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DS2290

T1 Isolation Stik

Dallas Semiconductor -> Maxim Integrated 

DS2290

OVERVIEW

The DS2290 contains all the isolation and surge protec-

tion required to connect equipment to T1 lines. The Iso-

lation Stik has a receive and a transmit section. (See

Figure 1.) In the receive section, inputs RXTIP and

RXRING are connected directly to the receive T1

twisted pair. These inputs are terminated at 100 ohms.

The T1 signal received at RXTIP and RXRING is

coupled through a 2:1 transformer and presented at the

RX+ and RX– outputs. See Figure 2. There is a full

1500 volts of isolation between the Network Side pins

and the Customer Side pins.

In the transmit section, data that is to be transmitted is

sourced from either the TPOS and TNEG inputs or the

LPOS and LNEG inputs. The Data Mux will transmit

data at the TCLK rate from the TPOS and TNEG inputs if

the LB pin is either tied low or left open. It will transmit

data at the LCLK rate from the LPOS and LNEG inputs if

the LB pin is tied high. In order to comply with the latest

T1 standards, the clock presented at either TCLK or

LCLK must be at a 1.544 MHz rate (±32 ppm) and must

not jitter beyond 0.05 unit intervals peak–to–peak

(UIpp). TPOS and TNEG can be tied together if the

source of the transmit data is in a NRZ format. The

DS2290 will automatically sense that these inputs are

tied together and will create a bipolar data stream from

them. The same holds true for the LPOS and LNEG in-

puts.

Data out of the Data Mux is passed to a B8ZS encoder

and AIS generator. If the B8ZS pin is tied high, then the

DS2290 will properly encode the transmit data stream

for the B8ZS zero code suppression scheme. If the

B8ZS pin is tied low or left open, the DS2290 will not en-

code the transmit data for B8ZS. Also, the DS2290 can

be configured to transmit an AIS (Alarm Indication Sig-

nal). If the TAIS pin is tied high, the DS2290 will transmit

an unframed, all ones signal at either the TCLK (LB=0 )

or LCLK (LB=1) rate.

The data to be transmitted is fed to the line driver. The

line driver creates the T1 pulse that will be transmitted.

The line build out pins LB0 to LB2 select whether the

output pulse level will be 0, –7.5, or –15 dB (see Table

3). If 0 dB of build out is selected, the output pulse will

conform to the shape described in Figure 2. This pulse

shape is congruent with the latest T1 specifications

such as TR 62411 and T1.403–1989. If the –7.5 dB or

–15 dB line build outs are selected, then the pulse

shown in Figure 3 will be attenuated according to the

transfer function as described in FCC Part 68, Subpart

D. Once the T1 pulse has been created, it is then trans-

mitted onto the transmit T1 twisted pair via the TTIP and

TRING outputs.

The DS2290 contains provisions for line powering. If

the DS2290 is to be powered from the T1 line using a DC

simplex power arrangement, then an external DC–to–

DC converter can connected to the LPWR+ and LPWR–

pins. Requirements for line powering are currently be-

ing relaxed and will be totally removed in the future. If

the DS2290 is not line powered, the LPWR+ and

LPWR– pins should be tied together.

Figure 4 shows a typical application using the DS2290.

The transmit and receive T1 twisted pairs are connected

directly to the DS2290. The DS2291 T1 Long Loop Stik

recovers clock and data from the protected signal pro-

vided by the Isolation Stik. The DS2180A T1 Transceiv-

er frames to the recovered data and interfaces to the

system backplane. The DS2250 Soft Microcontroller

Stik is used to control and monitor the status of the other

devices.

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