GS61004B-EVBCD
GaN E-HEMT Full Bridge Evaluation Board
User’s Guide
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GS61004B-EVBCD Rev 200106
© 2020 GaN Systems Inc.
www.gansystems.com 9
Please refer to the Evaluation Board/Kit Important Notice on page 27
load, such as a loudspeaker. A common mode, lower frequency version of these is also provided
downstream of the audio filter by R29 and C21. Diodes CR10, 3, 9 and 5 protect the switch nodes
from being taken either above the HV supply rail range or below ground. CR7 protects against
accidental polarity reversal at the input, but only up to 1 Amp – so at first, power up here using a
suitably safe low current limit setting (for example, 100mA).
Capacitors C11 and C23 (in conjunction with diodes CR1 and 2 and CR4 and 6, respectively) provide the
bootstrapping action for each of the high side device gate drives.
The capacitor C20 forms a low-pass filter with L1 and L2 from each pair of E-HEMTs, rolling off the
frequency response at 12 dB/Octave above approximately 107 kHz. All other capacitors are for local
decoupling of the various stages of this high-frequency circuit.
The main output is on J8 which connects to a loudspeaker for audio use: Note that these terminals
should be left "floating" (that is, isolated from ground at all times). There is a high-impedance DC path
provided by R28 and R40, plus the optional filter capacitors C32 and 33, which are not normally
installed. TP3 and 4 and TP6 and 7 provide a way to monitor either side of the output relative to
ground using an oscilloscope. DO NOT ground TP6 or TP3. JP2 and JP3 provide a way to monitor each
switch node to ground on an oscilloscope. TP5 is used to provide a monitor point for the HV rail as well
as a passive or electronic load connection to ground so as to set/ calibrate the maximum current
threshold that protects the output devices.
Figure 5 •
PE29102 Dead-time Waveforms
