MCU

Via to ground

SN65HVD33

R

R

C

5

6

6

4

R

5

R

R

7

R

R

7

5

R

1

TVS

5

R

1

TVS

5

SN65HVD30-EP, SN65HVD31-EP, SN65HVD32-EP

SN65HVD33-EP, SN65HVD34-EP, SN65HVD35-EP

www.ti.com

SGLS367E – SEPTEMBER 2006 – REVISED SEPTEMBER 2015

11 Power Supply Recommendations

To ensure reliable operation at all data rates and supply voltages, each supply must be decoupled with a

100-nF ceramic capacitor located as close as possible to the supply pins. This helps to reduce supply voltage

ripple present on the outputs of switched-mode power supplies and also helps compensate for the resistance

and inductance of the PCB power planes.

12 Layout

12.1 Layout Guidelines

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

against EFT and surge transients that can occur in industrial environments. Because these transients have a

wide frequency bandwidth (from approximately 3 MHz to 3 GHz), high-frequency layout techniques must be

applied during PCB design.

•

Place the protection circuitry close to the bus connector to prevent noise transients from entering the board.

•

inductance and not the path of least impedance.

•

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

divert from the signal path to reach the protection device.

•

controller ICs on the board.

•

minimize effective via inductance.

•

Use 1-k

Ω to 10-kΩ pullup or pulldown resistors for enable lines to limit noise currents in these lines during

transient events.

•

Insert series 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.

•

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

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

blocking units (TBUs) that limit transient current to 200 mA.

12.2 Layout Example

Figure 32. SN65HVD33-EP Layout Example

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