I need help with DRV8811, I need work with Vm = 4,2 V

Houari, DRV8811 can be used only till 8V as LT has mentioned. However, you might be able to use DRV8833 to run a stepper motor. This device will go into production this month end. We are already giving samples. You can find more information here: http://focus.ti.com/docs/prod/folders/print/drv8833.html

The DRV8833 doesn't use a STEP/ DIR interface. It uses a xIN1, xIN2 interface.

It can drive upto 1 A continuous current. Please go thru' the datasheet and I will be happy to answer any further questions.

Vivek

Vivek Shankar

Applications Engineer

Motor Applications Team

Texas Instruments Inc.

Leslie and Vivek,

Thank you very much for your help. I really apreciate it.

Iknow know that´s no possible to work with DRV8811 in my application.

You gave me two options to work, DRV8412 wich hav working voltages between 0 and 52 V and 3 A of maximum current. Vivek giave me too the option DRV8833 but this circuit is up to 1 A.

I forgot to put my current limit.

My steper motor (1,8°)  have the following characteristics:

Nominal Voltage        4,2 V

Current                         2,1 A

Fase resistance         2 ohm

fase inductance        6,8 mH

Holding torque           18 Kgf.cm

Detent torque             700 gF.cm

Rotor inertia               460 gF.cm^2

Taking those data into account i think the driver DRV8833 will not have the necesary current to deal with. There is some way to externaly increase such current limit?

By the other way, the other solution is the driver DRV8412.

It could be possible to implement an 1/8 microstep with such driver? there is another external circuitry i could use with the driver to get such microstep?

Once more time thank you very much for your help.

I could appreciate you talk to me if you need som help from me any time. 

my email is hcobas_gomez@yahoo.com.br, ou   hcobas@usp.br

Houari Cobas

Houari,

The DRV8412 can go down to 1/512 microsteps, the DRV8412 is a PWM Control Interface so you must send the appropriate signals. Part 6 of the Motor Control Video at about the 5 min mark talks about how microstepping is implemented. The DRV8412-C2-KIT comes with a C2000 microcontroller that has all the code to operate down to 1/128 microsteps. If you wanted to use the DRV8833 instead you could send your PWM signals in such a way that the max current pulled is 1A instead of 2A by adjusting the duty cycle of the signals.

LT 

Hi Houri,

Sorry to interrupt this thread, but I wanted to check on one item. When you say the voltage is 4.2V, is this the voltage as read from the motor label or is it the actual application voltage? When read from a motor label, this parameter often confuses people into believing that only this voltage may be used. This is misleading, as the stepper can be used with any voltage larger than this, as long as the current parameter is not exceeded. In fact, using larger voltages is desirable as this increases the rate of current charge and increases the speed range and available torque at higher speeds.

By looking at the motor ratings it is clear this motor is rather large. Possibly a NEMA 23? If so, I find it hard to believe you will want to use 4.2V. I would use either 24V or 36V if available.

Note that the 4.2V rating is only applicable if you are using an LR drive. To be honest, I believe this drive topology is most probably extinct as it is too inefficient (due to losses on the R component). The most efficient way of driving a stepper is to use a current chopper, which is the topology around which our devices operate.

If all of the above is still in play and my assumptions have been correct, then the DRV8811 can be used to drive this motor. However, do note that at 2.1A per phase, the DRV8811 will get quite hot. A better option would be the DRV8825 which has lower RDSon and can give you up to 32 degrees of microstepping.

Can you validate whether we are on the same page with the voltage rating? I want to make sure we recommend the right part for this application. Thanks!

Best regards,

Jose Quinones

Hello, before of all, thanks you very much for your help LT and Jose Quinones.

In fact Jose Quinones we are talking about the stepper motor  NEMA 23 SM 1.8-D18-MN. Such data I had already posted are the data provided by the manufacturer in the datasheet. Excuse me, probably i should start by the model of the motor i should use. Tomorrow i´ll have the final model of steper motor to work with, but it should be NEMA 23 SM 1.8-D18-MN or NEMA 23 SM 1.8-D12-MN. 

thank you very much for the help youáre giving to me

I forgot, the motor´s datasheet can be found in the site:

http://www.actionmotors.com.br/upload/fichas/SM1.8D18MN.pdf

thank you

Hi Houri,

You can definitely use the DRV8811 with your supply larger than 8V to drive this motor. The driver will regulate the current so in essence the motor will see a voltage analogous to the 4.2V.

I would use Bipolar Parallel configuration, however, with an analogous voltage of 2.1V. Your inductance is optimized so you can move the motor faster and with larger torque capabilities.

Hope the info helps. Best regards,

Jose Quinones

Thank you very much Jose. If i can do the way you say, then it would be better for me because i already have the driver. I´ll use then parallel configuration.

thank you for your help

Houari cobas