24V 1A SMPS Unit Design for Industrial Environment

[electronx]

Hi everyone,

I have a 48V input and I want to regulate it down to 24V 1A output for an industrial SMPS unit. My available space is quite limited, so I plan to use an integrated MOSFET SMPS IC. Since the inductor also needs to be small, I’m considering increasing the switching frequency to around 2MHz. (Higher switching frequency allows for lower inductance, which means a smaller inductor, but also increases losses.)

Up to this point, everything is clear. When I look at DC-DC converter ICs with integrated MOSFETs, I see that the typical efficiency at 500kHz is around 88–90%. If I operate at a higher frequency, efficiency will drop; let's assume the worst-case scenario is 85%.

If I can get 24V 1A output at 85% efficiency, that means about 4.24W of power loss, so I’ll need to dissipate this heat from the package.

The datasheet gives θJA (°C/W) as 35.

If I multiply by 4.24 W, that's 148,4°C, plus 85°C ambient temperature, totaling 233,4°C. But the maximum junction temperature is only 150°C, so in this case, it seems I can't use it.

However, the RAA211650 datasheet says it supports 60V 5A, which seems to contradict my thermal calculation.

Is my calculation correct, or can I safely use this IC for 24V 1A output?

Thanks in advance for your help!
For example, the SIC472ED-T1-GE3 gives a θJA of 12°C/W.

The LT8641A datasheet specifies θJA = 30°C/W on a JEDEC board and 17°C/W on their demo board.

Both of these are relatively expensive ICs.

Is it more reasonable to use these types of more expensive ICs with better thermal performance,

or should I go for cheaper chips like AP66200 or RAA2116504GNP, which claim to support above 2A output (even if the thermal dissipation might not be sufficient)?

Even if the datasheets claim higher output currents, I’m concerned about whether the actual thermal performance will be sufficient in a small enclosure.

What would you recommend in terms of cost versus thermal reliability for a compact industrial design?

[mtwieg]

However, the RAA211650 datasheet says it supports 60V 5A, which seems to contradict my thermal calculation.

That just means its max operating voltage is 60V and its max operating current is 5A. Doesn't mean it can do both at the same time.

The datasheet only gives efficiency specs at 500kHz. Can't really estimate what it would be at 2MHz.

Also you should look at figure 53. It looks like at 2MHz you can't make 24V from 48V at any current level.

[electronx]

yes   1.886 MHz  max its around 15uH inductor its also okay, in that case can it give 1 A  without any heat damage?

[Doctorandus_P]

So it must be extremely small, have a high efficiency, be of "industrial quality" and may cost nothing.

Reaching two of those goals is relatively easy, three may be doable, but all 4 won't work.

[mikeselectricstuff]

However, the RAA211650 datasheet says it supports 60V 5A, which seems to contradict my thermal calculation.

That just means its max operating voltage is 60V and its max operating current is 5A. Doesn't mean it can do both at the same time.

..or continuously

[mikeselectricstuff]

If you're looking for small, take a look at converters with integrated magnetics - the onboard inductor reduces capaitance & allows higher operating frequencies with lower losses.
There are plenty around nowadays  but I've not looked at how many support 48V.
As well as buck converters, There will be plenty in the "DC/DC converter" section of Digikey etc. Integrated inductor converters sort-of straddle buck ICs and integrated DC/DCs so can appear in either category

 Also, look at converters with a significantly higher current rating than you need - these will tyopically have lower RdsON MOSFETs, and hence better efficiency

[mikeselectricstuff]

Microchip Mic28514 is worth a look - quoted efficiency 92% at 1A for 28V out, pretty cheap.

[voltsandjolts]

There's a bunch of units on DK for $15 or so, like this.

[mikeselectricstuff]

If you need small
https://www.digikey.co.uk/en/products/detail/analog-devices-inc/LTM4653EY-PBF/8572272

[PCB.Wiz]

You need to give actual dimensions on your ‘small enclosure’.
Does this need to be isolated?