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Teilenummer | USBDF01W5 |
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Beschreibung | EMI FILTER AND LINE TERMINATION FOR USB DOWNSTREAM PORTS | |
Hersteller | STMicroelectronics | |
Logo | ||
Gesamt 9 Seiten ®
A.S.D.™
USBDFxxW5
EMI FILTER AND LINE TERMINATION
FOR USB DOWNSTREAM PORTS
APPLICATIONS
EMI Filter and line termination for USB down-
stream ports on:
- Desktop computer
- Notebooks
- Workstations
- USB Hubs
FEATURES
n Monolithic device with recommended line termi-
nation for USB downstream ports
n Integrated Rt series termination and Ct bypass-
ing capacitors.
n Integrated ESD protection
n 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
the smallest available lead frame package (50%
smaller than the standard SOT23).
BENEFITS
n EMI / RFI noise suppression
n Required line termination for USB downstream
ports
n ESD protection exceeding IEC61000-4-2 level 4
n High flexibility in the design of high density
boards
n Tailored to meet USB 1.1 standard
TM: ASD and TRANSIL are a trademarks of STMicroelectronics.
May 2000 Ed : 1C
SOT323-5L
FUNCTIONAL DIAGRAM
D+ In
Gnd
D- In
Rt
Ct Rd
Ct Rd
Rt
Code 01
Code 02
Tolerance
Rt
33Ω
15Ω
±10%
Rd
15kΩ
15kΩ
±10%
D+ Out
D- Out
Ct
47pF
47pF
±20%
1/9
USBDFxxW5
Fig. A6: Remaining voltage at both stages S1 (Vinput) and S2 (Voutput) during ESD surge.
a. Positive surge
b.Negative surge
Please note that the USBDFxxW5 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. A6b.
LATCH-UP PHENOMENA
The early ageing and destruction of IC’s is often due to latch-up phenomena which is mainly induced by
dV/dt. Thanks to its structure, the USBDFxxW5 provides a high immunity to latch-up phenomena by
smoothing very fast edges.
CROSSTALK BEHAVIOR
Fig. A7: Crosstalk phenomena
RG1
Line 1
VG1
RG2 Line 2
RL1 α1 VG1 + β12 VG2
VG2 RL2 α2 VG2 + β21 VG1
DRIVERS
RECEIVERS
The crosstalk phenomena is due to the coupling between 2 lines. The coupling factor ( β12 or β21 ) increases
when the gap across lines decreases, this is the reason why we provide crosstalk measurements for
monolithic device to guarantee negligeable crosstalk between the lines. In the example above the ex-
pected signal on load RL2 is α2VG2, in fact the real voltage at this point has got an extra value β21VG1. This
part of the VG1 signal represents the effect of the crosstalk phenomenon of the line 1 on the line 2. This phe-
nomenon 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 kΩ).
6/9
6 Page | ||
Seiten | Gesamt 9 Seiten | |
PDF Download | [ USBDF01W5 Schematic.PDF ] |
Teilenummer | Beschreibung | Hersteller |
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