LMR14010AEVM: LMR14010AEVM Files

Hello Amir,

I've attached the Gerbers below.BSR037A_Gerbers.zip 

Could you please share your schematic and layout as well as the following information:

Input Voltage (minimum, typical, maximum)

Output Voltage

Output current

switching frequency

Also can you please share your inductor part number. Thanks.

Regards,

Harrison Overturf

Hi

Below are my schematic and Layout as you requested. 

Vin = 16V-24V
Vout = 5V
Output Current = 250mA

Switching freq = 700Khz
Inductor: 74437346220

Please let me know if you need anything else.

Hello Amir,

Thank you for sharing your schematic and layout. The component values in your schematic look fine, however the layout could be improved.

1. It looks like you're connecting the GND plane on a lower layer rather than having a solid copper area on the top layer. It is best practice to include a large copper plane on the top layer to help dissipate heat
2. The input capacitor should be closer to the VIN pin.

Take a look at the Gerber files I sent over for a better idea of the layout.

What is the ambient temperature that the device is operating at? By how much does the inductor temperature rise?

Have you checked the SW node and Output node to ensure the waveforms are stable?

What is the input current at 0.25A output load?

Regards,

Harrison Overturf

Hi

Thanks for the quick replay. Regarding the layout, this board is 4 layers and I have a ground plane on all layers as you can see on gerber file. Regarding the Vin capacitor, I move it as close as possible, and thanks for the feedback.

 I also attached the Gerber file for you. This part is located at the bottom layer.

The board is running in ambient temp, but the inductor and surrounding parts temp go close to 50C.

Vin is 24V the input current is around 100mA 

Also, I put an image of the switch signal which is not correct. 

A-1302 X1.zip

Please let me know if you have any other questions.

Thank you

Hi Amir,

Thanks for the answers you've provided.

Yes the scope photos you've sent over seem to indicate that the device is operating in ECO mode which would mean that the inductor current reaches 0A during steady state which should not be occurring. I calculate the inductor current ripple should be around 250mApk-pk.

If you increase the load current, does the SW waveform behavior change? Does the temperature change?

What if you decrease the load current, does the SW waveform change? Does the temperature change?

If you increase/decrease input voltage is there any change in SW node performance or temperature?

Given the input power at 24Vin, Pin=2.4W, and the output power Pout=5V*0.25A=1.25W, I calculate the overall efficiency to be 52%. According to the datasheet, the efficiency should be somewhere above 80%. This 1.15W loss of power would certainly lead to the almost 25C rise in temperature that you're seeing. Where did you measure the input voltage? Did you measure directly across the VIN pin and the GND pin of the device? The screenshots seem to indicate input voltage of 13.5V. Perhaps the long trace connecting VIN pin to VSYS is leading to copper loss which is contributing to the loss we are calculating.

Using Wurth Electronics RedExpert tool, I estimate the total loss of the inductor to be around 37mW which would not be enough to account for the rise in temperature that you're experiencing.

https://redexpert.we-online.com/redexpert/

Please expect delayed response time due to the Thanksgiving holiday, I will get back to you by end of day 11/30.

Regards,

Harrison Overturf

HI

I hope you had good thanks giving. This morning I tired to change input voltage and you can see the effect on switch pin.(Same Load)  First shot Vin = 20V and second is 15V.

The load to the device is a single microcontroller and some LEDS.  Also 22uF 50V Cout also getting very hot too. Please let me know if you need any thing else. 

Hi Amir,

Thank you, I did have a nice Thanksgiving, and thank you for the screen shots. It looks as though the switching behavior remains unchanged even though the input voltage has changed. I wonder if the particular device that is under test is damaged somehow.

Have you noticed this same behavior across multiple devices?

Is it possible to try testing a new LMR14010 device and see if the behavior remains the same?

Regards,

Harrison Overturf

Hi Harrison,

I have tried with different boards and all have same issue and getting hot. I even tried to solder new chip and same effect.

Thank you

HI

Thanks for the quick replay, I am planning to change layout any way since this was rev X0, and some other parts need be changed too.

I have followed as much as possible the layout guide line from datasheet as you can see on Gerber file attached below.

I will be apricated if I can get any help possible.

A-1302 v117_2020-12-01.zip

Thank you

Hello Amir, 

In terms of layout improvements, the GND terminal of the input capacitor C40 should be right next to the anode (GND) of the schottky diode D3. This is a high di/dt path and you should minimize the inductance in it.

Note how the components are placed on the evaluation board LMR14010A.

How hot does the inductor get?

Are there other hot components around the inductor?

Cheers, 

Denislav

Hi Denislav

Thanks again for quick respond. As you can see on below image I moved the C40 close to D3. But my question is in the board I am testing C40 is already close to D3.

The C39 get around 50-55C and Inductor around 48-55C. C39(The output cap 22uF 50V) is the hottest component.

There is no other equipment next to the inductor. 

This is current circuit C40 position. which is close to D3. this the board which is getting hot and not stable

Hello Amir,

The output capacitor is connected to the inductor and the GND copper.

I wouldn't expect the output capacitor to be hotter than the inductor.

Is the GND copper on the output cap getting hot from other circuits connected to GND?

I wonder if it is bridging the heat over to the inductor. I must say 20 degrees C rise is not much and is well within the operating range of the components.

Can you measure the efficiency of the buck regulator to see if it is in the expected range, compared to the datasheet?

Cheers,
Denislav