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| (R) USBUFxxW6 EMI FILTER AND LINE TERMINATION FOR USB UPSTREAM PORTS A.S.D.TM APPLICATIONS 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 s s s s SOT323-6L 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 IEC61000-4-2 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 s s FUNCTIONAL DIAGRAM 3.3 V Rt D1 Ct Rp D4 Grd 3.3 V Rt D2 Ct D3 s s s EMI / RFI noise suppression Required line termination for USB upstream ports ESD protection exceeding IEC61000-4-2 level 4 High flexibility in the design of high density boards Tailored to meet USB 1.1 standard Rt CODE 01 CODE 02 Tolerance 33 22 10% Rp 1.5k 1.5k 10% Ct 47pF 47pF 20% TM: ASD and TRANSIL are a trademarks of STMicroelectronics. March 2002 - Ed: 3A 1/9 USBUFxxW6 COMPLIES WITH THE FOLLOWING ESD STANDARDS: IEC61000-4-2, level 4 15 kV (air discharge) 8 kV (contact discharge) MIL STD 883E, Method 3015-7 Class 3 C = 100 pF R = 1500 3 positive strikes and 3 negative strikes (F = 1 Hz) ABSOLUTE RATINGS (Tamb = 25C) Symbol VPP Parameter 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 Storage temperature range Lead solder temperature (10 second duration) Operating temperature range Power rating per resistor Value 16 9 25 150 - 55 to +150 260 0 to 70 100 Unit kV kV kV C C C C mW Tj Tstg TL Top Pr TECHNICAL INFORMATION Fig. A1: USB Standard requirements 3.3V 1.5k Rt D+ Twisted pair shielded D+ Rt Ct Rt Full-speed or Low-speed USB Transceiver Ct Rt Full-speed USB Transceiver DHost or Hub port Ct 15k 15k Zo = 90ohms 5m max DCt Hub 0 or Full-speed function FULL SPEED CONNECTION 3.3V 1.5k Rt D+ Untwisted unshielded D+ Rt Ct Rt Full-speed or Low-speed USB Transceiver Ct Rt Low-speed USB Transceiver DHost or Hub port Ct 15k 15k 3m max DCt Hub 0 or Low-speed function LOW SPEED CONNECTION 2/9 USBUFxxW6 APPLICATION EXAMPLE Fig. A2: Implementation of ST' solutions for USB ports Downstream port Host/Hub USB por transceivert USBDF01W5 Rt D+ in Ct Rd D+ out USBUF01W6 D2 Gnd D1 Upstream port D+ Peripheral transceiver D+ D+ CABLE D+ Ct Rt Ct Rt 3.3 V Rp Gnd Gnd Ct Rd D- in Rt D- out D- D- DD3 3.3V D4 D- FULL SPEED CONNECTION Downstream port Host/Hub USB por transceivert USBDF01W5 Rt D+ in Ct Rd D+ out USBUF01W6 D2 Gnd D1 Upstream port D+ Peripheral transceiver D+ D+ CABLE D+ Ct Rt Ct Rt 3.3 V Rp Gnd Gnd Ct Rd D- in Rt D- out D- D- DD3 3.3V D4 D- LOW SPEED CONNECTION 3/9 USBUFxxW6 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 30MHz to 1GHz. - Conducted EMI covers the 450kHz to 30MHz 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 USB connectors. Distance between the USB controller and the USB connector must be minimized. The 47pF (Ct) 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. Fig. A3: USBUFxxW6 typical attenuation curve. S21 (dB) 0 Fig. A4: Measurement configuration -10 50 TEST BOARD UUx Vg 50 -20 -30 1 10 100 Frequency (MHz) 1,000 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 : Vcl = VBR + Rd .IPP This protection function is splitted in 2 stages. As shown in figure A5, 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. 4/9 USBUFxxW6 Fig. A5: USBUFxxW6 ESD clamping behavior Rg S1 Rt S2 Rd VPP Vinput Voutput Rd Rload VBR VBR Device to be protected ESD Surge USBUF01W6 Fig. A6: Measurement board ESD SURGE 16kV Air Discharge TEST BOARD UUx Vin Vout To have a good approximation of the remaining voltages at both Vin and Vout stages, we give the typical dynamical resistance value Rd. By taking into account these following hypothesis : Rt>Rd, Rg>Rd and Rload>Rd, it gives these formulas: Rg .VBR + Rd .Vg Vinput = Rg Rt.VBR + Rd .Vinput Voutput = Rt The results of the calculation done for Vg=8kV, Rg=330 (IEC61000-4-2 standard), V BR=7V (typ.) and Rd = 1 (typ.) give: Vinput = 31.2 V Voutput = 7.95 V This confirms the very low remaining voltage across the device to be protected. It is also important to note that in this approximation the parasitic inductance effect was not taken into account. This could be few tenths of volts during few ns at the Vinput side. This parasitic effect is not present at the Voutput side due the low current involved after the resistance Rt. The measurements done hereafter show very clearly (Fig. A7) the high efficiency of the ESD protection : - no influence of the parasitic inductances on Voutput stage - Voutput clamping voltage very close to VBR (breakdown voltage) in the positive way and -VF (forward voltage) in the negative way 5/9 USBUFxxW6 Fig. A7: Remaining voltage at both stages S1 (Vinput) and S2 (Voutput) during ESD surge. Vin Vin Vout Vout a. Positive surge b.Negative surge Please note that the USBUFxxW6 is not only acting for positive ESD surges but also for negative ones. For these kinds of disturbances it clamps close to ground voltage as shown in Fig. A7b. LATCH-UP PHENOMENA The early ageing and destruction of IC's is often due to latch-up phenomenon which is mainly induced by dV/dt. Thanks to its structure, the USBUFxxW6 provides a high immunity to latch-up phenomenon by smoothing very fast edges. CROSSTALK BEHAVIOR Fig. A8: Crosstalk phenomenon RG1 Line 1 VG1 RG2 Line 2 RL1 1 VG1 + 12 VG2 VG2 RL2 2 VG2 + 21 VG1 DRIVERS RECEIVERS The crosstalk phenomenon is due to the coupling between 2 lines. The coupling factor ( 12 or 21 ) increases when the gap across lines decreases, particularly in silicon dice. In the example above the expected signal on load RL2 is 2VG2, in fact the real voltage at this point has got an extra value 21VG1. This part of the VG1 signal represents the effect of the crosstalk phenomenon of the line 1 on the line 2. This phenomenon has to be taken into account when the drivers impose fast digital data or high frequency analog signals in the disturbing line. The perturbed line will be more affected if it works with low voltage signal or high load impedance (few k). 6/9 USBUFxxW6 Fig. A9: Analog crosstalk measurements Fig. A10: Typical analog crosstalk results Analog crosstalk (dB) 0 -20 TEST BOARD 50 UUx -40 50 Vg -60 -80 -100 1 10 100 Frequency (MHz) 1,000 Figure A9 gives the measurement circuit for the analog crosstalk application. In figure A10, the curve shows the effect of the D+ cell on the D- cell. In usual frequency range of analog signals (up to 100MHz) the effect on disturbed line is less than -37dB. Fig. A11: Digital crosstalk measurements configuration +5V 74HC04 3.3 V +5V 74HC04 D+ D1 Rt Ct Rp D4 Square Pulse Generator VG1 +5V DD2 Gnd Rt Ct D3 3.3 V 21 VG1 Figure A11 shows the measurement circuit used to quantify the crosstalk effect in a classical digital application. Fig. A12: Digital crosstalk results Figure A12 shows, with a signal from 0 to 5V and rise time of few ns, the impact on the disturbed line is less than 250mV peak to peak. No data disturbance was noted on the other line.The measurements performed with falling edges gives an impact within the same range. VG1 21VG1 7/9 USBUFxxW6 TRANSITION TIMES This low pass filter has been designed in order to meet the USB 1.1 standard requirements that implies the signal edges are maintained within the 4ns-20ns stipulated USB specification limits. To verify this point, we have measured the rise time of VD+ voltage (please refer to Fig. A13) with and without the USBUFxxW6 device. Fig. A13: Typical rise and fall times: measurements configuration Fig. A14: Typical rise times with and without protection device without +5V 74HC04 D+ +5V +5V 74HC04 Square Pulse Generator +5V D- USBUF -xxW6 VD+ with Figure A13 shows the circuit used to perform measurements of the transition times. In Figure A14, we see the results of such measurements: trise = 3.8ns driver alone trise = 7.8ns with protection device The adding of the protection device causes the rise time increase of roughly 4ns. Note: Rise time has been measured between 10% and 90% of the signal (resp. 90% and 10%) 8/9 USBUFxxW6 PACKAGE MECHANICAL DATA. SOT323-6L DIMENSIONS A A2 A1 REF. Millimeters Min. Max. 1.1 0.1 1 0.3 0.18 2.2 1.35 Inches Min. 0.031 0 0.031 0.006 0.004 0.071 0.045 Max. 0.043 0.004 0.039 0.012 0.007 0.086 0.053 A D 0.8 0 0.8 0.15 0.1 1.8 1.15 A1 e e A2 b c H E D E e 0.65 Typ. 1.8 0.1 2.4 0.4 0.025 Typ. 0.071 0.004 0.094 0.016 Q c b H Q RECOMMENDED FOOTPRINT (mm) 0.3mm MECHANICAL SPECIFICATIONS Lead plating Lead plating thickness Tin-lead 5m min 25m max Sn / Pb (70% to 90%Sn) 10m max Molded epoxy UL94V-0 1mm Lead material 2.9mm Lead coplanarity 1mm Body material Flammability 0.35mm MARKING Ordering code USBUF01W6 USBUF02W6 Marking UU1 UU2 Package SOT323-6L SOT323-6L Weight 5.4 mg 5.4 mg Base qty 3000 3000 Delivery mode Tape & reel Tape & reel Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics. The ST logo is a registered trademark of STMicroelectronics (c) 2002 STMicroelectronics - Printed in Italy - All rights reserved. STMicroelectronics GROUP OF COMPANIES Australia - Brazil - Canada - China - Finland - France - Germany Hong Kong - India - Israel - Italy - Japan - Malaysia - Malta - Morocco - Singapore Spain - Sweden - Switzerland - United Kingdom - United States. http://www.st.com 9/9 |
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