ST USBUF01W6, USBUF02W6 User Manual

A. S. D.

EMI filter and line termination for USB upstream ports

Application

EMI Filter and line termination for USB upstream ports on:

■ USB Hubs

■ PC peripherals

Features

■ Monolithic device with recommended line

termination for USB upstream ports

■ Integrated Rt series termination and Ct

bypassing capacitors.

■ Integrated ESD protection

■ Small package size

USBUFxxW6

SOTT323-6L

Table 1. Order Codes

Part N umber Marking

USBUF01W6 UU1

USBUF02W6 UU2

Description

The USB specification requires upstream ports to be terminated with pull-up resistors from the D+ and D- lines to Vbus. On the implementation of USB systems, the radiated and conducted EMI should be kept within the required levels as stated by the FCC regulations. In addition to the requirements of termination and EMC compatibility, the computing devices are required to be tested for ESD susceptibility.

The USBUFxxW6 provides the recommended line termination while implementing a low pass filter to limit EMI levels and providing ESD protection which exceeds IEC 61000-4-2 level 4 standard. The device is packaged in a SOT323-6L which is the smallest available lead frame package (50% smaller than the standard SOT23).

Benefits

■ EMI / RFI noise suppression

■ Required line termination for USB upstream

ports

■ ESD protection exceeding

IEC 61000-4-2 level 4

■ High flexibility in the design of high density

boards

■ Tailored to meet USB 1.1 standard

Figure 1. Functional diagram

3.3 V

Grd

CODE 01 33 Ω 1.5 kΩ 47 pF

CODE 02 22 Ω 1.5 kΩ 47 pF

Tolerance ± 10% ± 10% ± 20%

Rt Rp Ct

3.3 V

Complies with the following standards:

IEC 61000-4-2, level 4 ± 15 kV (air discharge)

± 8 kV (contact discharge)

MIL STD 883E, Method 3015-7

Class 3 C = 100 pF R = 1500 Ω 3 positive strikes and 3 negative strikes (F = 1 Hz)

February 2006 Rev 5 1/11

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Characteristics USBUFxxW6

1 Characteristics

Table 2. Absolute ratings (T

Symbol Parameter Value Unit

amb

= 25° C)

ESD discharge IEC 61000-4-2, air discharge

ESD discharge IEC 61000-4-2, contact discharge ESD discharge - MIL STD 883E - Method 3015-7

Maximum junction temperature 150 °C

Storage temperature range - 55 to + 150 °C

stg

Lead solder temperature (10 second duration) 260 °C

Operating temperature range -40 to 70 °C

P Power rating per resistor 100 mW

2 Technical information

Figure 2. USB standard requirements

Full-speed or Low-speed USB Transceiver

Host or Hub port

15k

D+

D-

Twisted pair shielded

Zo = 90ohms

5m max

D+

D-

3.3V

1.5k

±16

±9

±25

Full-speed USB

Transceiver

Hub 0 or Full-speed function

FULL SPEED CONNECTION

Full-speed or Low-speed USB Transceiver

Host or Hub port

15k

D+

Untwisted unshielded

D-

LOW SPEED CONNECTION

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3m max

D+

D-

3.3V

1.5k

Low-speed USB

Transceiver

Hub 0 or Low-speed function

USBUFxxW6 Technical information

2.1 Application example

Figure 3. Implementation of ST solutions for USB ports

Downstream port

D+

Gnd

D-

Host/Hub USB por transceivert

Downstream port

D+

Gnd

D-

Host/Hub USB por transceivert

D+ in

Gnd

D- in

D+ in

Gnd

D- in

USBDF01W5

D+ out

D-

D- out

D+

D-

CABLE

D+

FULL SPEED CONNECTION

CABLE

D+

D+ out

D-

D- out

D+

D-

USBUF01W6

Upstream port

Gnd

3.3V

Gnd

3.3V

3.3 V

D+

Peripheral transceiver

D-

Upstream port

D+

Peripheral transceiver

D-

2.2 EMI filtering

Current FCC regulations requires that class B computing devices meet specified maximum levels for both radiated and conducted EMI.

● Radiated EMI covers the frequency range from 30 MHz to 1 GHz.

● Conducted EMI covers the 450 kHz to 30 MHz range.

For the types of devices utilizing the USB, the most difficult test to pass is usually the radiated EMI test. For this reason the USBUFxxW6 device is aiming to minimize radiated EMI.

The differential signal (D+ and D-) of the USB does not contribute significantly to radiated or conducted EMI because the magnetic field of both conductors cancels each other.

The inside of the PC environment is very noisy and designers must minimize noise coupling from the different sources. D+ and D-must not be routed near high speed lines (clocks spikes).

Induced common mode noise can be minimized by running pairs of USB signals parallel to each other and running grounded guard trace on each side of the signal pair from the USB controller to the USBUF device. If possible, locate the USBUF device physically near the

LOW SPEED CONNECTION

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Technical information USBUFxxW6

USB connectors. Distance between the USB controller and the USB connector must be minimized.

The 47 pF (C

) capacitors are used to bypass high frequency energy to ground and for edge

control, and are placed between the driver chip and the series termination resistors (Rt). Both Ct and Rt should be placed as close to the driver chip as is practicable.

The USBUFxxW6 ensures a filtering protection against ElectroMagnetic and RadioFrequency Interferences thanks to its low-pass filter structure. This filter is characterized by the following parameters:

● cut-off frequency

● Insertion loss

● high frequency rejection.

Figure 4. USBUFxxW6 typical

Figure 5. Measurement configuration

attenuation

S21 (dB)

-10

-20

-30 1 10 100 1,000

Frequency (MHz)

Ω

TEST BOARD

UUx

Ω

2.3 ESD PROTECTION

In addition to the requirements of termination and EMC compatibility, computing devices are required to be tested for ESD susceptibility. This test is described in the IEC 61000-4-2 and is already in place in Europe. This test requires that a device tolerates ESD events and remains operational without user intervention.

The USBUFxxW6 is particularly optimized to perform ESD protection. ESD protection is based on the use of device which clamps at:

This protection function is splitted in 2 stages. As shown in figure 6, the ESD strikes are clamped by the first stage S1 and then its remaining overvoltage is applied to the second stage through the resistor Rt. Such a configuration makes the output voltage very low at the output.

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= VBR + Rd.I

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