DRV8825: Current setting & heat sink requirement

Hey AG,

Thank you for your question.

In order to better assist you, I would like to ask for what is the value of the sense resistor being used in your design. Please provide a pdf of your schematic to better understand your design.

Best,

Akshay

Hi Akshay,

please find the image for ckt diagram.

Hi i am using below mentioned board for evaluation, sense resistor on by board are 0.25E

https://robu.in/product/drv8825-stepper-motor-driver-with-aluminum-heat-sink/ 

Hi Akshay,

Thanks for reply,

motor spec (24V ±10% current: 1 phase 0.6A, 2 phase: 1.2A) these are specs mentioned in stepper motor datasheet, as max. continuous current, peak can be 1.5A

considering the current capacity of chip, i am using it with half capacity, is it correct?

I want to maintain min. power/ thermal dissipation, so want to maintain the case temperature less than 70degC , with out any external aluminum heatsink 

is there any way to calculate it in reverse way?

regards,

Hey AG, 

In a stepper motor, the set full-scale current (IFS) is the maximum current driven through either winding. I chop is the full scale chopping current. So from the info you provided this is 0.6A. So not the half capacity. 

You can use this formula to back calculate total power dissipated based on junction temp, ambient temp, and theta JA.

Since the PCB design also affects the temperature seen it might be best to measure the temperature with a thermal camera if possible.

Best,
Akshay

Hi akshay,

DRV8825 datasheet mention driving current of 2.5A for each coil at 24V & 25degC, i am setting current approx. 0.6A for single coil, will it help me in achieving less power dissipation ? 

Hey AG,

Yes, having less current pass through the RDSon of the FET will result in less power dissipation. 

Hope this offers some clarification.

Best,

Akshay

Thanks Akshay,

what will be the max. safe power dissipation at 25degC above which we need to use the heatsink (considering all layout recommendation already implemented on 2 layer, 1Oz copper board)

unable to find max. operating junction temperature range in datasheet

regards,

Hey AG,

The use of heat sink really depends on your specific need. If you see very high temperature during operation you can add heat sink to prevent damage ton components.

It is hard to suggest a safe power dissipation at any given temperature since a lot of factors go into it. The main consideration is preventing damage to any components on board and to ensure device functionality. 

The max operating junction temperature is shown in this table;

The following power dissipation app note might be a good resource for more info.

https://www.ti.com/lit/an/slva504a/slva504a.pdf

Best,

Akshay

Hi Akshay,

Thanks for reply

i was trying to limit the power dissipation max. to higher limit of operating junction temperature...

the values mentioned there are still in the absolute section, not in the recommended

Regards,

Hey AG,

I understand your concern. I would suggest using the formulas mentioned above to get an approximate idea of power dissipated and then using the thermal resistance in table 7.4 to estimate the temperature and add a heat sink if the IC is running hot. Or work backwards and use a thermal camera to measure case temp during operation and find power loss under operation.

Hope this helps.

Best,
Akshay