MCU

Via to ground

THVD1500

R

R

R

C

5

6

1

4

R

5

Via to VCC

TVS

5

6

20

THVD1500

SLLSEY4A – JULY 2017 – REVISED NOVEMBER 2018

www.ti.com

Product Folder Links: THVD1500

Submit Documentation Feedback

Copyright © 2017–2018, Texas Instruments Incorporated

11 Layout

11.1 Layout Guidelines

Robust and reliable bus node design often requires the use of external transient protection devices in order to

protect against surge transients that may occur in industrial environments. Since these transients have a wide

frequency bandwidth (from approximately 3 MHz to 300 MHz), high-frequency layout techniques should be

applied during PCB design.

1. Place the protection circuitry close to the bus connector to prevent noise transients from propagating across

the board.

2. Use VCC and ground planes to provide low inductance. Note that high-frequency currents tend to follow the

path of least impedance and not the path of least resistance.

3. Design the protection components into the direction of the signal path. Do not force the transient currents to

divert from the signal path to reach the protection device.

4. Apply 100-nF to 220-nF bypass capacitors as close as possible to the VCC pins of transceiver, UART and/or

controller ICs on the board.

5. Use at least two vias for VCC and ground connections of bypass capacitors and protection devices to

minimize effective via inductance.

6. Use 1-kΩ to 10-kΩ pullup and pulldown resistors for enable lines to limit noise currents in theses lines during

transient events.

7. Insert pulse-proof resistors into the A and B bus lines if the TVS clamping voltage is higher than the specified

maximum voltage of the transceiver bus pins. These resistors limit the residual clamping current into the

transceiver and prevent it from latching up.

8. While pure TVS protection is sufficient for surge transients up to 1 kV, higher transients require metal-oxide

varistors (MOVs) which reduce the transients to a few hundred volts of clamping voltage, and transient

blocking units (TBUs) that limit transient current to less than 1 mA.

11.2 Layout Example

Figure 24. Layout Example