### Application Note: AN-157 Increased LITELINK™ III Transmit Power

```Application Note: AN-157
Transmit Power
AN-157-R04
www.ixysic.com
1
Application Note: AN-157
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 III
application circuits to provide the transmit gain needed
for a particular application.
R NTF <
5. Use the values from step 4 in the following formulas to solve for the new RNTX and RHTX values:
Note: The recommended maximum drive level into the
line from LITELINK III is 6 mA peak, which is
Datasheet specifications for maximum line-side
current draw (IDDL) do not apply with higher-thanspecified output power. Minimum line operating
current is defined as follows:
0.625V + 5.5mA
I MIN = -----------------------------R ZTX || R ZNT
Where RZNT is the resistive component of ZZNT.
Higher transmit signal levels may require a higher dc
bias level on the loop to meet peak voltage
requirements and avoid signal compression. The
value of RDCS2 may be reduced to increase the dc
loop bias level if necessary. See AN-158, LITELINK
III Application Circuit Calculations for more
information.
R NTF
-----------AV
(
(•
(
(•
R ZNT
R NTX = 1 + --------------2R ZTX
R ZNT
R HTX = 1 + -----------R ZTX
R NTF
------------2
200kΩ
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.
3. Examples
3.1 PBX Example
To meet +3.18 dBm into 900 Ω, use the following
calculations:
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 values:
+3.18 dBm into 900 Ω = 1.935 VP.
1.935 V/1.1 V = 1.76.
The calculations work out as follows:
Z ZNT < Z ZNT ⁄ A V
AN-157-R04
www.ixysic.com
R ZNT = 453 ⁄ 1.76 = 256.9
R NTF = 499kΩ ⁄ 1.76 = 282938
The closest standard resistor values are
255 Ω for RZNT and 280 kΩ for RNTF. Use
these values to find for RNTX and RHTX as
follows:
2
Application Note: AN-157
255
R NTX = 1 + -----------6640
(
( • 140000 = 145.38kΩ
(
( • 200000 = 215.36kΩ
255
R HTX = 1 + -----------3320
The closest standard resistor values are
147 kΩ for RNTX, and 215 kΩ for RHTX.
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 = 1.4. The calculations work out as follows:
R ZNT = 301 ⁄ 1.4 = 215
R NTF = 499kΩ ⁄ 1.4 = 356429
The closest standard resistor values are
215 Ω for RZNT and 357 kΩ for RNTF. Use
these values to find for RNTX and RHTX as
follows:
(
( •178500 = 184.28kΩ
(
( • 200000 = 212.95kΩ
215
R NTX = 1 + -----------6640
215
R HTX = 1 + -----------3320
Standard resistor values have been substituted in the
circuit in Figure 1.
AN-157-R04
www.ixysic.com
3
Application Note: AN-157
Figure 1. +3 dBm Application Circuit
3.3 or 5 V
R23²
10
C1
1
FB1
600 Ω
200 mA
C16
10
C9
0.1
A
U1
A
1
R1 (RTX) 80.6K 1%
2
C13 0.1
3
TX-
C2 0.1
TX+
4
5
6
7
8
OH
VDD
REFL
TXSM
TXF
TX-
ZTX
TX+
ZNT
TX
TXSL
MODE
BR-
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
C10
0.01
500V
BR-
NTF
DCS1
DCS2
ZDC
BRRPB
RXS
VDDL
R2
(RRXF)
130K
1%
32
31
R5 (RTXF)
60.4K
1%
C15
0.01
500V
30
29
28
27
25
24
R12 (RNTF) 357K 1%
22
R15 (RDCS2)
1.69M 1%
21
20
R16 (RZDC) 8.2 1%
19
R76 (RHNTF)
200K 1%
18
R21 (RDCS1B)
6.2 M 1%
C12 (CDCS)
0.027
C21 (CGAT) 100 pF
BR-
R20
(RVDDL)
2
BR-
+ DB1
17
R4
(RPB)
68.1
1%
BR-
R18
(RZTX)
3.32 K
1%
R8 (RHTX)
215K 1%
TIP
-
SP1¹
1
BR-
C18
15 pF³
BR-
R10
(RZNT)
215
1%
BR-
2
RING
NOTE: Unless otherwise
noted, all resistors are in
Ohms, 5%. All capacitors
C7
(CSNP-)
220pF
2000V
R3
(RSNPD)
1.5M
1%
R22 (RDCS1A)
6.8 M 1%
R14
(RGAT)
47
26
23
BR-
Q1
CPC5602C
R13
(RNTS)
1M
1%
R75 (RNTX)
182K 1%
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%
gain. It must be noted, however, that increasing
corresponding amount. For instance, increasing
transmit power to +3 dBm results in receive gain of -3
dB. This difference can be accounted for by adding a 6
dB gain block between the RX+/RX- pins and the host
circuitry, but can be adjusted using CODEC gain (for
CODEC applications).
5.1 Design Resources
www.ixysic.com 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
Application note AN-117 Customize Caller-ID Gain
and Ring Detect Voltage Threshold
AN-157-R04
www.ixysic.com
4
Application Note: AN-157
Application note AN-146, Guidelines for Effective
Design Conversion
Display Feature Signal Routing and Applications
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-157-R04