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DRV8837: PWM Ramp

Shiwei Mao
Prodigy 10 points
Part Number: DRV8837
Other Parts Discussed in Thread: DRV8213EVM, DRV8213

Tool/software:

Hello, 

I'm currently using a DRV8837 in my design. 

I evaluated a DRV8213EVM for its current regulation capabilities and really liked what the GUI was able to do with the PWM ramp up. 

Therefore, I am attempting to duplicate the PWM ramp up in the DRV8213EVM with the DRV8837 chip by monitoring the DRV8213EVM's IN1 and IN2 signals. 

First question - the frequency selected on the GUI (50kHz) does not represent the frequency of what is monitored (25-50Hz) on IN1 and IN2 for the DRV8213EVM.

Secondly, even when I have the DRV8837's IN1 and IN2 identical to the DRV8213EVM, and turning off the current monitoring and regulation features of the DRV8213EVM - I am noticing that the DRV8213EVM's start up current is much lower than the DRV8837's (with the same load, VM bulk capacitors, etc).  Is there something fundamentally different about the DRV8213 that is not in the DRV8837 that allows it to have a better PWM ramp?  

  • 0
    TI__Genius 17510 points

    Hello,

    The adjustable frequency in the GUI of the DRV8213EVM should directly correlate to the input PWM frequency of IN1 and IN2 signals. The firmware files for the frequency settings and ramp functions are located on the DRV8213EVM product page. In the drv82xx.h file the PWM frequencies are defined as follows:

    The frequency setting in the GUI should directly correspond to the IN1 and IN2 frequencies. Are you only observing 25-50 Hz PWM frequencies on IN1 and IN2 regardless of GUI settings?

    The DRV8213EVM has an input ramp rate to limit the initial inrush current. Are the INx Ramp Rate settings on the GUI set to 0?

    Best,

    David

  • 0 in reply to David Medis
    Prodigy 10 points

    Hi David, 

    My apologies for my late reply.
    I am not observing IN1 and IN to be close to the 50kHz set in the GUI, I have not tested the other frequencies. Perhaps it's my machine because a colleague is telling me he can see the 50kHz on his machine using the same dev kit hardware, so we will look into this further.

    Is there anything special about the PWM ramp that is unique to the DRV8213? Would a DRV8837 be able to replicate the ramp? 

    Thank you,

    Tom

  • +1 in reply to Shiwei Mao
    TI__Mastermind 23361 points

    Shiwei,

    I tested it on an EVM and I am getting 50kHz.  Flash the firmware from the GUI (File, Program Device) and make sure you're using the latest version (2.0.2 right now) - https://dev.ti.com/gallery/view/MotorDriversBSM/DRV821x_DRV823x-EVM-GUI/ 

    As for the startup current, the main difference between the two devices is the RDSon - DRV8837 is 280mΩ, DRV8213 is 240mΩ.  And with a lower RDSon I would expect a larger startup spike not smaller, so I'm not sure what could be causing that difference.  If you could post a scope shot of the two each starting up that might help.  

    Also, I recommend using DRV8212 instead of DRV8837 - it's the newer version of the device.  

    Best,

    Jacob