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RE: DRV8701: Vref Adjustment based on motor size

March 17, 2017, 5:56 am
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Hi Mat,

Is it possible a capacitor is placed across the motor windings? This can cause problems with current regulation.
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RE: DRV8881: PWM off time

March 17, 2017, 6:15 am
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Hi Umberto,

In most use cases, the outputs can be set to a logic high or low and allow the DRV8881 to regulate the outputs.

If an application is trying to PWM the inputs at high frequencies, the current regulation settings can adjusted such that it is not operating. This would allow the inputs to control the outputs.
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DRV8881: PWM off time

March 17, 2017, 3:43 am
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Part Number: DRV8881

Hi,

 I do not understand clearly the specification of PWM offtime in the datasheet and specifically the logic low/logic high numbers that are typically 20usec/30usec.

How can they be consistent with an application that uses the driver at 100Khz(10usec period)?

Thanks

Umberto

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RE: DRV8842: DRV8842 about the OCP issues

March 17, 2017, 6:25 am
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Hi Mickey,

Q1: The OCP value is 6A. This value cannot be changed. Is my understanding correct?

Yes, the OCP value cannot be changed.

Q2: What is ICHOP? Is ICHOP the output current for DRV8842?

ICHOP is used to limit the current through the load.

Q3: Is the customer's idea correct? I don't think the customer use this low level signal as a detection signal.

The customer may be able to use the concept in this application report: www.ti.com/.../slva858.pdf
Current chopping should occur during starting the motor and stalls. Monitoring the outputs can be used to detect when the current is being regulated.

Q4: Why is the motor stall current less than the ICHOP set value?

How is the stall current measured? If using a meter, this is an average current. The ICHOP uses a peak current.
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DRV8842: DRV8842 about the OCP issues

March 17, 2017, 12:53 am
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Part Number: DRV8842

Hi Team,

The customer is using DRV8842. When OCP occurs, the nFAULT outputs a low level. The customer would like to use this low level signal as a detection

signal in his design when the motor stalls. But he sets the ICHOP value. He made the mistake of ICHOP as the overcurrent value.

When he set ICHOP is 3.3A, then the motor stall current is test 2A.  When he set ICHOP is 0.66A, then the motor stall current is test 0.5A.

I would like to confirm the following information:

Q1: The OCP value is 6A. This value cannot be changed. Is my understanding correct?

Q2: What is ICHOP? Is ICHOP the output current for DRV8842?

Q3: Is the customer's idea correct? I don't think the customer use this low level signal as a detection signal.

Q4: Why is the motor stall current less than the ICHOP set value?

Best Wishes,
Mickey Zhang
Asia Customer Support Center
Texas Instruments

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RE: DRV8871: Is there any equivalent IC but for higher currend needs?

March 17, 2017, 6:30 am
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RE: DRV10983EVM: Motor velocity constant

March 17, 2017, 6:55 am
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Hi Anders,

Sorry for delayed response.

Comment about BEMF constant calculation :
DRV10983 has built in BEMF observer and it estimates BEMF internally. It calculates BEMF constant by integrating estimated BEMF.
My experience has been that Motor Datasheet always are not always straight forward and accurate enough, can you measure it on bench while spinning motor manually.

BEMF constant is used in closed loop for abnormal Kt lock and calculating voltage limit based on current limit using formula Ulimit = (Acceleration_Current_limit) * motor resistance + speed * motor kt

Comment about open loop drive:

Generally for BEMF based sensorless solution, motor is driven blindly in open loop i.e. commutation is based on open loop parameters without any feedback from BEMF observer. Whereas in close loop it is driven based on calculated BEMF. There will be difference in current because the commutation in open loop is inefficient because phase current and BEMF are out of phase (drive angle is not optimized).

Regards,
Krushal
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RE: DRV10983: Speed control between Analog input and PWM

March 17, 2017, 7:00 am
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Hi Matsumoto-san,


Question 1: 511 corresponds to 100 % input duty cycle. Motor will be able to run at maximum speed when speed command is 511. 511 is just digital representation of input duty cycle.

Question 2: Customer should be able to use DRV10983 to spin motor at 4500 RPM, I don't see any problem.

Regards,
Krushal
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RE: DRV 10983 EVM

March 17, 2017, 7:12 am
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Jung Chun Sik,

To store parameters in excel  press save on GUI

Regards,

Krushal 

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DRV 10983 EVM

May 19, 2015, 5:01 am
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This is for Mr.  Milan Rajane.

I have used the  EVM and am not able to write  on to EEPROM.  Upon clicking of eeWrite message displayed is " make sure power supply is higher than 22V" even though it is 24 V.

Few  minutes back motor stopped rotating even though with the parameters filled in, it was rotating at 260 RPM with load, as desired, for few hours.  It is powered by 24 V battery. Can you please advise as to what may be going wrong?

I have not reported that I lost a 10983, with current limit of 2A

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RE: DRV8701: DRV8701 Operation out of Spec Voltage

March 17, 2017, 7:25 am
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Mat,
I would use relays as last resort as they are not very reliable. Rather, I would look into 200V Power Mosfets or IGBT with their respective drivers (IPMs). Thank you.
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RE: DRV8871: Is there any equivalent IC but for higher currend needs?

March 17, 2017, 7:41 am
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Hi Nathan,

If such a high current is not required, the DRV8871 can limit the current using ILIM pin. Section 7.3.3 in the datasheet talks about current regulation. I hope this helps, thank you.
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DRV8871: Is there any equivalent IC but for higher currend needs?

March 17, 2017, 6:29 am
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Part Number: DRV8871

Hello there! 

I'm currently working on a battle robot's motors control and I was thinking of using the DRV8871. But, since the motor we chose for the robot (a beetleweight, 1.36kg) has a stall current of 5.6A and probably peak currents that far exceed such value, the DRV8871 isn't able to properly supply it. 

Therefore, I'd like to know: is there any equivalent IC to the DRV8871 that supplies higher currents or should I amplify my current signal? 

Thank you all in advance! 

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RE: DRV10983EVM: Motor velocity constant

March 17, 2017, 7:52 am
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Hi Krushal!
Thanks for your reply.
In the section motor parameters Phase to Phase Kt found in DRV10983 EVM GUI.
My understanding then is that this figure then should come from the motor spec or or by spinning motor manually.
Then based on your information I come to the following conclusion. The provided BMF (Kt) is only valid for the open loop.
Is this correct understood?

At the first instant of the closed loop.
Is the inital BEMF(kt) first estimate of the observer the same as the one that is given in the GUI?
From the information about closed loop then the BEMF is a calculated value not a constant.

My understanding then is that the critical parameter from my point of view is to make sure that the open loop BEMF is accurate in a way so it can start all possible motor individuals of the same motor type.
The problem here is what you know and what I recently have learned. The BEMF is not very defined from the motor supplier.
This in turn can then lead to that we have non starting motors.
Do you have any suggestions on how to cop with this?
Should I spin 100rds of motors manually?
This is impractical.
How should I state the requirements to the motor manufacturer so that I know that the motors will start with the DRV10983 device?

Kindest regards Anders
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DRV10983EVM: Motor velocity constant

March 9, 2017, 8:29 am
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Part Number: DRV10983EVM

Dear whomever it concerns!

From the display tab I can monitor the motor velocity constant.

When running at no-load the constant is almost constant across the possible speed range.

Applying a load like a fan wheel that creates a load that increases with speed.

Increasing the shaft load from noload will lower the speed but now also significant change in the velovity speed constant.

What velocity constant should I use in the application?

The constant at full load and full speed or something else?

From the SLOU395C I can not find any advice regaring this.

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RE: DRV10983: Speed control between Analog input and PWM

March 17, 2017, 8:07 am
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Krushal san

Thank you very much for your prompt reply!

We would like to confirm one point about Question2.

We guess that speed(rpm)'s formula is as follows;
-speed (rpm) = motor speed (Hz) × 120/pole

Motor speed(Hz) is maximum velocity = 512 (0x01FF) / 10 = 51 Hz, so if we choice pole 4 motor, speed(rpm) maximum will be 1530rpm.

Is our recognition incorrect??

Kind regards,

Hirotaka Matsumoto

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RE: DRV10983: Speed control between Analog input and PWM

March 17, 2017, 10:36 am
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Hi Matsumoto-san,

There is correlation between Motor Speed (0x11 and 0x12 )and Speed Ctrl (0x00)

Motor speed is output register, it indicates the actual speed of motor. It is 16 bit register and maximum value is 65535.

511 is input for speed and its corresponds to 100 % duty cycle, refer 9.3.3 Motor Speed Control in datasheet.

Regards,
Krushal
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DRV10983: Speed control between Analog input and PWM

March 16, 2017, 6:58 pm
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Part Number: DRV10983

Hi all

Would you mind if we ask DRV10983?

<Question1>
On the I2C speed control, Maximum Velocity is 51Hz.
-MotorSpeed1 = 0x01;
-MotorSpeed2 = 0xFF;
-Velocity = 512 (0x01FF) / 10 = 51 Hz
-SpeedCtrl1 : 0xFF, SpeedCtrl2 : 0xX1
In case of speed control between Analog input and PWM, is Maximum Speed Command the same value 51Hz?

<Question2>
If our customer would like to use RPM=4500 with pole=4, we guess that it is impossible, isn't it?

Kind regards,

Hirotaka Matsumoto

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RE: drv110

March 17, 2017, 11:10 am
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Thank you James, for the information missing from the datasheet. But, as of 17 March 2017, the datasheet available from TI is Rev E, updated Nov 2916. This datasheet is still incomplete/wrong; in particular: "the data sheet does not mention that the STATUS pin will go high when EN is low."

I hope you can understand why this upsets me. The omission has cost me DOZENS of engineering hours. Designing a circuit making use of the advertised function of the status pin, laying out a PCB, sending out the GERBERS to have the PCB fabricated, populating the board, then troubleshooting, troubleshooting, troubleshooting, and finally doing a web search and finding this forum entry. Then the time spent explaining to my bosses why the board didn't work and explaining to our customer why the product is late.

Please fix the datasheet.
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drv110

November 20, 2015, 1:28 pm
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Would like a live Engineer to contact me directly at 781-565-1370 to discuss the following observation:

STATUS pin goes high even though I do not see a thermal issue or under-voltage condition on the VIN pin. According to datasheet, those are the only 2 conditions that would cause the STATUS line to go high.

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