A4983 5V voltage regulator getting hot ?!?!

Dear all,

I am powering a pic microcontroller, an XBee RF module and 5 indicating leds out of the 5V voltage regulator that is built in in the A4983 stepper motor controller and it is getting pretty hot. Is it normal ? My pcb consumes about 115 mA when I switch the main power on (15V 4A switch mode power supply) with the stepper motor disconnected (to figure out what the rest of my circuit consumes). Is 115mA over the top ?

Also the 3.3 Voltage regulator gets hot although my circuit doesn’t use it. Is that normal?

Finally, I need to use two A4983 in the same PCB. How should I connect the power rails (15V, 5V, 3.3V) so they are not parallelised.
I guess both of the modules get 15V 4A from the same power supply (in parallel) but I think it’s not right to connect the 5V and the 3.3 V outputs of the two modules together. Should I just ignore the 5V and 3.3V (let them disconnected) of one of the two modules?

Thanks in advance,


The 5V regulator is a 100 mA regulator. The data sheet has a graph of output current vs input voltage that indicates you can get up to around 150 mA of output current for input voltages under 20 V (when the ambient temperature is 25°C), but the output voltage accuracy, dropout voltage, and quiescent current will all get worse for output currents above 100 mA.

It is not necessarily bad for the regulator to get hot to the touch; plenty of electronics can operate comfortably at temperatures that can burn you. Also, it shouldn’t be surprising that the regulator gets hot. It is a linear regulator, which means that you can compute the power it needs to dissipate from the equation:

Pdis = (Vin - Vout) * I

In your case, Vin is 15 V, Vout is 5 V, and I is 115 mA, which means that you are dissipating a little over a watt in that tiny regulator package.

I would not expect the 3.3 V regulator to get hot if you are not using it. Are you sure you’re not just feeling heat transferred from the 5 V regulator?

You should not be connecting the regulated voltage outputs of different units as they could be at slightly different voltage levels. I suggest you connect your 15 V supply to both boards and use each board’s 5 V regulator to power that particular board. Perhaps you could use the regulated voltage from one board to power your PIC and the regulated voltage from the other board to power your XBee so that you aren’t straining a single regulator quite as much.

- Ben