USS820FD datasheet(49/56 Pages) AGERE

49 / 56 page

Agere Systems Inc.

Data Sheet, Rev. 1

August 2004

USB Device Controller

USS-820FD

Electrical Characteristics (continued)

Connection Requirements

USB Transceiver Connection

The physical connection of the USS-820FD to the USB

bus requires only minimal components to provide

proper USB electrical terminations.

Both DPLS and DMNS require 24

Ω ± 1% series resis-

tors for USB impedance matching. Additionally, a

1.5 k

Ω pull-up resistor is required on DPLS for full-

speed/low-speed differentiation.

5-8119

Figure 8. USB Transceiver Connection

Example for Bus-Powered

Application

When using the USS-820FD in a self-powered device,

there are some additional considerations. The device

must refrain from supplying power through the pull-up

resistor if plugged into an unpowered bus. It must also

ensure that the DPLS and DMNS lines are in an appro-

priate state when the device is powered but not

plugged in. Figure 9 shows an example connection to

meet these requirements.

5-8120

Figure 9.

USB Transceiver Connection

Example for Self-Powered

Application

+3.3 V

± 0.3 V

DPLS

DMNS

1.5 k

Ω

± 5%

Ω ± 1%

DPLS

DMNS

Ω ± 1%

+3.3 V

± 0.3 V

1.5 k

Ω ± 5%

1.5 M

Ω

CLOSE SWITCH ONLY WHEN

VBUS IS POWERED

1.5 M

Ω

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