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STF202-30TC Folha de dados(PDF) 4 Page - Semtech Corporation |
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STF202-30TC Folha de dados(HTML) 4 Page - Semtech Corporation |
4 / 6 page © 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320 Objective - March 03, 2000 USB Upstream Port Filter & TVS For EMI Filtering and ESD Protection STF202-22 & STF202-30 APPLICATIONS INFORMATION Figure 1 - STF202 Circuit Diagram Device Connection The STF202 is designed to provide termination, EMI filtering and ESD protection for two USB I/O lines. The equivalent circuit diagram is shown in Figure 1. The device is connected as follows: 1. Full-Speed Devices: For full-speed devices the pull-up resistor is connected to the D+ line. Pin 1 is connected to the voltage supply line (V BUS). The input of the D+ line is routed into pin 3 and out of pin 4. The input of the D- line is connected at pin 2 and the output at pin 5. Pin 6 is connected to ground. • Low-Speed Devices: For low speed devices the pull-up resistor is connected to the D- line. Pins 1 is connected to the voltage supply line (V BUS). The input of the D- line is connected at pin 3 with the output taken at pin 4. The input of the D+ line is connected to pin 2 and the output is at pin 5. Pin 6 is connected to ground. USB Port Design Considerations The Universal Serial Bus (USB) specification requires termination and filtering components for proper operation. In addition, an open USB socket is vulnerable to hazardous ESD discharges in excess of 15kV. These discharges can may occur on the data lines or the voltage bus. The STF202 is an easily implemented solution designed to meet the termination & EMI filter requirements of the USB specification revision 1.1. It also provides ESD protection to IEC 61000-4-2, level 4. A simplified USB port is shown in Figure 3. USB line termination is achieved with series resistors on both the D+ and D- lines. These resistors preserve signal integrity by matching the cable impedance to that of the differential driver. 15k Ω pull-down resistors are used to identify a downstream port while an upstream port is identified with a 1.5K Ω pull up resistor on either the D+ (full speed devices) or the D- (low speed devices) data line. Capacitors are used to bypass high frequency energy to ground and for edge rate control of the USB signals. TVS diodes are added for ESD protection of both (D+ & D-) data lines and the voltage bus (V BUS). A power distribution switch and voltage regulator provide the power management functions of the port. Semtech provides a complete solution to simplify USB port design (Figure 4). The STF201 & STF202 Figure 2 - STF202 Connection Diagram (Full Speed Devices) 1 2 34 5 6 integrate all of the components necessary for line termination, bidirectional EMI filtering, and ESD protection on downstream (STF201) or upstream (STF202) ports. The SC5826 is a dual port power switch that provides individual or ganged port switching, fault reporting, and inrush current limiting as required by the USB specification. The SC5205 ULDO provides a stable voltage to the USB controller. Board Placement & Layout Guidelines. Designing a USB hub to meet EMI & ESD immunity requirements requires a combination of optimum component placement, trace routing, and good circuit design practices. Some general guidelines are given below: • Avoid running D+ & D- signal line traces near high speed clock lines or similar signal lines. • Avoid running critical signal lines near board edges. • Locate the USB controller chip near the USB connectors. • Place the STF202 near the USB connector to restrict transient coupling. • Minimize the path length between the USB connector and the STF202 . |
Nº de peça semelhante - STF202-30TC |
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Descrição semelhante - STF202-30TC |
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