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USB 2.0 Isolator
Electrically Isolated Connections for USB Devices
In most cases, connecting peripherals to a PC is not a problem. The fact that a USB stick, for example, has the same ground potential as a laptop is hardly a problem. But when it comes to measuring devices connected via USB, the situation is different. Here, electrical isolation protects the PC from potentially harmful voltages. Isolation also helps to avoid ground loops. Specific chips are available for this purpose. The circuit presented here uses such a chip to provide electrical isolation for a USB connection.
Component list
Component List
Resistors:
Unless otherwise specified:
Thin film SMD 0603, 1%
R1, R14, R15 = 0Ω1, 1206
R2…R13 = 10 kΩ *
R16 = 261 Ω
R17 = 820 Ω
R18 = 39 kΩ
Capacitors:
C1, C16, C17, C19, C20 = 22 µF / 16 V, electrolytic, tantalum, SMC-B
C2…C4, C7…C11, C14, C15, C18 = 100 nF, X7R, SMD 0603
C5, C6, C12, C13 = 2.2 µF / 16 V, X7R, SMD 0805
Semiconductors:
D1, D2 = SK56, Schottky diode, DO214AA
IC1, IC3 = LT1117CST-1.8, SOT223
IC2 = ISOUSB211DPR, DP0028A
IC4 = LM317MABT, TO220
Miscellaneous:
JP2…JP4 = 3-pin header, 1/10″ pitch
JP6, JP7 = 2-pin header, 1/10″ pitch
X2 = 2-pin screw terminal, 5 mm pitch, AK300/2,
J1 = USB socket for PCB mounting, type B
J2 = USB socket for PCB mounting, type A
Enclosure Hammond 1593NTBU
Circuit board 240616-01
* see text
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