L6480 cannot switch on my 170 nC transistors

alexing · ‎2014-09-06

Posted on September 06, 2014 at 14:57

Greetings,

I am doing a test series of stepper drivers with L6480 for furnace rotation control.

There seems to be a problem with the device.

The circuit is a copy of Eval 6480.

SPI is up and functional, every register is correctly set.

The problem is that L6480 cannot switch on all high-end transistors.

The transistors I use are IRFB4310ZPBF (hexfet power mosfet, Vdss-100V, Ids -120 A, Rds-5mOhm, Qg-170nC)

compared to the Eval 6480 (stripfet power mosfet, Vdss-100V, Ids - 25 A, Rds-35mOhm, Qg- 14nC)

The device is running on 28 V DC, with Vboot-Vs=10,5 V, with GateConfig set to 96 mA / 3750 nS ( a total of over 330 nC).

But even if the OCD is disabled it is unable to switch on the upper transistors.

Could you help ?

Thanks in advance!

Eng. Tom Draganov , Alex Engineering Ltd.

#l6480

larken · ‎2014-09-07

Posted on September 08, 2014 at 02:51

That MOSFET has a very large input capacitance of 6860pF @ 50V . Thats too hard to drive at a high switching frequency. Even a IR2104 would have trouble driving those.

That must be a massive stepper motor, those are rated at 120 amps !! I hope you have a 2 board design and are not putting that much current though the same ground plane that the control IC is on.