Datasheet

AD8531/AD8532/AD8534
Rev. F | Page 16 of 20
DIRECT ACCESS ARRANGEMENT FOR TELEPHONE
LINE INTERFACE
6.2V
6.2V
TRANSMIT
TxA
RECEIVE
RxA
C1
0.1µF
R1
10kΩ
R2
9.09kΩ
2kΩ
P1
Tx GAIN
ADJUST
A1
A2
A3
A4
A1, A2 = 1/2 AD8532
A3, A4 = 1/2 AD8532
R3
360Ω
1:1
T1
T
OTELEPHONE
LINE
1
2
3
7
6
5
2
3
1
6
5
7
10µF
R7
10kΩ
R8
10kΩ
R5
10kΩ
R6
10kΩ
R9
10kΩ
R14
14.3kΩ
R10
10kΩ
R11
10kΩ
R12
10kΩ
R13
10kΩ
C2
0.1µF
P2
Rx GAIN
ADJUST
2kΩ
Z
O
600Ω
5V DC
MIDCOM
671-8005
01099-046
Figure 46 illustrates a 5 V only transmit/receive telephone line
interface for 600 Ω transmission systems. It allows full duplex
transmission of signals on a transformer-coupled 600 Ω line in
a differential manner. A1 provides gain that can be adjusted to
meet the modem output drive requirements. Both A1 and A2
are configured to apply the largest possible signal on a single
supply to the transformer. Because of the high output current
drive and low dropout voltage of the AD8531/AD8532/AD8534,
the largest signal available on a single 5 V supply is approximately
4.5 V p-p into a 600 Ω transmission system. A3 is configured as
a difference amplifier for two reasons: it prevents the transmit
signal from interfering with the receive signal, and it extracts
the receive signal from the transmission line for amplification
by A4. The gain of A4 can be adjusted in the same manner as
that of A1 to meet the input signal requirements of the modem.
Standard resistor values permit the use of single in-line package
(SIP) format resistor arrays.
Figure 46. Single-Supply Direct Access Arrangement for Modems