Other Parts Discussed in Thread: UCC21520, UCC5390, UCC27531, ISO7710, UCC27517A, LMG1210
Hello.
I have to develop a board with half-bridge.
The upper side is P-MOS (FQD3P50), the lower is N-MOS (IRFR420).
Lower side is connected to GND, upper to +440V.
The output of this bridge is connected to 50Ω throw +220V polarized decoupling capacitor in order to obtain bipolar pulse (±220V).
The half bridge has to produce this pattern ...
To drive this half bridge I buy a demo board UCC21520-286.
Because I need short rise/fall time (theoretically less than 1ns) I insert no resistance between drive output and mos gate and I use no death time (DT pin 6 is connected to VCCI).
I supply 18V to VDDB,VDDA from isolated DCV01015P (I use no bootstrap supply for nigh side).
I substitute R13,R12 (2.2Ω) with short.
I parallelize C16 with another one 10uF ceramic capacitor and C15 with two 10uF ceramic capacitor.
When I set-up 8 pulse with less or equal than 60ns duration pulse-train begin to corrupt ... here the image
PUT A PICTURE WITH DRIVER OUTPUTS
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To understand the problem I modify demo board UCC21520EVM-286 in this way.
I solder 1.5nF ceramic capacitor as CL_B (that absorb 1.5nFx15V=22.5nC every edge equivalent to IRFR420 19nC Miller-Plateau charge).
I supply 18Vto VDDB.
I generate train pulse to INB input by function generator.
When I set 8 pulses 105ns of positive/negative duration (210ns of period) the driver work properly. Here the waveforms.
When I reduce the width to 60ns (120ns of period) I observe randomly missing pulses at the end of the train.
If I disconnect the capacitor (no load to the output) the signal is perfect.
If I solder RL_B = 24Ω and CL_B=0Ω (short circuit) the output OUTB of the driver is OK. I notice that last pulses are shorter than initials.
If I reduce RL_B (for example to 22Ω) last pulse became more short until it disappear.
If I freeze the IC this problem gets worse. If I reduce VDDB this problem improves.