ST USBDF01W5, USBDF02W5 User Manual

EMI filter and line termination for USB downstream ports

Applications

EMI Filter and line termination for USB downstream ports on:

■ Desktop computer

■ Notebooks

■ Workstations

■ USB Hubs

USBDFxxW5

SOT323-5L

Functional diagram

Features

■ Monolithic device with recommended line

termination for USB downstream ports

■ Integrated Rt series termination and Ct

bypassing capacitors.

■ Integrated ESD protection

■ Small package size

Description

The USB specification requires USB downstream ports to be terminated with pull-down resistors from the D+ and D- lines to ground. 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 USBDFxxW5 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 SOT323-5L, which is a very small (50% smaller than the standard SOT23).

Complies with the following standards

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

±8 kV (contact discharge)

MIL STD 883C, Method 3015-6 Class 3 C = 100 pF R = 1500 W 3 positive strikes and 3 negative strikes (F = 1 Hz)

D+ In

Gnd

D- In

D+ Out

D- Out

USBDF01W5 33 Ω 15 kΩ 47 pF

USBDF02W5 15 Ω 15 kΩ 47 pF

Tolerance ±10% ±10% ±20%

Order codes

Part number Marking

USBDF01W5 UD1

USBDF02W5 UD2

Benefits

■ EMI / RFI noise suppression

■ Required line termination for USB downstream

ports

■ ESD protection exceeding

IEC61000-4-2 level 4

■ IPAD™ technology provides high flexibility in

the design of high density boards

■ Tailored to meet USB 1.1 standard

TM: IPAD is a trademark of STMicroelectronics

September 2006 Rev 3 1/11

www.st.com

Characteristics USBDFxxW5

1 Characteristics

Table 1. Absolute maximum ratings (T

Symbol Parameter Value Unit

amb

= 25° C)

stg

Table 2. Electrical characteristics (T

ESD discharge IEC 61000-4-2, contact discharge ESD discharge - MIL STD 883 - Method 3015-6

Operating junction temperature range -40 to 150 °C

Storage temperature range - 55 to +150 °C

Lead solder temperature (10 second duration) 260 °C

Power rating per resistor 100 mW

Symbol Parameters Test conditions Min Typ Max Unit

Diode breakdown voltage IR = 1 mA 6 V

Diode forward voltage drop IF = 50 mA 0.9 V

2 Application information

Figure 1. USB Standard requirements

Full-speed or Low-speed USB Transceiver

Host or Hub port

15k

D+

D-

= 25° C)

amb

Twisted pair shielded

Zo = 90ohms

5m max

D+

D-

+Vbus

1.5k

±15 ±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

2/11

3m max

D+

D-

+Vbus

1.5k

Low-speed USB

Transceiver

Hub 0 or Low-speed function

USBDFxxW5 Application information

Figure 2. Application example

Upstream portDownstream port

Host/Hub USB

port transceiver

2.1 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 USBDF device aims 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 the two conductors exactly cancels each other.

D+

USBDF

xxW5

D-

(1) for a low-speed port (2) for a full-speed port

CABLE

D+ (1) D- (2)

+Vbus

D- (1) D+ (2)

USBUF

xxW6

Peripheral

transceiver

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

Induced common mode noise can be minimised 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 USBDF device.

If possible, locate the USBDF device physically near the USB connectors. Distance between the USB controller and the USB connector must be minimized.

The 47 pF (C

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

control, and must be placed between the USB Controller and the series termination resistors (R

). Both Ct and Rt should be placed as close to the mSB Controller as

practicable.

The USBDFxxW5 ensure a filtering protection against electroMagnetic and radio-frequency Interference 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. shows the attenuation curve for frequencies up to 3 GHz.

3/11

Application information USBDFxxW5

Figure 3. Measurement configuration Figure 4. USBDFxxW5 attenuation

curve

Insertion loss (dB)

TG OUT

50 Ω

2.2 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 remain operational without user intervention.

The USBDFxxW5 is particularly optimized to perform ESD protection. ESD protection is based on the use of device which clamps at :

V=V+ R.I

INPUT BR d pp

This protection function is split in 2 stages. As shown in Figure 5., the ESD strikes are clamped by the first stage S1 and then the remaining overvoltage is applied to the second stage through the resistor R. Such a configuration makes the output voltage very low at the V

level.

out

TEST BOARD

UD1

RF IN

-10

50 Ω

-20

-30 1 10 100 1000 3000

F (MHz)

Figure 5. USBDFxxW5 ESD clamping behavior

ESD Surge

4/11

Vinput

Voutput

USBDFxxW5

Rload

Device

to be

protected

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