States Code of Federal Regulations, CFR 47 Part 68.3 Application note AN-140, Understanding LITELINK Application note AN-146, Guidelines for Effective LITELINK Designs For additional information please visit our website at: www.ixysic.com IXYS Integrated Circuits Division makes no representations or warranties with respect to the accuracy or completeness of the contents of this publication and reser t descriptions at any time without notice. Neither circuit patent licenses nor indemnity are expressed or implied. Except as set forth in IXYS Integrated Circuits Division’s Standard Terms and Conditions of Sale, IXYS Integrated Circuits Division assumes no liability whatsoever, and disclaims any express or implied warranty, relating to its products including, but not limited to, the implied warranty of merchantability or a particular purpose, or infringement of any intellectual property right. The products described in this document are not designed, intended, authorized or warranted for use as components in systems intended for surgical implant into the body, or in other applications intended to support or sustain life, or where malfunction of IXYS Integrated Circuits Division’s product may result in direct physical harm, injury, or death to a person or severe property or environmental damage. IXYS Integrated Circuits Division reserves the right to discontinue or make changes to its products at any time without notice. Specification: AN-149-R03 ©Copyright 2014, IXYS Integrated Circuits Division All rights reserved. Printed in USA. 4/14/2014 AN-149-R03 www.ixysic.com 4