Question 2 - Clamping Circuits (5 marks] 2.1 A USB 2.0 interface primarily consists of 5V power (VUSB), ground return (G

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Question 2 Clamping Circuits 5 Marks 2 1 A Usb 2 0 Interface Primarily Consists Of 5v Power Vusb Ground Return G 1 (343.03 KiB) Viewed 52 times

Question 2 - Clamping Circuits (5 marks] 2.1 A USB 2.0 interface primarily consists of 5V power (VUSB), ground return (GND), and two data lines (D+ and D- as a differential pair). The data lines normally range between 5V and ground. However, a common concern with USB is to ensure that, if there were to be a fault in the external device (e.g. a cheap USB flash drive), the data lines of the local device should never be allowed to exceed the input voltage range of the local interfacing USB controller IC (a valuable chip), which would forward bias internal ESD diodes of that IC and will usually lead to destruction of the USB port. Figure 2 below illustrates a common solution which uses an array of diodes to clamp the data line voltages to supply and ground. However, 10m resistances have been modelled to represent the resistance of the wires within the USB cable, through which all current in the USB circuit is supplied and returned. RI -ww TR USB R2 www VUSB DATA OUTI Omit D+ USB D- GND DATA OUT 2 Figure 2 Given that . VUSB=5 V, GND = 0 V and neither of these lines experience any load regulation. VF = 0.2 V (Forward Voltage of the normal Diodes) 4 . Vz= 5.5 V (Reverse Breakdown "Zener" Voltage of the Zener Diode) ● All diodes are otherwise ideal in their characteristics. . All current drawn by devices not shown in Figure 2 (e.g. the USB controller IC) is negligible (DATA_OUT is high impedance, no supply current drawn from VUSB). Plot the data line DC input (D+ or D-, as sent from the upstream device before the cable) to output (DATA_OUT, as received by the downstream device) voltage of a single data line DC voltage ranging from -5V to +10V. Clearly label all axes, gradients and axis values of significant points of change. The plot does not need to be to scale. [5 marks] Answer on the following page or one of the extra pages. J R3 www TOR R4 ww 10m KIKH KH-Kh