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# The power inductor,MOS and Schottky Diode are hot situation

Other Parts Discussed in Thread: TPS40210, TPS40210EVM, TPS54140

I use the TPS40210 to achieve 12V to 24V at 2A regulator, but the power inductor, MOS and Schottky diode in a load of 400mA will have a hot situation.
This is what factors or how to improve this problem?

• I have uploaded the schematics, such as the link shown below.

http://i.imgur.com/NFyRI.jpg

• Hi Pohua,

I took a look and have a few questions for you.

When it begins to heat up, is the output voltage stable? Can you quantify how hot it is?

Is this on a custom layout? The main way to help thermal performance is to ensure there is to use some copper area to aid in dissipating the heat.

After a look at your schematic you may also need to look again at your inductor. What is the saturation current rating for the part you are using? In a boost topology, the peak inductor current is equal to the input current plus one half the ripple current (Iin+Iripple/2, see equation 39 on the TPS40210 datasheet). At full load there will be at least 4A DC through the inductor not including the efficiency. Without going through the calculations I estimate about 6A peak current.

Regards,
Anthony

• Dear Anthony:
This circuit is not load, the power inductor, MOS and Schottky diode will not be hot situation, the output as shown below:
http://i.imgur.com/Hr61J.png

When the load of this circuit,the power inductor, MOS and Schottky diode will have a hot situation and about 4-5 sensonds the temperature reached 70 degree C,the output as shown below:
http://i.imgur.com/SZvt6.png

The power inductor specifications currently in use as follows:
Mmanufacture:Coilcraft
Part number:DO3316P-153MLB
Inductance:15uH
Tolerance:20,10
DCR max:0.046Ohms
SRF typ:27MHz
Isat:3A
Irms:3.1A

The MOS specifications currently in use as follows:
Mmanufacture: Vishay
Part number:Si4470EY

Thanks!

Best Regards
Pohua

• Hi Pohua,

Thank you for the specifics on the components your using and the screenshots. Based on the screenshots your supply looks stable with the load.

To be sure, was the 70 degree measurement taken with the 400mA load? The thermal performance is largely layout dependent. In a non synchronous device operating with about 50% or less duty cycle you can expect the diode to be your hottest component. With a typical layout similar to that of the EVM, a temperature around 80 degree C at full 2A load is expected.

Lastly you will need an inductor higher saturation current for your full 2A load. Without going through the calculations thoroughly, I recommend at least ~6A saturation rating.

Regards,
Anthony

• Dear Anthony:

I'm sure the load 1A about 4-5 seconds when the temperature reached 70 degrees C.
So do you think of the layout problems caused by the phenomenon of power inductor, MOS and Schottky Diode hot?

Thanks!

Best Regards
Pohua

• Hi Pohua,

I cannot say for sure it is the layout without seeing it but it is likely. I suggest comparing your layout to the TPS40210EVM for an idea of how much copper we have connected to the inductor, switch and diode to aid with thermal performance. Also with a 1A load you are operating very close to the saturation current rating of your inductor and the currents may be higher than expected.

Regards,
Anthony

• Dear Anthony:

When I replace the power inductor and load 1A from DO3316P-153MLB SPT68H-183, the hot time of approximately 15 minutes to reach 70 degrees C, compared to DO3316P-153MLB be extended to 10 minutes.
However, power inductor, MOS and Schottky Diode is still hot.
layout as below.
http://i.imgur.com/dxc7D.png

Thansk!

Best Regards

• Dear Anthony:

In addition to the above conditions, we use the TPS54140 specification layout rule to layout, but the TPS40210 specification documents did not provide any the layout rule.
Could you provide layout rule for TPS40210?

Thanks!

Best Regards

Pohua

• Looking at the layout I cannot tell if you use any copper planes to aid with the thermal dissipation. It appears everything is connected with traces only. Please see attached picture for some recommendations based on what was done for the TPS40210 layout to help with thermal performance. In your application I expect the diode to be the hottest component.

Some guidelines to follow for layout of the TPS40210:
-The important path to minimize in a boost converter is that including the output capacitor, diode and FET.
-Use a ceramic input capacitor located next to the VDD pin with a short return path to the "power" GND copper
-The VBP capacitor should be close to the BP pin with a short return path to the "power" GND copper
-All other analog components should be kept close to the IC such as those connected to RC, SS, COMP, FB, and ISNS. It is recommend to isolate this ground return used for these components to create a "quiet" ground minimizing any noise as done in the EVM example.
-See attached image for tips for help with thermal performance
-Use footprint and vias pattern for the TPS40210 given at the end of the datasheet.

Let me know if you have any questions.

Best Regards,
Anthony