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| DRV2700 HV piezo driver problem [SOLVED] |
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| Unixon:
--- Quote from: hv222 on August 17, 2019, 09:15:35 pm ---That explains negative values of voltage here ;) --- End quote --- OK, here's correct shots of SW node at Vout set to 10V, 50V and 100V. At 100V actual Vout is degraded to 63V. |
| Unixon:
--- Quote from: hv222 on August 17, 2019, 08:50:13 pm ---Check REXT resistor. Is responsible for current limit. Maybe is damaged or have bad solder joint. --- End quote --- No, it's OK. I've changed that to several values in allowed range. By default I put there 10k as in demo board, I've also tried 7.5k as a minimum value (max. current) and 30k as max. value (min. current). With Rext=30k Vout becomes limited at 16-17V, with 7.5k vs. default 10k Vout is probably raises a bit, but I can't say that definitely. --- Quote from: hv222 on August 17, 2019, 08:50:13 pm ---What is feedback voltage, when you set output to maximum value? If feedback voltage is close to 1.3V then check again feedback circuit and R38/C37. If it's below check around Q2. Maybe discharging circuit is on all time. --- End quote --- When Vout is below desired value, Vfb is also below Vref, it could be anywhere down to zero, 0.4-0.5V for example. But Q2 is closed at that time! |
| Unixon:
I think I found the problem. After all, it was the excessive loading by the H-bridge MOSFETS. When H-bridge is enabled and low side is turned on, due to resistor ratios high side also gets turned on and I observe a short across safeguard 1k resistor. |
| Unixon:
I suppose this mod should fix the problem... But then I will have to re-spin the board, even at best pads selection this may not look very nice on existing boards. |
| Unixon:
OK, now this works fine. So it wasn't a DRV2700 problem, my schematics for H-bridge was insufficient. Thanks everyone, problem solved. |
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