Unstable driving voltage for 4 haptic by DRV2605 and mux??

Hi element 14! I am designing a Device which needs four vibrator to perform some haptic patten! I use four DRV2605 to drive one vibrator, and a multiplexer to control each DRV2605 through I2C! the main MCU I am using is ESP32.

Unfortunately, when all vribrators vribrate at the same time, one of the haptic motor vibrate solfer than other three. and I dont know why...

I tested the voltage of that weak one, it cant rich 0.8V, which other virator can achieve.

Those are powered by RT9013 has max. 500mA should be enough.

here is the schematic and PCB design, which i think have no problem....

what is the reason behind this ???

Did anyone have the same expriance of this scenario? Welcome to comment if you are facing mux current/voltage problem. I wanna learn more as well!

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Chuitoto over 1 year ago

I mean four DRV2605 to drive four vibrators separately!
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charlieo21 over 1 year ago

My first thought is that the vibrator that can't achieve 0.8V has a higher resistance than the other ones.
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BigG over 1 year ago

I recall looking at Seeed Studio's use of DRV2605 and they used an inductor to handle inrush current etc.

I tried something similar with this hack for a single vibrating motor attached to a BBC::microbit (you probably don't need to use all the caps shown):
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dougw over 1 year ago in reply to Chuitoto

Check the trace widths on power and ground to each driver - maybe the traces are too thin to supply enough current without a voltage drop. This could starve one of the drivers. Does the voltage at the driver in question decrease when other drivers are active?
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Gough Lui over 1 year ago

Not sure a maximum of 500mA in is enough - current loads for motors and drivers can be peaky and so it's the peak current you need to worry about, rather than the average.

Use a scope or DMM to measure the input voltage at each chip and the output waveform. If the waveform is unstable, a DMM may not give you an accurate result!

- Gough
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