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USBUF01P6
EMI FILTER AND LINE TERMINATION
FOR USB UPSTREAM PORTS
REV. 2
SOT-666IP
(Internal Pad)
May 2004
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
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 USBUF01P6 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 SOT-666 which is the
smallest available lead frame package (45%
smaller than the standard SOT323).
BENEFITS
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 2.0 standard (low speed
and high speed data transmission)
Order Codes
Part Number
Marking
USBUF01P6
U
IPADTM
FUNCTIONAL DIAGRAM
3.3 V
Rp
Ct
Rt
Ct
Rt
D1
Grd
D2
D4
D3
3.3 V
COMPLIES WITH THE FOLLOWING STANDARDS:
IEC61000-4-2 level4:
15kV
(air discharge)
8kV
(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)
USBUF01P6
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ABSOLUTE MAXIMUM RATING (T
amb
= 25C)
ELECTRICAL CHARACTERISTICS (T
amb
= 25C)
Symbol
Parameter
Value
Unit
V
PP
ESD discharge
IEC61000-4-2 air discharge
IEC61000-4-2 contact discharge
MIL STD 883E - Method 3015-7
16
9
25
kV
T
j
Junction temperature
150
C
T
stg
Storage temperature range
-55 to +150
C
T
L
Maximum lead temperature for soldering during 10 s at 5mm for case
260
C
T
op
Operating temperature range
-40 to + 85
C
Symbol
Parameter
V
RM
Stand-off voltage
V
BR
Breakdown voltage
V
CL
Clamping voltage
I
RM
Leakage current
I
PP
Peak pulse current
T
Voltage temperature coefficient
V
F
Forward voltage drop
Rd
Dynamic resistance
Symbol
Test conditions
Min.
Typ.
Max.
Unit
V
BR
I
R
= 1 mA
6
10
V
I
RM
V
RM
= 3.3V per line
500
nA
R
t
Tolerance 10%
33
W
R
p
Tolerance 10%
1.5
kW
C
t
Tolerance 20%
47
pF
I
V
I
F
I
RM
I
PP
V
RM
V
F
V
BR
Slope = 1/Rd
V
CL
USBUF01P6
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TECHNICAL INFORMATION
APPLICATION EXAMPLE
Fig. A2: Implementation of ST' solutions for USB ports.
Fig. A1: USB Standard requirements.
Host or
Hub port
Twisted pair shielded
Zo = 90ohms
5m max
Hub 0 or
Full-speed function
Untwisted unshielded
3m max
FULL SPEED CONNECTION
LOW SPEED CONNECTION
3.3V
3.3V
D+
D-
D+
D-
D+
D-
D+
D-
1.5k
1.5k
Hub 0 or
Low-speed function
Low-speed USB
Transceiver
Full-speed or
Low-speed USB
Transceiver
15k
Rt
Rt
Ct
Ct
Host or
Hub port
Full-speed or
Low-speed USB
Transceiver
15k
Rt
Rt
Ct
Ct
Rt
Rt
Ct
Ct
Full-speed USB
Transceiver
Rt
Rt
Ct
Ct
15k
15k
D+
D-
CABLE
Host/Hub USB por transceiver
t
D-
D+
D+
D-
Upstream port
Downstream port
USBDF01W5
D+
D-
Rt
D+ in
Gnd
D- in
D+ out
D- out
Rt
Rd
Rd
Ct
Ct
Gnd
3.3 V
Rp
Ct
Rt
Ct
Rt
D1
Gnd
D2
D4
D3
3.3V
P
eripheral transceiver
USBUF01W6
D+
D-
CABLE
Host/Hub USB por transceiver
t
D-
D+
D+
D-
Upstream port
Downstream port
USBDF01W5
D+
D-
Rt
D+ in
Gnd
D- in
D+ out
D- out
Rt
Rd
Rd
Ct
Ct
Gnd
3.3 V
Rp
Ct
Rt
Ct
Rt
D1
Gnd
D2
D4
D3
3.3V
P
eripheral transceiver
USBUF01W6
FULL SPEED CONNECTION
LOW SPEED CONNECTION
USBUF01P6
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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 USBUF01P6 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 (C
t
) 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 (R
t
). Both C
t
and R
t
should be
placed as close to the driver chip as is practicable.
The USBUF01P6 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.
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 USBUF01P6 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 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 R
t
.
Such a configuration makes the output voltage very low at the output.
Fig. A3: USBUF01P6 typical attenuation curve.
Fig. A4: Measurement configuration.
f/Hz
1.0M
3.0M
10.0M
30.0M
100.0M
300.0M
1.0G
3.0G
-25.00
-22.50
-20.00
-17.50
-15.00
-12.50
-10.00
-7.50
-5.00
-2.50
0.00
dB
-
-
-
-
-
-
-
-
-
-
TEST BOARD
50
Vg
50
UUx
V
CL
V
BR
R
d
I
PP
+
=
USBUF01P6
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Fig. A5: USBUF01P6 ESD clamping behavior.
Fig. A6: Measurement board.
To have a good approximation of the remaining voltages at both Vin and Vout stages, we give the typical
dynamical resistance value R
d
. By taking into account these following hypothesis : R
t
>R
d
, R
g
>R
d
and
R
load
>R
d
, it gives these formulas:
The results of the calculation done for V
g
=8kV, R
g
=330
(IEC61000-4-2 standard), V
BR
=7V (typ.) and
R
d
= 2
(typ.) give:
Vinput = 55.48 V
Voutput = 10.36 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 R
t
.
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 V
BR
(breakdown voltage) in the positive way and -V
F
(forward
voltage) in the negative way
ESD Surge
Vinput
Voutput
Rload
Rg
Rt
S1
Rd
V
BR
V
BR
V
PP
Device
to be
protected
USBUF01P6
Rd
S2
TEST BOARD
ESD
SURGE
15kV
Air
Discharge
Vin
Vout
U
Vinput
R
g
V
BR
R
d
V
g
+
R
g
-----------------------------------------------
=
Voutput
R
t
V
BR
R
d
Vinput
+
R
t
----------------------------------------------------------
=
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