TPS61175: Power Delivery Issue

Hi Hafiz,

Thank you for reaching out.

It seems the loop is not so stable.

For the output capacitor, I choose from Murata and only find one: GRM158R61A226ME, which is 22uF,0402 with 10V rated voltage.

Its effective capacitance at 9v is only 1.7uF.

This is the main cause of the loop unstable.

Also, the large inductor causes the frequency of RHPZ too low.

Please see the recommended design.

https://webench.ti.com/appinfo/webench/scripts/SDP.cgi?ID=B2C6E31EBB0404E0

Main changes contain inductor, output capacitor and Rcomp.

For the output capacitors, the take care of its effective capacitance.

Best Regards,

Fergus

Thanks for your prompt response, Fergus.

Do you see any issue with the choice of diode we have done here? or is it good to go?

This is Screenshot from IC datasheet. We are using 22uH as you can see. We are using this same inductor. Is it okay or should we change it according to your design in shared link?

Hi Hafiz,

The diode is ok.

The datasheet shows some recommends for the inductor.

I attach the webench in case you cannot see it.

Actually, 22uH and 4.7uH are both acceptable in your case.

The difference in inductor causes different in output capacitors and Rcomp.

For 22uH, the frequency of RHPZ is lower, there should be more output capacitors and Rcomp is smaller to ensure loop stable and enough margin. The total loop cross frequency will be lower.

For 4.7uH, the frequency of RHPZ is higher, and the output capacitors could be smaller, and the total loop cross frequency will be higher.

The cross frequency influences the dynamic response and usually we want it to be as higher as possible.

For the output capacitors, we also want them to be smaller and less.

As a result, the Webench result is more recommended.

 It is highly recommended to log in Webench to see all the result, and you can change any of the component parameter to see the change caused. For example, change the inductance to 22uH, we can see the loop will be not stable unless adding the output capacitance or decrease Rcomp.

Best Regards,

Fergus

Hi Fergus, 
We have tried exact circuit as in your mentioned link. Please check attached test report from thermal cam. IC is overheating and restarting again and again. Please suggest what should we do in this scenario. Note that the most heated part in report at 144 degrees is TPS61175.FLUKE-1674FF07F.docx

Hi Hafiz,

The device could be thermal shutdown due to large loss and bad heat dissipation conditions

Here are two ways to improve:

1. decrease the switching frequency from 1.2Mhz to 500k or less.

Please take care of other component parameters like inductor saturation current, output capacitor, compensation parameters and so on.

2. Minimum the switching loop.

When the switching loop is large, the device will have higher spike, and the loss will be higher accordingly.

3. Increase the dissipation condition

In our EVM, it is a 4 layer PCB and has some vias conduct to heat from device to the whole board.

It is recommended to use thicker copper and more vias to improve the dissipation condition.

Please try solution 1 first.

Best Regards,

Fergus

Hi Hafiz,

I have test the same condition at our EVM.

Vin=4V,VO=9V,Io=0.9A and Iin is around 2.62A;

The frequency is about 1.1Mhz;

The stable temperature for device is only 50C vs 20C Ta;

BTW, the inductor is not close to the device that its loss will not influence the device.

So, could the device work in an abnormal way that causes large loss?

Please check the input current and SW waveform as well.

Best Regards,

Fergus