Transformer Selection

The MXL1535E is a pin-for-pin compatible upgrade of

the LTC1535, making any transformer designed for that

device suitable for the MXL1535E (see Table 4). These

transformers all have a turns ratio of about 1:1.3CT.

The MAX3535E can operate with any of the transformers

listed in Table 4, in addition to smaller, thinner transform-

ers designed for the MAX845 and MAX253. The 420kHz

transformer driver operates with single primary and cen-

ter-tapped secondary transformers. When selecting a

transformer, do not exceed its ET product, the product of

the maximum primary voltage and half the highest period

of oscillation (lowest oscillating frequency). This ensures

that the transformer does not enter saturation. Calculate

the minimum ET product for the transformer primary as:

Using +5.5V and 290kHz gives a required minimum ET

Transceivers with ±15kV ESD Protection

20

______________________________________________________________________________________

TGM-250

1/2

BAT54C

TRANSFORMER

DRIVER

BARRIER

TRANSCEIVER

ISOLATION BARRIER

BARRIER

TRANSCEIVER

1/2

BAT54C

VOLTAGE

REGULATOR

GND2

+5V

DRIVER

RECEIVER

A

B

Y

Z

Y

Z

SLO

RO2

ST1

RO1

RO

RE

DE

DI

DI

GND1

ST2

0.1

µF

0.1

µF

CONTROL GROUND

RS-422 GROUND

10

µF

10

µF

MAX3535E

MXL1535E

MAX488

R

D

A

B

120

Ω

120

Ω

R

D

D

R

Figure 12. Using the MAX3535E/MXL1535E as an RS-422 Line Repeater

TRANSFORMER DRIVER OUTPUT STAGE

TRANSFORMER

PRIMARY

GND1

ST1

ST2

Figure 13. Transformer Driver Output Stage