TPSM83100: Power efficiency simulations and frequency response simulations with the specific conditions

Hi  Shunsuke,

May i know why the effective Cout is so small? Concern from my side we may have loop stability issue with this Cout.

Regards

Tao

Hi Tao, 

My customer plans to use GRM155C80J106ME18 from Murata as output capacitor. When taking into account customer's use case, the effective capacitance is calculated as below.

Based on DC bias characteristics of the capacitor, 10uF x 0.247 =  2.47uF.

Based on temperature characteristics of the capacitor, 2.47uF x 0.926 = 2.28722uF.

Based on the capacitance torelance of the capacitor, 2.28722uF x 0.8 = 1.829776uF

The calculated effective capacitance is even worse than the effecitve capacitance I mentioned.

When we apply this calculation the recommended capacitor datasheet stated, the effecitive capacitance of CL10A476MQ8QRN is 3.7uF. 

Is this calculation correct?

Best regards,

Shunsuke Yamamoto

Hi  Shunsuke,

Our recommend Cout is two GRT188R61A226ME13 in parallel. then the effective capacitance should be 8.9uF. Please check.

Regards

Tao

Hi Tao,

I am asking the calculation is correct or not. What do you think?

Best regards,

Shunsuke Yamamoto

Hi  Shunsuke,

Yes, you are correct, 

Regards

Tao

Hi Tao, 

Thank you for the answer. Where can I find the recommendation of two parallel capacitances on the datasheet or user guide? This information can be more persuasive.

Best regards,

Shunsuke Yamamoto

Hi  Shunsuke,

You can find it in the user guider of EVM.

Regards

Tao

Hi Tao,

May I ask you questions again?

May I know if it is possible to take power efficiency simulations and frequency response simulations with the condition below? My customer cannot use pspice for TI due to IT security issue.

1. Vin=+3.3V, Vout=+4.7V, Iout=0.84A, Effective capacitance of Cout is 2.6uF

2. Vin=+3.3V, Vout=+5.0V, Iout=0.4A, Effective capacitance of Cout is 2.6uF

x-axis of power efficiency simulations is load current while y-axis of power efficiency simulations is efficiency.

x-axis of frequency response simulations is frequency while y-axis of frequency response simulations is amplitude and phase.

Best regards,

Shunsuke Yamamoto

Hi   Shunsuke,

Yes, i can do that, but first, i think we should solve the potential risk of instable loop, right? Customer still insist with 2.6uF Cout?

Regard

Tao

Hi Tao,

At first, my customer requested us to take the simulations. not solving the instable loop.

Best regards,

Shunsuke Yamamoto

Hi  Shunsuke,

Ok, will do bench test to confirm. Simulation is not a good idea, because we can not get a correct efficiency by simulation.

Regards

Tao

Hi Tao,

Do we have excel tools to calculate gain vs frequency response and phase and frequency response of TPSM83100? 

Best regards,

Shunsuke Yamamoto

Hi   Shunsuke,

Sorry, we do not have such tool for this device.

Regards

Tao