LM5116 simulation limitation: Vin 48, Vout 24V 10A is not possible to simulate

WEBENCH uses available components in the our database to provide a complete design BOM. At some cases, the design just wasn't able to be created with the available components.

BTW, I was able to create a LM5116 design in WEBENCH with your inputs: Vin=48V, Vout=24V and Iout=10A

Can you please clearly your question on 'Why is there limitation in the simulation SW at 7A??'

LM5116 25V 10A 300kHz toHoward.docxHi Howard

After some manipulation with the temp. setting I manage 10A out in the simulation.

Hovever ther is still some challenges.

Please see the attached explanation and problems.

Thank you for your support

Regards

Jørgen

Hi Jorgen,

I have reviewed your attached document and please see my response below:

Looking at your TPS40170 design,  I still think it will work fine if you were to change out the FETs to either BSC340N08NS3G, BSZ340N08NS3G, or BSZ440N10NS3G. All three of these FETs have their Qg less than 8nC and it will help reducing driver power. Also, removing the gate resistors (R328, R192, R330, R221) will also help to reduce IC power. Let me know if this helps to improve the IC Tj.

So, what types of FETs are on the board now? part number?

I was not able to completely to create a WEBENCH design to meet your design requirement of 48-50Vin, Vout=25V and Iout=10A for 300kHz. However, please try the suggested design inputs: 48-50Vin, Vout=25V and Iout= 8.5A and Ambient Temp=-40. This should create the LM5116 design with switching frequency of 320kHz. You can then run the bode plot sim.

The LM5116 is capable of be designed with Iout up to 20A with some limitations.

 

 

Hi Howard,

Your proposed FETs has Rdson of 34mR and Typ. Qg 6,8nC

The current FETs on the board (BSC039N06NS) has 3,9mR and Typ. Qg 27nC

The difference is a factor 4 for Qg but a factor 10 in Rdson.

Do you have a link how to calculate or can you teach me what the difference in power dissipation in the FETs are for the two cases at Vin 48V Vout 25V 10A switch speed on 5ns off 10ns?

To remove the 2,2R may cause parasitic oscillation, not acceptable.

Even with the reduced Qg for new FETs the temperature rise for TPS40170 is far from acceptable.

The only thermal acceptable solution is to use the LM5116 and the Vccx input with 12V applied.

I in webench I tried to apply 12V to the Vccx but failed as it not was possible to set the voltage to 12V, do you have an explanation for that?

To run the simulation at -40degC. make me unsure of the capability of the LM5116 (with 12V applied to Vccx) to run at +40degC, 300kHz and Vin 48V Vout 25V 10A. Please tell me if this is feasible or not.

If possible for you then please run a simulation at Tamb +40degC, 300kHz and Vin 48V Vout 25V 10A with the inductor = 22uH 2.6mR 15A saturation (Coilcraft SER2918H-223KL) and FETs of your choice.

Rgds,

Jørgen

Hi Jorgen,

To reduce the power of the controller is to reduce the power of the driver by using lower Qg FETs. The trade off is the higher Rdson  which you have two pairs of FETs to help dissipate the mainly condition power loss.  

The LM5116 is fully capable but WEBENCH uses theta JA values for all components so it's fairly conservative.    I have attached a LM5116 quick start component calculator excel and it can create a design without any restriction.  Please note that your design is 250Watts and I will pass you on to our high power design specialist.  

snvu051.zip

Hi Jorgen

If you have a difficulty to use VCCX of LM5116, please try to connect your 12V external power supply to VCC pin (not VCCX) through a diode (Cathode to VCC. Adode to 12V).

Regards,

Hi Eric,

The problem is that I am not able to set the voltage level on the 2nd supply to 12V, despite what browser setting I try.

If possible for you then please run a simulation at Tamb +40degC, 300kHz and Vin 48V Vout 25V 10A with the inductor = 22uH 2.6mR 15A saturation (Coilcraft SER2918H-223KL) and FETs of your choice.

For further details I have attached a copy of the background for the design first forwarded to Howard the 3 feb.

rgds

Jørgen6013.LM5116 25V 10A 300kHz toHoward.docx