7 Detailed Description

7.1 Overview

The THVD1400 is a low-power, half-duplex RS-485 transceiver suitable for data transmission up to 500 kbps.

The THVD1420 is a low-power, half-duplex RS-485 transceiver suitable for data transmission up to 12 Mbps.

7.2 Functional Block Diagrams

R

D

DE

RE

B

A

GND

V

CC

7.3 Feature Description

Internal ESD protection circuits protect the transceiver against Electrostatic Discharges (ESD) according to IEC

61000-4-2 of up to ±12 kV (Contact Discharge), ±15 kV (Air Gap Discharge) and against electrical fast transients

(EFT) according to IEC 61000-4-4 of up to ±4 kV.

7.4 Device Functional Modes

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

D. A logic high at D causes A to turn high and B to turn low. In this case, the differential output voltage defined

as VOD = VA – VB is positive. When D is low, the output states reverse, B turns high, A 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 pull-down resistor to ground; thus, when left open, the driver is disabled (high-impedance) by

default. The D pin has an internal pull-up resistor to VCC, thus, when left open while the driver is enabled, output

A turns high and B turns low.

Table 7-1. Driver Function Table

INPUT

ENABLE

OUTPUTS

FUNCTION

D

DE

A

B

H

H

H

L

Actively drive bus high

L

H

L

H

Actively drive bus low

X

L

Z

Z

Driver disabled

X

OPEN

Z

Z

Driver disabled by default

OPEN

H

H

L

Actively drive bus high by default

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

defined as VID = VA – VB is positive and higher than the positive input threshold, VIT+, the receiver output, R,

turns high. When VID is 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).

www.ti.com

THVD1400, THVD1420

SLLSF78B – DECEMBER 2020 – REVISED OCTOBER 2021

Copyright © 2021 Texas Instruments Incorporated

Submit Document Feedback

13

Product Folder Links: THVD1400 THVD1420