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RE: Need +/- 2.5% speed regulation with DRV10983 on a fractional motor liquid pump.

February 5, 2016, 11:22 am
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Michel,

To estimate the pumped liquid, do you have any other controller in your system ?

If you have , that controller can read FG for speed and control the PWM input to change the speed and the controller will decide the speed regulation.

DRV10983 does not support speed control loop .

Thanks,

Jasraj

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RE: Need +/- 2.5% speed regulation with DRV10983 on a fractional motor liquid pump.

February 5, 2016, 11:31 am
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Jasraj,

We do have another controller supervising the values of this motor driver. This should provide proper speed regulation. However the instruction talks about open and close loop operation. I though that close loop was indirectly related for speed regulation?

Thanks,

Michel
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RE: Need +/- 2.5% speed regulation with DRV10983 on a fractional motor liquid pump.

February 5, 2016, 11:38 am
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Michel,

Sensor less BLDC motor drive works with estimating rotor position because hall sensor feedback is not present.
The term open and close loop is defined in that context here. While starting since we don't have back emf to estimate the rotor position we have to spin in open loop. Once we gain speed, back emf is available and then we can accurately predict the rotor position which referred as closed loop.

The speed close loop needs to be implemented externally. Your controller will be able to realize this.

Thanks
Jasraj
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Need +/- 2.5% speed regulation with DRV10983 on a fractional motor liquid pump.

February 5, 2016, 10:19 am
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Hi,

I need +/- 2.5% speed regulation with  DRV10983 on a fractional motor liquid pump. We are pumping a liquid with variable viscosity and we need to estimate the pumped liquid volume using the motor speed. How do you suggest this can be done?

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RE: Importing PCB footprint files into SolidWorks

February 5, 2016, 12:29 pm
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Hi Rick - OK, that's what I thought, but thank you for confirming. I followed your workflow and was able to verify the through hole locations using the workflow steps you outlined. I think I now have the information I need to manually create a SolidWorks model of the DRV8312EVM board so I can design the mechanical assembly to mount it. I wish it would have been easier, but I do have the information I needed thanks to you.

Thanks again Rick, much appreciated.
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RE: General getting-started BLDC driving/control questions

February 5, 2016, 2:03 pm
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Rick,

Thanks for the quick response.  In the anticipated application, it's typical to have a 3 cell LiPo battery, so 11-12vdc is available.  The BLDC motor I'm currently using as a prototype is about 1" dia. and with the gearcase is about 3" long, so a 1"x3" PCB wouldn't be too large (but smaller is desirable -- I'm used to designing and building wearable wireless devices somewhat smaller than that :-)

Since this is for an educational application, cost is always a consideration.  For reference, the motor I'm now using is $5 (from China).  The ultimate goal is to release it to the community as an open-source design.

Mike

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RE: General getting-started BLDC driving/control questions

February 5, 2016, 2:31 pm
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Chris,

Thanks for the detailed reply. Responding by group:
• Sensorless for RPM, accel/decel: Got it.
• Hold, count steps, single step with Hall sensors and encoder: I'm hoping that all of this can be done without an encoder at the resolution(!) of a single BLDC step, i.e., coarse, but made much finer effectively by the gearbox.
• Similarly, for "micro stepping", presuming a delta UVW wiring for the motor stator, couldn't I position the motor at a "half step" with U positive, and V and W negative with equivalent currents? And move within that single step be varying the average current through V and W via PWM?
• Re force, I'm presuming I can vary the torque generated by the motor at fixed voltage by varying the drive current (via PWM again). Correct? Conversely, (as I've noted with a simple speed control coupled to the motor), I can estimate the resisting torque of the mechanical load by the average current (useful up to stall torque).

Yes, there are advantages with stepper motors. But in high-end robotics, I understand it's much more common to use DC servo motors to get a wider range of speeds and force feedback. I'm just trying to bring those advantages down to small, low-cost platforms, especially taking advantage of the plethora of cheap, powerful BLDC motors (e.g., for helicopter drones).

Thanks again,

Mike
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General getting-started BLDC driving/control questions

February 5, 2016, 2:31 am
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Folks,

I'm interested in developing a motor controller/driver for a range of small BLDC motors (5-12v, <1amp) generally with a gear train (100-250x), to be used in small mobile robotic devices for K12 education.  General idea is to package MCU, driver and motor in a standardized module, with multiple modules to be used for various functions,

Here's where it gets interesting.  Would like to be able to monitor/control all of the following:

  • RPM, for continuous motion, from very slow speed to max motor RPM.
  • Acceleration/deceleration curves.
  • Count "steps", i.e., changes in pole positions (with n pole pairs per rev)
  • Hold position, like a stepper motor.
  • Single "step", like a stepper (where this will correspond with a small output angle, determined by n and the gear ratio
  • "Micro step" (Is this practical with a BLDC motor?)
  • Force control/feedback by modulating/measuring drive current (via PWM I presume)
  • For motors with and without Hall effect sensors

I'm presuming that I can jump right into the InstaSPIN tool for the continuous motion design, but what about very low speed and stepping?  Treat them as two different control regions, with InstaSPIN for the high end and typical stepper motor control for the low end?

BTW, for purposes of focusing the discussion, assume that I'm a competent embedded system HW and SW designer with MSP430, ARM and (a little) C2000 experience.

Any general pointers or words of wisdom?

TIA,

Mike

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RE: DRV8835: Overcurrent Period Specification

February 5, 2016, 11:19 pm
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Hi Colin,

Yes. If the real OCP condition > tDEG (1us), the device is in OCP protection and turns off the output for 1ms (tOCP) and retrys the outputs. Then if the OCP event is still there, the ouputs will only turn on for another tDEG (1us) time then OFF again for tOCP time. If the OCP condition <tDEG and not presented any more, there will be no OCP action.

Best regards,
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RE: DRV8835: Overcurrent Period Specification

February 6, 2016, 1:17 am
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Hi Wilson,

Many thanks for the prompt confirmation of the overcurrent behavior of the DRV8835!

Best regards,
Colin Campbell
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DRV8835: Overcurrent Period Specification

February 5, 2016, 10:07 pm
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Hi TI,

The DRV8835 Data Sheet (see segment of page 5 below) defines an Output Overcurrent Deglitch period (Tdeg) of 1us, but is silent on the actual Overcurrent Period (e.g. 100us) prior to the MOSFET Gate drive being turned off under this fault condition. My interpretation of the Data Sheet at this stage is that if an Overcurrent condition >= Iocp exists for the Deglitch period (Tdeg), the MOSFET drive is turned off - is this correct or is there a separate Overcurrent Period? Thank you for the assistance and clarification.

Best regards - Colin Campbell

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RE: DRV8835: Output Configuration with four independent Resistive Loads

February 6, 2016, 8:53 am
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Hi Colin,

The configuration described should work, although you may not get the same amount of current out of the system. The reason is that the high side RDSon is usually a higher than the low side. This may lead into thermal issues at higher currents.

What value is VM and the resistive load?
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RE: DRV8835: Output Configuration with four independent Resistive Loads

February 6, 2016, 2:04 pm
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Hi Rick,

Thanks for the quick follow up, and feedback on the MOSFET Rdson. For one application, we will be running a VM supply of 5 Vdc with a nominal 20 mA resistive load (250R); our second application has a VM supply of 10 Vdc, with the same nominal 20 mA resistive load (500R). We do not anticipate any issues with a low current load of this nature? Thank you for your confirmation and guidance on any issues we need to be aware of with this configuration. Many thanks.

Best regards,
Colin Campbell
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DRV8835: Output Configuration with four independent Resistive Loads

February 6, 2016, 1:15 am
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Hi TI,

I'm planning to use the DVR8835 to drive an output configuration consisting of four independent resistive loads, each connected from a single Output pin to the common Ground reference (GND). Hence in this configuration, all four Output Bridges would operate independently - there is no load connected between a pair of Outputs (e.g. AOUT1 to AOUT2). The Data Sheet infers that this is a legal configuration with the state of each Output being independently set by its associated Input (with consideration for the MODE pin setting). Could you please confirm that this configuration is practical for use of the DRV8835? Many thanks for your assistance.

Best regards,
Colin Campbell

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RE: Need +/- 2.5% speed regulation with DRV10983 on a fractional motor liquid pump.

February 7, 2016, 2:20 am
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Jasraj,

In this case, I assume it is normal for motor to slow down under load? Is it possible to establish a load-speed relationship?

Is it possible to know the power, torque or current injected into the motor from the motor drive?

Thanks,

Michel

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RE: DRV8412

February 7, 2016, 5:45 am
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Hi Eli,

Yes, the decoupling can be reduced. An example is the DRV8412EVM (figure 20 in the datasheet) and DRV8432EVM (LINK to zip files)

Both use a single 47uF instead of a 330uF.

We will investigate the 330uF recommendation. It appears to be unnecessary based on the fact the DRV8432EVM (with higher current rating than the DRV8412)operates.

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DRV8412

February 7, 2016, 1:31 am
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In datasheet of DR8412 Application diagram. Recommended decoupling capacitor for GVDD 300uF. Can we reduce a value of it without reducing performance of the driver?

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BLDC Motor with current regulation

February 7, 2016, 11:20 pm
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Hello,

Our customer looks for BLDC motor driver IC.

His application is below.

1) Take up a tape from reel with constant speed

2) When it finished, strain a tape with constant current

Do you have any driver IC which is possible to regulate the current?

(not current limit)

Regards,

Naoki Aoyama

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DRV8870 Tharmal resistance

February 8, 2016, 12:25 am
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Hello

I have a question about thermal resistance of DRV8870DDA.
Please tell me board information of 6.4 thermal infomation in datasheet.

We would like to use it under the following conditions.

- Ta=60℃
- Power=1.81W
- 6-layer PCB(FR4)

Best regards,

Noda

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RE: Need +/- 2.5% speed regulation with DRV10983 on a fractional motor liquid pump.

February 8, 2016, 12:53 am
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Michel,

Motor will definitely slow down under load. By how much, largely depends on the complete system and load (including inertia, electrical power input, motor efficiency etc). You can establish this relationship by running load tests with the drive. If the relationship is linear across all the variations (like input voltage, loads) you can drive is with x duty cycle for y output.

From DRV10983, You can read the speed directly (on FG pin or I2C register). The current is measured inside the device (for algorithm and protection) but is not given out to user.

Thanks,

Jasraj

 

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