DRV8711 Motor voltage

184063

Other Parts Discussed in Thread: DRV8711

Hello,

I have a question regarding DRV8711 predriver for stepper motors. It clearly states that this device operates from 8V, which I guess is due to the fact it needs ~10V for MOSFETs gates.

However, I do have a stepper which is 1.76V/2A. Motors should be of course driven by current source, but voltage has its part in faster current rise in inductance (windings). So higher voltage for given stepper means not only faster current rise and potential greater operating frequency but more power dissipated in winding (if I'm wrong - correct me).

So DRV8711 question: can I separate VM to the IC and the VM to the H-bridge? Then the IC will have its >=8V and my H-bridge, hence the motor, will operate on its voltage (~2V). Or should I only use motors that operate from 8V and higher with this predriver?

I know I could use a normal driver for this application, but I have my reasons.

Respectfully,

Mikołaj

over 11 years ago

0 Sonia Ghelani over 11 years ago

TI__Intellectual 1230 points

Mikolaj,

I will move this thread to the Motors forum so the appropriate team will see this and answer.

Regards,

Sonia

0 184063 over 11 years ago in reply to Sonia Ghelani

Prodigy 90 points

Ok, great!

Thank you Sonia :) I thought no one knows the answer. I've put this to linear because this driver was in linear category, my mistake.

0 Nicholas Oborny over 11 years ago

TI__Mastermind 21320 points

Hi Miko,

It is not recommended to separate VM to the IC and the H-Bridge.

Reason being, the gate drive voltage (VM+10V) is derived from VM to the IC with a charge pump. To get the proper bias for the high side NFET you will need the H-bridge VM to also be present for the charge pump.

In theory, if the H-Bridge voltage was below that of the DRV8711 and the charge pump voltage did not violate the Vgs spec of the FET this configuration may work. But this would not make any sense from a system level.

0 Nicholas Oborny over 11 years ago in reply to Nicholas Oborny

TI__Mastermind 21320 points

Motor voltage ratings are tricky. They are not true voltage ratings. I would pay more attention to the current rating.

These blogs gives a good explanation.

http://e2e.ti.com/blogs_/b/motordrivecontrol/archive/2012/01/17/the-5-2v-stepper-motor-and-50v-stepper-driver-paradox.aspx

https://www.selene.co/Blog/2011/07/stepper-motor-voltages-explained/

0 184063 over 11 years ago in reply to Nicholas Oborny

Prodigy 90 points

Thanks Nicolas, great read and very fast response, thanks!!

Just as I thought, they are current driven, but due to inductance the voltage matters to load it fast.

So I guess the mosfets will have to disspate remaining power, but that's ok, will consider it while choosing mosfets.

0 Nicholas Oborny over 11 years ago in reply to 184063

TI__Mastermind 21320 points

Hi Miko,

The DRV8711 and most TI stepper drivers utilize a current regulation loop (using a sense resistor) to ensure the proper current is being sent to the motor coil. The DRV8711 will only switch the H-bridge as much is needed to maintain the proper curret. The main losses are incurred in switching losses and Rds(on) losses within the FETs.

Here is some additional literature.

http://www.ti.com/lit/an/slva321/slva321.pdf

Motor drivers

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DRV8711 Motor voltage