USB 2.0 Hi-Speed Differential

8:1 Multiplexer

8

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Applications Information

Increasing USB Channels

The MAX4999 features an enable input that allows two

MAX4999s to be connected, allowing multiplexing

between 16 USB channels. Figure 4 shows the typical

application with a single USB common terminal multi-

plexed to eight channels (8:1). See the Eye Diagram -

Single graph in the

Typical Operating Characteristics.

Figure 5 shows two MAX4999 devices configured with

the USB common terminal multiplexed to 16 USB chan-

nels (16:1). See the Eye Diagram - Double graph in the

Typical Operating Characteristics. The MAX4999 was

designed to be symmetrical so that the two common

ports may be wired in parallel with very short wiring to

create a 16:1 configuration. When operating in 16:1 con-

figuration, interchange COM0 and COM1 on the second

device to reverse the D+ and D- pins. This minimizes

vias and crossovers (Figure 5).

USB Switching

The MAX4999 analog multiplexers are fully compliant

with the USB 2.0 specification. The low on-resistance

and low on-capacitance of the MAX4999 make it ideal

for high-performance switching applications.

Board Layout

Hi-Speed switches require proper layout and design pro-

cedures for optimum performance. Keep design-con-

trolled impedance PCB traces as short as possible.

Ensure that high-quality bypass ceramic capacitors

(X7R, X5R or better) are placed as close to the device as

possible and use large ground planes where possible.

GND

C0

EN

C1

C2

CONTROL

LOGIC

CHARGE

PUMP

MAX4999

COM1

MUX

D0 _1

D1 _1

D2 _1

D3 _1

D4 _1

D5 _1

D6 _1

D7 _1

COM0

MUX

D0 _0

D1 _0

D2 _0

D3 _0

D4 _0

D5 _0

D6 _0

D7 _0

Functional Diagram/Truth Table

X = DON’T CARE

MAX4999

EN

C2

C1

C0

FUNCTION

1

0

0

0

COM_

→D0_ _

1

0

0

1

COM_

→D1_ _

1

0

1

0

COM_

→D2_ _

1

0

1

1

COM_

→D3_ _

1

1

0

0

COM_

→D4_ _

1

1

0

1

COM_

→D5_ _

1

1

1

0

COM_

→D6_ _

1

1

1

1

COM_

→D7_ _

0X

X

X

STANDBY MODE.

ALL SWITCHES IN HIGH-

IMPEDANCE STATE.

CHARGE PUMP IS OFF.