PCA9646

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© NXP B.V. 2011. All rights reserved.

Product data sheet

Rev. 1 — 1 March 2011

13 of 22

NXP Semiconductors

PCA9646

Buffered 4-channel 2-wire bus switch

The PCA9646 may also be driven in series. Figure 17 shows this configuration. In this

scenario, each of the four outputs of the first device (U2) has six more PCA9646’s

connected to it. Each of those six devices has four outputs, thus giving

4

 7  4 = 112 outputs. If the RESET pin on U2 was also driven from the master, it would

be possible to reproduce this entire structure multiple times, giving a truly massive

address space capability. Such a configuration may be applied to situations such as

display drivers.

Fig 17. PCA9646 series implementation for large I/O fan-out

002aaf378

SCL

SCL

SDA

PCA9646

SC0

SC1

U2

RESET

5 V

R1

180

Ω

R2

180

Ω

A[2:0]

SD0

SD1

SC2

SC3

SD2

SD3

3

BUS

MASTER

U1

SCL

SDA

000b

up to seven PCA9646s

on each output pair

(address: 001b to 111b)

structure in

dashed box

repeated

etc.

R4

180

Ω

R3

180

Ω

SCL

SDA

PCA9646

SC0

SC1

U3

RESET

SD0

SD1

SC2

SC3

SD2

SD3

A[2:0]

3

001b

total output of

4

× 7 × 4 = 112

individually enabled

fully isolated buses,

each with full

capacitance load

(e.g., 400 pF at 1 MHz)

5 V

SCL

SDA

PCA9646

SC0

SC1

U4

RESET

SD0

SD1

SC2

SC3

SD2

SD3

A[2:0]

3

010b

connect, for example,

8 LED driver ICs,

each with 8 LED

outputs = 7168 LEDs

up to seven devices

(address: 001b to 111b)