DRV110: DRV110 regulation instability

Hi Tobias,

Appreciate your interest in using DRV110. I am reviewing your concerns and will follow-up with you by end of week. Any chance you could provide a copy of your schematic?

Thanks,
Kevin

Hi Kevin,

thanks a lot! Of course, this is the pretty simple basic schematic I used. The top 2 labels are the connections to the Coil, LfSbrkP is supplied by 24V when active. But as I mentioned I fiddled quite a lot with the circuit without anything having an impact on the behaviour I mentioned.

Kind regards,

Tobias

Thanks Tobias for providing schematic capture. Please give me a moment to respond to your concern buy Wednesday of next week, as I will be out for the remainder of the week.

Thanks,

Kevin

Hi Tobias,

To confirm, your primary concern is the noise coming from brakes which the DRV110 is controlling the current supplied?

I'm curious to see you calculations on how you chose the component values to achieve desired peak, hold, fosc, tpeak values. It surprises me that I do not see following parameter values in your system:

Reference voltage is derived from your choice of peak/hold current and sense resistor. "Zener-like circuit" refers to the zener diode placed at VIN, this acts as a voltage clamp for DRV110, however it is important to limit current (RS value) supplied to VIN in order to prevent damage to zener. 

Please share your thoughts on this.

Thanks,
Kevin

Hi Kevin,

yes, the audible noise is my main concern, we are powering electromechanical brakes with the DRV110 and the sound is pretty loud and annoying.

For the component selection the first thing to note is that I use the 8pin version. So HOLD is not configurable with a separate resistor, which led to the 250mR sense resistor (2x500mR), which was not correcly transferred into yor sheet. For Rosc under a certain threshold fosc is 20kHz, so I chose 0R in the first try.

My question now is if it really is a Zener diode - as the input voltage does not really behave the way I would expect it from a Zener. It looks more like a digital regulator that imitates a Zener and causes some pretty visible ripple that is also mentioned in the data sheet on p5. This would be pretty misleading and adding a real zener could be beneficial for stabilizing the input voltage.

Cheers, Tobias

Hi Tobias,

Checking on this, let me get back to you early next week.

Thanks,

Kevin

Hi Tobias,

Apologize for the delay here. Yes the Zener is real, could you include more details to your concern on Zener behavior?

Here are some additional suggestions that may improve your noise issues, copied from the other thread we have been collaborating on - https://e2e.ti.com/support/motor-drivers-group/motor-drivers/f/motor-drivers-forum/1017326/drv110-problems-with-hold-current-keep-time-and-noisy-fet-gate-drive/3793871#3793871

• Increase frequency/decrease ROSC. This may pull the frequency out of the audible range.
• Use a better RC filter on SENSE pin. Sometimes audible noise is created by the ripple current created by noise on the sense pin.
• Increase the hold current. This changes the charging/discharging characteristic of the the solenoid, reducing ripple current.

Thanks,
Kevin

Hi Kevin,

my concerns are that the supply voltage has a rather high voltage ripple that is nearly independent from the capacity that I place there - a behavior that I would not really expect from a real zener and the sentence "The DRV110 is able to regulate VIN voltage from a higher external supply voltage, VS, by an internal bypass regulator that replicates the function of an ideal Zener diode." in the datasheet. If this is a real Zener the datasheet should be adjusted.

I already tried different Rosc, but due to the frequency halfing effect that I noted at the beginning I cannot get the noise out of the audible range. I got the best results with 25kHz as the 12.5KHz noise is less annoying. Different Vsense filters did not change much and the hold current of the electromechanical brake is specified by the manufacturer, so I cannot change that too much.

I could achieve the greatest noise reduction by supplying the DRV110 with an external voltage source without much voltage ripple. That way I could get rid of the really annoying intermodulation-like sounds that were changing over time. This is also the reason why I focus so much on the nature of the input regulation.

kind regards,

Tobias

Hi Tobias,

How stable is your supply voltage to the device, regardless of filtering/decoupling caps?

Also, have you tried supply VIN and solenoid with separate supplies? I think you said you did, but just so we are clear.

VIN scope caps would also be helpful!

Thanks,
Kevin