DE

5

D

6

R

3

4

RE

Y

Z

B

A

14

11

12

13

ISO35x

ISO15x

D

R

B

A

13

12

DE

6

5

3

4

RE

ISO15, ISO35, ISO15M, ISO35M

www.ti.com

SLOS580G – MAY 2008 – REVISED MARCH 2015

9 Detailed Description

9.1 Overview

The ISO15 and ISO15M are isolated half-duplex differential line drivers and receivers while the ISO35 and

ISO35M are isolated full-duplex differential line transceivers for TIA/EIA 485/422 applications. They are rated to

provide galvanic isolation of up to 2500 Vrms for 60 sec as per the standard. They have active-high driver enables

and active-low receiver enables to control the data flow.

When the driver enable pin, DE, is logic high, the differential outputs Y and Z follow the logic states at data input

D. A logic high at D causes Y to turn high and Z to turn low. In this case the differential output voltage defined as

VOD = V(Y) – V(Z) is positive. When D is low, the output states reverse, Z turns high, Y becomes low, and VOD is

negative. When DE is low, both outputs turn high-impedance. In this condition the logic state at D is irrelevant.

The DE pin has an internal pulldown resistor to ground, thus when left open the driver is disabled (high-

impedance) by default. The D pin has an internal pullup resistor to VCC, thus, when left open while the driver is

enabled, output Y turns high and Z turns low.

When the receiver enable pin, RE, is logic low, the receiver is enabled. When the differential input voltage

defined as VID = V(A) – V(B) is positive and higher than the positive input threshold, VIT+, the receiver output, R,

turns high. When VID is negative and less than the negative and lower than the negative input threshold, VIT– ,

the receiver output, R, turns low. If VID is between VIT+ and VIT– the output is indeterminate. When RE is logic

high or left open, the receiver output is high-impedance and the magnitude and polarity of VID are irrelevant.

Internal biasing of the receiver inputs causes the output to go failsafe-high when the transceiver is disconnected

from the bus (open-circuit), the bus lines are shorted (short-circuit), or the bus is not actively driven (idle bus).

9.2 Functional Block Diagrams

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Product Folder Links: ISO15 ISO35 ISO15M ISO35M