A4983 Cooling and Current limiting

I order three boards from a distributor of yours, and as i am waiting for the delivery i have some time to check for the details.
So i have some questions about cooling the chip and setting the current limit.
According to Allegro manual found on your site:

“Layout The printed circuit board should use a heavy groundplane.
For optimum electrical and thermal performance, the
A4983 must be soldered directly onto the board. On the underside
of the A4983 package is an exposed pad, which provides a
path for enhanced thermal dissipation. The thermal pad should be
soldered directly to an exposed surface on the PCB. Thermal vias
are used to transfer heat to other layers of the PCB. Thermal vias
should not have any thermal relief and should be connected to
internal layers, if available, to maximize the dissipation area.”

Is this implemented in your board? and if so, is the plane electrically isolated or is connected to the ground? have you any suggestions of how to secure a heat sink on the board ?

The second thing is about current limiting. Again according to the manual :

“The transconductance
function is approximated by the maximum value of current
limiting, ITripMAX (A), which is set by
ITripMAX = VREF / ( 8 * RS)
where RS is the resistance of the sense resistor (Ω) and VREF is
the input voltage on the REF pin (V).”

And later:

“It is critical that the maximum rating (0.5 V) on the SENSE1 and
SENSE2 pins is not exceeded.”

With the value of Rs = 0.05 Ohms the above equation gives us a maximum of 1.25A which is much lower than the 2A written in the description of your board. Am i missing something.

Thank you in advance.


The thermal pad is connected to ground, as it needs to be. This is small, 2-layer board, so the heat sinking provided by the board will be limited, and there is no specific provision for adding heat sinks. You can thermal epoxy or tape small heat sinks to the chip itself or to the back of the PCB; just make sure not to short anything out.

The multiplication by 8 does not apply to the actual voltage on the sense pins. With 50 mohm resistors, it would take 10A to get to 0.5V.

- Jan


Thank you very much for your response.


You might want to look at the chip cooler Enzotech mos c10 r at new egg.
newegg.com/Product/Product.a … 6835708012
This is a small copper heat sink that will work. be careful not to short the components in the vicinity.
newegg.com/Product/Product.a … -_-Product
here is a good non conduction epoxy to use to attach the heat sink.
Still I would recommend putting scotch tape on the heat sink in areas that might short other components. better safe than sorry.


I have not used this one, but it should fit on the chip pretty well:

- Ryan