Maximum current for Nucleo board's regulator when powered with 12V supply

[JDick.2]

Hi all,

I want to use Nucleo-F302R8 or Nucleo-F303K8 and want to power it from a 12V supply. Nucleo board also supplies current to a sensor ect. so the board regulator sinks up to 100mA. In that case I measured the current sinked by the board's regulator as around 100mA.

Both boards use SOT223 type 5 volt linear regulator(LD1117S50TR) as shown below:

 

And the boards have the following tables for current limitation at several VIN:

 

 

And in my case the voltage drop will be (12.5)=7V and since the board will sink 100mA, it means the regulator of the board needs to dissipate 700mW. As I know SOT223 types cannot be heatsinked. And I'm wondering is it really fine to use this board up to 100mA at 12 VIN voltage.

Again to sum up, in my case my power supply is 12V 6A and the voltage regulator of the Nucleo board sinks 100mA in my case. The table says 250mA/300mA limit at 12V VIN; but I'm a bit confused how they dissipate such heat.

How can I know whether the regulator on this board can withstand the heating? Can I rely on the table? And at up to what ambient temperature this is valid for?

(It is impossible for me to contact the designer or how calculations done but at least if I can know whether I can rely on it and whether I can use the board safe by 12V VIN upto 100mA would be nice.)

[AScha.3]

so loss will be about 0,7W , from 1117 data can see:

0,7 * 110 = 77° rise, with ambient at 30° you should get about 107° C at the 1117 chip.

-> it should survive for some time.

• dont touch, could burn your finger
• design will work, but is not "long time no service" , if cool chip, would have long life
• i would put some part in 12V input, to dissipate part of the power, some diodes or 39 ohm (1W) resistor

[S.Ma]

You can probably rely on the table. The original design probably was done to be compatiblr witg Arduino Uno connector and functionality. Checkout their forum for xtra info. Otherwise a dcdc voltage regulator board piece will do a better job at higher current than linear cheaper linear regulator.