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I am working on a design that utilizes a LDO Fixed Voltage Regulator. The voltage in is 24V and expected voltage out is 3.3V. I know the part is spec'd for 24V (Vin-max) and output of 3.3V, but should I be worried about the part overheating if the expected current draw on the load side is 0.2A (max)?

Power dissipation: 24V-3.3 = 21.7V --> 21.7V * 0.2A = 4.34W

4.34W seems like a lot of power dissipation for such a small part.

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  • \$\begingroup\$ You need at 12 mm²/W of exposed copper to a node in convection air otherwise case Rja __'C/W with 100'C absolute max \$\endgroup\$ – Tony Stewart EE75 Feb 4 '20 at 21:47
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It is a lot. Even large packages have a listed thermal resistance from junction to ambient of about 65K/W. Small packages are more than double that. Try not to use a linear regultaor step something down by more than a few volts.

Your LDO is listed as 63K/W or 235K/W depending on the package you choose. That's really hot.

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If you look at the thermal resistance figures in the datasheet you can calculate the resulting die temperature rise.

It’s not remotely practical.

Use a switching regulator. You can buy modules from Murata and others if you don’t want to worry about choosing the inductor etc.

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  • \$\begingroup\$ So why the heck would they make a voltage regulator with 24V input and 3.3 output? Seems a bit silly if it can't handle the power dissipation. \$\endgroup\$ – be-ee Feb 4 '20 at 20:11
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    \$\begingroup\$ @be-ee, some customers might only need 0.1 mA output. Others might use it in an adjustable mode with a higher output voltage. Others might use it where the load has very low duty cycle so there's no time for it to heat up before the load current drops to negligible. \$\endgroup\$ – The Photon Feb 4 '20 at 20:34
  • \$\begingroup\$ Great point! Thanks. It makes sense now. \$\endgroup\$ – be-ee Feb 4 '20 at 20:37
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    \$\begingroup\$ What Photon said, also there might be applications where the input voltage is low but the regulator has to withstand brief input transients that a TVS catches most of. A regulator rated at abs. max. input voltage 5.5V would be difficult to protect. This one part can fit a number of scenarios. \$\endgroup\$ – Spehro Pefhany Feb 4 '20 at 20:44
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    \$\begingroup\$ Also consider it's a bit irresponsible to make a device that needlessly wastes almost 10x as much energy as it uses. At $0.15/kWh it wastes $5.70 a year in electricity if powered 24/7. \$\endgroup\$ – Spehro Pefhany Feb 4 '20 at 20:49

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