iC-VX

3-CHANNEL DIFFERENTIAL LINE DRIVER

Rev C1, Page 7/11

L=5m, CL=500pF

PLC

24V

Z

5V

B

A

BIAS

THERMAL SHUTDOWN

iC-VX

CHAN3

CHAN2

CHAN1

2k

2k

2k

C1

1µF

C2

1µF

VSUB

12

E2

2

E1

1

E3

7

PROG

5

VEE

4

VB2

8

NA1 14

A1 15

A2 13

NA2 11

A3 10

NA3 9

VB1

16

VT

6

VCC

3

Fig. 1: Balanced data transmission at low capacitive load, PROG pin open: I(A)

$ 30mA

f

200

kHz ×

500

pF

CL

×

24

V

VB

2

×

413

K

&T

a

70

K

×

75

K/W

R

thja

×

2

channels

(1.1)

f

30

mA

4×

VB×(CL

%1nF)

(1.2)

EXAMPLE 1: Short lines

Short lines of 5m, for example, are approximations of capacitive load for the iC; no adjustment of characteristic

impedance is required. With each switching slope changeover losses of Pc= 1/2 VB × I(A) per channel occur in

the iC. The load capacity is reloaded with the guaranteed driver current I(A)

$ 30mA. These changeover losses

determine the possible cut-off frequency, since the high chip power loss without cooling results in shutdown of

the iC. At high capacitive load the transmission rate can also be limited by the fall and rise times wich reduce the

signal strength.

As a typical application, Fig. 1 shows the transmission of the output signals of an incremental rotary encoder

(track A, track B, index pulse Z) to a programmable control (PLC). The maximum signal frequency which is

limited by the power loss can be estimated by standardizing the limiting values of the example for short lines:

If the slew-rate is the limiting factor, the following applies for the maximum signal frequency (saturation voltages

neglected):

CL

= Capacitive load at output A to output NA

VB

= Supply voltage

T

a

= Ambient temperature

R

thja

= Thermal resistance chip/board/ambient (R