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L6470 Step motor driver and VS caps run hot even when bridges are in HiZ

sdillier
Associate

‎2025-02-13 8:43 AM

I have a custom board that uses the L6470 for driving step motors.  All motor functions are working fine.  Circuit attached. Picture attached.

What I have noticed and concerns me is that in instances where the motors are off or not even connected the chip and my 440 uF caps on the VSA and VSB run at about 125F 52C.

I have tried setting the bridges to HiZ with no effect.

Why is this happening?

What do I need to do to have the chip and caps run cool?

Thanks for your help !!!

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Peter BENSCH
ST Employee

‎2025-03-02 11:40 AM

You are not using the recommended capacitors for the Charge Pump:

  • C27 should be 10nF and currently has 47nF
  • C28 should be 220nF and currently has 47nF

Furthermore, you only have the electrolytic capacitors C2 and C3 on VSA/VSB. I recommend connecting 1...2 ceramic caps with 100nF each in parallel.

Regards
/Peter

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