20

I

(mA)

MC

0.1

15

5

10

R

(k )

RIS

W

0

Typical

V

= Voltage on pin RIS

R

= Programming resistor

I

= Programmable current

I

= Modulation current

I

= Modulation supply current (220 µA typ)

RIS

RIS

CS3

MC

MS

R

=

RIS

=

V

RIS

I

CS3

V

RIS

I

– I

MC

MS

0.2

0.5

1

BR

VB

BUSL1

GND

BUSL2

I

CS3

R

RIS

RIS

CS3

TC4

RX

RXI

I

MS

V

= Constant

BUS

I

MC

I

SPACE

I

MARK

V

I

BUS

BUS

V

RXI

V

RX

I

BUS

to IC

I

= I

+ I

MC

MS

CS3

TSS521

SLAS980 – SEPTEMBER 2013

www.ti.com

Data Transmission, Slave to Master

The device uses current modulation to transmit information from the slave to the master while the bus voltage

remains constant. The current source CS3 modulates the bus current and the master detects the modulation.

The constant current source CS3 is controlled by the inverted input RXI or the noninverted input RX. The current

source CS3 can be programmed by an external resistor RRIS. The modulation supply current IMS flows in addition

to the current source CS3 during the modulation time.

Figure 2. Data Transmission, Slave to Master

Because the TSS521 is configured for half-duplex only, the current modulation from RX or RXI is repeated

concurrently as ECHO on the outputs TX and TXI. If the slave, as well as the master, is trying to send

information on the lines, the added signals appear on the outputs TX and TXI, which indicates the data collision

to the slave (see ).

The bus topology requires a constant current consumption by each connected slave.

To calculate the value of the programming resistor RRIS, use the formula shown in Figure 3.

Figure 3. Calculate Programming Resistor RRIS

4

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