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# Calculating current with Vref pin (a4982, a4988, a5984)

Posted by asrt
 Calculating current with Vref pin (a4982, a4988, a5984) May 11, 2018 01:26AM Registered: 2 years ago Posts: 29
Good morning.
I recently burn one of my stepper driver and I want to make sure that my calculations are correct.
a4982, a4988, a5984 stepper drivers have the same equation to calculate max current with VREF pin:

ItripMAX = VREF / (8×RS)

Questions:
One stepper driver have 2 bridges with RS = 0.05ohm for each, so i supose put in equation 0.05 or 0.1 ohm ?
Stepper motor can handle 2A of current, this means that ItripMAX shouldn’t cross 1A (because there are 2 bridges) ?

P.S I put 0.65V on VREF
 Re: Calculating current with Vref pin (a4982, a4988, a5984) May 11, 2018 03:12AM Registered: 3 years ago Posts: 5,232
The current setting and the stepper rating is meant for each motor coil individually. The motor can hande 2A on each coil and the driver regulates current based on the two independant shunt resistors.
You don't have to half the values or such.

0.65V means 1.65A, which is fine for the stepper, but probably too much for the driver.

Edited 1 time(s). Last edit at 05/11/2018 03:16AM by o_lampe.
 Re: Calculating current with Vref pin (a4982, a4988, a5984) May 11, 2018 04:08AM Registered: 2 years ago Posts: 29
Thank You for answer.
I have 1.7A motors and stepper driver that i burned (a4982) can handle up to 2A according to doc.
My mistake.

Anyway from which current I should use heat sink on stepper drivers ?
Maybe he can handle up to 2A but he needs heat sink above X amount of current ?
 Re: Calculating current with Vref pin (a4982, a4988, a5984) May 12, 2018 02:54AM Registered: 3 years ago Posts: 5,232
I use heatsink and fan for all my controllers . Just to be on the safe side during overnight print jobs.
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