GND

By-pass/De-coupling

capacitors

1

A0

2

A1

3

4

P0

5

P1

6

P2

7

P3

8

GND

9

P4

10

P5

11

P6

12

P7

13

14

SCL

15

SDA

16

VCC

RESET

INT

VIA to Power Plane

Power or GND Plane

VIA to GND Plane

LEGEND

V

CC

To I2C Master

28

TCA9538

SCPS199D – AUGUST 2014 – REVISED OCTOBER 2016

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Copyright © 2014–2016, Texas Instruments Incorporated

11 Layout

11.1 Layout Guidelines

For printed circuit board (PCB) layout of the TCA9538, common PCB layout practices must be followed but

additional concerns related to high-speed data transfer such as matched impedances and differential pairs are

not a concern for I2C signal speeds.

In all PCB layouts, it is a best practice to avoid right angles in signal traces, to fan out signal traces away from

each other upon leaving the vicinity of an integrated circuit (IC), and to use thicker trace widths to carry higher

amounts of current that commonly pass through power and ground traces. By-pass and de-coupling capacitors

are commonly used to control the voltage on the VCC pin, using a larger capacitor to provide additional power in

the event of a short power supply glitch and a smaller capacitor to filter out high-frequency ripple. These

capacitors must be placed as close to the TCA9538 as possible. These best practices are shown in Figure 32.

For the layout example provided in Figure 32, it would be possible to fabricate a PCB with only 2 layers by using

the top layer for signal routing and the bottom layer as a split plane for power (VCC) and ground (GND). However,

a 4 layer board is preferable for boards with higher density signal routing. On a 4 layer PCB, it is common to

route signals on the top and bottom layer, dedicate one internal layer to a ground plane, and dedicate the other

internal layer to a power plane. In a board layout using planes or split planes for power and ground, vias are

placed directly next to the surface mount component pad which needs to attach to VCC or GND and the via is

connected electrically to the internal layer or the other side of the board. Vias are also used when a signal trace

needs to be routed to the opposite side of the board, but this technique is not demonstrated in Figure 32.

11.2 Layout Example

Figure 32. TCA9538 Layout