Part Number: DRV8801
Hi,
I'm using a motor that has a PWM range of 0-16v. I have a Pololu DRV8801 driver that is triggered by a WeMos micro controller. Though the prototype is working, and the Vbb = 16v, the max voltage available voltage to the motor during the PWM operation seems to be only 5~6v.
a. Is this normal?
b. If so, are there driver boards that will deliver the entire Vbb to the motor?
Thanks
Hello Rick,
Thank you for advice, I tried but I did not find still any difference in PWM delivery...
...But I measured that both signals, Fault_n and OTW_n go to "0" close after the motor control start in both (previous and a new) SW versions. After power up, the signals fault_n and otw_n are "1", and thay are latched to "0" when reset_a_n , reset_b_n and reset_c_n go to "1" simultaneously for several milliseconds. PWM commands are "0" at that time.
Additional detail:
The new SW version works well after replacement of driver chip on the same board. May be some driver series are more durable/robust ?
Part Number: DRV8312
Hello ,
I am a new user of E2E , I signed the previous post as “resolved” by mistake. I need the support still.
Also thank you for previous post reply.
The details are following :
- We are using PWM driver chip DRV8312DDW for about 2 years to control brushless DC motor.
- We used this chips for a relatively long time, but at the last time 3 chips in new cards were damaged.
- We are using CBC (cycle by cycle) current limit mode to control the brushless dc motor.
- The current limit is set to 4A, when according to data sheet the limit of the device is 3.5A continuous
(for the chip with the thermal pad on the bottom side).
- Some time ago we performed minor change in microcontroller SW version that delivers PWM to driver DRV8312.
- Before the SW version change, the motor driver DRV8312 worked well (device with code 62COZXTG4) .
- After the SW version change, running the motor driver under motor load caused to irreversible damage, i.e. previous SW version does work well also ...
- The problem occurred till now in three devices, we did not try to run the new SW with another devices from the same batch yet.
- The failure seems as "loss of driver strength", i.e. the motor is not able to deliver enough moment again the load, it stops soon after the motor start up.
- After replacement of the above devices with another ones (with code 38C34NTG4 ) - the design returned to work well again, but with old SW version, I don’t want to run them again with new SW version.
- The additional card with driver device signed 38C34NTG4 works well also with new version of SW.
I would like to ask:
· Can overcurrent cause to the damage of the device in this case ?
· May be there are some problems with devices batch (any errata, etc.) ? The device that we suspect as problematic is marked:
DRV8312
62COZXTG4
Best regards,
Y D
Hey Ganesan,
If the driver does not trigger any other fault during operation after disabling the fault detection for the BEMF then there could be problem with the programmed Kt. As a result, let’s make sure that verify your measured Kt value with a different method highlighted in the tuning guide.
Take your motor and manually spin it with your fingers when the driver is turned off. In addition, probe any of the phase voltages in reference to ground. You should see an induced sinusoidal type voltage waveform (known as the Back EMF) appear on the oscilloscope. Then measure the voltage of the waveform, peak to peak, and the frequency of the waveform. Then, using the equation below, you should be able to find Kt.
Kt = (V_pk-pk/2)*(1/f_BEMF)
BEMF abnormal checks the programmed Kt and actively measures the Kt (in the same way mentioned above) and compares them. If they are not within a threshold for a certain amount of time, then the fault will trigger. Usually, this is helpful when the motor is stuck and the BEMF isn't being generated because the motor isn't moving. But this could be a false trigger based on your description. Look at section 8.4.8.3 in the datasheet for more information
Measure Kt in the new method above, insert the new value, and see if BEMF abnormal continues to trigger. Let me know if anything else unexpected happens from here.
Best,
-Cole
Hey wenjun,
It sounds like you motor profile needs to be tuned a bit. To start, the DRV10983-Q1 needs the Phase Motor Resistance and Motor Torque Constant (Kt). To measure these, please refer to section 2.2 and 2.3 the DRV10983-Q1 Tuning guide if you need help.
Then, feel free to use some default settings provided below through the use of the GUI or the appropiate registers. Be sure to add in the appropiate values that you found for the Phase Resistance and Kt.
This should get the motor spinning and allow you to start tuning. If the motor continues to stop, please monitor the faults that are shown on the display tab and report back which fault is triggering.
Best,
-Cole
Part Number: DRV8308
Hello,
The DRV8308 and DRV8307 datasheets do not specify any tolerance for the CLK50 and TBLANK specifications; only the typical values are specified. I presume that the TBLANK time is based off of the CLK50 internal oascillator, so I can determine the TBLANK tolerance based on the CLK50 tolerance.
Is there any information available on the tolerance or range of CLK50 or TBLANK?
Thank you,
Jim
Hi ,
One more update is that the we use both 1/4 and 1/2 stepping modes in our design. Two PWM frequency also used - 400Hz and 800Hz.
Is there any register setting to update TRQ ?
Part Number: DRV8412
Hi
We have been using the DRV8870 device for an application to drive an LF Antenna loop very successfully.
Although we think that the DRV8870 3.6A Peak current limit has limited our emitted range, so we have been looking to use a DRV8412 device to test whether this is the case.
We have read the data sheet for the DRV8412 device and we cannot seem to find what in the DRV8870 device datasheet is called the brake/slow decay (pg 8 of DRV8870 datasheet) function. Everything else in the DRV8412 datasheet looks fine and it will do what we require.
My question is when there is no input to PWM_A, PWM_B, PWM_C or PWM_D what state does the output sit in, is it effectively a brake/slow decay condition, there is no table to show this in the DRV8412 datasheet as there is in the DRV8870 datasheet. This is important as the majority of the time the DRV8412 will be sat in this state waiting for data to arrive.
I appreciate this is a very unconventional use of the DRV8412, but we are trying to replicate some BPSK data at LF frequency so being able to reverse the current flow within the loop in important and the DRV8870 does what we want it to do.
Regards
Darren
Hi Rick,
I am still having some issues and wondering if you can explain how 100% duty cycle can work?
I would have thought that at static condition (100% duty cycle) that the bootstrap power supply would stop working.
This in turn would mean that the high side FET driver would no longer work.
Yet it mentions 100% duty cycle in a few p[laces in the data sheet.
Kind Regards,
Conor.
Part Number: DRV8871EVM
Hi,
I have a DRV8871 Evaluation board and I am using external PWM and was wondering if the full 0% to 100% duty cycle range can be used if the PWM frequency is 100khz.
The reason I ask this is to know whether or not the internal charge pump has any special requirements.
Also:
I am using a sinusoidal PWM, with INA1 set high and sinusoidally pulsing the INA2 for the positive half cycle and INA2 set high and sinusoidally pulsing INA1 for the negative half cycle.
I am seeing a 1Mhz chopping of the output current for part of the negative cycle, and was wondering where this originates from, I don't think it is the current limit as the current is only +/- 0.25Amp.
Any thoughts welcome,
Kind Regards,
Conor.
Part Number: DRV8308
Is it possible to use a lower motor voltage than 8.5V by using a different voltage supply for the VM pin than the actual motor voltage supplied to the half bridges? For example, would there be an issue if I supply the VM pin with 15 VDC and the half bridges 5 VDC? See example in the image below. The only consideration that I can think of is the gate-source voltage of the FETs. Is there anything else?
Part Number: DRV8308
What is the balance between PWM frequency, duty cycle and the control loop for closed-loop control with Clock Frequency Mode?
I have an application that normally needs a motor RMS current of 5 to 20 mA and has a maximum current limit of 340 mA (calculated from the maximum torque limit). The motor has low winding inductance (85 uH) and resistance (5.5-ohm). I plan to operate the DRV8308 with a supply voltage of 8.5 V. Due to the low winding inductance, the di/dt is very fast, so I would like to understand the relationship between using a high PWM frequency and the ability to manage speed and current.
Also, if the PWM Ton time (PWM pulse width) is shorter than the Current Limit blank time (TBLANK), does the Current Limit circuitry even have an impact? (I presume the blank time is reset at the beginning of every PWM cycle.)
As for the PWM output for the MOSFET pre-drivers (assuming 120° commutation, not sine-wave-drive), my understanding is that the duty cycle is based on the output of the speed control loop (differentiator, integrator, digital filter, etc.) which results in a 12-bit duty cycle to be applied as Ton for the next PWM cycle. That said, if the PWM frequency is set to 200 kHz, the PWM cycle time is 1/200 kHz = 5 us. Then with the 12-bit duty cycle, the PWM Ton time can be as small as 5 us / 4095 = 1.22 ns (e.g. a 50% duty cycle would have a 2.5 us Ton time or a count of 2048 where 2048*1.22 = 2.5 us). Is this the correct understanding of how the PWM output works?
However, a minimum PWM Ton time (PWM pulse width) of 1.22 ns doesn't even seem realistic since it would require a transistor gate charge of about 0.15 nC just to turn on with the DRV8308 maximum output drive current of 130 mA (rise time = gate charge [C] / pre-driver current [A]). That doesn't even allow the FET to fully conduct and a power MOSFET with that low of a gate charge is not readily available to the masses.
Overall, I'd like to make sure I am correctly understanding the closed-loop speed control operation and the associated PWM output duty cycle operation and timing resolution. Once I correctly understand those and the relationship between PWM Ton time and Current Limit blank time, I believe I can determine how to properly use the DRV8308 in my application.
Thank you,
Jim
Part Number: DRV8884
Hi,
The current input to the motor is measured as 60mA, but the design value is 75mA. What could have caused this change?
Please see the details..
1. RREF = 562K
2. TRQ = 1
3. DECAY = tied to DVDD (slow decay)
4. We use both 1/4 and 1/2 stepping modes in our design and two PWM frequency - 400Hz and 800Hz.
5. Motor current waveform is shown below.
Part Number: UC2625
Hi everyone,
We are using UC2625 for BLDC control along with LM5100A gate drivers and CSD88539ND mosfets. Our problem is that during the LOW side of the PWM generated by the UC2625, all gates are disabled and only diode freewheeling becomes active. Without the active freewheeling, when the PWM duty steps to zero from a non-zero PWM duty, the motor just coasts to zero speed slowly.
With the following speed control loop (from slua106), it can be seen that motor can quickly accelerate to the target speed but cannot decelerate to zero speed as quickly due to this diode freewheeling behaviour.
We could use the brake feature of the UC2625 to quickly stop the motor. However, to quickly decelerate to a non-zero speed or to follow a sharp speed ramp, we can't use this feature.
We have built a speed control loop along with a current control loop that actively slows the motor by applying an opposite current. This way it is possible to slow down the motor very quickly. However, in our application we can't use a closed loop speed control due to other reasons.
If there is a method or circuitry that we can implement to achieve an active freewheeling behaviour with UC2625, we would be glad to know it.
Best Regards.