PCA9554

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5

SCL

SDA IN

SDA OUT

Pin Description

SCL: Serial Clock

The serial clock input clocks all data transferred into or out

of the device. The SCL line requires a pull−up resistor if it

is driven by an open drain output.

SDA: Serial Data/Address

The bidirectional serial data/address pin is used to transfer

all data into and out of the device. The SDA pin is an open

drain output and can be wire−ORed with other open drain or

open collector outputs. A pull−up resistor must be connected

can be calculated based on minimum and maximum values

from Figure 3 and Figure 4 (see Note).

A0, A1, A2: Device Address Inputs

These inputs are used for extended addressing capability.

When hardwired, up to eight PCA9554s may be addressed

on a single bus system. The levels on these inputs are

compared with corresponding bits, A2, A1, A0, from the

slave address byte.

Any of these pins may be configured as input or output.

Figure 5. When an I/O is configured as an input, the Q1 and

Q2 output transistors are off creating a high impedance input

with a weak pull−up resistor (typical 100 k

W). If the I/O pin

is configured as an output, the push−pull output stage is

enabled. Care should be taken if an external voltage is

applied to an I/O pin configured as an output due to the low

Supply Voltage

Bus Capacitance

4.8

4.4

4.0

3.6

3.2

2.8

2.4

2.0

0

0.5

1.0

1.5

2.0

2.5

400

350

300

200

150

100

50

0

0

1

2

3

4

6

7

8

5.2

5.6

250

5

tr max − 300 ns

NOTE:

loads between 200 pF and 400 pF, the pull−up device can be a current source (Imax = 3 mA) or a switched resistor circuit.