The 1 kilohm impedance still results in a large voltage spike. If the pullup resistance is
dramatically reduced to 50 Ohms, the coupled voltage spike is also reduced:
Top: +1.5 kV HV pulse
Bottom: Logic out into open circuit
no DUT, R2 = 1kΩ, 100 ns/div
Top: -1.5 kV HV pulse
Bottom: Logic out into open circuit
no DUT, R2 = 1kΩ, 100 ns/div
This is not usually a practical circuit setup for a real DUT (since they are not normally
capable of driving 50 Ohm impedances, unless they are gate drivers), but it lets us
estimate the parasitic capacitance present on the daughterboard. A spike on the order
of 2V is observed, giving:
I = C dV/dt
C = I dt / dV
C = (2V / 50 Ohms) × 4 ns / (1500V × (90% - 10%))
C = 0.13 pF
This is a physically reasonable value for the parasitic capacitance between the high
voltage pulse and output logic signal lines on the daughterboard.
The effects of capacitive coupling will be especially significant for devices with open-
collector outputs when the outputs are passively pulled high through a resistance of a
few kilohms or higher. For example, if an HCPL-2601 is tested using R2 = 1 kΩ (and R6
= R9 = R10 = 0Ω), the logic outputs are quite similar to the results on the previous page
(which used no DUT, and R2 = 1 kΩ):
63
Summary of Contents for AVRQ-5-B
Page 52: ...Bottom side 52 ...
Page 57: ...PCB 299B FOR ADUM241E0BRWZ 57 ...
Page 82: ...PCB 158R2 LOW VOLTAGE POWER SUPPLY ...
Page 87: ...DUT WIRING ON STANDARD DAUGHTERBOARD PCB 267C ...
Page 88: ...DUT WIRING ON CUSTOMIZED TLP2366 DAUGHTERBOARD PCB 298B ...
Page 89: ...DUT WIRING ON CUSTOMIZED ADUM241E0BRWZ DAUGHTERBOARD PCB 299B ...
Page 91: ...PERFORMANCE CHECK SHEET 91 ...