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Original question:
Tool/software:
I am using 3 LM5109BMAX/NOPB in an automotive VFD application.
The MOSFET Module is an On-Semi NXV08V110DB1.
My driver circuit looks like this:
I think I have met all the requirements from the datasheet,
- VDD is between 8 and 14 Volts - a Voltage regulator takes care of that.
- HS is between -1 and 90 Volts, my DC-Supply is limited to 60 Volts, usually the DC Bus is set to 12 - 15 Volts ...
- HO and LO are clamped against negative voltages
except one, i don't know hot to make sure HB to HS stays within the limits:
Chapter 7.5 "HS Transient Voltages Below Ground" says:
In the application, the HS node is clamped by the body diode of the external lower N-MOSFET, therefore the HS voltage will generally
not exceed –1 V. However in some applications, board resistance and inductance may result in the HS node exceeding this stated
voltage transiently. If negative transients occur on HS, the HS voltage must never be more negative than VDD – 15 V. For example, if
VDD = 10 V, the negative transients at HS must not exceed –5 V.
How can I make sure that HB stays within it's limits?
If I'd try to enforce that with a 12 Volt Zener Diode from HS (Anode) to HB (Cathode), I'd literally connect the Motor Phase with the Driver Supply. That sounds like a really bad idea to me?
Is there anyone who has a practical advice for me, how this can be achieved? Thank you very much
Hello,
A negative voltage transient on HS could cause the bootstrap cap C1 to overcharge. A 2.2 to 10 Ohms resistance in series with the boot strap diode D3 can limit the boot capacitor overcharging during negative HS transients.
A diode across HB-HO might also helo.
Thanks,
Walter
Hello Walter,
thank you for your reply and your suggestions.
I have added a series resistor to the bootstrap diode, but I am not sure about the diode. Did you mean it that way as in the screenshot below?
Yes, you are right. If I had thought twice it would have been obvious, that a diode with anode at HB and Cathode on HO might turn on the MOSFET. Which is definitively something, I don't want ...
And I guess A 1N5819 with it's 40 Volt won't do the trick.
Besides that, I guess I will have to test that with and without D50. ATM i think D44 should prevent HS negative Transients on HS.
Thank you very much for your input!
