ADM2485

Preliminary Technical Data

APPLICATIONS INFORMATION

PC BOARD LAYOUT

The ADM2485 isolated RS-485 transceiver requires no external

interface circuitry for the logic interfaces. Power supply

bypassing is strongly recommended at the input and output

supply pins (see Figure ).

Bypass capacitors are most conveniently connected between Pin

The capacitor value should be between 0.01 µF and 0.1 µF. The

total lead length between both ends of the capacitor and the

input power supply pin should not exceed 20 mm.

Bypassing between Pin 1 and Pin 8 and between Pin 9 and Pin

16 should also be considered unless the ground pair on each

package side is connected close to the package.

D1

ADM2485

D2

B

RxD

A

RE

RTS

DE OUT

TxD

Figure 19. Recommended Printed Circuit Board Layout

In applications involving high common-mode transients, care

should be taken to ensure that board coupling across the isola­

tion barrier is minimized. Furthermore, the board layout should

be designed such that any coupling that does occur equally

affects all pins on a given component side.

Failure to ensure this could cause voltage differentials between

pins exceeding the device’s absolute maximum ratings, thereby

leading to latch-up or permanent damage.

APPLICATIONS DIAGRAM

The ADM2485 integrates a transformer driver which when

used with an external transformer and LDO generates an

Pins D1 and D2 of the ADM2485 drive a center-tapped

transformer T1, A pair of Schottky diodes and a smoothing

capacitor are used to create a rectified signal from the

provides a regulated 5V power supply to the ADM2485’s bus-

When the ADM2485 is powered by 3V on the logic side a

1CT:2.2CT transformer T1 is required to step up the 3V to 6V,

output a regulated 5V output.

If ADM2485 is powered by 5V on the logic side a 1CT:1.5CT

transformer T1 is required so that therefore is enough

output.

ISOLATION BARRIER

100nF

V

CC

ADP667

IN

OUT

GND

SET

SHDN

V

DD2

GND

2

V

DD1

GND

1

V

CC

1N5817

1N5817

22µF

+5V

T1

10µF

D1 D2

ADM2485

100nF

ISO 5V

Figure 20. Applications Diagram

Rev. PrK | Page 14 of 15