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STF202-22

USB Filter with ESD Protection

ON Semiconductor 

STF202–22

As previously mentioned, there are two types of

configurations for the USB port which are upstream and

downstream. If your port connects to the host either in a

direct way or through a hub, you are upstream (data flows

“up” to the host) and in the other hand, if you are the host or

your port provides access to the host then you are

downstream (data flows “down” from the host to the

device). In the case of the STF202 device, it provides

upstream termination. The Figure 7 represents the

termination for an upstream USB port.

VCC

Rpu

RS

C

C

RS

Figure 7.

The USB Line termination is reached through the series

resistors placed in the D+ and D– lines. These resistors

insure the proper termination to maintain the integrity of the

signal. The Pull up Resistor of 1.5 kW on either the D+ or D–

data lines is used to identify the equipment as either

full–speed or low–speed device.

Connection for Full–Speed

and Low–Speed Devices

As mentioned before, there are two kinds of port devices:

Full–Speed devices – operates in 12 Mb/s

Low–Speed devices that work in 1.5 Mb/s

The STF202 device can be shaped to be used for either

Full–Speed or Low–Speed devices which is achieved as

described below:

Full–Speed Devices

The Pull up resistor (Rpu) is connected to the D+ Line.

The terminal 1 is connected to the Voltage Supply Line

(VBUS) while the terminal 6 is connected to ground. The

input of the D+ line is connected in the terminal 3 which

outputs from the terminal 4. Finally, the input of the D– line

is connected in the terminal 2 which outputs from the

terminal 5. The Figure 8 shows the connections of the

STF202 device for “Full–Speed devices”.

3.3 V

Peripheral

1

6

D–

2 STF202 5

D+

3

4

USB

Controller

D–

D+

GND

Figure 8.

Low–Speed Devices

The Pull up resistor (Rpu) is connected to the D– Line. The

terminal 1 is connected to the Voltage Supply Line (VBUS)

while the terminal 6 is connected to ground. The input of the

D– line is connected in the terminal 3 which outputs from the

terminal 4. Finally, the input of the D+ line is connected in

the terminal 2 which outputs from the terminal 5. The Figure

9 shows the connections of the STF202 device for

“Low–Speed devices”.

3.3 V

Peripheral

USB

1

6

Controller

D+

2 STF202 5

D+

D–

3

4

D–

GND

Figure 9.

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